Parametric Ram Air Channel Model for Flow Optimization

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PARAMETRIC RAM AIR CHANNEL MODEL

FOR

FLOW OPTIMIZATION

Ravichandra kumar. Kumar Bhaskar

Chetan kumar. Nangunoori

Division of Fluid and Mechatronic Systems

Linkoping University

Master’s Degree Project

Department of Management and Engineering

LIU-IEI-TEK-A--12/01295—SE

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ABSTRACT

Ram air channel or NACA channel is used to direct the ambient air for various purposes in an aircraft, such as pressurizing the cabin or as a coolant to heat exchangers and even more other applications like a cooling of the coolant. It is designed; such that it supplies the required amount of ambient air for various operations as mentioned, even aero-dynamical features should be taken into consideration while designing.

In past, the developed prototypes are to be designed first and then experimented to optimize the design which gives accurate predictions and makes easy to understand the phenomenon occurring. These methods can lead to lot of waste in resources and time, in order to avoid these, some new mathematical methods have been implemented before finalizing the prototype which might save resources, time and minimize the possibility of having wrong outcomes. Some additional steps are included during calculation stage prior to the prototype stage; they are the computer aided simulations. These simulations can be as accurate as real time simulations and can bring closer to accuracy rate which is a needed prior to prototype stage.

The aim is to design a tool chain for a Ram air channel which in turn is used to optimize the flow, then supplied to heat exchangers for cooling the hot refrigerant from the avionics systems. The requirements of the heat exchanger are decided on the applications it is used and the range of temperature to be cooled.

In this study work, firstly estimate the size of the heat exchanger for the required performance, followed by the geometry of Ram air channel designing in CAD application so that it maintains the required amount of mass flow rate for the performance of heat exchanger. Finally these both components are implemented in simulation loop to iterate the designs of NACA channel in order to get the final model to optimize the flow for a heat exchanger.

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ACKNOWLEDGEMENTS

It gives us a huge pleasure to thank all wonderful people who helped us in the passage of master thesis.

We would first like to thank our examiner Professor. Petter Krus for giving us this opportunity and finish our Master’s Programme. We also thank our Supervisors Ingo Staack and Edris Safavi for their immense support and patience and for helping us in many ways to come out of the difficulties all through the journey of this thesis work.

We would like to give a special thanks to PhD student Hossein Nadali Najafabadi from Applied Thermodynamics and Fluid Mechanics Division for helping us out in fixing the problems related CFD related topics.

We would also like to be grateful all our near and dear friends for their wishes and full support to us in completion of this program.

Finally, we extend our warm regards to our Parents and Family members for giving us support and opportunity to experience all this and backing us in all our endeavors.

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NOMENCLATURE

 V - Volume of the Heat exchanger  T1 - Inlet temperature of the coolant  T2 - Outlet temperature of the coolant  T2r - Outlet temperature of Ram air  ε - Effectiveness of the Heat exchanger

 λ - Specific heat ratios

 Ntu - Number of thermal units  m_f - Mass flow rate at coolant side  mr_f - Mass flow rate at ram air side

 Cp - Specific heat of the gas

 η0 - Overall efficiency

 h - Heat transfer at coolant side  hr - Heat transfer at ram side

 A - Total heat transfer area at coolant side  Ar - Total heat transfer area at ram air side

 kw - Thermal conductivity

 Aw - Average heat transfer area

 η0r - Overall efficiency at ram air side

 - Plate spacing at coolant side

 - Ratio of heat transfer area/volume at coolant side

 - Plate spacing at ram air side

 - Ratio of heat transfer area/volume at ram air side

 - Wall thickness

 ζ - Ratio of free flow to frontal area at coolant side  ζr - Ratio of free flow to frontal area at ram air side

 Afr - Frontal area at coolant side

 Afr r - Frontal area at ram air side

 Ac - Free flow area at coolant side

 Acr - Free flow area at ram air side

 Re - Reynolds number at coolant side  Rer - Reynolds number at ram air side

 h - Hydraulic diameter at coolant side  - Hydraulic diameter at ram air side

 - Mass velocity at coolant side

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 - Dynamic viscosity at coolant side

 - Dynamic viscosity at ram air side

 St - Stanton number at coolant side  Str - Stanton number at ram air side

 Af - Fin area

 ηf - Fin efficiency

 δ - Fin thickness

 P1 - Pressure at the entry of the heat exchanger  P2 - Pressure at the exit of the heat exchanger  ρ1 - Density at the entry of the heat exchanger

 sp_v1 - Specific volume at the entry of the heat exchanger  sp_v2 - Specific volume at the exit of the heat exchanger  sp_vm - Mean specific volume of the heat exchanger  f - Friction coefficient

 R - Gas constant

 T - Temperature

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1. INTRODUCTION

In an Aircraft system, in order to make an Environmental Control Systems (ECS) simulation, calculation of the drag generated by the complete aircraft system is one of the requirements. From which the major drag is contributed by the ram air channel, since it is largest opening on the surface of the aircraft for the entire system. The purpose of ram air channel is to supply the ambient air with sufficient mass flow for the heat exchanger to perform. During the calculations at a design phase it is very complex to predict the drag created by the NACA channel or ram air channel where there is no detailed geometry.

1.1 Objective

In this work, the main objective function is to create a tool chain for calculating the air flow in the NACA channel, heat transfer in the heat exchanger and (approx.) drag contributed based on the highly simplified NACA channel or ram air channel model. The constraints taken here are the pressure recovery at the NACA channel and the pressure drop over the heat exchanger by taking the design parameters as W/D ratio over the NACA channel, ramp angle, pipe area, heat exchanger frontal area and the lip configurations of the NACA channel.

The geometry model of the NACA Inlet, Pre-HEX pipe, Heat exchanger (HEX) and outlet tube or Post-Hex pipe of CAD are totally built in solid works. The volume of the heat exchanger, frontal area of the heat exchanger and the pressure drop over heat exchanger are calculated in MATLAB. Hand books methods are used to calculate the airflow for heat transfer simulation. Later on, the air flow properties through the NACA channel are calculated by the computational analysis (CFD), importing the flow as an input parameter in to the simulation model, finally creating a iteration loop for further analysis to fix the final model.

1.2 Approach

In order to design a Ram air channel the following needs are to be must available, they are 1. Flight Mission, which has the range of altitudes with their respective operating speeds. 2. Application usage, like cooling for avionics or pressurising the cabin.

3. Space domain, like the volume restriction for the NACA channel and HEX installation 4. Refrigerant coolant and the range of temperature to be cooled.

