Prediction of Noise from Turbulent Boundary Layers Attached to Porous Media

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 flowfield statistics. These statistics are calculated through a steady Reynolds-averaged 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 nonporous solution. The flowfield is validated through comparison with acoustic measurement. Predictions are conducted to ascertain changes in acoustic radiation with varying porosity. It is found that noise is amplified or reduced in a nonintuitive way with the introduction of porosity, variation of frequency, and increase of Mach number.