Experimental Study on the Wake Characteristics of Composite Secondary Grooved Cylinder
Round 1
Reviewer 1 Report
I opined that this paper has some merits for potential publication in Water given the comprehensive study of the numerical study of vortex around grooved cylinder. Several major and minor comments are as below:
1) Introduction. Many theoretical studies were mentioned but not on experimental PIV study. The author should justify why PIV method is chosen in this study rather than numerical experimental study.
2) There are many indicators used in this study but was not explained clearly. For viscous dissipation, the physical meaning is that the energy is transferred in the form of form and viscous drag. Please refer to this suggested recent reference (https://doi.org/10.1016/j.memsci.2021.119599) to support your sentence. Additionally, the other physical meaning of Reynolds Stress should be mentioned in the introduction. Lastly, the physical meaning of the turbulent kinetic energy which is the square of velocity should be mentioned in the Introduction.
3) In figure 1, it is difficult to view what is the difference between b and c. I think the difference is the zoom-in picture in c, which I strongly recommend that a similar zoom-in to be included for b as well to tell the difference
4)Line 134. Does 0.37m/s corresponds to Reynolds number of 7400? This need to be mentioned.
5) What type of Reynolds number is used? Hydraulic or channel Reynolds number? Please specifically mention what is the characteristic length used in this work for calculation of Reynolds number.
6) Figure 7. What is u bar?
7) The optimal frequency is about 7 to 10 Hz, which in the reviewer opinion is quite small for such a high Reynolds number 7400. Please explain this via Strouhal number definition or anything similar.
English writing quality is acceptable
Author Response
We are very grateful for the review’s detailed comments that have helped us improve significantly this manuscript. The major changes to the manuscript have been highlighted in red. Following are actions we have taken to address specific issues raised by the reviewer.
Point 1: Introduction. Many theoretical studies were mentioned but not on experimental PIV study. The author should justify why PIV method is chosen in this study rather than numerical experimental study.
Response 1: As suggested by the reviewer, we have modified the introduction. (line 56-59)
Point 2: There are many indicators used in this study but was not explained clearly. For viscous dissipation, the physical meaning is that the energy is transferred in the form of form and viscous drag. Please refer to this suggested recent reference (https://doi.org/10.1016/j.memsci.2021.119599) to support your sentence. Additionally, the other physical meaning of Reynolds Stress should be mentioned in the introduction. Lastly, the physical meaning of the turbulent kinetic energy which is the square of velocity should be mentioned in the Introduction.
Response 2: We very appreciate your specifications from your constructive comment. Accordingly, the following changes have been made in the revised manuscript.
- We added the reference you are suggested and had a discussion about the wake flow. (Line 33, 46-55)
- The physical meaning of Reynolds Stress and turbulent kinetic energy shows in the section 3.2;
(Line 297, 336)
Point 3: In figure 1, it is difficult to view what is the difference between b and c. I think the difference is the zoom-in picture in c, which I strongly recommend that a similar zoom-in to be included for b as well to tell the difference
Response 3: We have modified the picture. (Line 121)
Point 4: Line 134. Does 0.37m/s corresponds to Reynolds number of 7400? This need to be mentioned.
Response 4: We have modified it. (Line 138)
Point 5: What type of Reynolds number is used? Hydraulic or channel Reynolds number? Please specifically mention what is the characteristic length used in this work for calculation of Reynolds number.
Response 5: We calculated the Reynolds number by , and the fluid density and the dynamical viscosity coefficient, v and L is velocity and characteristic length of the flow field. (Line 134-136 )
Point 6: Figure 7. What is u bar?
Response 6: Figure 7 has been modified. (Line 281)
Point 7: The optimal frequency is about 7 to 10 Hz, which in the reviewer opinion is quite small for such a high Reynolds number 7400. Please explain this via Strouhal number definition or anything similar.
Response 7: We have modified the section 3.3. We explained the phenomenon of double or multiple peaks. And the reason for the optimal frequency is quite small, the research “PIV measurements on the passive control of flow past a circular cylinder” carried out the experiment at Re=6850, the result shows almost the same vortex shedding frequency as this paper. (http://dx.doi.org/10.1016/j.expthermflusci.2015.09.019)
Reviewer 2 Report
The work presented for review is an interesting study. The authors describe the analysed issue in a clear and readable way, at the same time referring to the literature on the subject at each stage.
The research and analysis carried out do not raise any doubts in my mind. The included research results are given in a clear and readable manner.
I have no critical comments on the work presented.