From the flight mission available, the application usage decision and upon the performance of heat exchanger, firstly the volume of heat exchanger is predicted from which the frontal area

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is calculated. This frontal area which is calculated remains the same for the pipe integrating the NACA air channel and the heat exchanger, depending on this area and the Ramp angle of the NACA channel, W/D ratio of the NACA air channel is calculated.

Fig. 1: Approach Flow Chart

From fig. 1 the flow of approach to design the Ram air channel and the final flow model is shown. The Approach starts with Flight mission, and other data mentioned above are used to estimate the size of the Heat Exchanger which satisfies at all given conditions in flight mission using MATLAB, followed by calculating the pressure drop over the heat exchanger. Once the pressure drop over the heat exchanger is estimated, it is replaced by a simplified Convergent-Divergent nozzle or C-D Nozzle which represents the same pressure difference over the heat exchanger, to make computational system analysis easy, thus implemented in the model with NACA air channel for flow analysis and check the pressure difference, thus obtaining the flow analysis model.

The flow analysis model goes through the iteration loop (fig 20) for the flow analysis to get the final flow model. This approach tried here is to reduce the time taken for the desired output without compromising the quality of the results from which drag analysis is made at the final stage. Finally creating a chain between various tools is used to make it automated.

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1.3 Limitations

There are some limitations to these approaches

1. Designed for single level Heat transfer process only.

2. The flow after the heat exchanger is inaccurate since the temperature calculated here in CFX differs from the actual flow; since the project concentrates mostly on pressure difference over the heat exchanger and NACA analysis but not the heat transfer.

3. It’s not a generic model because of the following reasons.

a) The heat exchanger is an application oriented therefore if there is a change of application it leads to a change in range of cooling temperature.

b) The equations used in the code are specifically for air to air heat exchangers; hence the model is not applicable to other cooling mediums.

c) It works for sub-sonic and transonic but it is not applicable for sonic and supersonic because of the shocks formation.

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2. SYSTEM DISCRIPTION

In this chapter, the detail design description of each component, the characteristics and the role played by each component are explained.The Ram air channel system comprises of series of components which starts with NACA channel for pressure increment and routing the air to HEX for heat transfer to take place and, releasing the heated air to atmosphere. The most common places used to keep are under the belly fairing or in the wing or at an appropriate distance from the nose which has more exposing to air current. Hence the system is built between the surface and the internal structures of an aircraft. The system is divided in to four important sub-components, they are

1.

NACA Inlet.

2.

Pre-HEX Inlet tube.

3.

Heat Exchanger (HEX).

4.

Post-HEX Outlet tube.

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2.1 NACA Inlet:

Fig. 3: NACA Inlet (with reference dimension) [1]

There are different designs of inlets that provide or supply the ambient air for various applications such as simple circular cross section tubes and circular scoops etc. In this project the inlet needed must attain characteristics of pressure recovery with sufficient mass flow rate. NACA Inlet is a submerged duct with a divergent wall and a ramp floor, this is also called flushed inlet. It has good pressure recovery characteristics at low speeds and at high subsonic speeds [1]. The divergent wall follows definite profile which is designed to build up the pressure. The NACA inlet pressure recovery characteristics is governed by some of the geometrical parameters namely the ramp angle, aspect ratio between width and depth of the NACA inlet and the length of the NACA inlet [2].

These inlets are placed where the system has a maximum exposure to ambient air, hence it is placed side or under the belly of the fuselage and if the application is near the wing it can be used under the wing but that may reduce the lift created by the wing.

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Fig. 4: A sample installation of the NACA inlets in a single engine jet-propelled airplane [12].

2.2 Heat Exchangers (HEX):

The heat exchangers used in aircraft applications should be compact; as it has limited volume to be occupied hence compact honey comb heat exchangers are used. There are different sizes of heat exchangers depending on the flight mission and on the application it is used [3]. The various applications of it in an aircrafts are such as cooling of the engines, pressurizing cabins, avionics cooling and even preheating of the fuel.

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2.3 Pre-HEX Inlet tube:

The Pre-HEX inlet tube is a channel used to supply ambient air from NACA inlet to the heat exchanger. The tube arrangement should be designed for minimum pressure losses so that in maintains required amount for the heat exchanger to perform and to maintain the mass flow rate required.

2.4 Post-HEX Outlet tube:

The Post-Hex outlet tube is similar to the Pre- Hex inlet tube which passes the hot air from heat exchanger to the atmosphere. It is designed such that the pressure from the heat exchanger to the atmosphere should be balanced to avoid the counter flow.

The pipe characteristics also depends on the cross sectional of the flow, length and height between the two heads. These characteristics are restricted due to other factors such as space domain and mass flow rate etc. Detail analysis is done in order to get the specific characteristics required.

The angel of the post hex out let tube plays a vital role in over all drag produced. The lesser the orthogonal angle the lesser the drag is produced. The suction of the flow from the free stream at the exit of this pipe effect’s the pressure difference over the heat exchanger.

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3. CALCULATION OF HEAT EXCHANGER

In this chapter reader will identify the requirements, tools used and the equations, formulas and the methods or the procedures used to estimate the size of the heat exchanger. The reader will even go through an idea of replacement of heat exchanger with convergent-divergent(C-D) nozzle in flow analysis and why it is replaced.

3.1 Estimation of volume of a Heat Exchanger:

In order to estimate the size of the heat exchanger with the given input data as mentioned in the approach, it is done with the help of MATLAB. MATLAB is a language of technical computing which is more suitable for numerical computing; it is very effective at handling the matrix calculations and plotting of data, hence MATLAB is the more appropriate tool to be used to determine the volume of a heat exchanger. The algorithm is based on the approach from the Pre - cooler section from Optimization of commercial aircraft [4].

3.1.1 Algorithm:

1. Flight mission, coolant’s mass flow rate and Temperature range are given as inputs. 2. Heat exchanger’s geometrical parameters such as fin plate thickness and hydraulic

diameter etc. are given as constant parameters and gas constant.

3. The data to interpolate as in order to get the data of Cp, Viscosity, Density and thermal conductivity with respect to temperature. The source of interpolation data is taken from web source [5].

4. In section 1, ‘for’ loop is made to compare all the conditions in MATLAB with all the possible combinations from the flight mission.

5. Increment the Length, width and height of Heat exchanger until it meets the performance where the coolant gets cool down to required temperature.

6. Then minimum required volume and mass flow rate is stored.

7. From the volume required for various conditions choose the maximum volume and check the performance of a Heat Exchanger.

