Numerical Investigation of Multi-SDBD Plasma Actuators for Controlling Fluctuating Wind Load on Building Roofs
Round 1
Reviewer 1 Report
Please consider these comments:
L. 131: confusing: body force is parallel to the boundary AB: one could look for boundary in CFD sense. AB is more a plasma region.
L. 151: Rectangular instead of Square.
L. 188. Please provide more ref. to DEFINE SOURCE, at least to the equations, e.g. (3)
L. 192: please comment time step in non-dimensional form (with respect to free stream velocity and model scale - where appropriate)
L.208: p0 is probably reference static pressure (free stream)
L.212: Eq. 10, absolute values for RMS obsolete.
L216: absolute values are increased.... should be formulated that mean and fluctuating pressures increase, which is not desirable.
L219, please repeat Vh (it is in L.199, but need some search to find out)
L222, Tab.1: it is not stated which sub-grid model is used for grid independence study, please refer.
L253: in figure caption, please refer to Fig 2b to repeat what case ABC means.
L256: Figure 7: case A induced flow direction differs from case A in Figure 2a. Please unify. The same for Fig. 8 and 9.
L300-306: The analysis of the signal shows noisy, difficult to identify clear peak. I would be careful talking about vortex shedding influenced by actuation.
L310: "f is the frequency", integrate this sentence into the text.
L319: oncoming - incoming?
L358: Figure 11. If possible, unify color map of iso-lines, numbers can stay, but this way it is difficult to figure out differences. Figure 12. The same.
L379: Fig13. Again, consistency with Fig2b, flow from right to left, please, be consistent.
So far it is enough from me, I'm looking forward
Author Response
Dear Editors and Reviewers:
Thank you for your letter and comments concerning the manuscript entitled “Numerical investigation of multi-SDBD plasma actuators for controlling fluctuating wind load on building roofs” (ID: applsci-576200). Those comments are all valuable and very helpful in revising and improving the paper, as well as in providing guidance significance to the researches. The comments have been studied carefully and the corresponding changes have been made. The main revised contents are marked in red in this paper, and all revisions have been highlighted in the manuscript by using the “Track Changes” function in Microsoft Word. The main modifications and the responds to the editors and reviewers’ comments are as follows:
Reviewer #1:
Please consider these comments:
Comment 1: L.131: confusing: body force is parallel to the boundary AB: one could look for boundary in CFD sense. AB is more a plasma region.
Response: Thanks for your comment. We have modified Fig. 1 (See line 129), added the explanation for the wedge region and described the relationship between the plasma and the body force. “The wedge region AOBB'O'A' in the figure is depicted by the dashed line. A high-frequency voltage is applied on the upper and lower electrodes of the plasma actuator to ionize the air and generate the plasma. The plasma is assumed by the phenomenological model to exist only in the wedge region with the width b and the height a; namely, the wedge region is the plasma active region after the actuator is ignited. Under the influence of the electric field, the plasma can collide with surrounding neutral molecules to cause directional movement of the surrounding fluid, so the phenomenological model considers that the plasma actuators can apply the body force to the surrounding fluid. The phenomenological model assumes that the body force exists only in the wedge region, and the body force is parallel to the plane ABB'A' and points to the lower right.” (See line 133-141)
Comment 2: L.151: Rectangular instead of Square.
Response: Thanks for your suggestion, and we have replaced the word “square” with “rectangular”, as shown in Line 161.
Comment 3: L.188. Please provide more ref. to DEFINE SOURCE, at least to the equations, e.g. (3)
Response: Thanks for your suggestion, and we have added more description for the macro function DEFINE_SOURCE. The description of this macro function is given only in the response. The basic form of this macro function DEFINE_SOURCE is as follows:
DEFINE_SOURCE(xmom_source, c, t, dS, eqn)
{
real x[ND_ND];
real SOURCE;
C_CENTRID(x,c,t)
SOURCE=
dS[eqn]=
return SOURCE;
}
In the actual calculation, the full-field grid is scanned by the predefined function C_CENTROID(x, c, t) to obtain the grid coordinates required for the calculation. Then, the body force value of each grid node is obtained by the body force formula, and this body force value needs to be returned to SOURCE. In addition, dS[eqn] is the derivative term of SOURCE.