Author Response
Reviewer 2 has no critical comments on the work presented.
Reviewer 3 Report
Manuscript Number: water-2381324
Full Title: Experimental study on the wake characteristics of composite secondary grooved cylinder
I - General Comments
The manuscript presents an experimental study aiming to compare the turbulent structure between the wakes of different grooved cylinders (the original grooved cylinder and the secondary grooved cylinder) and the smooth cylinder. For that purpose, a circulation water channel is used for experimental PIV measurements at the Reynolds number of 7,400. In general, the authors have concluded that recirculation region of the grooved cylinders is reduced because of change in the location of boundary layer separation point and the interference from small-scale vortices. In my opinion, the manuscript needs to attend important physical/mathematical/numerical aspects, before its acceptation to be published in Water.
II - Specific Comments
(i) In “Abstract”, the main contribution of the present work must be better clarified and the present state of the art concerning the investigated topic must also be introduced and contextualized. So, it will be more effective to demonstrate the contribution of the present manuscript into the specialized literature.
(ii) It is suggested to substitute the term “circulation water tunnel” for “recirculation water channel”. It is also suggested to substitute the term “vortices” for “vortical structures” or at least to include some comment about it when starting section 1. In fact, it is more popular the use of term “vortices”, however, technically, the correct technical term must be “vortical structures”.
(iii) In “Introduction” it is recommended that authors include some short discussion about turbulence transition in the viscous wake for the investigated problem. What is the results sensitivity as the Reynolds number increases and the 3D effects manifest? In the literature, it can be found scatter results with up to 60%, even for the same relative roughness height and Reynolds number. A justification for that behavior is that, although the Reynolds number governs this kind of flow, it is so difficulty to guarantee that two experimental tests have exactly the same roughness surface; besides that, there are some influencing parameters which can cause a premature initiation of a flow regime or even its modification. So, the authors must include short/objective comments concerning both experimental and numerical approaches by contemplating surface roughness effects to investigate the same FSI problem. The following references can be included:
[1] https://doi.org/10.1016/j.oceaneng.2021.108690.
[2] https://doi.org/10.3390/en14248237.
(iv) Still in “Introduction”, there is no citation of previous work in Water. Why? The authors must justify the intended publication into the Water’s scope.
(v) In section 2.1, important dimensionless parameters, such as Reynolds number, Strouhal number, drag and lift coefficients, and pressure coefficient could be defined and interpreted by using a “Table”. What are the scales of length, velocity and time in Figure 2(a)?
(vi) In section 2.2, a Table summarizing measured quantities and uncertainties is welcome. Please, include a better discussion about turbulence level of the water channel for the experiments.
(vii) Still in Section 2.2, I would like to present the following comment: “In general, a solid blockage effect is commonly observed in wind tunnel testing that in turn produces an increase in the local wind velocity in the working section. Solid blockage is created by a reduction in the test-section area for flow to pass compared to an undisturbed freestream. By continuity, Bernoulli's equation and all of the associated assumptions, velocity increases in the vicinity of a model. Wake blockage is more difficult to control for a stationary body. In addition, wake patterns because of surface roughness effect produced by a cylinder, when tested at different physical scales and in two different wind tunnels, can present some divergence.”
So, it is recommended to authors some technical discussion about all those aspects in the context of the present experimental configuration.
(viii) The Reynolds number for all experiments was kept constant at Re = 7,400. It is recommended a technical discussion about turbulence transition in both viscous wake and boundary layer for the investigated problem with no roughened wall. How sensitive are the results as the Reynolds number increases and 3D effects cannot be neglected? What is expected for the investigated problem under surface roughness effects? Thus, the author must include short/objective comments concerning those topics.
(ix) The Strouhal number behaviour under roughness effects needs to be better explained by authors.
(x) The manuscript did not include results linking Strouhal number, separation angle behaviour, drag and lift forces, and time-mean pressure coefficient. Unfortunately, the aerodynamic characteristics of the cylinder, as well as the control of intermittence and partial interruption of von Kármán-type vortex shedding were not clarified. So, I would like to recommend some attention about all those aspects.
(xi) In “Conclusion”, it is necessary to include comments with respect the experimental results behaviour as compared as previous works, when possible. The authors have claimed that the main novelty of their study lies in identification of a reduction in the recirculation region of the grooved cylinders because of change in the location of boundary layer separation point and the interference from small-scale vortices. However, the readers need to be better convinced. More sense of physics in conclusions is recommended.
