Development of Ultra-Low Specific Speed Centrifugal Pumps Design Method for Small Liquid Rocket Engines
Round 1
Reviewer 1 Report
please find attached
Comments for author File: 
Comments.pdf
Author Response
The authors appreciate the reviewer’s thoughtful comments.
In this study, many empirical formulars were used for designing ultra-low specific speed centrifugal pumps. The empirical coefficients are derived from each empirical formular, most of which are determined by the specific speed value, so if the design point changes and the specific speed changes, then the coefficient values may vary. In addition, rather than adjusting the coefficient, it can be said to be a value calculated through an empirical formular by the design point. In this study, there is no part where arbitrary coefficients are applied in the design of the pump.
The commercial CFD program, Star-CCM+ 2021.1, was used. Cavitation occurs when the pressure is lower than the vapor pressure of the fluid. Cavitation modeling is built on Star-CCM+, but this study predicted cavitation by confirming whether the lowest pressure in the pump is higher than the vapor pressure. Both the design method proposed in this study and the Stepanoff design method confirmed that the pressure is higher than the vapor pressure within the pump. However, the authors found that the lowest pressure was different with design methods. When the design method suggested in this study was applied, it was confirmed that the minimum pressure was larger and safer from cavitation.
In this study, the simulation performed a three-dimensional RANS steady-state analysis of incompressible flow, and the water density was specified as a constant value of 997.561 kg/m3, so the effect of the compressibility of the fluid was not considered.
Although the CFD simulation results were not compared with the experimental results, the numerical method applied in the present study is the same as in several previous studies for performing flow analysis in the pump [1-3]. In addition, the results show that the CFD results are similar to the theoretical values. From these, the authors believe that the simulation results derived in this study are sufficiently reliable.
The above has been supplemented in the manuscript.
[1] Ayad, A. F.; Abdalla, H. M.; El-Azm, A. A. Study of the Effect of Impeller Side Clearance on the Centrifugal Pump Performance Using CFD, Proceedings of the ASME 2015 International Mechanical Engineering Congress and Exposition, 2015
[2] Pyun, K. B.; Kim, J. H.; Choi, Y. S.; Yoon, J. Y. Design Optimization of a Centrifugal Pump Impeller using RSM and Design of Volute, The KSFM Journal of Fluid Machinery, 2012, 15, 39-45
[3] Shim, HS.; Kim, KY.; Choi, YS. Internal Flow Characteristics of a Centrifugal Pump with Various Specific Speeds, The KSFM Journal of Fluid Machinery, 2017, 20, 26-35
Reviewer 2 Report
A schematic representation of the proposed method is suggested.
I think that the work is well done as it provides very interesting results and comparisons with classical methods adopted for the design of Ultra-Low Specific Speed Centrifugal Pumps for Small Liquid Rocket Engines. Then, as far as I am converned the work should be published after this minor revision.
Author Response
The authors deeply appreciate the reviewer’s efforts in reviewing the manuscript and the recommendation for publication.
Figure 2 shows the design procedure for the proposed method in this study. This flow chart presents the entire design process, from the required inputs at the beginning of the design to determine the design parameters for the whole procedure. The efficiency calculation of a pump has been added to present the procedure more clearly.
This has been supplemented in the manuscript.
Reviewer 3 Report
This manuscript is on the design of low flow rate pumps for small form factor liquid rocket engines. The authors have submitted a thorough and well-received body of research. This reviewer suggests this paper for publication. This reviewer only has a couple of items/questions mentioned below.
lines 253, 259, and 403 are not properly referencing their respective figures and need to be addressed.
The CFD study uses water as a liquid surrogate which does help limit the scope of the research. It would be worthwhile to mention and include a citation for this justification to address how most fuels that are liquid at room temperature will benefit from their study.
Author Response
The authors thank the reviewer’s thoughtful comments and recommendation for publication.
The reference to each figure in lines 253, 259, and 463 of the manuscript has been modified.
In this study, water was used as a working fluid, and there have been several cases using water as a similar medium for pump design [1-3]. In particular, there are cases where the performance of pump has been tested using kerosene and water, and according to the report, the hydraulic performance is known to be the same, but there was only difference in density with each medium[1]. In addition, the turbopump of a liquid rocket is a fully turbulence system in which the Reynolds effect remains relatively constant because it operates at high speed. Accordingly, it is known that the similarity of the pump performance is preserved even if the Reynolds number according to the fluid is not perfectly scaled[2]. Thus, it has the advantage of being able to confirm the pump performance in advance using water before using the real medium.
This has been supplemented in the manuscript.
[1] Kwak, H. D.; Kim, DJ.; Kim, JS.; Kim, J.; Noh, JG.; Park, PG.; Bae, JH.; Shin, JH.; Yoon, SH.; Lee, H.; Jeon, SM.; Jeong, E.; Choi, CH.; Hong, SS.; Kim, SL.; Kim, SH.; Han, YM. Performance Test of a 7 tonf Liquid Rocket Engine Turbopump, Journal of the Korean Society of Propulsion Engineers, 2015, 19, 65-72
[2] Welle, R. P.; Murdock, J. W.; Hardy, B. S. A Water Test Facility for Liquid Rocket Engine Turbopump Cavitation Testing, Proceedings of the 7th International Symposium on Cavitation, 2009, 11
[3] Pauw, J. D.; Veggi, L.; Wagner, Bernd.; Mondal, J.; Klotz, M.; Haidn, O. J. Design Procedure of a Turbopump Test Bench, International Symposium on Transport Phenomena and Dynamics of Rotating Machinery, 2017
Round 2
Reviewer 1 Report
I don't have any comments anymore.