8. By checking the performance from previous stage, if the temperature of the hot refrigerant is cooled below the required temperature range, then the required condition is obtained, the volume is finalized.

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3.1.2 Numerical procedure:

The whole procedure is derived from the source [4]. The paper is based on ECS system to pressurize the cabin. This procedure concentrates on the pre-cooling section where the heated air is cooled down before going in further process. This section has various equations to derive the volume of the heat exchanger. In order to find the right required volume, firstly we need to assume the volume and check it with its performance to the performance required. There are some constant geometrical parameters of Heat Exchanger used in this procedure.

1. Assuming the volume of the Heat Exchanger in terms of length, width and height of the heat exchanger.

2. In order to calculate the performance of the Heat Exchangers the effectiveness is calculated and compared in two different ways

ε =

(1)

ε= 1 - exp [λ Ntu0.22

(exp (-λ-1 Ntu0.78 ) - 1)] (2)

3. In the above 2nd equation of effectiveness equations, Ntu need to be applied. To calculate the Ntu we use the following equation

1Ntu

= m_f.C

p [(1/η0.h .A )+( 1 / kw.Aw )+ (1/η0r.hr.Ar)] (3)

To calculate the Ntu we need the values of ‘m’, ‘ƞ0’, ‘h’, ‘A’, ‘kw’, ‘Aw’, ‘ƞ0r’, ‘hr’ and

‘Ar’ to be known.

4. Calculate the ratio of total heat transfer area to Exchanger volume on both the ram air side and the coolant.

α=

,

Coolant side (4)

α

r

=

,

Ram – Air side (5)

5. Then total heat transferred area is calculated with the ratio and volume by A=α .V, Coolant side

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Ar=αr .V, Ram air side

Arithmetic mean, Aw= (A + Ar)/2

6. Calculate the ratio of free flow area to frontal area in order to calculate free flow areas. ζ= α.rh and ζr= αr.rhr

This gives, free flow areas

Ac = ζ .Afr and Acr = ζr .Afr r.

7. Then the mass velocities is calculated by the areas, then with the along with it and hydraulic diameter, we will calculate the Reynolds number.

G =

m_f.A

candGr =

m

r_f.

A

cr

Re =

and Re

r

=

8. Then we need to find the corresponding Prandtl and Stanton number in order to calculate the heat transfer on both sides

St_a=Nu_a/(Re_a*Pr_a),Stanton number[14] Pr =Cp.μ.ρ/k, Prandtl number [15]

Nu= 0.023*Re_a^(4/5)*Pr_a^0.4,Nusselt number

Dittus-Boelter equation,Forced convection in turbulent pipe flow [15] h=St.G.cp and hr = Str.Gr.cp

9. The overall effectiveness is given by

η0 = 1 – (Af/A)(1- ηf)

where ηf = Fin effectiveness

ηf = tanh (m.b / 2)/ (m.b / 2)

m = (2.h/kw.δ)(1/2)

10. Finally substitute the value in Ntu equation and find Ntu. Then substitute to get the effectiveness of the heat exchanger and compare the desired effectiveness which is derived from temperature dependent equation. The results are

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● Plot of the minimum volume required for the Heat exchanger for the all the possibilities in flight mission.’

● Choose the maximum volume of the heat exchangers among the plot and fix the volume.

Results are discussed in the upcoming chapter 8.

3.2 Estimation of pressure drops in a Heat Exchanger:

In heat exchanger during the process of the heat exchanging between the coolant and the hot fluids, pressure drop occurs due to the changes in the temperature when it flows across the heat exchanger. This pressure drop plays a vital role in determining the arrangement of pre hex inlet and post hex outlet pipes.

The calculation or estimation of pressure drop over a heat exchanger cannot be done by a direct method. As by the equation below taken from source [13], the unknowns are the exit pressure which is P2 on LHS of the equation and mean specific volume or density. Whereas this mean specific volume or density depends on average value of both the inlet and exit specific volume, which in turn depends on exit pressure. Therefore iteration has to be done until the both sides of the equations are stabilized.

P1-P2= (m/ρ1)2/ (2* ρ1)*A_a/A_c_a*(sp_v1/sp_vm)*f

3.2.1 Algorithm

It’s an iteration process as a particular variable is changed according to the requirement and tries to equalise the value of the equations on both sides.

1. We have most of the variables calculated in the previous section 3.1. The variables need to be iterated is P2 which starts from 0.

2. Then we need to calculate the mean specific volume sp_vm by Sp_vm=(sp_v1+sp_v2)/2

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3. Friction factor is consider in which depends on the material of the hydraulic tube is made of which is mostly aluminum-steel alloy or aluminum based components. Hence the friction factor for the aluminum-steel alloy is 0.61[6].

4. Then the value on LHS and RHS of the equations is calculated and compared. If it is equal or approximately equal we can exit the iteration or increase the value of the P2 and

calculate again.

5. Step 4 is repeated until the both values are approximately equal.

6. Once it’s done the LHS value gives the pressure drop in the Heat exchanger.

3.3 Designing of convergent-divergent nozzle

Design of the nozzle, is to represent the pressure drop over the heat exchanger in flow model. This is due to the difficulties of modelling of heat exchanger and simulating the actual heat exchanger might make the procedure complicated and time consuming. Hence in order to make it simpler in simulating the pressures drop over heat exchanger it is replaced by a nozzle. The main focus is on the pressure distribution across the pipes; hence it represents only pressure drop but not the entire heat exchanging process. This can lead to problem that the flow aft of heat exchanger that is in post hex tube the values can be inaccurate as temperature is not the same as the actual heat exchanger gives out.

3.3.1 Method and Approach

As mentioned in above that the heat exchanger is replaced by the Nozzle, the design of the nozzle based on the pressure drop calculated in the heat exchanger from numerical procedure followed from section 3.2. The nozzle used here is a convergent divergent type where it has three notifying areas entry at section 1, throat at section 3 and exit at section 2 form the below figure of the nozzle. In order to get the final pressure at post heat exchanger, P2 at the exit we need to decrease the pressure further at the throat such that it will regain the pressure equivalent to the P2, the exit pressure of the heat exchanger.

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Fig. 6: Convergent-Divergent nozzle

In order to design the nozzle for the corresponding pressure drop in the heat exchangers some conditions are to be assumed. The convergent section of the nozzle must be lengthier than the divergent section whereas the diameter at the entry and the exit should remain the same. Since the needed pressure at the exit must be smaller than the entry pressure so, the regaining section of the pressure should be smaller.

The next step is to start the throat diameter from same as pipe diameter and decrease grease gradually and monitor the exit pressure of the nozzle until it reaches the pressure P2. Thus, a nozzle is designed which represents the pressure difference in the heat exchanger.

