Experimental and Numerical Study of Cavitation Number Limitations for Hydrodynamic Cavitation Inception Prediction

Round 1

Reviewer 1 Report

Title: Experimental and Numerical Study of Hydrodynamic Cavitation Inception.

MS NO: fluids-1702421

 

In this study, different parameters which affect cavitation inception and development are investigated. The authors concluded that cavitation number calculation is insufficient to predict cavitation inception and development in the fluid flow. Both experimental and numerical analyses are presented for this purpose. Ansys software is used for numerical simulation. The following comments should be addressed before a final decision.

 

• The title of the paper is so general. It is better to choose a more illustrative title.
• Has the repeatability of the experiments been checked?
• It is necessary to explain the characteristics of the test equipment in more detail.
• For the mesh grid study (Fig. 4c), the mesh size must be doubled in each step (compared to the previous state). In this case, the common points between two grids of different sizes are recognizable and the comparison is more meaningful.
• Please be more careful about using the word "validation" and “verification”. Please see the following reference for more information:

ASME, Standard for Verification and Validation in Computational Fluid Dynamics and Heat Transfer, ASME V & V, 20-2009, 2009, New York: American Society of Mechanical Engineers.

• Using ultrasonic vibration is another way to generate micro-bubbles. In fact, acoustic cavitation is a very interesting phenomenon in engineering applications and can affect the efficiency of exchangers. It is suggested that this phenomenon be mentioned in the introduction to make readers more familiar. Referring to the following papers will be useful in this regard.

https://doi.org/10.1016/j.ultsonch.2018.10.032; https://doi.org/10.1016/j.applthermaleng.2018.09.113

Author Response

• The title of the paper is so general. It is better to choose a more illustrative title.

Good point. Title was changed to more specific.

• Has the repeatability of the experiments been checked?

Yes, we were running these experiments 2-3 times for each flow regime and had a good repeatability for cavitation inception and development scenario. 

It is necessary to explain the characteristics of the test equipment in more detail.

More details were added

• For the mesh grid study (Fig. 4c), the mesh size must be doubled in each step (compared to the previous state). In this case, the common points between two grids of different sizes are recognizable and the comparison is more meaningful.

More of the mesh study discussion was added and Figure 4 was modified.

• Please be more careful about using the word "validation" and “verification”. Please see the following reference for more information:

ASME, Standard for Verification and Validation in Computational Fluid Dynamics and Heat Transfer, ASME V & V, 20-2009, 2009, New York: American Society of Mechanical Engineers.

Good point. “Verification” sentence was modified.

• Using ultrasonic vibration is another way to generate micro-bubbles. In fact, acoustic cavitation is a very interesting phenomenon in engineering applications and can affect the efficiency of exchangers. It is suggested that this phenomenon be mentioned in the introduction to make readers more familiar. Referring to the following papers will be useful in this regard.

https://doi.org/10.1016/j.ultsonch.2018.10.032 ; https://doi.org/10.1016/j.applthermaleng.2018.09.113

Papers were added to introduction.

 

Reviewer 2 Report

1.This paper studies the phenomenon of hydrodynamic cavitation, shows the cavitation phenomena of several cavitators with different structures through experiments and simulations, and also discusses the cavitation number, which is relatively innovative.

2.The unstructured mesh is used in the model meshing process, and the boundary layer is not set, which may have some influence on the simulation results, and it is suggested to add the boundary layer in the meshing process.

3.The experimentally taken images are not particularly clear, and the cavitation at the boundary cannot be seen to compare well with the simulation results. It is recommended to increase the ambient brightness or use a high-speed camera to take pictures.

4.Line 341 for convergent and divergent nozzles in the conclusion of the description of only textual descriptions, lacking the support of data diagram and simulation results. It is recommended to give simulation results for several data points near the critical pressure drop.

5.There is a punctuation problem in line 374 of the article. Is the temperature range 25-25°C correct in line 386? It is recommended to double check the article statements and vocabulary.

 

Author Response

2.The unstructured mesh is used in the model meshing process, and the boundary layer is not set, which may have some influence on the simulation results, and it is suggested to add the boundary layer in the meshing process.

More details about mesh study were added.

3.The experimentally taken images are not particularly clear, and the cavitation at the boundary cannot be seen to compare well with the simulation results. It is recommended to increase the ambient brightness or use a high-speed camera to take pictures.

4.Line 341 for convergent and divergent nozzles in the conclusion of the description of only textual descriptions, lacking the support of data diagram and simulation results. It is recommended to give simulation results for several data points near the critical pressure drop.

Cavitation zone was marked on the pictures and scale was added to CFD results for better comparison.

5.There is a punctuation problem in line 374 of the article. Is the temperature range 25-25°C correct in line 386? It is recommended to double check the article statements and vocabulary.

