Pressure Fluctuations in Aerodynamic Boundary Layers

Abstract

Pressure fluctuations in boundary layers of airplanes have been measured by various groups. In one case, the pressure fluctuations were measured by flush-mounting a microphone at the surface of the airplane fuselage. In all other cases, the pressure fluctuations are estimated from sound measurements made inside the fuselage, and measurements or estimations of the sound pressure reduction of the fuselage. This paper reviews and compares these measurements in the light of dimensional analysis, and indicates possible extrapolation methods. Preliminary results indicate that (1) the boundary layer pressure fluctuations can be related to the free-stream dynamic pressure (considering the airplane to be stationary and the air to be moving), (2) the spectra can be related to the free-stream velocity and to an unknown length l, and (3) the length l is a constant for approximately alike airplanes at corresponding positions along the fuselage. The measurements used in this study have been supplied or reported by Convair Division of General Dynamics Corporation, Douglas Aircraft Company, Royal Aircraft Establishment [M. E. Department Test Note No. 562, 1. I. McNaughton], and Wright Air Development Center [Technical Report No. 52-341, O. R. Rogers and R. F. Cook]. L. L. Beranek, E. M. Kerwin, and D. N. Keast have also contributed greatly to this study.