Large scale model measurements of airframe noise using cross-correlation techniques

Abstract

Cross-correlation techniques are used to measure the sound radiated by wing/flap airfoil configurations in the NASA–Ames 40- by 80- foot wind tunnel using a 6.7-m semispan model with three deployed flaps. The sound from the flap side edges exceeds other airframe noise sources by more than 10 dB, with the noise from the side edges of the leading flaps the strongest. The radiated sound is estimated using two formulas based on the standard aeroacoustic theory and one method using only the near and farfield cross correlation. The last method is essentially independent of such theory. The classic dipole angular distribution pattern is modified by wing diffraction effects to yield stronger radiation in the forward direction. The radiated intensity increases at slightly higher than the fifth power of the mean flow speed U0. The location of the flap track fairings is found to have a substantial effect on the radiated intensity: placing the fairings at or near the lateral edges of the flaps substantially reduces the radiated noise.