Misprint was corrected

 

 

Reviewer 3 Report

Below is the list of my objections:

• In the abstract, only the background was shown enough. The methods, results, and conclusion of the article should be also briefly presented.
• The purpose and scope of the carried out research need to be better communicated at the end of the introduction. Now we do not know what and how will be investigated. (Line 100-103)
• The parameters of the flowmeter, pressure gauge, and microphone must be presented (manufacturer, model, measuring range, accuracy).
• The hydraulics entrance length was included during the simulation?
• What was y+ parameter? Which wall function was used?
• The investigation of the velocity in point M is insufficient to determine the correct mesh size. The description in figure 5 is also unconvincing.
• The experimental and numerical investigation was made in the paper. Therefore, you should always mark what data is presented on the chart (experimental or numerical).
• From where are the data presented in fig. 13, 14, 15? They are from your simulation, or from another paper? Nowhere has it been mentioned before that such research will be done.
• 5 from 22 (number 2, 5, 14, 15, 16) references were made by the authors of this article. Moreover, they are cited collectively, which shows that their citation does not contribute anything significant to the work eg. line 31 "...hole drilling [3 – 5]." or line 93 "In [14-16] cavitating...". It is an abuse, especially the authors not mentioned many interesting investigations about cavitations eg.
  • https://doi.org/10.1017/jfm.2021.114
  • https://doi.org/10.1007/s00348-021-03260-1
  • https://doi.org/10.1038/s41467-021-27383-5
  • https://doi.org/10.1073/pnas.1702502114

Literature is outdated and poor. Please do a wider review of the literature and complete it with the latest (max 5 years) research.

Author Response

• In the abstract, only the background was shown enough. The methods, results, and conclusion of the article should be also briefly presented.

Abstract was modified and some details and results were added.

• The purpose and scope of the carried out research need to be better communicated at the end of the introduction. Now we do not know what and how will be investigated. (Line 100-103)

More details were added to Lines 100-103

• The parameters of the flowmeter, pressure gauge, and microphone must be presented (manufacturer, model, measuring range, accuracy).

More information was added.

• The hydraulics entrance length was included during the simulation?

No, it was not included. Clarification is added to text.

• What was y+ parameter? Which wall function was used?

Information about y+ parameter was added.

• The investigation of the velocity in point M is insufficient to determine the correct mesh size. The description in figure 5 is also unconvincing.

More of the mesh study discussion was added and Figure 4 was modified.

• The experimental and numerical investigation was made in the paper. Therefore, you should always mark what data is presented on the chart (experimental or numerical).
• From where are the data presented in fig. 13, 14, 15? They are from your simulation, or from another paper? Nowhere has it been mentioned before that such research will be done.

Information was added

• 5 from 22 (number 2, 5, 14, 15, 16) references were made by the authors of this article. Moreover, they are cited collectively, which shows that their citation does not contribute anything significant to the work eg. line 31 "...hole drilling [3 – 5]." or line 93

This literature was re-arranged.

• "In [14-16] cavitating...".

This part was modified, more details were provided, to justify citations (in the context of cavitation number calculation and value review) and one paper was removed.

•  It is an abuse, especially the authors not mentioned many interesting investigations about cavitations eg.
• https://doi.org/10.1017/jfm.2021.114

This paper was added to literature review.

• https://doi.org/10.1007/s00348-021-03260-1

This paper is related to hydrodynamic cavitation and cavitation number, and the main goal of literature review was to demonstrate wide spread of cavitation numbers in hydrodynamic cavitation applications as well as different modifications of classic cavitation number.   “Podbevšek, D., Lokar, Ž., Podobnikar, J., Petkovšek, R., & Dular, M. (2021). Experimental evaluation of methodologies for single transient cavitation bubble generation in liquids. Experiments in Fluids, 62(8)” is related to study of single bubble dynamics and doesn’t study cavitation inception and development conditions based on cavitation number.   

• https://doi.org/10.1038/s41467-021-27383-5

This paper was added to literature review.

 

• https://doi.org/10.1073/pnas.1702502114

This paper was added to literature review.

 

Literature is outdated and poor. Please do a wider review of the literature and complete it with the latest (max 5 years) research.

2 more recent papers were added in addition to papers added above

 

Round 2

Reviewer 1 Report

All the comments are addressed now.

Reviewer 3 Report

The authors complied with the comments. It is a pity that they are sometimes completely uncritical, for example as regards the cited papers. However, the quality of the article has improved, which was the main focus of the review.

It must be noted that the used y+ value is very large and should be lower than 1 in the case of k – ω model. But the experimental and simulation results are similar and therefore I believe there is no need to improve the simulation model.