Relative velocity fluctuations in turbulent Rayleigh-Bénard convection

Abstract

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)∼${\mathit{L}}^{0.6}$ being the characteristic turbulent velocity at the legth scale L and q the scattering vector. It is also found that the lower cutoff length ${\mathit{l}}_{\mathit{c}}$ of the scaling range obeys a power law ${\mathit{l}}_{\mathit{c}}$∼${\mathrm{Ra}}^{\mathrm{-}0.3}$. The measured power-law exponents are in excellent agreement with theoretical predictions.