Porosity effects in large wind screening structures.

Abstract

Recently completed research indicates that the dominant source of wind noise for infrasonic microphones placed on open ground is the interaction pressure of the average wind velocity profile and the vertical turbulence. The source region at infrasonic frequencies is quite large and therefore can only be reduced with relatively large structures. It is hypothesized that such a structure does not need to completely block the wind from the source region; it only has to reduce the wind velocity gradient above the microphone and perhaps modify the turbulence field. If so then a porous wind barrier or screen may be used. To investigate this hypothesis a 3 m high decagonal wind barrier with variable porosity has been constructed. Initial results indicate that reductions are strongest for intermediate porosities and for frequencies between 0.5 and 7 Hz. In addition, a near constant 3–5 dB reduction was also observed for frequencies below 0.5 Hz. The noise reduction results will be related to the measured wind profiles and turbulence spectra inside the enclosure. The enclosure is quite open and should have little effect on acoustic waveforms, unlike pipe arrays and porous hose arrays.