3.3.2 Numerical Procedure:

The above method is applied using the set of equations which is used for convergent-divergent nozzle design [7].

1. The know values are pressure, temperature, velocity of the flow and density at the entry of the heat exchanger as the inputs. Then we keep the length of convergent and divergent as constant. The nozzle throat area is reduced starting from pipe diameter. Therefore we calculate other variables based on the iterating value of nozzle throat area which will be finalised once the exit pressure gets equivalent to the exit pressure in the heat exchanger in the ram side of the heat exchanger.

2. Firstly, calculate the rate of change in area (dA) for bith convergent and divergent sections followed by calculating rate of change in velocity (dv) and rate of change in density (dρ) respectively in the convergent section.

3. Substitute the above calculated values to get the velocity and Mach number and density respectively at the throat section.

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4. Once the values are derived at the throat section, substitute these values of velocity and rate of change of velocity to get the rate of change of pressure. This is further used to calculate the pressure at the throat.

5. Then the values of pressure, velocity and density at the throat section are calculated in region of convergent section. In divergent section the regions involved are the throat and the exit sections. The values derived at throat are used to calculate the pressure, velocity and density at the exit following same as calculated in the convergent section.

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4. GEOMETRIC MODEL

The Ram Air Channel or NACA channel and the entire system are designed parametrically so that it can change the features of the geometry to run simulations on different configurations. There are two types of geometry in this system. Actual model or solid model which virtually represents the system as it is. This model gives a clear view how the features looks in actual space domain. The other model is an inverse model or upturned model which represents the flow in a system. This model is called flow model, which is used in a flow analysis for further investigation.

Fig.7 Solid Model (Actual model)

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As mentioned in the system descriptions there are 4 main components in a Ram air channel. The above solid model is a non- optimized model which is initially designed for optimization design loop. This model is mainly used to show how the actual system looks like and which makes it easy to understand the situation and physical restrictions easily.

The flow model is inverse of solid model as said before which have same geometrical features as a solid model. Hence whatever changes made on either of the model its exclusive. The flow model is to analyze the pressure flow from the air entry at the NACA inlet through the entire system till the release to the atmosphere.

As mentioned above the geometry is controlled parametrically for the entire system to do the flow analysis and finalize the final flow model. To make a final flow model the parametric design consideration is made on all the four main components of the Ram air channel System.

4.1 NACA Inlet

The NACA inlet follows a definite profile alignment of divergent walls which provides an increment in pressure. This profile is constructed based on a coordinates taken from source [1]. The coordination used as a reference is small scale model then we have scaled it in terms of length wise.

The NACA Inlet is designed based on the mass flow rate required for the heat exchanger hence the key factor is the area of the inlet passage of the NACA Inlet. The area is a rectangular Cross section made of width and depth of NACA inlet. The area is also interrelated through depth of the NACA inlet as the depth is controlled by the Ramp angle and the Length of the NACA Inlet.

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Fig. 9: NACA Inlet

The NACA channel model is designed parametrically by controlling the length of the NACA inlet, W/D ratio and the ramp angle. The depth is controlled by the length and the ramp angle by using Pythagoras rule and width is varied according to the area what we need hence the area remains constant at all times unless we change it manually.

4.2 Pre-HEX Pipe

The Pre-HEX pipe is used to connect the flow between the NACA inlet and the HEX. This connection has some specific features to be considered. The pipe is built such way that ramp angle and the axis of the flow should remain in same axis until it reaches the height of the HEX [8], this attains the good pressure recovery across the pipe to the HEX. The pipe is constructed to follow the ramp angle and to maintain the frontal area of the HEX which is also the same for NACA inlet area.

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4.3 Convergent-Divergent Nozzle

Heat exchanger here in flow model is represented by a C-D nozzle as explained in the section 3.3. A nozzle is used in the flow analysis where it represents the pressure drop in the HEX. The nozzle is controlled by changing the throat area and keeping the length of nozzle and area of the entry and exit as of the nozzle as constant. The Area at the entry and exit of the nozzle are calculated from MATLAB and it is designed accordingly.

Fig11 (a): Orifice area equals Pipe area Fig11 (b): Orifice area not equals Pipe area

Fig11(c): Final Orifice area of Nozzle.

4.4 Post-HEX Pipe:

The post-HEX pipe is similar to the pre-HEX pipe which allows the heated air to flow from HEX to outlet. This follows the same area as frontal area of the HEX. This pipe has an influence at the outlet, as the angle of outlet exposed to atmosphere creates a drag. Since temperature plays the major role in the properties of air it is proportional to drag created from this region of the entire system.

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5. SETUP FOR FLOW ANALYSIS

Once the designed geometric model is ready, it is integrated into ANSYS CFX for the flow analysis and run simulations to get the final flow model. So in turn to get the final model the initial model has to undergo through some system or setup procedure to run simulations. The procedures to follow are to give the boundary conditions for the model, the material used to run the simulations, meshing of the model followed by the mathematical methods used to solve the problem finally with the post set up to take the desired outputs.

5.1 Boundary Conditions

[10]

Inlet: The Inlet boundary condition is always taken as the Normal speed to the domain since

the incoming flow is parallel but in opposite track to the movement direction of the aircraft. The normal speed is taken according to the flight conditions given at different altitudes.

Fig12: Inlet Boundary

Outlet: The Outlet boundary conditions are taken as reference pressure but not the normal

speed to domain because, the air flow faces the friction flow on one of the surfaces of the aircraft, so the velocity may not be the same as inlet flow condition, but the reference pressure that is the atmospheric pressure at that given altitude almost remains unchanged.

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Moving walls: The side walls and the bottom wall of the box set up are taken as the walls

moving with the same velocity as that of speed normal to the inlet boundary state, since the flow is free air stream flow it represents that the total air is moving with same speed with minimal friction effects of the walls, so that the quality of flow doesn’t affect the properties of air entering the NACA channel.

Fig 14: Moving Walls Boundary

Friction walls: The top wall of the box domain represents one of the surfaces of the aircraft

which is made of metal and has friction effect on the flow and as well as the walls of the NACA Inlet, heat exchanger and pipes have the flow with friction effects because of the materials used so these wall conditions are taken as walls with friction effects.

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5.2 Material Description

The Gas used is an ‘Ideal Air’. Since the analysis is done at different elevations or altitudes, the reference temperature, pressure, viscosity and density of the material changes accordingly. All the above mentioned properties of air are set in the form of the expressions, which are used as input parameters instead of entering the direct numerical values in the material.