Comment 4: L.192: please comment time step in non-dimensional form (with respect to free stream velocity and model scale - where appropriate)
Response: Thanks for your suggestion, and we have made the time step dimensionless. “the most economical non-dimensional time step of ∆t×U∞/h = 0.175 (∆t = 0.005 s) is adopted by the present study with 25 sub-iterations, where U∞ is the wind speed of 7 m/s.” (See Line 205-207)
Comment 5: L.208: p0 is probably reference static pressure (free stream)
Response: Thanks for your suggestion, and the related content has been modified to “p0 is the reference static pressure of the free stream” (See Line 223).
Comment 6: L.212: Eq. 10, absolute values for RMS obsolete.
Response: Thanks for your suggestion. Since the RMS value is always bigger than zero, we have removed the absolute value symbol of RMS, as shown in Eq. 10 (See Line 228).
Comment 7: L.216: absolute values are increased.... should be formulated that mean and fluctuating pressures increase, which is not desirable.
Response: Thanks for your suggestion, and the related content has been modified to “If ηp,mean < 0, it means that the absolute value of the mean pressure coefficient decreases after the actuators are ignited; otherwise, the absolute value of the mean pressure coefficient increases after the actuators are ignited. If ηp,rms < 0, it means that the fluctuating pressure coefficient decreases with the plasma actuation; otherwise, the fluctuating pressure coefficient increases with the plasma actuation” (See Line 231-234).
Comment 8: L.219, please repeat Vh (it is in L.199, but need some search to find out)
Response: Thanks for your suggestion, and we have repeated the definition of Vh. “Vh represents the free stream velocity at the building height h” (See Line 238).
Comment 9: L.222, Tab.1: it is not stated which sub-grid model is used for grid independence study, please refer.
Response: Thanks for your suggestion, and we have added the description of three different mesh numbers in the table caption. “Table 1. Grid independence test of the computational domain with three different mesh numbers” (See Line 239). In addition, we have mentioned that “To check the mesh sensitivity, a comparative study is conducted by varying the grid numbers without the plasma actuation, and the detail information is shown in Table 1” (See Line 240).
Comment 10: L.253: in figure caption, please refer to Fig 2b to repeat what case ABC means.
Response: Thanks for your suggestion, and we have repeated the meaning of each case in the figure caption. “Figure 6. Mean pressure coefficient change rates along the roof centerline. (a) Case A with the wall-jet direction from the trailing edge to the leading edge; (b) Case B with the wall-jet direction from the roof middle to the leading and trailing edges; (c) Case C with the wall-jet direction from the leading and trailing edges to the roof middle.” (See Line 273-276)
Comment 11: L.256: Figure 7: case A induced flow direction differs from case A in Figure 2a. Please unify. The same for Fig. 8 and 9.
Response: Thanks for your suggestion. The flow direction and wall-jet direction of Fig. 2 have been modified to have the same wall-jet directions with Figures 7, 8 and 9, as shown in Fig. 2 (See Line 157). In addition, the x-axis direction of Fig. 3(a) has been modified to have the same x-axis direction with Fig. 3(b) and Figures 7, 8 and 9, as shown in Fig. 3(a) (See Line 177).
Comment 12: L.300-306: The analysis of the signal shows noisy, difficult to identify clear peak. I would be careful talking about vortex shedding influenced by actuation.
Response: Thanks for your suggestion. To identify easily the peak, we have modified Fig. 11 (See line 333). In addition, we have added the time history of drag coefficient. “Fig. 10 shows the time histories of the drag coefficients acting on the building model from the simulation results of different cases. It can be seen that the drag coefficient of the no actuation situation is highly unsteady with its amplitude fluctuating randomly and significantly as a function of the time. The drag coefficient fluctuation amplitudes of all cases are obviously reduced in comparison to the no actuation situation. This indicates that the active actuators can reduce the instability of the drag coefficient.” (See line 330-332, 335-339)
Comment 13: L.310: "f is the frequency", integrate this sentence into the text.
Response: Thanks for your suggestion, and this sentence has been added into the text. “In this figure, f is the frequency.” (See Line 341)
Comment 14: L.319: oncoming - incoming?
Response: Thanks for your suggestion, and we have replaced “oncoming flow” with “incoming flow”, as shown in Line 351, 353, 370, 417, 418, 421 and 492.
Comment 15: L.358: Figure 11. If possible, unify color map of iso-lines, numbers can stay, but this way it is difficult to figure out differences. Figure 12. The same.
Response: Thanks for your suggestion, and we have unified the color map of the iso-lines, as shown in Figures 12 and 13 (See Line 390 and 393).
Comment 16: L.379: Fig13. Again, consistency with Fig2b, flow from right to left, please, be consistent.
