Acoustic Source Created by Turbulent Flow over Orifices and Louvers,

摘要

Orifice and louver sound power spectra are investigated, using an intensity probe, at various wind speeds in a low noise, semi-anechoic, subsonic wind tunnel for free stream velocities below 50 meters per second. The radiated noise is created by turbulent flow over various orifice and louver geometries which are flushed mounted into the wall of a long duct. Five orifice samples of rectangular shape and various transverse dimensions as well as four louver samples with multiple rectangular and circular orifices are tested. Also investigated is the effect of the leading and trailing edge angle on the radiated sound power. The scaling laws of the excitation frequencies and the speed/power laws are presented for ratios of the boundary layer thickness to the transverse orifice dimension from 1.01 to 4.29. A detailed theoretical model is developed for rectangular shaped aperture orifices and louvers based on the work by other authors. The model describes the predominant variables which effect the radiated flow noise. To ascertain the validity of the model, it is used to collapse the experimental power spectra for two orifice and one louver geometry. The model showed excellent agreement with the actual sound power measurements. Directivity plots are also presented to further describe the orifice/louver source. (mjm)