5.3 Mesh

[9]

Mesh plays a major role in order to get the desired outputs, which are reliable for further analysis. The method used is ‘Patch Conforming method’ with different face sizings used at different regions, with inflation number of layers as 7 with first layers thickness as 1E-3 m (meter) for the regions where the flow analysis is done for calculating the desired outputs.

Fig 16 (a): Mesh of Total system.

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5.3.1 Mesh Refining

Mesh refining is taken into consideration at the regions where the project is focused onto i.e., at the NACA inlet region where the pressure recovery is calculated and the regions where the pressure drop over the heat exchanger is calculated. Minimum sizing is taken to considerat ion on the regions where we do not focus on, in which this reflection doesn’t affect the results of the outputs required.

Fig17 (a): Mesh Refinement

Fig17 (b): Refinement at NACA

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5.3.2 Mesh Independency

Making the mesh independency was one of the challenging tasks in this project. The number of mesh elements taken for the mesh independency is around 1.55 million elements. Since this project has many elevations to be taken into consideration, the mesh independency is done for the highest Reynolds number (Re) from the given data so that this mesh configuration can be

used for any state or at any elevation with given operating speed. The highest Re is taken at the state of ground level elevation with operation speed of 0.9 Mach (M) with the diameter of the pipe as 0.3859 m. The obtained Reynolds number for the mesh independency is 7.823 E6.

The major breakthrough for the mesh independency comes at a stage where the pressure recovery at the NACA Inlet and pressure difference over the heat exchanger remains almost constant even after the numbers of the elements are increased. There are many methods to follow in order to attain the mesh independency, in general the technique followed is that the numbers of element are increased by two times with the previous number and check with the desired output required. A stage reaches where the output remains almost constant even after the numbers of elements are doubled.

It was tough to follow the above mentioned method to get the mesh independency as an alternative we tried to reach the goal separately. Firstly, fix the sizing of other regions like heat exchanger and other pipe surfaces and keep on varying the sizing of the NACA inlet to reach independency of the pressure recovery. After the independency of the NACA inlet is achieved, the sizing of the NACA is fixed and the sizing of the other regions like pipes are fixed and the independency of the Heat Exchanger is calculated by varying the size of the Heat exchanger to calculate the independent pressure drop over it.

As mentioned above, the major breakthrough comes at a stage where the NACA pressure recovery and the pressure drop over the heat exchanger remains constant, the values of the total pressure or the pressure recovery at the NACA and the pressure drop over heat exchanger are calculated separately, but the value of NACA pressure recovery should remain almost the same even when the independency for the pressure drop over heat exchanger is calculated, that is the point where the mesh independency is achieved. The value of the NACA pressure recovery which is done independently is 240705 Pa with number of mesh elements is 1.45 Million.

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The value of the pressure drop over heat exchanger after NACA independence is done is 1028 Pa with number of mesh elements is 1.55 million. The value of the NACA pressure recovery at the stage of calculating pressure drop over heat exchanger is 240744 Pa with number of mesh elements as 1.55 million. The graphs of the inlet pressure recovery and the pressure drop over the heat exchanger of the achieved independent vales are given below.

Graph 1: Mesh independence over NACA

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5.3.3 Convergence Criteria

The convergence criterion with residual target is taken as 1E-5. This was finalized after testing 1E-4, 1E-5 and 1E-6. The testing criterion is the pressure values at the NACA recovery. The error for 1E-5 values turned out to be better as mentioned in Mesh Independency. The values obtained from 1E-6 are good but the time taken for convergence is 3 times and the number of iterations was almost 4 times more and there is not much significant improvement in the output values. So a compromise was made between running time and accuracy so that the required task can be achieved within the specified time.

Mesh independency is also defined by the convergence criteria as well, if the solution doesn’t converge for higher residual target this means that given residual target entered is high for the given mesh, either refine the mesh to reach the given residual target or reduce the value of the given residual target for the given mesh so that the solution converges fine. Here in this project the given taken mesh converges for all the given residual targets given above. For the ground level operations all mass and momentum, turbulence equations converges except for heat transfer equations, it reaches close to the residual target but doesn’t reach the converging point but remains constant close to the given residual target, this indicates that the solver is capable of solving till that particular error, so it can be considered as converged solution.

5.4 Discretization Methods

[10]

There are several discretization models available in ANSYS CFX like Laminar, K and Epsilon (K &

ε), Shear Stress Transport (SST), BSL Reynolds Stress, SSG Reynolds Stress.

From the above mentioned models the term ‘Laminar’ itself mentions that this solving method is used for Laminar flows, whereas the others are used for solving turbulent flows. As mentioned above in mesh independency by calculating the Re number the flow falls into

turbulence model, so the discretization model used to solve is one of the turbulence solving methods.

The method used for solving is K and Epsilon (K &

ε

). Since there are many models to use as mentioned but started with K & Epsilon and the results were very satisfactory so, did not opt for any other discretization models. If in case if the results were not satisfactory, then would have been going in search for other models till the results were satisfactory.

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5.4.1 Activation Schemes [10]

There are three activation schemes available in ANSYS CFX; they are upwind, high resolution and specified bled factor. The scheme used is High resolution, scheme in solving the K &

ε

discretization method and the continuity equations used for the solution to converge for the given residual target, even taking the turbulence as high resolution.

The heat transfer model used in fluid models is the total energy. This model has been selected to use since the operating speed is not only subsonic but also in transonic region, so the inlet should have an option of changing speed to mixed state from subsonic state at the cruise level operations.

5.5 Post Setup

[11]

The Post setup is used in calculating the desired out puts. Planes are created at the locations of the NACA pressure recovery and at the entry and exit of the heat exchanger to calculate the total pressure at NACA and the pressure difference over the heat exchanger. Then isoclips are created on the respective planes as a variable on Y-distance of 10mm on respected planes, to calculate the outputs required. Isoclips are the cut section of the created planes to get the desired output on particular location of that plane. The equation used to calculate output depends on the outputs required i.e the basic equations remains same but the output variable is changed to take the desired output. The equation used is ‘Area Average’ of that isoclips which calculates the average value of the each element and sums up the value which is more precise than the ‘Average’ values. The example of the used equation is as follows ‘areaAve (Total Pressure)@Iso Clip 1’, which calculates the value of total pressure at Isoclip1. This CEL expression is given as output parameter. Details of setup of planes and Isoclips are explained in Appendix.

