Numerical Study on Dynamical Structures and the Destratification of Vertical Turbulent Jets in Stratified Environment

Round 1

Reviewer 1 Report

REVIEW:

 

Numerical study on dynamical structures and the destratification of vertical turbulent jets in stratified environment

 

This manuscript studies through numerical means the interaction between vertical turbulent jets and stratified flows. A broad set of vertical jets and varying densities were cross-compared. The work herein presented is certainly within the scope of the journal of Water. However, the incompleteness and the lack of clarity in some parts of the text should be amended prior to publication. My current decision is major revision and I reckon the author to take into consideration all the queries listed below to improve the overall quality of the manuscript.

Major comments:

- A research question or goal is lacking. It seems that the manuscript has one goal: evaluation of the vertical jets by means of LES simulations and with a varying set of Froude and Reynolds number. This goal is not explained or justified, why did the authors choose to assess the performance of those parameters?, and why those values?. Where can we find the novelty in the approach outlined in this manuscript?.

- The introduction does not frame sufficiently the problematic of stratified flows. In lines 35 and 37 the authors should stress the importance of such flows in the control of turbidity currents in lakes and reservoirs. Authors should read and acknowledge the following references [1,2].

-Line 38: “…to control stratification”. Authors should mention that artificial re-suspension of particles by means of jets (i.e. stratification due to the entrainment of sediment particles within the water column) is used in reservoirs to mitigate sedimentation, specifically for venting techniques. Please, check [2].

- The results and discussed sections are mixed. A thorough discussion section is missing. Results are given, but what do we learn from the results? What do we learn about modeling of vertical jets, or practice and strategies in real engineering life?.

- The study is based on numerical results computed by means of LES. Vertical jets and stratified flows modeling on a small numerical domains needs at least a short discussion about scaling issues. Application of a model in a toy-domain does not say much about the model capabilities in a real-scale situation. Thus, please discuss whether the results and model are applicable for real-scale situations, and whether there would be any differences in the model results.

- Units of the variables plotted in each figure are missing. For instance, Figure 17, displays the vorticity, however this is not a dimensionless variable and thus, the units need to be amended. Please, check all the figures. 

 

 

REFERENCES

 [1] J. Zordan, C. Juez, A. J. Schleiss and M. J. Franca. Entrainment, transport and deposition of sediment by saline gravity currents. ADVANCES IN WATER RESOURCES. 2018.

 [2] Schleiss A.J. et al.  Reservoir Sedimentation. JOURNAL OF HYDRAULIC RESEARCH. 2016.

 

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

• Justify the numerical values used for $C_s, Pr, Pr_t$ (where have those values been validated, what for ?)
• Justify better the improved disturbance method (how was Menow method validated ? and if your improvement is only to get 4 equiprobable configurations with respect to the probabilistic variations of theta_r, say it more explicitly from the beginning of that section)

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The authors present LES results of jets in stratified layers of water.
I am not a expert of jets or stratified water. But I believe the paper is not very clear overall.
Individual ingredients are there but overal story is not goed enough.
A lot of data is given but it is hard to distil the bigger picture.

The main question that pops up is... is this numerical or physical? This should be adressed by a proper mesh convergence study.

1) line 72: buoyancy frequency --> this term is new for me. Please introduce and explain.

2) Section 2.1: Jet velocity is not mentioned.

3) Eq 2 is for constant density. Dividing the mom. eq by density will give eq 2 IF the density is constant.
If this is not the case an error is made in the viscous term. Please correct this.

4) Line 164: 4 quadrants very hard to read. Perhaps a small fig instead?

5) Section 2.4: What about Re and Fr? Also dimensionless, so appropriate to discuss here, I would guess.

6) Line 174 -176: Cases A1-9 B1-6 mentioned but not introduced yet. Although...
"Numerical cases are detailed in Table 1." Not sufficient... why is table 1 the way it is.

7) Fig 4: No mesh refinement study. Matching results could be due to accidental cancelation of errors.

8) Fig 8 and 9: It is very hard for me to judge if the instabilities we look at are physical or numerical...
This should be addressed!. Perhaps give more insight in numerical method used, or show what happens if mesh and/or timestep changes.

9) Fig 10: Fitting lines not discussed.

10) Fig 13: Fits and fig b not discussed in text. Line 300: Figure 12(b) --> 13(b) ??

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors took into considerations my comments listed in my previous review form. I thus think the manuscript is in good shape to be published.

Author Response

Thank you so much for your time and help.

Reviewer 3 Report

  The authors have not clearly indicated how the comments have been addressed. As far as I can see there is not rebuttal, this makes it hard to judge the changes.   What I can see is the following, the main issue is not tackled adequately. The chaotic solutions depicted in the bottom of Fig 13 shows some form of instability.  Is this physical or numerical? To answer this question more info on the time step,  such as CFL number, needs to be given. As far as i can judge is this is not given.   Furthermore a formal mesh study would be indispensable, the authors however have chosen to  perform a convergence study on a laminar case (A1). This is fundamentally flawed.   1) First validation of A0.  While (mesh) verification needs to be performed first, otherwise the validation might be non-sense. On top of that it is performed using different cases (A0 & A1) while A9 is a much more interesting case.   2) The change from 100 elements to 90 and 110 is to small.   3) The changed solution in Fig 10 on the other hand is relatively large considering the small change in the mesh.   4) In the third direction the mesh is not refined  (80 elements in all 3 cases) this is not a valid mesh convergence study for that reason.     There my verdict is mayor revision. In the revised version please improve:   1) Please indicate in a separate document how the concerns have been addressed.   2) Do a proper mesh convergence study: - larger change in element numbers - in all directions - also for an "interesting" case   3) Perform validation on a verified case.   4) Report and study CFL effects.   5) Convince me that the instability in figure 13e&f is physical and not numerical (see points 2&4).

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

No rebuttal

Round 4

Reviewer 3 Report

Altough, the authors have sufficiently proven adequacy of the solution to be accepted. Nonetheless I remain somewhat sceptic, simulating physical instabilities puts a very high burden of proof of correctness for the method/parameters used.