The Prediction of Noise from Turbulent Boundary Layers Attached to Porous Media

Abstract

Aerospace vehicles, wind tunnel test section walls, and other structures often contain porosity that alters the turbulent boundary layer and radiated noise. A semi-empirical mathematical model is developed to predict and analyze the acoustic radiation from turbulent boundary layers over porous media. The model is an acoustic analogy that depends on local flow-field statistics. These statistics are calculated through a steady Reynoldsaveraged Navier-Stokes computational fluid dynamics solver that includes porous material. Acoustic predictions are conducted for four subsonic Mach numbers without a pressure gradient. At each Mach number, four porosities with constant liner depth and porous turbulent length scale are examined along with the non-porous solution. The flow-field is validated through comparison with acoustic measurement. Predictions are conducted to ascertain changes in acoustic radiation with varying porosity. We find that noise is amplified or reduced in a non-intuitive way with the introduction of porosity, variation of frequency, and increase of Mach number.