Study of Turbulence by Photon PE- 6110eCorrelation Spectroscopy PR- 2307

Approved for public release; distribution is unlimited U3. limaC Was~ ~ jogWWW We have studied grid-generated turbulence in a water tunnel at moderate Reynolds numbers. The method used was the standard one of Laser Doppler Velocimetry (LDV) and an novel scheme, which we call photon homodyne correlation spectroscopy(HCS). With LDV, we measured the probability density function of velocity differences P(6v(e)) on varying spatial scales e, by invoking the frozen turbulence hypothesis. The HCS ft technique permits measuring P without using this hypothesis. Of special interest to-.ini us was the behavior of the system at and above a Reynolds number (Re,) where the | I turbulence becomes self-similar, in that <6bv(1)2>, 6. Above Re, the exponent " increases from 0 to 2/3 with increasing Re