Computational Study of the Plasma Actuator Flow Control for an Airfoil at Pre-Stall Angles of Attack
Round 1
Reviewer 1 Report
The authors of the paper “Optimal control of stacked multi-kite systems for utility-scale airborne wind energy” have performed large eddy simulations of the flow over an airfoil with a body force to model a plasma actuator at the upper surface of the blade. The analysis of their results shows that a continuous and burst plasma actuator increases the efficiency of the NACA0015 airfoil at pre-stall angles.
They have shown that the lift-to-drag ratio increases mainly due to the decrease in pressure drag due to the shrinkage of the recirculation region on top of the blade. In addition, it is shown that the burst plasma actuation-induced vortical structures delay the transition to turbulent flow over the blade.
I may recommend the research article “Computational study of the plasma actuator flow control for an airfoil at pre-stall angles of attack” be published in the Applied Science Journal, given that the following concerns are addressed.
Major concerns:
- The authors claim that the increase in lift-to-drag ratio mechanism at pre-stall angles may differ from post-stall angles of attacks. However, this claim could have been more evident by including in their analysis the LES simulation of alpha=12.
- Results of Hajipour and Ebrahimi (2018) indicate that the decrease in pressure drag due to the plasma actuator at post-stalled angles is caused by the breakdown of the shear layer closer to the separation point. Therefore, weakening the recirculation region over the blade. How those the results of the mentioned authors compare to yours for pre-stall and post-stall angles of attacks?
Minor concerns:
- The grid resolution in wall-spacing units suggests that the numerical simulation is a wall-resolved LES. Is this correct? If so, was the turbulent viscosity damped near the blade?
- The Suzen-Huang model does not seems to depend on the velocity field. Were the model equations solved concurrently with filtered Navier-Stokes equations? Was this necessary?
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Large-eddy simulations of the flows over a NACA0015 airfoil were conducted to investigate a flow control authority of a dielectric barrier discharge plasma actuator at pre-stall angles of attack. The paper topic is interesting to the reader. The LES simulation is quite challenging. The simulation results are explained. However, the novelty is not apparent. The discussion and analysis need to be more profound. Therefore, the recommendation for the publication is a revision, and provide the following comments for correction.
1. I recommend that the author add some literature and rewrite their introduction by identifying the previous research gap in the computational study of plasma actuator flow control. What is the strong point of using the LES simulations? What is the novelty of this paper?
2. The paper uses a NACA0015 airfoil for computational simulation. It is a symmetrical airfoil, and a few real wings use this kind of airfoil. Therefore, the reason for determining the geometrical model and setup needs to be explained in detail. Moreover, the limitation of the simulation results should be stated in the paper due to only a specific model, and a numerical setup was selected.
3. The CFD simulation uses experiment data for validation (Figure 5). Therefore, I strongly recommend that the experiment data limitation and condition for validation need to be explained. Moreover, the mean absolute percentage error (MAPE) between the experiment and simulation should be presented.
4. The main topic is a computational study of Plasma actuator Flow Control. Therefore, results and discussion should be expanded by describing the research's major findings numerically and comparing them to previous studies. In addition, the current research area's gaps must be highlighted, and future study directions must be presented.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors of the paper "Optimal control of stacked multi-kite systems for utility-scale airborne wind energy" have significantly improved the article's quality and have fully addressed my concerns. Therefore, I recommend the article for publication in the Applied Science journal.
Reviewer 2 Report
The quality of the paper has been improved in the revised version and the authors have been accomodated reviewer suggestions. I think the paper can be accepted in the present form.