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6. ANALYSIS AND RESULTS

Once all the setup is fixed as mentioned in above chapter to run the simulations on the flow model, it’s time to check with the analysis done and the results to discuss. Here in this chapter the reader will go through the final results of the total model, that is how the volume of the heat exchanger is finalized, and then followed by the iteration process used to get the final flow model, finally the analysis of the NACA channel and its characteristics are discussed.

6.1 Volume of the heat exchanger

The volume of the heat exchanger is determined by using the procedure as explained in section 3.1.2. The minimum volume is estimated for all the possible conditions within the range of velocities and altitudes given in flight mission. Different combinations have been tried to observe the volume requirement of the heat exchanger with the help of MATLAB. The code is done in such that it determines the volume of all combinations as per the requirements explained above.

Implementing the inputs as explained in Volume_estimation.m, in the code and 60 different random velocity and altitude within the limit has been used to produce 60 x 60 combinations to investigate minimum volume requirement of the heat exchanger. The given maximum altitude and velocity as 9 km and 0.9M respectively similarly minimum velocity and altitude is given as take-off speed (0.2M) and sea level. The resulting collection of volume is plotted as surface plot with altitude, velocity and volume on x, y and z axis.

Fig19: Surface plot of volume of the heat exchanger for various combinations of velocity and altitude.

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As it is clear from the above plot that minimum volume requirement distribution is at its best of 0.04 m3 roughly for low speed and low altitude of 0.2865 M and 0.2 km which is nearly same as sea level. As the speed or the altitude or both increases the volume requirement decreases. From this plot it concludes that the volume of heat exchanger is fixed by the minimum velocity and sea level altitude as it has maximum of minimum volume requirement other then the variables from coolant side.

6.2 Iteration Process to Determine Nozzle Area

Manual iteration process is done in order to determine the nozzle area according to pressure drop in heat exchanger. This process is done with the results produced by 2 different plat forms. They are Ansys (CFX) and MATLAB which dependent on each other as their inputs and outputs are inter-connected to each other.

As the data from pre-HEX location such as pressure, temperature, velocity and density are determined from Ansys(CFX) are used as an inputs in MATLAB to estimate the pressure drop and nozzle area to represent the pressure drop which is updated in the flow analysis model and simulated in Ansys(CFX) and this goes in cyclic process to get the difference in the pressure difference smaller by every iteration or this iteration process stops when the nozzle area calculated by MATALAB is consecutively same.

This process is observed on two different conditions, they are at ground level and cruise level conditions with their respective operating speeds. These two conditions are extreme conditions hence if the procedure is applicable at these both conditions it can be said that it is even applicable for intermediate conditions. In cruise level the flow analysis is done based on the cruise speed, the analysis setup is changed based on cruise speed is sub-sonic or transonic.

The simple representation of the above mentioned iteration process is given in form of flow chart for the reader to understand in a better way.

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With the above mentioned iteration process at ground level with an operating speed of 85m/s, the iteration process run two loops and attained a same nozzle area as previous hence iteration process is stopped. The final nozzle area form the iteration process turned out to be about 73400mm2 with pipe area as 117000mm2. The difference in the calculated pressure drop between two platforms ANSYS and MATLAB is 5pa. The pressure drop in Ansys-CFX is 580pa and from MATLAB it’s about 585pa.

At cruise level condition of altitude 9.144km with an operation speed of 272.7m/s has also gone through the iteration process as mentioned above, since it is a transonic state the input state is changed to mix condition in the setup and simulated in Ansys-CFX. The iteration is done for the same pipe area as ground level.

Graph3: The plot between nozzle area vs. pressure drop compared between results Ansys-CFX and MATLAB for cruise level conditions (Pipe area =117000mm2)

As it’s clear from the above graph, the nozzle area converges for few iteration steps with difference in pressure drop getting reduced till the nozzle area of 71200mm2. After reaching to this range of area, the nozzle area starts to increase and make the solution to diverge. A closed loop is formed between this converged point and the diverged area, so the final nozzle area is tough to decide within this loop created.

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In order to get the iteration to converge to a point or to stay constant after certain area, the method tried is by reducing the frontal area of the pipe by reducing width of the heat exchanger but by maintain the volume of the heat exchanger constant so that the effectiveness of the heat exchanger increases. Therefore the tried reduced areas are in terms of the percentage of the standard area taken with 10%, 20% and 25% reduction of the width which in turn reduce the pipe area or the frontal area. The graphs of the performance of the iteration loop area given below for the reduced areas in terms of percentages mentioned above.

Graph4: The plot between nozzle areas vs. pressure drop compared between results Ansys-CFX and MATLAB for cruise level conditions for 10% decreased Pipe area

Graph5: The plot between nozzle areas vs. pressure drop compared between results Ansys-CFX and MATLAB for cruise level conditions for 20% decreased Pipe area

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Graph6: The plot between nozzle areas vs. pressure drop compared between results Ansys-CFX and MATLAB for cruise level conditions for 25% decreased Pipe area.

From the above graphs of reduced area it’s understandable that the area converges to certain point and remains constant but it doesn’t diverge after, from this we can say that reducing the area have more efficient results than the original area and it seems to be more effective in reducing the area to some extent. All the three graphs show that the area remains constant at certain point but from the graph of 20 % decrement in area, the difference between the pressure differences of the two separate platforms ANSYS and MATALAB is very close comparatively to the other decrements. The difference has been observed as 200pa roughly for the cruise level operation and 70pa at the ground level operation. Therefore 20% decrement may be applicable and most effective for both the operating conditions in which error difference is negligible. The pipe area after reducing 20 % of width is about 93600mm2. The final nozzle areas are59300 mm2 for ground level and 58500 mm2 for cruise level.

6.3 NACA INLET

NACA Inlet is usually a common form of low-drag air inlet design in aircrafts. When implemented properly, it allows the air to flow internally into a duct which is basically used for the cooling purpose. It is shown that this type of entrance possesses pressure recovery

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characteristics even at critical speed because of the combination of the easy-going ramp angle and the curvature profile of the walls.

The analysis of NACA inlet is done with the final flow model in which the different configurations of NACA inlet are taken into consideration. The main parameters on which the analysis is done are the ‘length’ and ‘ramp angle’, which are parameterized based upon the geometrical features in turn controls the ‘Width’ and ‘Depth’ of the NACA Inlet. The analysis part is done by Computational Fluid Dynamics (CFD) using ANSYS CFX on workbench. As mentioned, the analysis is done on parameters of ‘length’ and ‘ramp angle’ ranging from 1000mm-2000mm and 7deg-15deg respectively. The flow model is imported to ANSYS from SOLIDWORKS, in which the parameters are controlled directly in ANSYS, which in turn is controlled in SOLIDWORKS. The graph of the range of W/D ratio with respect to the length of the NACA inlet at different Ramp angles is given below.

