Numerical Simulation of Cavitation Performance in Engine Cooling Water Pump Based on a Corrected Cavitation Model

Round 1

Reviewer 1 Report

This paper deals with a computational study for the conditions under which bubbles are formed inside a cooling water pump; a process that the usually denoted as "cavitation".

The authors show that the cavitation process is enhanced at higher temperatures, which in my opinion is a problem since obviously a lack of performance in the cooling pump creates more cavitation that in turn will damage more the system.

The authors develop their methods correctly and the manuscript presents a number of plots with results of interest.

I recommend publication in the Processes journal.

However, the authors should take care of a series of points that can be improved:

1- The manuscript is too long. The results can be presented coherently in a reduced version of the paper. I find the introductory part of the computational methods unnecessarily long (the verification model sections can probably be shortened).

2- On the contrary, I miss more explanation on the software used by the authors and also on the theoretical basis for the used set of equations; i.e., eqs. (1)-(2).

3- English mistakes are abundant. The manuscript should be thoroughly revised in this aspect before publication.

Author Response

Thanks again to the reviewer. Your comments and insights are very help for revising our paper, as well as the important guiding significance to our following research. We are looking forward to getting more guidance from you.

Best regards,

Wei Li

Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper, the authors study numerically the evaporation due to cavitation in a water pump using a commercial CFD software. In particular, the role of the temperature in the cavitation effect is studied. For this purpose, a "corrected model" of phase change is introduced.

Overall, the paper is readable and interesting. However, some comments below should be addressed by the authors before the paper can be recommended for publication.

Comments

* The main weakness of the paper is the presentation and justification of the new model. The novelty and the need for the "correction" should be more clearly presented.

The authors states that the model of Zwart et al is inaccurate from a thermodynamical point of view. I agree with them: Zwart et al seems to make the hypothesis of an isothermal flow. It is a very strong hypothesis since phase change may involves temperature variations and temperature gradients.

If I understood correctly the paper, the "correction" proposed by the authors is only to take the same isothermal model at a different fixed temperature. Wouldn't it be fairer to summarize the paper as a sensibility study of the temperature dependency in Zwart-Gerbert-Belamri's model, rather than implying that a new model has been developed?

* The temperature dependency seems to be evaluated using a linearization of the saturation pressure p_v:
p_v(T) = p_v(T_∞) + dp_v/dT (T - T_∞),
where dp_v/dT is given by the Clapeyron relation.
Wouldn't it be easier and more accurate to just get the value of the saturation pressure at 25°C, 50°C and 70°C in any reference table and use it in (4-5)?

* Although the authors provide a nice overview of some previous papers in the introduction, it is not really clear why they preferred their model instead of the other mentioned models.

* What kind of fluid mechanics model are you using? I'm guessing incompressible isothermal Navier-Stokes equation, but it should be stated more explicitly.

* l. 153-154: did you take these temperature dependencies into account? Which value did you use for the material properties at each temperature?

* l. 214: "the thermodynamic effect has been taken into account".
Only a single 70°C experimental test case seems to be presented for the validation. Can you really state the influence of temperature is correctly modeled with a single value of temperature?

* l.349: "otherwise, cavitation will be inhibited in some extend by thermodynamic effect". Did the authors actually test any temperature above 70°C? This statement is very surprising to me, since I would have expected cavitation to become easier when the temperature rises. At 100°C the water should even start to evaporate without any pressure variation (assuming a reference pressure of 1 bar).

Typos and presentation

* Title and abstract: "the corrected cavitation model" -> "a corrected cavitation model"

* Author affiliation 3 is missing?

* Eq. (4-5): I guess you are using m+ when p < p_v and m- when p > p_v. It should be stated more explicitly. Same for eq. (6-7).

* l.123 and l. 137 seem to give two different values for the average bubble radius: 1·10^-6 (no unit) and 2·10^-6 mm. Could the authors clarify that?

* Eq. (6-7-8), the model seems to be independent of the dynamical pressure p. Should p_∞ be instead p?

* l.166: "ρv is the vapor pressure of the surrounding liquid"?

* l.167: "ρl is the pressure of the surrounding liquid"?

* Is the "NACA66" from the introduction the same as the "NACA0066" from section 3.2?

Author Response

Thanks again to the reviewer. Your comments and insights are very help for revising our paper, as well as the important guiding significance to our following research. We are looking forward to getting more guidance from you.

Best regards,

Wei Li

Author Response File: Author Response.pdf

Reviewer 3 Report

Cavitation can severely limit performance of hydraulic machines and its computational prediction is of great importance in the design process.

Authors, in their simulation of ECWP pump, decided to make a correction of the currently used cavitation model to account for the the influence of the water temperature and first test it on available data from hydrofoil experiment and then apply it to two-phase simulation of pump impeller.

