Effect of Dissolved Carbon Dioxide on Cavitation in a Circular Orifice
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsSee below in comments.doc.
Comments for author File: 
Comments.pdf
It is fine.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors present a study on orifice cavitation. They reproduced the experiment by Nurick and extended it by a variation of the non-condensable gas content.
Major comments:
1. The introduction is somewhat verbose, with some secondary information. For example, it is not necessary to review all details of experimental procedure in the review, but rather focus on the results / conclusions from literature studies. As another example, there are some fundamentals of multiphase CFD listed at the beginning of section 1.2. I recommend making the introduction more concise.
2. Related to comment 1: the introduction contains repetitions, for example, L 37/38 and 49/50.
3. Although the intro is lengthy, it seems somewhat incomplete. For example, the experimental studies by Freudigmann et al., which are similar as the one by Kowalski et al. [23], are not considered (https://doi.org/10.1115/1.4037048).
4. Eq. (2): what is p_cav1,2?
5. Section 3.2: is the experiment performed continuously, or in batch mode? In the latter case: what is the feasible measurement duration?
6. Section 3.2: what is the exact geometry of the test section? Is the cross-section rectangular (due to optical reasons) or circular? The former may be better for flow visualization, but generates secondary flow in the corners. What is the inlet conditions (fully developed flow?), relevant for boundary conditions of CFD.
7. Section 3.3: as far I understand the authors use somewhat like a Mie scatter technique. Why not using shadowgraphy / transmission light technique as many other studies? This should be critically discussed.
8. I guess the model by Lifante as well as the one by Zwart contains empirical parameters which are case-dependent and should be calibrated to data? Could the authors discuss this in the paper? In this context, the simulation study by Limbach et al. (https://doi.org/10.1115/1.4040069) may be relevant.
9. Section 4: while sufficient information is provided on the mathematical model, essentially no information is provided on the numerical scheme. It is not sufficient to simply mention which commercial software has been used. Information on solution scheme (steady/unsteady), discretization, grid dependence … is indispensable.
10. L586-590: the explanation / discussion looks rather speculative. What about reproducibility of the experiments?
11. In Fig. 1, flow direction seems from left to right, while in Fig. 8, it seems to be from right to left. Please, clarify.
12. Fig. 9/10: regarding the cavity length evaluation: could the authors provide information / a critical discussion on sensitivity of optical threshold for evaluations the “maximum zone length”?
13. In Fig. 13, error bars indicate a deviation of instantaneous CD measurement from the mean. Therefore, Eq. 3 requires instantaneous evaluation of m^Dot_a and m^Dot_t. Which is the temporal resolution and measurement accuracy of flow rate and pressure sensors?
14. L957 ff and Fig. 16: the mass flow rate and of course the local void (vapor or non-condensable gas) distribution considerably depends on peculiarities of the simulation setup (wall resolution, turbulence model, circumferential extent of the computational domain (1° vs 360°), cavitation model parameters). Little information has been provided on this, so it is hard to evaluate the simulation results. To my assumption, they should be asses rather from a qualitative point of view. The authors may want to point out limitations of the simulation more clearly.
Minor Comments:
15. I recommend a carful English check. For example, present tense and perfect are mixed in the review in the introduction.
16. Fig. 14: labels in the figure are too small, and number illustration is inappropriate.
Recommendation:
The study is interesting and merits publications. It is very long and verbose, so I recommend to shorten the paper considerably. I have doubt in the reasonability of the simulation results, so they could considerably be reduced or even omitted. Al least, a more critical discussion of the simulation setup and results is required.
After considering this, and my comments listed above, the paper may be published.
Comments on the Quality of English Languagesee comments above.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThank you for considering my comments.