Response: Thanks for your suggestion. The flow direction of Fig. 2 has been modified to have the same flow direction with Fig 13, as shown in Fig. 2 (See Line 157).
The revised manuscript had been modified and made some changes according to your comments.
We appreciate for the editors and reviewers’ warm work earnestly, and hope that the modifications will meet with approval.
Once again, thank you very much for your comments and suggestions.
Best regards!
Yours sincerely,
Xuewen Zhang
E-mail: [email protected]
Tel: +86-18508401589
Address: Key Laboratory of Building Safety and Efficiency of the Ministry of Education, Hunan University, Changsha, Hunan 410082, China.
Reviewer 2 Report
It is a nice piece of work that will be of good interest to the plasma actuator community. In this paper, the authors investigated the effect of multi-SDBD plasma actuation on flow control around box-shaped reference model. Based on CFD simulation, the authors quantified the changes in aerodynamic characteristics and discussed them in detail. I recommend this paper to be accepted after the following minor concerns are addressed.
1) In the abstract, “case A” (line 27, page 1) should be replaced with a simple description of corresponding multi-SDBD configuration.
2) In section 2.3, the computational domain size was described as 18h x 8h x 4h. This size looks to be too small for subsonic/incompressible CFD simulations. In typical subsonic/incompressible airfoil CFD, the outer boundary of the domain is taken at 20 or even 50 times the characteristic length away from the airfoil to eliminate any error caused by the boundary conditions. Did authors check the effect of the outer boundary distance on the CFD results, especially on CL and CD as a part of grid convergence check?
3) There is a typo error at line 163 in page 5; Δz/h should be a non-dimensional parameter but a unit “m” is attached as “0.0003 m”. This should be a value without the unit “m”. Similar typo errors were found in the main text such as in the figure caption of Fig3, which should be corrected.
4) Vz,Iz profiles are shown in Fig 4, page 6 but the location where these profiles were taken is not specified in the text. Please add a description of the location of these profiles.
5) In page 6, please add some more description of the numerical schemes. What was the time integration scheme? And what was the order of accuracy of spatial discretization and time integration schemes? (1st , 2nd or 3rd order in time/space?) Since this study simulated unsteady flowfield with vortices, I assume the accuracy is more than 2nd order in time.
6) How much was the measurement errors of experimental data shown in Fig5 & 6?
7) In Fig6, page 8, authors state that the numerical results agreed well with the experimental data by comparing ηp,mean. However, some data points show nonnegligible error, e.g. x/w ~ -0.4 in Fig6(c), case C, shows more than 10% error. Is there any specific reason of this discrepancy?
8) This is just a comment: in the introduction part, authors described that the proposed multi-SDBD may be an effective strategy for mitigating the wind pressures acting on low-rise buildings during typhoon. Does multi-SDBD work good even in typhoon with rain or high-moisture condition? Do you have any idea?
Author Response
Dear Editors and Reviewers:
Thank you for your letter and comments concerning the manuscript entitled “Numerical investigation of multi-SDBD plasma actuators for controlling fluctuating wind load on building roofs” (ID: applsci-576200). Those comments are all valuable and very helpful in revising and improving the paper, as well as in providing guidance significance to the researches. The comments have been studied carefully and the corresponding changes have been made. The main revised contents are marked in red in this paper, and all revisions have been highlighted in the manuscript by using the “Track Changes” function in Microsoft Word. The main modifications and the responds to the editors and reviewers’ comments are as follows:
Reviewer #2:
It is a nice piece of work that will be of good interest to the plasma actuator community. In this paper, the authors investigated the effect of multi-SDBD plasma actuation on flow control around box-shaped reference model. Based on CFD simulation, the authors quantified the changes in aerodynamic characteristics and discussed them in detail. I recommend this paper to be accepted after the following minor concerns are addressed.
Comment 1: In the abstract, “case A” (line 27, page 1) should be replaced with a simple description of corresponding multi-SDBD configuration.
Response: Thanks for your suggestion, and we have replaced “case A” with a simple description of the corresponding actuator configuration. The sentence has been modified to “Under the action of the wall jet blowing from the trailing edge to the leading edge, the fluctuating lift and drag coefficients can be reduced by over 15% and the fluctuating pressure coefficient can be mostly reduced by 20% from the no actuation situation.” (See Line 27-29)
Comment 2: In section 2.3, the computational domain size was described as 18h x 8h x 4h. This size looks to be too small for subsonic/incompressible CFD simulations. In typical subsonic/incompressible airfoil CFD, the outer boundary of the domain is taken at 20 or even 50 times the characteristic length away from the airfoil to eliminate any error caused by the boundary conditions. Did authors check the effect of the outer boundary distance on the CFD results, especially on CL and CD as a part of grid convergence check?
