Control of flow separation over an aerofoil by external acoustic excitation at a high Reynolds number

• Published in: Physics of fluids (1994) Vol. 36; no. 1
• Main Authors: Coskun, S., Rajendran, D. J., Bacic, M.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 01.01.2024
• Subjects: Acoustic excitation; Acoustic frequencies; Acoustics; Aerodynamics; Airfoil profiles; Airfoils; Amplitudes; Boundary conditions; Detached eddy simulation; Drag coefficients; Effectiveness; Flow control; Flow separation; Fluid dynamics; Fluid flow; Frequency ranges; Gas turbine engines; High Reynolds number; Laminar flow; Lift; Normal distribution; Reattached flow; Reynolds number; Turbulent flow
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/5.0179439

The effectiveness of acoustic excitation as a means of flow control at high Reynolds number turbulent flows is investigated numerically by using improved delayed detached eddy simulations (IDDES). Previous studies on low Reynolds number laminar flows have shown that acoustic excitation can substantially suppress flow separation for specific effective frequency and amplitude ranges. However, the effect of acoustic excitation on higher Reynolds number turbulent flow separation has not yet been explored due to limitations on appropriate fidelity computational methods or experimental facility constraints. Therefore, this paper addresses this research gap. A NACA0015 airfoil profile at 1 × 106 Reynolds number based on the airfoil chord length is used for the investigations. Acoustic excitation is applied to the baseline flow field in the form of transient boundary conditions at the computational domain inlet. A parametric study revealed that the effective sound frequency range shows a Gaussian distribution around the frequency of the dominant disturbances in the baseline flow. A maximum of ∼ 43 % increase in lift-to-drag ratio is observed for the most effective excitation frequency F + = 1.0 at a constant excitation amplitude of A m = 1.8 %. The effect of excitation amplitude follows an asymptotic trend with a maximum effective excitation amplitude above which the gains are not significant. A fully reattached flow is observed for the highest excitation level considered ( A m = 10 %) that results in ∼ 120 % rise in airfoil lift-to-drag coefficient. Overall, the findings of the current work demonstrate the higher Reynolds number effectiveness of acoustic excitation on separated turbulent flows, thereby paving the way for application in realistic flow scenarios observed in aircraft and gas turbine engine flow fields.