Unfortunately as a reviewer I have to state that from both technical and formal aspects they did not deliver a good paper. It seems that the text was prepared very quickly and lacks a lot.

Logic of the text flow is strange. First the pump is introduced including computational mesh details, followed by theory concerning cavitation modeling, then simulation of hydrofoil and then again jump to the pump. Authors present extensive review by Chinese authors on cavitation modelling of pumps (and it is completely ok), but almost completely exclude some principal papers by authors of other nationalities: Fortes Patella, Sedlář, Watanabe to name a few. It would help if also specific speed, as the principal parameter of the impeller, was tabulated (yes, it can be computed from speed, head and flow rate, but it would be nice to see it immediately) It is not apparent from chapter 3.2 whether 2D or 3D simulation was performed. While hydrofoil span is mentioned on line 175, there is no information about BCs on the sidewalls. Also the graphs 6 and 7 look like from 2D simulation. Once again incomplete and confusing information is provided to the reader. One of the main chapters in the paper should be introduction of the correction term, which accounts for thermal effects. However this part is missing and also authors do not provide at least some reference to previous work (theirs or other author’s ?). Equation (8) is not equation, it misses equal sign, it is merely algebraic relation What is the unit of R_B on line 123 (probably meters)? Average bubble radius diameter 2x10^{-6} mm on line 137 is not very likely, probably it should be meters not milimeters What were the sizes of meshes used for mesh independence study of ECPW pump? It is not advised to make any conclusions about cavitation development from frozen rotor simulation, moreover for one fixed rotor-stator position! Cavitation itself is highly unsteady and unstable phenomenon and transient simulation is required! It is recommended to use well established parameters for description of cavitation regime like NPSH_3 (or Thoma cavitation number) instead of the inlet pressure. Cavitation in hot water does not have so high erosive potential as in cold one. I am not sure whether it also applies to kerosene, but probably yes. Authors should be careful in drawing conclusions about aggressiveness of cavitation in liquid with higher temperature. Text needs careful English proofreading (e.g. line 327 … energy of allover the impeller…, line 176 … at 100 mm front of …., line 347 An critical …, line 366 … expandgradually …, and many other locations)

From above mentioned reasons I cannot make any other conclusion than to recommend rejection of the paper. It is reviewer’s opinion that the paper was done in a hurry and reviewer believes that even the authors do not have good feeling from the work they submitted.

If the authors decide to submit a new paper with the same or similar topic (and reviewer encourages them to do so) reviewer would recommend to start completely from the scratch. Below I summarize some recommendations.

Recommendations for new paper submission:

Perform transient simulations of the two-phase flow within pump impeller. Thoroughly document development of the cavitation model corrections. All equations have to be correct. All quantities, if specified with numbers, should have correct units.

Author Response

We really appreciate and admire your valuable help. Your responsible and careful comments are not only conducive to the improvement of this paper, but also conducive to our following research. We have been tried our best to revise, and we really hope you could approve our efforts on this manuscript. We are looking forward to getting more guidance and help from you.

Best regards,

Wei Li

Author Response File: Author Response.pdf

Reviewer 4 Report

Review of 

Numerical simulation of cavitation performance in engine cooling water pump based on the corrected cavitation model

Abstract:

It should be more consistent. For the most part, it is repeated from the article The Correction and Evaluation of Cavitation Model considering the Thermodynamic Effect, https://doi.org/10.1155/2018/7217513

In order to analyze the internal flow of the engine cooling water pump (ECWP) under thermodynamic effect, Zwart-Gerber-Belamri cavitation model based on the Rayleigh-Plesset equation is corrected, and NACA0015 hydrofoil was selected to verify the corrected model.

What really is the topic of the paper?

Analyze the internal flow or verification of the corrected Zwart-Gerber-Belamri cavitation model. Or both?

Introduction – line 28 – 59 mostly same as in the article The Correction and Evaluation of Cavitation Model considering the Thermodynamic Effect, 2018, https://doi.org/10.1155/2018/7217513

The convergence criterion was set as 10^-4    line 135   ??? More details should be given about this. What criteria?

10^-4 is probably not sufficient accuracy for all criteria (energy equation!).

Table 2 - Provides only part of the mesh information. In this form, the question is whether it is necessary.

line 138 - vaporization pressure pv is set as 3574 Pa   - How was this value selected? It would be good to explain these values.

Grid independence verification

Results for the 2.4 mil element mesh are described (only). Not shown a diagram which shows difference in head.

line 175, 236, 237, 287 etc. - typos errors, needs a space between the amount and the unit of measure.

There are many more typos in text.