Response: The building height h is usually considered as the characteristic length of buildings. With regard to the computational domain size of the building model with the incompressible flow, various references have been provided by the previous studies. For example, the computational domain size of 4.92h × 4.92h × 2.73h was employed by the Mou et al. [22] to obtain wind pressures on the building surface. The computational domain size of 10.5h × 6.875h × 5.625h was adopted by the Liu and Niu [23] to get the mean velocity field around the high-rise building. The computational domain dimension of 4.92h × 3.28h × 2.19h was used by the Meng et al. [24] to study the sensitivity of building wind pressures to different turbulence models and wind directions. On accordance with above researches, we determined the computational domain size of 18h × 8h × 4h, which is bigger than the corresponding size of these researches. Therefore, we believe that the computational domain size of this manuscript is sufficient.
We are very grateful for your suggestion. Since the limitation of article length, the effect of the outer boundary distance on the numerical results is not considered by this manuscript. This effect will be further studied in the future.
Comment 3: There is a typo error at line 163 in page 5; Δz/h should be a non-dimensional parameter but a unit “m” is attached as “0.0003 m”. This should be a value without the unit “m”. Similar typo errors were found in the main text such as in the figure caption of Fig3, which should be corrected.
Response: We are very sorry for our negligence, and we have removed the unnecessary unit “m”, as shown in Line 173 and 179.
Comment 4: Vz,Iz profiles are shown in Fig 4, page 6 but the location where these profiles were taken is not specified in the text. Please add a description of the location of these profiles.
Response: Thanks for your suggestion, and we have added the location description of Vz and Iz profiles. “the dimensionless vertical profiles of the streamwise mean velocity and turbulence intensity at the inlet boundary from the present simulation are compared with the experimental data [19], as shown in Fig 4” (See Line 183-185). In addition, the definition of I2h has been added in the form of “I2h means the turbulence intensity at the double building height” (See Line 186-187).
Comment 5: In page 6, please add some more description of the numerical schemes. What was the time integration scheme? And what was the order of accuracy of spatial discretization and time integration schemes? (1st , 2nd or 3rd order in time/space?) Since this study simulated unsteady flowfield with vortices, I assume the accuracy is more than 2nd order in time.
Response: Thanks for your suggestion, and we have added more descriptions about the numerical scheme. “The spatial discretization has a second-order accuracy, and the bounded second order implicit Euler scheme is adopted for the time integration.” (See Line 201-203).
Comment 6: How much was the measurement errors of experimental data shown in Fig5 & 6?
Response: The measurement error of experimental data is ±0.05%.
Comment 7: In Fig6, page 8, authors state that the numerical results agreed well with the experimental data by comparing ηp,mean. However, some data points show nonnegligible error, e.g. x/w ~ -0.4 in Fig6(c), case C, shows more than 10% error. Is there any specific reason of this discrepancy?
Response: Thanks for your suggestion, and we have added the explanation. “When the wind speed is small, there is an obvious difference between the experimental data and the simulation results at some data points. The reason for this difference may be that the heating effect and chemical reaction of the active actuators are not considered in the present simulation.” (See Line 265-268)
Comment 8: This is just a comment: in the introduction part, authors described that the proposed multi-SDBD may be an effective strategy for mitigating the wind pressures acting on low-rise buildings during typhoon. Does multi-SDBD work good even in typhoon with rain or high-moisture condition? Do you have any idea?
Response: Thanks for your comment. Since the plasma actuators can be used to de-ice, we believe that they can work under the condition of rain or high humidity. We have added our idea in this aspect to the text. “The nanosecond pulsed plasma actuators can release large amounts of heat and generate shock waves, so they may be used to remove water droplets from the building surface in a high humidity environment.” (See Line 503-505)
The revised manuscript had been modified and made some changes according to your comments.
We appreciate for the editors and reviewers’ warm work earnestly, and hope that the modifications will meet with approval.
Once again, thank you very much for your comments and suggestions.
Best regards!
Yours sincerely,
Xuewen Zhang
E-mail: [email protected]
Tel: +86-18508401589
Address: Key Laboratory of Building Safety and Efficiency of the Ministry of Education, Hunan University, Changsha, Hunan 410082, China.
