Numerical Study on the Flow Past Three Cylinders in Equilateral-Triangular Arrangement at Re = 3 × 106
Round 1
Reviewer 1 Report
The manuscript shows and discusses a series of fluid flow simulations of equilateral-triangular arrangement. In general, the manuscript is well-written and I consider that it has the potential for publication in Applied Sciences. Here are some comments and questions that the authors must address for publication:
1) Please for the general reader define what a super-critical flow regime is and why is important its study.
2) Is it a full 3D simulation or 2.5D? no cylinder end effects are included in the simulation.
3) Please include the version of StarCCM used.
4) Please include as much details of the mesh and computational setup as possible for example: mesh quality, type of elements, sizes of the different refinement boxes used, convergence criteria, number of iterations per time-step, type of initialization used, boundary conditions for the turbulence at the inlet (why?). This is important for the reader and for the study to be replicated.
5) Why not used a fully couple scheme? instead of SIMPLE, for example PISO.
6) Please discuss the computational cost and parallelarization used.
7) Why not using a higher order scheme for spatial discretization? for example muscl or a TVD scheme.
8) Why a symmetric boundary condition was used instead of periodic? What is the impact of this boundary condition in the turbulence?
9) Please explicitly show the values used for D, U_freestream and fluid properties.
10) I consider that the meshes used are not fine enough. For example in Travin's work (ref 44) upto 6M elements were used for a single cylinder... and this was in 2000. Please explain and discuss.
11) Figure 3 is instantaneous or averaged?
12) Please check all the paper so that consistant definitions are used. For exaple U, Uo, U_infinity is used in different parts of the manuscript i think making reference to the free stream velocity, this is very confusing.
13) Aren't any LES or DNS studies on flow around a cylinder reported in the literature? please check and include in the introduction and table 2.
14) minor: ln 277 analysis instead of transformation, ln 299 these instead of this, ln 363 section instead of chapter... etc. There are several minor corrections that must be done all along the manuscript.
15) Please show figure 12 in non-dimensional units.
16) Why Q=1.5 Uo^2/D was selected as the theshold value for figure 13?
17) It does not seem a complete convergence in the results show in table 1.
Author Response
Please check the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Review of a manuscript titled " Numerical study on the flow past three cylinders in equilateral-triangular arrangement at Re = 3E+6" by Zhang et al.
In the present work, the authors have very clearly distinct flow regimes for an equilateral triangular arrangement at super-critical Re = 3E6.  The analysis was good, and the authors detailed of literature really well and gave a perfect justification for the present work.
The following aspects have to take care of before the manuscript can be accepted 
1. In table 2, the authors have to present the mean Cd for specific Re = 3E6 (not the range). This will help us understand how good the validation is with respect to experimental results.
2. It would be essential to clarify for what time period the average solution is presented here. Typically how many flow-throughs is the solution averaged?
3.  what is the typical number of grid points in z direction, 4/0.025 = 160. Is this correct?
4. In several explanations 4.2, the authors explain the force variation based on the pressure field, it would be better to show this using contours if possible.
5. Figure 13, the regimes are not clear. how the vortex shedding phase is. especially anti-phase and in-phase. Please try to present it a little bit better way
6. will it possible for authors to present POD analysis to understand the underlying modes for various regimes?
7. How did the authors calculate the phase lag in figure 8, does this phase Cl ?
Author Response
Please check the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors correctly addressed all my comments and suggestions, so that the manuscript can be published.
