Vortex Breakdown Control by the Plasma Swirl Injector

Round 1

Reviewer 1 Report

please check attached pdf file

Comments for author File: Comments.pdf

Author Response

1) Page 3, Line 143: Figure 1 shows the sketch and the photograph of the plasma swirl injector used in the experiment. Design parameters and advantages of the helical shape electrode had been discussed previously [55].

Despite authors presented the details on plasma swirl injector in their previous paper and cite it as a reference [55], I would encouraged them to present shortly selected parameters of the injector, e.g. diameter and length of the quartz tube, length of electrodes etc. It would help a reader and also avoid any confusion (see below).

Response: In the revised version, those parameters have been supplemented.

2) Page 3, Line 145: Compared to that of 170 mm in the earlier study [55], the helix pitch is shortened to 100 mm which means the electrode is longer and more plasma can be generated at the same voltage.

Comparing the figure in the manuscript with the one in [55] it seems the helix pitch was prolonged (more swirls), not shortened (the length of the electrode). Or what is the difference between ‘helix pitch’ and the ‘length of electrodes’ as it seems it is not the same thing. Can you please clarify? Also can you specify the reasons why you changed a shape of swirl compared to the [55]?

Response: Pitch is the distance from any point on the thread of a screw to the corresponding point on an adjacent thread measured parallel to the axis. In the present study, the electrodes are arranged perpendicular to the blades at the inlet of the electrode. Thus, the losses caused by the difference in velocity direction can be reduced, and the flow control of plasma actuation can be effectively enhanced. Increasing the electrode length can produce more plasma and improve its effect of flow control.

3) Page 5, Fig 2: I think a figure should be self-explaining, i.e. either the figure itself or its caption should include information on what are individual objects/parts presented in the figure. The description of the figure is in the main text, but basic information should be also with the figure.

Response: In the revised version, more illustrations have been added in Figure 2.

4) Page 6, Fig. 3: It would be nice to show, where is the edge of a quartz tube (injector) as dimensions of the tube are not mentioned in the manuscript. The text (ab), (cd) …. are identical. I think one common description for a pair of images in one line is enough. In a caption, please clearly separate the description of the two types of images to make it clear what is on left and right. I hope the color scheme for mean axial velocity is constant or normalized (with respect to the maximum velocity) for every image?

Response: In the revised version, the position of the edge of the injector has been added. The color scheme for mean axial velocity is constant for every image. Those captions of images in Figure 3 have been modified. 

5) Page 6, Line 201: This shows that the actuation does not significantly affect the overall location of the bubble, although it enhances its size. The interior structures of the bubble are nearly the same for the two cases.

 In case it was possible to increase the voltage even further (far above 18 kV) what would be an expected change/development of stagnation points and size of the breakdown bubble? Is there a critical point when the current shape significantly changes or slips into another mode?

Response: The suggestion is highly appreciated. Attempts had been made to increase the voltage to 24 kV, but the results were almost the same as that of 21 kV. So far, no critical point has been found. We will explore this in future studies.

6) Page 8, Fig 4: Please specify the point for which axial velocity is presented also in caption (x=0). The maximum velocity is 1.2 m/s (at the injector outlet), however in Line 152 the bulk velocity inside the injector is reported to be 3 m/s. Any comment why such a velocity drop?

Response: The centerline passes through the point of X = 0 mm. Due to the flow restriction of the mesh plate, more airflow passes through the blade, resulting in the central non-swirling low speed region. Velocity in that region is lower than the bulk velocity.

 

Author Response File: Author Response.docx

Reviewer 2 Report

1) In the Introduction, the original scientific contribution of the proposed paper, in comparison with the wide scientific literature regarding the same topic, should be highlighted.

2) The experimental analysis were carried out for a single working conditions. It is suggested to consider different working conditions, to add a wider scientific value, from a perspective point of view, to the results.

3) It is suggested to add a numerical analysis to improve the scientific understanding of the revealed experimental results.

4) It is suggested to include a paragraph regarding the feasibility of the real application of the proposed technique on a full-scale burner.

5) In the Conclusions, it is suggested to add some considerations regarding the energy consumption and efficiency of the proposed technique, especially for a full-scale application.

6) In the Conclusion a more appropriate discussion of the fundamental behavior of the proposed technology is necessary. The Conclusions are quite generic – they look like an Introduction - and the original scientific contribution of the proposed paper, in comparison with the wide scientific literature regarding the same topic, should be highlighted.

Author Response

1)In the Introduction, the original scientific contribution of the proposed paper, in comparison with the wide scientific literature regarding the same topic, should be highlighted.

Response: In the revised version, the original scientific contributions of this research have been presented.

2)The experimental analysis were carried out for a single working conditions. It is suggested to consider different working conditions, to add a wider scientific value, from a perspective point of view, to the results.

Response: In the revised version, results of different working conditions have been supplemented.

3)It is suggested to add a numerical analysis to improve the scientific understanding of the revealed experimental results.

Response: The comment is highly appreciated. This study focuses on the experimental verification of the feasibility of vortex breakdown control by the plasma swirler. In the future, numerical simulation will be carried out to further clarify the detailed mechanism.

4)It is suggested to include a paragraph regarding the feasibility of the real application of the proposed technique on a full-scale burner.

Response: In the revised version, the feasibility of the real application of the proposed technique on a full-scale burner have been discussed.

5)In the Conclusions, it is suggested to add some considerations regarding the energy consumption and efficiency of the proposed technique, especially for a full-scale application.

Response: This study focuses on the experimental verification of the feasibility of vortex breakdown control by the plasma swirler and illustrates the advantages of this method compared with other methods. Currently the technique is not mature enough and a full understanding is required to develop the technique for full-scale application. Further research is needed to put this method into practical application. Please refer to Table 1 for energy consumption.

6)In the Conclusion a more appropriate discussion of the fundamental behavior of the proposed technology is necessary. The Conclusions are quite generic – they look like an Introduction - and the original scientific contribution of the proposed paper, in comparison with the wide scientific literature regarding the same topic, should be highlighted.

Response: In the revised version, the conclusion part has been modified to supplement the original scientific contributions of this research.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The Authors replied appropriately to the review comments.