Experimental Study on the Snowfall Flow Control of Backward-Facing Steps Using a High-Durability Designed Plasma Electrode

Round 1

Reviewer 1 Report

Title: Experimental Study on Snow falling flow control of backward facing steps using a high-durability designed plasma electrode

Authors: Tasuku Tanaka, Hisashi Matsuda, Toshiki Takahashi,Takahiro Chiba, Nobuyoshi Watanabe,  Hideaki Sato, Masafumi Takeyama

 

Article Type: Research paper

 

The paper presents the development of the plasma actuation effect on both a backward facing step flow and an arc-shaped backward facing step flow were investigated experimentally. The subject is both fundamental and applied. The article can be appealing to the mechanical engineering community.

The authors present a manuscript to study the process of flow and a snow deposition on the surface behind a backward facing step using experimental PIV and HFA techniques. The efforts fall very short of what is expected from such a paper. The experimental parts were not well reported in terms of the methodology and the results presented. The paper suffers from a huge lack of attention to detail. Hence, a complete overhaul will need to be performed and it is the reviewer’s view that the changes fall outside what will be done for a major correction. A rejection is thereby recommended but the reviewer encourages the authors to resubmit if they can address the issues raised. The paper will not be published in its current state. Detailed comments are listed below.

 

1. Experimental procedure and data reduction should be presented in more detail. The parameters of mean and fluctuational flows in wind tunnels should be added. The inlet profiles of mean streamwise velocity and turbulence intensity are welcomed too.

2. I understand that the flow is two-dimensional in the case of a simple backward-facing step (BFS). The ratio of step height to the duct width is small enough. Why did the authors believe that the flow in the case of arc-shaped type of BFS will be two-dimensional? The ratio of step height to the duct width is not small for this case. The ratio is up to 0.1 and the effect of the three-dimensionality on the flow cannot be ignored in this case.

3. The schematic view of the experimental setup should be added. What was the position of plasma actuator?

4. The parameters of PIV system. The diameter of soap tracers (0.9 mm) seems extremely large for the measurements of mean and fluctuational flow structure. What is their particle relaxation time?

5. The uncertainty analysis of flow visualization and PIV have to be performed.

6. “By using micro soap bubbles as a tracer, PIV measurement was possible even at a wind speed of 20 m/s (72 km/h, Re = 3.3×10^4), equivalent to the real railcar running conditions.”

I hope that it is the authors’ typo or authors did not know the similarity theory. Yes, the velocity and temperature conditions are equivalent to the reality, but the geometrical scales are very different. The Reynolds number of real railcar is much higher than Re = 3.3×10^4.

7. How authors did model the snowflakes?

8. The variable duty ratio should be explained before its appearance in the first time. The formula for it is also welcomed.

9. How authors did you determine the reattachment length? Did it base on the dividing streamline or on the zero value of streamwise velocity?

10. I do not understand the reason of Figures 13. Is it straight BFS or arc-type BFS? The results are strong depends on the value of gradient dY? What was the resolution of PIV in this region? What was the value of gradient dY? Did the PIV resolution able to show the complicated processes in mixing layer and in recirculation zone of the flow? How did the streamwise velocity gradient explain the flow physics? Do the profiles of streamwise velocity along the duct length give more information about the flow?

11. How authors did the effect of snowflakes take into account on the PIV method? If the PIV measurements were carried out without snowflakes it should be noted.

12. The using of hot-film anemometer (HFA) in the case of snowflakes has a lot of problems. The results are very doubt. Authors have to prove that the snowflakes did not effect on their results. If the PIV measurements were carried out without snowflakes it should be noted.

13. Did the plasma actuator position and their discharges effect on the HFA results?

14. The Figures 17-20 did not give any information for the readers and they can be removed.

15. How authors did the effect of snowflakes take on the PIV method (the Figures 21 and 22)? What was the accuracy of PIV in the presence of the second phase?

etc.

 

Minor

16. “Figure 1. Snow Deposition Condi-“.

The word “Condi-” was written without the end. The Figure caption should be improved.

Author Response

Thank you for your very careful review. There were some points that were not explained well. I have revised this paper according to your suggestion. Attached is the review response (Answer for Reviewer1), the resubmitted paper with corrections indicated in red (ID_ actuators-1944329_rev2_crarify.doc) and the resubmitted paper (ID_ actuators-1944329_rev2.doc). Please kindly check it.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments for author File: Comments.pdf

Author Response

Thank you for your very careful review. There were some points that were not explained well. I have revised this paper according to your suggestion. Attached is the review response (Answer for Reviewer2), the resubmitted paper with corrections indicated in red (ID_ actuators-1944329_rev2_crarify.doc) and the resubmitted paper (ID_ actuators-1944329_rev2.doc). Please kindly check it.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors have addressed the most of my comments. The topic is interesting and relevant. The paper is well written and well organized. Results are clearly discussed and the conclusions are overall well supported by the analysis of the results.

Author Response

Thanks to your very careful peer review, our paper could become very well organized. Thank you again. The manuscript was revised by adding a related study that investigated the effect of humidity on plasma actuators provided by the editor to the references. We are resubmitting the revised paper (ID_actuators-1944329_rev3_clarify.doc) with corrections in red. We are also resubmitting my paper (ID_ actuators-1944329_rev3.doc). Thank you for your consideration.