Remarks on the theory of aerodynamic noiseThe accuracy of approximations employed in the Lighthill theory in current aerodynamic noise research is critically evaluated. Based on the method of matched asymptotic expansions, the full Navier-Stokes equations are expanded for small Mach numbers. To the first order, the near-field is generally nonisentropic. The pressure field (pseudo-sound) is generated by the incompressible Reynolds stresses in the turbulent flow and the velocity, pressure perturbation, and their derivatives on the boundaries. In the far-field, the first-order pressure (acoustic) field satisfying a linear wave equation is obtained by matching with the pseudo-sound field. A uniformly valid solution for the pressure field in a stationary or uniformly moving medium is obtained. The solution shows that the generation of the first-order aerodynamic noise does not depend on the viscous, thermal, or entropy effects in the adiabatic flow nor on the shear stress on a smooth rigid boundary.
Document ID
19750058633
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Pan, Y. S. (NASA Langley Research Center Joint Institute for Acoustics and Flight Sciences, Hampton, Va., United States)