Broadband Noise Predictions for an Airfoil in a Turbulent Stream

J. Casper* and F. Farassat tNASA Langley Research CenterHampton, VirginiaP. F. Mish * and W. J. Devenport _Virginia Polytechnic Institute and State UniversityBlacksburg, VirginiaAbstractLoading noise is predicted from unsteady surfacepressure measurements on a NACA 0015 airfoilimmersed in grid-generated turbulence. The time-dependent pressure is obtained from an array ofsynchronized transducers on the airfoil surface. Farfield noise is predicted by using the time-dependentsurface pressure as input to Formulation 1A of Farassat,a solution of the Ffowcs Williams Hawkings equation.Acoustic predictions are performed with and withoutthe effects of airfoil surface curvature. Scaling rules aredeveloped to compare the present far field predictionswith acoustic measurements that are available in theliterature.Nomenclatureb airfoil semi-span (m)C airfoil chord (m)co ambient sound speed (m/s)f frequency (Hz)g velocity-to-pressure transfer fimctionk co/U, convective wave number (rad/m)L streamwise integral length scaleM Mach numberAP unsteady surface pressure jump (Pa)p unsteady surface pressure (Pa)p' sound pressure radiated to observer (Pa)