Effect of Acoustic Excitation Amplitude on Flow Separation over NACA0015 Aerofoil for Near-Stall Angle-of-Attacks

Abstract

The effectiveness of acoustic excitation on controlling the flow separation over a NACA0015 aerofoil at 1 million Reynolds number based on c=0.35m chord length is investigated numerically using Improved Delayed Detached-Eddy Simulation (IDDES) for a range of near-stall angle-of-attacks. The angle-of-attacks of interest are 9 degrees and 11 degrees for pre-stall investigations and 13 degrees for post-stall consideration. The aerofoil under investigation is exposed to considerable amount of flow separation for the current operating conditions, which results in severe aerodynamic performance degradations. The effect of acoustic excitation on flow separation is investigated as a means of flow control by introduction of planar sound waves upstream of the aerofoil. The excitation frequency is kept constant at the frequency of the most amplified disturbances in the uncontrolled flow that corresponds to F+=1 for each angle-of-attack. As the main focus of this study is the effect of excitation amplitude on controlling flow separation by acoustic excitation, the amplitude of sound waves is considered in the range from 1.8% to 10% of the freestream velocity that is defined in fractions of the freestream velocity. The findings illustrate a strong dependence of the effectiveness of acoustic excitation on excitation amplitude for the range of operating conditions under investigation. The results also suggest that acoustic excitation is most effective at 13 degrees that results in substantial aerodynamic performance improvement.