Acoustic radiation due to gust–airfoil and blade–vortex interactions

Abstract

The problem of acoustic radiation due to gust–airfoil and blade–vortex interaction in compressible mean flow is considered numerically. The acoustic perturbation field is calculated by solving the acoustic equations derived from the unsteady Euler equations by linearizing about a steady mean flow and assuming a single frequency disturbance. A computational code is developed which is validated by computing the unsteady loads on a flat plate due to a gust in incompressible flow (Sears problem), and unsteady loads and acoustic radiation due to a compact and noncompact gust in compressible flow. For these three cases the numerical results are compared with the exact analytical solutions and asymptotic solutions. Excellent agreement is obtained. The validated code is then employed to perform parametric studies by varying the Mach number of the mean flow, the angle of attack, and the geometry (thickness and camber) of the airfoil. Conclusions are drawn about the magnitude and phase of acoustic radiation due to gust–airfoil interaction for various Mach numbers, angles of attack, and airfoil geometries. The validated code is also employed to compute the acoustic radiation due to blade–vortex interaction. Calculations are compared with those of other investigations for both the mean flow and the acoustic variables.