Figure 3, 4 and 5 – source not given

Figure 6 and 7 not cited but same as in https://doi.org/10.1155/2018/7217513

line 227/228

Design condition – explain (with no cavitation?)

In picture P(Kw) - ??

line 237

Why 3700 r/min is selected? What about the lower values?

Line 236

Why is the temperature 70 °C selected?

Nomenclature not given

Author Response

We really appreciate and admire your valuable help. Your responsible and careful comments are not only conducive to the improvement of this paper, but also conducive to our following research. We have been tried our best to revise, and we really hope you could approve our efforts on this manuscript. We are looking forward to getting more guidance and help from you.

Best regards,

Wei Li

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The main comments in my previous review were misunderstandings due to missing information in the first version do the paper.
This has been improved in the revised version. Adding in Section 2.2 a reference to the derivation of the model in [24] might also be helpful for the reader.

Except for the few issues below, the paper is fine.

Major issue

The phase change term m+ (resp. m-) seems to be independent from the dynamical pressure p. It would mean that a change of pressure at constant temperature has no effect on the phase change rate. It is a strong hypothesis for a cavitation model. Could you please comment on that?

Minor issues

* Symbol L in eq. (3) and (6) is undefined.

* The phase change term m+ (resp. m-) does not appear in the main governing equations (1)-(3). Is another evolution equation missing?

* What equation of state or constitutive laws did you use to model the behavior of the fluids? Are they compressible or incompressible?

* The software that has been used for the numerical simulation does not seem to be mentioned in the revised version of the paper.

Several grammar errors and typos, including:
nomenclature: "coefficien" -> "coefficient"
l. 49: "to studied" -> "to study"
l. 116 "tabel" -> "table"
l. 189 "it's" -> "its"
fig. 4: "hydrofoi" -> "hydrofoil"
and others. A careful proof-reading is required.

Author Response

Thanks again to the reviewer. Your comments and insights are very help for revising our paper, as well as the important guiding significance to our following research. We are looking forward to getting more guidance from you.

Best regards,

Wei Li

Author Response File: Author Response.pdf

Reviewer 3 Report

Congratulations to authors for submitting significantly improved version of the paper!! Adding the chapter with transient simulations, evaluation of the frequency spectra of pressure fluctuations and influence of the cavitation on unsteady fluctuations of the head increased scientific level of the paper substantially together with more detailed description of the models.

I only have some minor comments, which shoud be reflected:

my only serious technical remark is that 6 degrees impeller rotation per times step is very rough, usually 1-3 degrees are recommended on line 225 there should be condesantion coefficient 0.002 (not 1) indication of millions is missing in the second column of Table 2 indication of non-dimensional time is missing on axis of fig.18 sentence „… NACA0066 model as the cavitation model, …“ is confusing and should be reformulated in nomenclature it would be better to use thermal term instead of thermal item throughout the paper term „velocity“ should be used instead of „speed“ (e.g. blade outlet speed -> blade outlet velocity) paper is still abundant with typos, bad English, improper terminology (e.g. steam line -> streamline on lines 290, 458; scaled -> scale on line 461; studied -> study l. 49; cavity number -> cavitation number l.54; Tabel -> Table l. 116; need->needs l. 145; considering->considers, and many many others]. Therefore English proofreading is necessary!

Author Response

Thanks again to the reviewer. Your comments and insights are very help for revising our paper, as well as the important guiding significance to our following research. We are looking forward to getting more guidance from you.

Best regards,

Wei Li

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear,

text is improved but still there are errors. For example:

Line 38 .... is mass fraction of gas phase; PrL and Prt r   ->  Pr to italic

Symbols

ρ: density (kg3 /m3 )   - I think that sign :  is not necessary

Not all variables defined in nomenclature. For example p∞, T∞

Line 179  temperatures is respectively set as 3574 Pa(25 ℃),

12310 Pa (50 ℃)  -

31164 Pa (70 ℃)  - 

Maybe is good to specify source of data

I can found 3170 Pa for 25 °C

I can found 12351 Pa for (50 ℃)

I can found  31201 Pa

(IF-97 Steam tables. By: Magnus Holmgren)

Still there are typos errors in text. For example 

164 under different temperatures. Total pressure was set as the inlet boundary condition,the reference

253 temperature is 25 ℃, flow rate is 150 L/min with3700 r/min rotation speed . When inlet absolute

Fig.10 Cavitation formation process. (line accross tekst?)

Kind regards,

Author Response

Thanks again to the reviewer. Your comments and insights are very help for revising our paper, as well as the important guiding significance to our following research. We are looking forward to getting more guidance from you.

Best regards,

Wei Li

Author Response File: Author Response.pdf