On the aeroacoustic characteristics of a plunging airfoil

The aeroacoustic characteristics of a two-dimensional (2D) plunging SD7003 airfoil at a Reynolds number of 10 000 are investigated using direct numerical simulations (DNS) based on an in-house 2D high-fidelity compressible Navier–Stokes solver. The plunging frequency is fixed as 1.25, while the Mach number is varied between 0.1, 0.2, and 0.3, denoted as M1, M2, and M3, respectively. The mean and root mean square values of the surface pressure coefficients at M3 are substantially different from those at M1 and M2, which is connected with the leading edge (LE) shear layer evolutions. Surface pressure fluctuations are found to be the dominant noise sources for all three Mach numbers. For the second harmonic (2fo), the airfoil is no longer acoustically compact for these three cases. This results in a sound pressure magnitude scaling different from M2.5. In particular, the power spectral magnitude and phase angle of the surface pressure jump (Δp) between the suction and pressure sides of M3 show a large magnitude near the trailing edge and a less destructive phase distribution near the LE, respectively. To enable rapid acoustic predictions, a compact linear model is developed by combining the Theodorsen model and Ffowcs Williams–Hawkings acoustic analogy, showing good agreement with DNS results.