Acoustic radiation due to gust-airfoil interaction in compressible flow

The problem of unsteady loading and acoustic radiation due to the interaction of an airfoil with a gust 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 by 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 the asymptotic solutions. Excellent agreement is obtained. In a companion paper, the validated code is 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.