Graph7: Range of W/D ratios for different lengths of NACA for various Ramp angles

From the flow model fig [8], the bottom box type setup is the free stream air flow of atmosphere and the remaining setup with NACA inlet, Pipes, Heat exchanger and Outlet of the pipe arrangement are positioned inside the aircraft which are used for the cooling purpose in this case.

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As mentioned on above statements the main purpose of implementing NACA Inlet is for the pressure recovery. The analysis is done accordingly with the given flight mission data at two different altitudes ‘Ground level’ and the ‘Cruise Altitude’ combined with different operating speeds at that particular altitudes as given per flight mission data. The operating speed at ground level is taken as 0.25 M whereas at cruise it is taken as 0.9M.

The position or location of plane selected for the calculating the pressure recovery value in ANSYS is exactly at the place where the NACA inlet is connected to the Pre-Hex pipe which is connected to the physical representation of a heat exchanger which is intended to have same pressure difference as made in hand calculations using MATLAB. The location of plane in the geometry for calculating the pressure recovery values is given below.

Fig21: Selection of location of Plane for calculating pressure recovery

The NACA pressure recovery values are calculated over the Isoclip, the cut section of the plane (Coloured part) created as shown in above figure at two different altitudes ground level and cruise level with their respective operating speeds.

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Ground level observations in two different Graphical formats

Graph8: Pressure Analysis of NACA with respect to length at Ground Level operations

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Cruise level observations in two different Graphical formats

Grapg10: Pressure Analysis of NACA with respect to Length at Cruise Level operations

Graph11: Pressure Analysis of NACA with respect to W/D ratio at Cruise Level operations

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7. OBSERVATIONS

From the analysis in the previous unit done the results are discussed in the upcoming chapter, whereas here in this unit we discuss about the other external observations what have been gone through the entire project, which might affect the results and by considering these observations the results or the outputs can be more precise or more accurate, to make the system entire air channel system work in more realistic way. Observations are done on how it effects on pressure recovery and the boundary layer by varying the source length, effect on pressure difference over heat exchange by varying the area of pipe and the drag generated by the NACA channel.

7.1 Varying Inlet Location along X-Direction

The position of the location of the NACA Inlet attached with the pipes and heat exchanger are placed at different locations (X) from the ‘INLET’ source to check whether the pressure recovery is varying by varying the position. Simulations are done at three different locations of (X) 2000mm, 3000mm and 4000mm from the Inlet source. The percentage change in pressure compared between 2000mm length to 3000mm and 4000mm are 0.82 and -1.28 respectively. As there is not much difference in change of the value of pressure recovery, to reduce the number of mesh elements as well as the computational time the location is of NACA Inlet is fixed at a distance of 2000mm length.

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7.2 Boundary Layer

[11]

The boundary layer is checked in the form of ‘Y+’ picture in the regions of the boundary of

the aircraft and the NACA inlet with the heat exchanger. ‘Y+’ is a dimensionless number

which is defined by the following way

Y+

_{= (u}

*

y)/ν

Where

u

* is the friction velocity at the nearest wall,

y

is the distance to the nearest wall and

ν

is the local kinematic viscosity of the fluid.

Y+

is checked by varying the inlet source length. Even though we are not very clear with the number range of this Y+_{, these were just the observations taken so that in future work this}

might be help full, since here it’s not the main focus. The observed pictures are given below.

Fig23: Position of NACA at1000 mm from inlet source

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Fig25: Position of NACA at 4000 mm from inlet source

Fig26: Position of NACA at 2000 mm from inlet source with 7 layers of inflation

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7.3 Area Changing

This analysis has been done just to test, how does the area of the pipe effects the pressure drop over the heat exchanger, when orifice area of C-D nozzle equal the pipe area. Analysis has been done on changing the pipe area ranging from 50000 mm2 _{to 142300 mm}2 _{with an}

increment of 10000 mm2._{. Here in this analysis the pressure difference over the heat exchanger}

is calculated with nozzle diameter equals the pipe diameter. The outputs taken are the pressure at pre hex location and the post hex location. The results are observed as that the area increases the pressure difference over the heat exchanger decreases or the other way we can say that the pressure at the pre hex value is increasing at lower rate whereas the pressure at the post hex location at faster rate and the difference between these two decreases as the pipe area increases. The graphical representation of the above discussion is given below

Graph12: Pressure Difference between Post hex and Pre hex locations of HEX by varying pipe area.

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7.4 DRAG ANALYSIS

Drag calculations at the NACA duct are one of the key observations of this project. The major drag is contributed by NACA duct in the system, whereas the other parts which supplement the drag are the exit pipe configuration. The drag values which are given below are calculated only for the NACA duct but not for the exit pipe configuration. The main geometrical section which generates drag in NACA duct is the lip [16], which is located at the rear part of the component. From the references gone through for this project it was clear that the lip radius, lip length, lip height and lip design plays major role in drag contribution. The thinner the lip the lesser the drag it is where as the thicker it becomes the larger the outcome [16]. The following graphs are the observations of the drag produced by NACA duct; the observations given are for both the cruise level and ground level operations.

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Graph15: Cruise level observations of Drag vs. W/D ratio

Ground level operation observations

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Graph17: Ground level observations of Drag vs. W/D ratio.

From the above four graphs of the drag analysis, both at ground level as well as at cruise level it is clear that at ramp angle of 7deg of the NACA channel has a minimum drag production compared with their respective positions of that of other ramp angles for a given Lip configuration.

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8. CONCLUSIONS AND FUTURE TASKS

From after all the setup and calculations are completed, the final conclusions of the project like the objective has been achieved or not and few other conclusions of NACA channel followed by the future task to get involved into this project more deeply to solve the complexities.

8.1 Conclusion

The objective of this project is to create a frame work for integrating various tools to calculate and design the NACA ram air channel which is to be analyzed for various factors and performances. The frame work has been made to calculate the volume of the heat exchanger which satisfies all the conditions in a flight mission, and then NACA inlet is designed for various configuration based on design variables.Finally the pressure drop in a heat exchanger is represented through nozzle which is calculated through iteration process which can be done manually or can be automated. This frame work can be used further to analyze the design such as drag, pressure recovery and other factors to improvise the performance.

