Geometry, Mesh and Numerical Scheme Influencing the Simulation of a Pelton Jet with the OpenFOAM Toolbox

Round 1

Reviewer 1 Report

In this paper, the numerical simulation analysis of Pelton turbine was introduced in detail, and the flow of Pelton jet is analyzed by OpenFOAM method. The influence of the nozzle geometry, the grid and the numerical schemes is discussed, and the influence of nozzle geometry on jet is obtained. It is recommended to receive the paper after the author has made the following revises:

1. Enrich the introduction part of the paper;

2. In Section 3, Geometry and computational domain, there is little information about geometric parameters of Pelton turbine, it is suggested to add this information.

3.In Figure 6, what are the factors that affect whether the surface is smooth?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Summary of The Paper:

This paper uses OpenFOAM toolbox to conduct numerical simulation on existing Pelton injector,focusing on the influence of nozzle geometry, mesh and numerical scheme on the jet detachment, thus affecting the jet shape and the discharge. The results show that the detachment,shape and discharge of the jet can be accurately calculated by selecting the refined mesh which is as consistent as possible with the geometric shape and combining with the "SUPERBEE" limiter. In addition, the discharge predicted by the simulation is compared with the measured one.

 

Main Review:

Basically, by studying the influence of related parameters on Pelton jet in the simulation, the author makes the prediction of jet detachment, which is of great significance to reveal the internal flow characteristics and quality of Pelton turbine. Most of the papers are well written and easy to understand. The discussion of simulation results is clear and detailed. But there are still some problems to consider.

 

There are the following problems that I think need to be improved:

1.     Figure 3 shows the grid view at the nozzle outlet, but the picture is blurred after enlargement. It is suggested to improve the picture quality.

2.     What is the specific definition of the two needle strokes S considered in the article? And is there any basis for choosing these two strokes?

3.     For the given equations 6 and 7, the meaning of the symbols should be explained.

4.    In Table 3, it is observed that  represents the difference between the non-dimensional flow predicted by the limitedLinear and SUPERBEE limiters. However, for the stroke of 85%,  is 1.4%. Please check carefully if there is a calculation error.

5.     In the design of simulation conditions, the design of the original geometry and mesh type 1, the stroke was 50% as control group, the single variables, mesh, geometry and stroke, were respectively changed as 3 experimental groups, whether can you consider increasing the multivariate group such as the design of grid type 2, the modified geometry shape, and 85% of stroke,on this basis,to supplement the simulation results, make the conclusion more convincing, and enrich the whole paper.

 

Summary of The Review:

In general, considering the significance of the researched problem, I suggest that this paper can be accepted by MDPI. However, some points should be clarified and strengthened in the revision. I would like to strongly support this paper if my concerns can be fully addressed.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

The reviewed paper presents the results of research on the influence of the nozzle shape on the jet detachment at the outlet of a Pelton injector. Fluid flow analysis was performed based on simulations obtained by numerical methods of computational fluid dynamics. The authors also analyzed the impact of the mesh resolution and the limiter used for the discretization of the convective fluxes on the result of numerical calculations. There are hundreds of works on fluid flow in Pelton turbines in the literature. However, I have not found a paper that analyzes the influence of the numerical scheme used to the discretization of the convective fluxes on the result of numerical calculations. Additionally, the results of the calculations were compared with the previously published results of measurements carried out in a small water power plant. For this reason, I believe that the work contains an element of scientific novelty. However, before publishing, I suggest introducing a few changes:

1. Introduction. The relevant works for stirred vessels with tubular baffles should be reviewed, for example: Tarodiya R., Khullar S. Levy A., Assessment of erosive wear performance of Pelton turbine injectors using CFD-DEM simulations, Powder Technology, Volume 408, 2022.

2. Authors should explain in the paper the reasons for the assumptions made, for example

Line 85: “ca is a user parameter set to 1 for the present study”

Lines 141-143: “Excepted for the simulation with the mesh type 2, the under-relaxation coefficients are set to 0.3 for the pressure and 0.7 for the velocity. For the simulation on the mesh type 2, these coefficients are set to 0.9 and 0.5 respectively.”

3. Lines 132: “The "limitedLinear" limiter is more diffusive than the "SUPERBEE" limiter.”

Why the limiter is more diffusive? Please explain in the article.

4. Chapter “6. Results”

The authors described in detail the results of numerical calculations. However, I have not found any information that explains the obtained research results. For example, why an anti-diffusive limiter gives better calculation results.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments:

1) Line 7-9: It is stated "The compactness of the jet is mainly dependent of the location of the jet detachment at the nozzle outlet, which is challenging for computation fluid dynamics simulations." Please add a sentence that explains why CFD computations of this problem is challenging. Is it difficult due to the numerical duffison and/or numerical dispersion during the numerical solution of dominant convective flow.

2) Line 15: Please correct the typo "SUPERBBEE" 

3) Why haven't you tested other schemes in your simulations, such as "MINMOD", "SMART", "OSHER", "QUICK", "UMIST", "LUST", "VANLEER" etc. ? 

4) Table 1 is quite confusing. Instead of using "mesh type" in the manuscript, please name your meshes as M(coarse) and M(fine) because you use same type of mesh elements, which is mainly hexhedral, in the simulations. When "mesh type" is used, one can understand the type of mesh elements (e.g., hex, tetra, prism etc.).

5) Please explain how the amount of number of cells are selected. As a rule of thumb or according to y+ value. 

Thanks

Author Response

Please see the attachment

Author Response File: Author Response.pdf