Multi-Scale Wake Characteristics of the Flow over a Cylinder with Different V-Groove Numbers

Round 1

Reviewer 1 Report

This study is interesting and important to the FM community. It provides experimental evidence to the effect of groove number on the wake characteristics over a (nearly infinite) circular cylinder. The experimental method and wavelet procedure are well established and adequate to the principle aim of the study. Several suggestions and remarks are listed along the manuscript in the attached pdf file (sorry for the messy appearance). There are several points which must be considered:

(1) Complete the introduction: The study of the flow over a circular cylinder has been extensively studied experimentally and numerically, as it involves complex physical phenomena such as flow separation due to the adverse pressure gradient, transition to turbulence and the shedding of vortices due to the interaction between the separated shear-layers. The introduction should account, at least in the context of the current study, for the general understanding of the wake shape and instability (in the subcritical regime of the flow)-- as these are mentioned and discussed in the results and conclusions; 

(2) In general, all statements regarding the figures,as well as the conclusions,  should be indicated and accompanied by actual numbers and/or figures for clarity and completeness. For example, the sentence in L352 should end with ($x\simless 2d$). 

(3) section 3.8 (Figures 17 and 18) is important and therefore needs ellaboration -- in particular L355-L360. The notion of 'instability', 'structures instability' should be explained in the introduction or in the section. 

(4) The data in Figs 15 and 16 are instantaneous. How typical are they?

(5) Experimental errors and convergence of the moments are not mentioned at all. For example, the lateral profile of the mean streamwise velocity shown in Figure 5 is not uniform. Any idea why the profiles seem to cross at $z\approx 4d$? 

(6) The conclusions is expected to  include the difference between the effect of groov number, as compared with groov shape on the studied wake. Based on the authors experience, it should also include suggestions from the authors on directions of future studies;

Author Response

We are thankful to the reviewers for taking the time to assess our manuscript, for their careful reading and for their suggestions and valuable comments which helped us to substantially improve the quality of our paper. In revising the manuscript, we have carefully considered all the raised comments and suggestions. We have attempted to succinctly explain the changes made in reaction to all comments. Our reply to each comment in point-by-point fashion is given in the appendix.

Author Response File: Author Response.docx

Reviewer 2 Report

In the considered article, the wake characteristics of the smooth cylinder and the cylinders with different numbers of grooves are measured by the high-speed particle image velocimetry. The wakes from cylinders with 12, 24 and 32 grooves are examined and compared with a wake from a smooth cylinder. Conclusions are drawn about the influence of grooves on the time-averaged velocity profiles, the recirculation region, the Reynolds shear stresses, the turbulent kinetic energy and the formation of the Karman-like vortices and the flow vorticity. The conclusions cover the large-scale, intermediate-scale and small-scale flow structures.

The article is well designed and has a clear logic of construction. Perhaps, there is some redundancy in the description of the figures. The topic of the article fits into the theme of the Journal. The article can be published, but before publication, the authors need to make some revision of the article on the follow issues:

1. In the Abstract, Keywords and Conclusions, it should be indicated that the research is carried out for the flow of water.

 2. Page 1 Line 36

“[6] investigated the wake characteristics…”  should be rephrased, for example: “In [6], the authors studied the wake characteristics...”

 3. Authors should describe in more detail the methodology by which Figures 6 et seq. are obtained. If standard packages or other software tools were used, a section describing the mathematical set of the problem, numerical methods used (and the analysis of grid convergence, if needed) should be included.

 

Author Response

We are thankful to the reviewers for taking the time to assess our manuscript, for their careful reading and for their suggestions and valuable comments which helped us to substantially improve the quality of our paper. In revising the manuscript, we have carefully considered all the raised comments and suggestions. We have attempted to succinctly explain the changes made in reaction to all comments. Our reply to each comment in point-by-point fashion is given in the appendix.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper can be accepted with few minor corrections;
(1)
The title indicates on a flow study over many/bed of  'cylinders' while it should be 'a cylinder'
I would then suggest
'Multi-scale wake characteristics of the flow over a cylinder with different v-groove numbers'
or
'Multi-scale  characteristics of the cylinder wake at  different v-groove numbers'
(2)
The manuscript still includes typos and unclear sentences.
(3)
The captions can be more informative.

Author Response

We are thankful to the reviewers for taking the time to assess our manuscript, for their careful reading and for their suggestions and valuable comments which helped us to substantially improve the quality of our paper. In revising the manuscript, we have carefully considered all the raised comments and suggestions. We have attempted to succinctly explain the changes made in reaction to all comments. Our reply to each comment in point-by-point fashion is given in what follows.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors did not answer the third question. The question was about which numerical method (or package) was used to model the results of the experiments. More specifically, what difference scheme was used? What equations were used to calculate? (Apparently, the system of Navier-Stokes equations was solved). How the geometry of the grids was chosen, whether the grid convergence was evaluated. In general, it would be necessary to describe all the details that are usually indicated in articles to describe the calculations performed. Since the reviewer, in principle, positively evaluates the article, the Section concerning the methodology of numerical calculations may not be too voluminous: 0.5-1.0 page.

Author Response

We are thankful to the reviewers for taking the time to assess our manuscript, for their careful reading and for their suggestions and valuable comments which helped us to substantially improve the quality of our paper. In revising the manuscript, we have carefully considered all the raised comments and suggestions. We have attempted to succinctly explain the changes made in reaction to all comments. Our reply to each comment in point-by-point fashion is given in what follows.

Author Response File: Author Response.docx