TRAILING EDGE NOISE AT LOW MACH NUMBERS, PART 2: ATTACHED AND SEPARATED EDGE FLOWS

✍ Scribed by M.S. HOWE

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 314 KB
• Volume: 234
• Category: Article
• ISSN: 0022-460X
• DOI: 10.1006/jsvi.1999.2861

✦ Synopsis

The di!raction theory of Part 1 [1] for estimating the sound generated by low Mach number #ow past the trailing edge of an airfoil of compact, but "nite thickness is applied to investigate the noise produced by turbulent #ow over an edge whose upper surface pro"le (the suction side) is rounded. The sound is expressed in terms of the &&upwash'' velocity #uctuations that the same boundary layer turbulence would generate if the airfoil were absent. An approximate method is proposed for expressing these #uctuations in terms of local properties of the blocked pressure generated on the surface exposed to the turbulent #ow. Predictions are made of the edge-noise spectrum for both fully attached #ow (that remains attached right up to the trailing edge) and for cases where separation occurs on the rounded pro"le. When premature separation occurs the amplitude of the edge-generated sound decreases exponentially with increasing frequency, and predicted edge-noise levels are signi"cantly smaller than estimates obtained when the airfoil is modelled by a rigid half-plane. For attached #ow turbulence on the suction side of the airfoil always passes close to the edge and interacts strongly with it, but contributions from the interaction of the same turbulence with the pressure side of the airfoil are reduced because of the "nite airfoil thickness. In this case sound levels fall short of those for a rigid half-plane typically by about 5}10 dB, the precise values being dependent on frequency, and on the ratio of the boundary layer thickness to the mean airfoil thickness.

2000 Academic Press.