Optimization of wind fence enclosures for infrasonic wind noise reduction

A large porous wind barrier enclosure has been built and tested to optimize wind noise reduction at infrasonic frequencies between 0.01-10 Hz in order to develop a technology that is simple, cost effective, and improves upon the limitations of pipe and porous hose arrays. The effects of varying the fence's porosity, modifying its top condition and bottom gap, doubling the height and diameter, and adding a secondary wind barrier were investigated. A simple mathematical model which estimates the wind noise measured at the center of the enclosure was derived based on the measured turbulence and velocity profiles measure outside the enclosure, inside the enclosure, and incident to its surface. The wind fence enclosure achieves wind noise reduction by minimizing the turbulence and velocity gradients at its center, and by decorrelating and area averaging the pressure fluctuations at its surface. The optimum wind fence has a surface porosity of 40-55%, a porous roof, no bottom gap, is very tall, wide, and is supplemented by a secondary wind barrier. The optimum wind fence can achieve a wind noise reduction of 20-27 dB over the 2-4 Hz frequency band, at least a 5 dB noise reduction for frequencies from 0.1 to 20 Hz, and a constant 4-6 dB of noise reduction for frequencies with turbulence wavelengths larger than the fence. At high wind speeds, 3-6 m/s, the optimized wind fence enclosure reduces wind noise sufficiently to detect microbaroms.