R EVIEWER ’ S COMMENTS
Author of the thesis: Anjelynn Mae Saligao Guanlao
Name of the thesis: Design and verification of a test rig for research of supersonic ejector
Type of the thesis: Diploma thesis
Reviewer: David Šimurda
Institution of the reviewer: Institute of Thermomechanics, AS CR, v.v.i.
A. Formal belongings of the thesis:
(Rate linguistic and typographical level of work, text structure, sorting chapters, illustrations, correctness and completeness of citations literary sources)
Formally, the thesis meets all necessary criteria. Order of chapters in the thesis is logical, but their numbering should start from the “Introduction”. Titles of individual chapters should be more highlighted since it would help reader with better orientation in the text. The thesis is easy to follow and English is in my opinion on a very good level. There are some mistypings and inaccuracies. E.g. brackets are missing in the equation 5.13 and in some cases indices are incorrect (there should be c3 in the denominator of eq. 5.31). Cells in the tables overflow to next page in one or two places, which makes orientation in the text more difficult. Figures are lucid, however, illustrations of the computational mesh and results of numerical simulations should be shown in more detail or at least in a better resolution. Resultant characteristics obtained by analytical methods and numerical simulations should be presented in one graph. Cited references are relevant and citations are complete.
(excellent minus)
B. Thesis theoretical part:
(Rate the extent and manner of research, a way of describing the problem solved or the suitability and complexity of used theoretical method.)
Literature review is relevant by both content and extent. Chapters dedicated to pressure measurement and mass flow measurement are in my opinion too extensive regarding the fact that no measurements were done in frame of the thesis. Part of the theoretical introduction could be focused on aerodynamic phenomena taking place in the flow through the ejector. However, absence of such chapter probably results from the study programme of the student and therefore it is not assessed as negative. The problem is described sufficiently. To solve parameters of the flow through the ejector and to determine
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characteristics of the ejector, both analytical methods based on balance equations for 1D flow and numerical simulations of 3D periodic flow are used. Using both approaches is assessed very positively.
(excellent)
C. Thesis practical part:
(Rate adequacy and sophistication of the methods used, the level and amount of data obtained.)
To solve parameters of the flow through the ejector and to determine characteristics of the ejector, both analytical methods based on balance equations for 1D flow and numerical simulations of 3D periodic flow are used. Both approaches are appropriate for the given problem and they are both widely used in praxis. Using both approaches proves ability of the student to use and exploit knowledge gained during her master studies. Obtained data are used to determine ejector characteristics and to analyse flow field in the ejector. From this perspective, amount of data is sufficient. Large discrepancies between results obtained by analytical solution and numerical simulations (without detailed explanation), however, rise questions about correct application of the two methods.
(very good)
D. Results analysis:
(Rate the level of processing of data, including the determination of measurement uncertainties, discussion of the results and formulated conclusions.)
No experiments were conducted in frame of the thesis. The student handles results of numerical simulations cautiously regarding problems with the computational mesh.
Insufficient attention is in my opinion paid to very significant discrepancy between results of the analytical solution and numerical simulations. According to numerical simulations, the entrainment ratio reaches value almost 1 at the choked regime while analytical solution predicts value of 0.17. Absolute difference between values of maximal efficiency obtained by the two methods is 15%. There are no explicit statements in the thesis, which of the two results better corresponds to reality (based on references).
Conclusions are formulated clearly and they follow out from the work done. Conclusion about the discrepancy between the results obtained by the two methods is missing, however.
(very good)
E. Level and quality of the thesis:
(Rate overall complexity and scope of work and original contribution of the student.)
A test rig for research on supersonic ejector was designed in frame of the thesis. Criteria of the design were clearly stated and the design take these into account. Work characteristics and parameters of the flow through the ejector were obtained using analytical methods and
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numerical simulations. Analysis of the flow filed in the ejector was done based on the results of numerical simulations. All these efforts make the thesis complex.
Original work of the student (as far as I can tell) consist of the design of the ejector, making of the geometric model, generating computational mesh, running numerical simulations using commercial code, and analysing the results. To determine ejector characteristics analytically, the student used knowledge gained from references. This proves student’s ability to deal with the problem. However, the student could also contribute by more detailed analysis of the differences between results.
(excellent minus) Overall evaluation:
The thesis meets all the necessary criteria regarding both content and form. The student proved ability to use in praxis knowledge gained during her studies. To solve the problem, the student exploited available literature and used several independent methods and approaches. The thesis contains several mistypings and inaccuracies. The most significant shortcoming of the thesis is in my opinion insufficient explanation of the differences between results obtained by analytical methods and numerical simulations.
Questions for the defense:
1) Derive the relation for efficiency of the ejector (eq. 5.13) and based on this relation, explain how the losses described in the paragraph 5.2 affect the efficiency.
2) What is the benefit of the analytical solution when the difference between the analytical and numerical solution is so significant?
3) What is the meaning of the pressure referred to as “Operation pressure” in Table 7?
Qualification:
Work meets the requirements for the granting of a degree, therefore I recommend it for the defense.
I suggest this work to classify as “Excellent minus”
In Prague datum 9.6. 2016
I certify that I am not in any personal relationship with the author of the work
Reviewer’s signature