(xii) In closing, it is important to complete “Conclusion” with perspectives for a future research. Finally, the main contribution of the present manuscript should be clarified aiming to justify its publication in Water
III - Recommendation for the Water editor
In my opinion, the present manuscript needs attend all topics above presented. Upon consideration of all points above, I think the paper could be considered for publication in Water.
Minor editing of English language required.
Author Response
We are very grateful for this review’s detailed comments that have helped us improve significantly this manuscript. The major changes to the manuscript have been highlighted in blue. Following are actions we have taken to address specific issues raised by the reviewer.
Point 1: In “Abstract”, the main contribution of the present work must be better clarified and the present state of the art concerning the investigated topic must also be introduced and contextualized. So, it will be more effective to demonstrate the contribution of the present manuscript into the specialized literature.
Response 1: As suggested by the reviewer, we have modified the Abstract. (Line 11-21)
Point 2: It is suggested to substitute the term “circulation water tunnel” for “recirculation water channel”. It is also suggested to substitute the term “vortices” for “vortical structures” or at least to include some comment about it when starting section 1. In fact, it is more popular the use of term “vortices”, however, technically, the correct technical term must be “vortical structures”.
Response 2: We have modified the term.
Point 3: In “Introduction” it is recommended that authors include some short discussion about turbulence transition in the viscous wake for the investigated problem. What is the results sensitivity as the Reynolds number increases and the 3D effects manifest? In the literature, it can be found scatter results with up to 60%, even for the same relative roughness height and Reynolds number. A justification for that behavior is that, although the Reynolds number governs this kind of flow, it is so difficulty to guarantee that two experimental tests have exactly the same roughness surface; besides that, there are some influencing parameters which can cause a premature initiation of a flow regime or even its modification. So, the authors must include short/objective comments concerning both experimental and numerical approaches by contemplating surface roughness effects to investigate the same FSI problem. The following references can be included:
[1] https://doi.org/10.1016/j.oceaneng.2021.108690.
[2] https://doi.org/10.3390/en14248237.
Response 3: We very appreciate your specifications from your constructive comment. Accordingly, the following changes have been made in the revised manuscript.
- In “introduction”, we made some short discussion about the turbulence transition in the near wake. (Line 49)
- In the critical Reynolds number range, Reynolds number has little effect on the cylindrical wake. The (x, z)-plane’s result shows the 3D effect in the wake region.
- The first reference was added to the paper. However, the second reference could not be found.
- In “introduction”, we also made some comments in the VIV problem with different roughness. (Line 53-55)
Point 4: Still in “Introduction”, there is no citation of previous work in Water. Why? The authors must justify the intended publication into the Water’s scope.
Response 4: We have modified the Introduction. (line 66-74)
Point 5: In section 2.1, important dimensionless parameters, such as Reynolds number, Strouhal number, drag and lift coefficients, and pressure coefficient could be defined and interpreted by using a “Table”. What are the scales of length, velocity and time in Figure 2(a)?
Response 5: We calculated the Reynolds number by , and are the fluid density and the dynamical viscosity coefficient, v and L is velocity and characteristic length of the flow field. (line 133-135)
Point 6: In section 2.2, a Table summarizing measured quantities and uncertainties is welcome. Please, include a better discussion about turbulence level of the water channel for the experiments.
Response 6:
Each measurement was repeated twice in order to eliminate experimental error. However, achieving even particle distribution in each recorded image was difficult because of laser defects or surface refections. Error may arise when performing cross-correlation. The error vector detection function can be defned as 40%.
where is the mean value of the surrounding eight vectors. When an error vector is detected, it is replaced by the median of the surrounding vectors for correction. (Line 167, 174-177)
Point 7: Still in Section 2.2, I would like to present the following comment: “In general, a solid blockage effect is commonly observed in wind tunnel testing that in turn produces an increase in the local wind velocity in the working section. Solid blockage is created by a reduction in the test-section area for flow to pass compared to an undisturbed freestream. By continuity, Bernoulli's equation and all of the associated assumptions, velocity increases in the vicinity of a model. Wake blockage is more difficult to control for a stationary body. In addition, wake patterns because of surface roughness effect produced by a cylinder, when tested at different physical scales and in two different wind tunnels, can present some divergence.”
So, it is recommended to authors some technical discussion about all those aspects in the context of the present experimental configuration.
Response 7: We have modified the technical discussion about all those aspects in the present experimental configuration in Section 2.2. (Line 143-147)
Point 8: The Reynolds number for all experiments was kept constant at Re = 7,400. It is recommended a technical discussion about turbulence transition in both viscous wake and boundary layer for the investigated problem with no roughened wall. How sensitive are the results as the Reynolds number increases and 3D effects cannot be neglected? What is expected for the investigated problem under surface roughness effects? Thus, the author must include short/objective comments concerning those topics.