As mentioned in above chapter 6, the NACA channel has been analyzed, and the graphs indicates very clearly that the pressure recovery is at its best for the W/D ratio between the range of 1 and 2 for ground level operation and whereas at cruise level it shows a better performance between a range of approximately 0.5 and 2 for all given combinations. From the references used for the analysis of NACA, it indicates that the W/D ratio ranging between 3 and 5 has a better performance, but from the analysis done in this project it shows that it has better performance between 0.5 and 2 for cruise level and 1 and 2 for ground level. From the graphs mentioned above it is clear that the ramp angle with value 7 deg has better performance in pressure recovery aspect as well as the less drag contribution, comparatively with the other ramp angles.

From the reference of ‘‘An Experimental Investigation of The Design Variables for NACA Submerged Duct Entrances” by ‘Emmet A. Mossman and Lauros M. Randall’ it says that the NACA channel performance best between 5-7deg ramp angle. From the tool chain designed here in this project also shows that the NACA channel has better performance in both the pressure recovery aspect and the minimum drag produced shows better performance at 7deg

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ramp angle comparatively to the other configurations. So we can conclude that the tools chain created here works in a perfect way so that the future tasks or further analysis can be done to optimize the flow by using this tool chain created.

8.2 Future Tasks

1) Calculation on drag has been analyzed to certain extent that is only the drag generated from NACA channel has been analyzed, but it can be done in more accurate way by calculating the drag generated by the exit pipe installation of the air channel system. 2) Temperature plays major role in the properties of air, which is directly proportional to

the drag generated by the exit section of the air channel system, so the implementation of temperature dependent flow analysis and its effects in post hex tube can be done to give the exact drag produced by the entire system.

3) Implementation of heat transfer analysis in flow by defining boundaries. 4) Investigation of Post Hex Pipe and angle of outlet section of post hex.

5) Detail study of Boundary Layers around the surface and pipes which can improve the flow performance.

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APPENDIX

A methodical explanation is given to understand the working of the files in a tool chain. This detail gives a clear understanding of how to execute the files and how to use them. There are five different files and three different tools were used in the frame work. The contents generally explain about the purpose of the file, the inputs and outputs.

File 1: Volume_estimation.m Type of file: MATLAB script

Objective: To estimate the volume requirement at all altitudes and velocity and among that

we take the maximum volume required as the volume of the HEX.

Source: The Optimization of commercial aircraft environmental control systems (Mainly

focused on pre-cooler section) @author Isabel Perez-Grande and Teresa J. Leo

Variable (input) declaration:

 From the altitude and velocity of a flight mission enter the ‘h’ and ‘vel’ which are the maximum values of altitude and velocity respectively.

 Mass flow rate of the coolant or refrigerant side, ‘m_dot_f’.

 Temperature range, ‘Tf1’ = inlet refrigerant temperature and required ‘Tf2’ outlet refrigerant temperature.

 Based on the altitude the values of pressure, temperature and density are calculated in ‘inp’ function. It is stored in F_M.F_M as matrix of values in order of columns in following way

i. s.no

ii. Velocity @ Mach number iii. Temperature [K]

iv. Pressure [Pa] v. Density [Kg/m^3]

Executing procedure:

Enter the value of maximum altitude and maximum velocity from a given flight mission

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The coding have been divided in following sections

1. Input setting: Inputs are flight mission, mass flow rate of refrigerant to be cooled, and inlet and outlet temperature of the fluid side [Required condition].

2. Data to interpolate: To get the values of Cp, Viscosity, Density and Thermal conductivity for corresponding temperature we are use the data to interpolate the values.

3. Fixed Data: This consist of fixed data of geometrical aspects taken from the source. 4. Calculation: Estimating the size of the Heat exchanger by iterating it in all individual

conditions with all combination of altitude and velocity given until it can satisfy the required condition. After estimating determine the maximum volume which can satisfy in all condition over all. Then Plot the surface model of volume with altitude and velocity.

File 2: Second_iteration_1.m Type of file: MATLAB script.

Objective: To predict the pressure loss in the HEX and to design a Convergent-Divergent

nozzle to represent the pressure loss in the HEX.

Source:

 The Optimization of commercial aircraft environmental control systems (Mainly focused on Pre-cooler section) Isabel Perez-Grande and Teresa J. Leo.

 Optimization of compact heat exchangers by a genetic algorithm G.N. Xiea, 1, B. Sundenb, 2, Q.W. Wanga.

 http://exploration.grc.nasa.gov/education/rocket/nozzle.html

Variable (input) declaration:

 Pressure, temperature, velocity and density at pre-HEX location (form Ansys) is given as input to ‘P2’, ‘Temp2’, ‘vel2’ and ‘den2’ respectively.

 Reduction of frontal area of heat exchanger in percentage, ‘u’.  Mass flow rate of the fluid side, ‘m_dot_f’.

 Temperature range, ‘Tf1’ = inlet refrigerant temperature and required ‘Tf2’ outlet refrigerant temperature.

The ‘P2’, ‘Temp2’, ‘vel2’ and ‘den2’ is stored in F_M.F_M as matrix of values in order of columns in following way

i. s.no

ii. Velocity @ Mach number iii. Temperature [K]

iv. Pressure [Pa] v. Density [Kg/m^3]

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Executing procedure:

Enter the pressure, temperature, velocity and density which are observed at the pre-HEX location (From Ansys). The volume and percentage decrease in dimension can also be entered if there is a change in its value

Note: use the similar setting for coolant as given in the volume_estimation.m

Contents:

The coding have been divided in following sections

1.) Input setting: Inputs are the pressure, temperature, velocity and density which are observed at the pre-HEX location (From Ansys). Mass flow rate of fluid, Inlet and outlet temperature of the fluid side [Required condition].

2.) Data to interpolate: To get the Cp, Viscosity, Density and thermal conductivity for corresponding temperature we are using the data to interpolate the values.

3.) Fixed Data: This consist of fixed data of geometrical aspects taken from the source. 4.) Calculation:

Section 1: The volume that is fixed in volume_estimation.m is checked once again whether it satisfies the cooling range.

Section 2: Estimating the pressure loss of a HEX.

Section 3: Designing of convergent - Divergent nozzle to represent the pressure loss in the HEX

Output

 Pressure drop over the HEX, ‘diff’.  Nozzle’s throat area, ‘A3’.

File 3: Geometry

Type of file: Solid Works Part Document (.SLDPRT)

Objective: To make the CAD model for the flows model of the geometry with parameters, so

that it can be integrated into the ANSYS directly. The main variables which are controlled in SOLIDWORKS are diameter of the pipe, diameter of the orifice for the nozzle, half width of the NACA, NACA length, NACA ramp angle, lip length and lip width.

Parametric Ram Air Channel Model for Flow Optimization