Leading Edge Noise from Thick Foils in Turbulent Flows
Abstract
The prediction of dipole sound from the diffraction of turbulence by the leading edge of a thick foil is made with the Kirchhoff integral for rigid surface scattering of the stagnation enthalpy. The incident field is determined from a volume integral and the rigid plane Green function using an equivalent form of Howe's (1975) acoustic analogy that is derived in terms of the mean free stream velocity and the fluctuating up-wash velocity found in Sears' (1941) analysis. A comparison of the measured and the predicted dipole sound made with the foil geometry and measured turbulence statistics from Paterson and Amiet (1976) shows good agreement. The thickness effect is incorporated in the governing Green function for the foil (Howe (1998a, 2001 a) and serves to exponentially attenuate the dipole sound pressure spectrum by the product of the convection wave number and half the maximum section thickness. The dipole sound from a foil cutting through a mean shear layer is then calculated using an acoustic analogy where the source has retained the mean shear term. The ratio of the dipole sound of the mean shear source to the source without mean shear from the earlier calculation is determined to be proportional to the ratio of the mean shear to the frequency of the sources. Estimates of the dipole sound with and without the mean shear source are made for Olsen and Wagner's (1982) experiment.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2003
- Accession Number
- ADA418125
Entities
People
- Jonathan Gershfeld
Organizations
- Naval Surface Warfare Center Carderock Division