RELATIVE VELOCITY FLUCTUATIONS IN TURBULENT RAYLEIGH-BENARD CONVECTION

High-Rayleigh-number turbulent convection has been studied using the technique of photon-correlation homodyne spectroscopy to measure velocity differences at various length scales. The measured intensity correlation function G(q,t,L) is found to be of the scaling form G(qu(L)t), with u(L) is similar to L0.6 being the characteristic turbulent velocity at the length scale L and q the scattering vector. It is also found that the lower cutoff length l(c) of the scaling range obeys a power law l(c) is similar to Ra-0.3. The measured power-law exponents are in excellent agreement with theoretical predictions.