Correlation Studies of Pressure Fluctuations on the Ground Beneath a Turbulent Boundary Layer

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Narrow-band pressure correlation measurements in the frequency range ,008 to 1 Hz(cps) were obtained from a cross spectral analysis between pairs of microphones placed on level ground beneath the wind stream. The measurements were made over a range of wind speeds from 2.1 to 7.2 meters per second and a range of hemispheric solar radiation conditions varying from 0 to 44 Langleys per hour. Plausibility arguments are presented which predict for the narrow-band longitudinal and lateral correlation coefficients: -0'~ Rw(£,0) = e cos(kg) and Rw(O~~) = e-S~ where~ and~ are the longitudinal and lateral separations, respectively, and 0', S, and k are determined by the experiment. Contrary to similarity considerations ct and k were found not to be strictly proportional, but rather 0' = 0.4lk 1 ' 28 , 0' and k being expressed in (meters)-1 , over a range 2 < (1/ot) < 500 meters. The relation between 2 .74 Q -1 ct and S was found to be: ~ = 1. 0' , 0' and ~ expressed in (meters) , over a range 3 < (1/~) < 500 meters. For an arbitrary angle with respect to wind direction evidence is presented which indicates that Rw(~,~) is very slightly larger than the product Rw(g,O)Rw(O,~). A small amount of data taken relating the convection velocity versus wavelength to anemometer readings indicates the possibility of predicting the wind profile from pressure fluctuations on the ground.