Response 8: We are concerned Re = 7,400 because the pile leges always at the critical Reynolds number range. Meanwhile, in the critical Reynolds number regime (300≤Re＜3×105), turbulent vortices alternate and the laminar flow transforms into turbulent flow. The Reynolds number increases and 3D effects refer the paper“PIV measurements on the passive control of flow past a circular cylinder”. In the critical Reynolds number range, Reynolds number has little effect on the cylindrical wake.
Point 9: The Strouhal number behaviour under roughness effects needs to be better explained by authors.
Response 9: We modified the description of the behavior of the Strouhal number under the influence of roughness. (Line 398-402)
Point 10: The manuscript did not include results linking Strouhal number, separation angle behaviour, drag and lift forces, and time-mean pressure coefficient. Unfortunately, the aerodynamic characteristics of the cylinder, as well as the control of intermittence and partial interruption of von Kármán-type vortex shedding were not clarified. So, I would like to recommend some attention about all those aspects.
Response 10: The Strouhal number, separation angle behaviour, drag and lift forces, and time-mean pressure coefficient need simulation calculation, but we did not make the simulation. This paper focuses on the dynamical behavior of the wake region and studies the periodic structure on the wake.
Point 11: In “Conclusion”, it is necessary to include comments with respect the experimental results behaviour as compared as previous works, when possible. The authors have claimed that the main novelty of their study lies in identification of a reduction in the recirculation region of the grooved cylinders because of change in the location of boundary layer separation point and the interference from small-scale vortices. However, the readers need to be better convinced. More sense of physics in conclusions is recommended.
Response 11: We have modified the“Conclusion”. The main novelty of this study is the small-scale vortices caused by the spike of the secondary grooved structure reduced the recirculation region and the turbulent energy. (Line 441, 457)
Point 12: In closing, it is important to complete “Conclusion” with perspectives for a future research. Finally, the main contribution of the present manuscript should be clarified aiming to justify its publication in Water
Response 12: As suggested by the reviewer, we have added future studies in the last paragraph. (Line 461)
Round 2
Reviewer 1 Report
The authors have partially revised the manuscript and some comments were not addressed by the author:
1) Only the physical meaning of Reynolds Stress and turbulent kinetic energy were addressed, but the physical meaning of viscous dissipation based on the suggested reference (https://doi.org/10.1016/j.memsci.2021.119599) was not discussed despite the authors mentioned in the author reply that this discussion was already included in the manuscript. The discussion of viscous dissipation is important for the readers from non-fluid mechanics background.
2) As pointed out by in my previous comment, the vortex shedding phenomena needs to be explained via Strouhal number but this comment was not addressed. Strouhal number is a dimensionless number to describe oscillating flow mechanisms and is useful to elucidate the flow mechanism.
English is fine
Author Response
We are very grateful for this review’s detailed comments that have helped us improve significantly this manuscript. The major changes to the manuscript have been highlighted in red. Following are actions we have taken to address specific issues raised by the reviewer.
Point 1: Only the physical meaning of Reynolds Stress and turbulent kinetic energy were addressed, but the physical meaning of viscous dissipation based on the suggested reference (https://doi.org/10.1016/j.memsci.2021.119599) was not discussed despite the authors mentioned in the author reply that this discussion was already included in the manuscript. The discussion of viscous dissipation is important for the readers from non-fluid mechanics background.
Response 1: As suggested by the reviewer, we have modified it. (line 296-300)
Point 2: As pointed out by in my previous comment, the vortex shedding phenomena needs to be explained via Strouhal number but this comment was not addressed. Strouhal number is a dimensionless number to describe oscillating flow mechanisms and is useful to elucidate the flow mechanism.
Response 2: As suggested by the reviewer, we also modified it. (line 394-396)
Reviewer 3 Report
Manuscript Number: water-2381324-v1
Full Title: Experimental study on the wake characteristics of composite secondary grooved cylinder
The authors have provided sufficient replies to my last questions. This research line is very interesting because of the rich gamma of intrinsic physical phenomenon. In my opinion, there is one major objection to the manuscript in its current form, which leads to the recommendation of its publication in Water.
Minor editing of English language required.
Author Response
We are very grateful for this review’s detailed comments that have helped us improve significantly this manuscript. The changes to the manuscript have been highlighted in blue.
