Measured velocity boundary layers in turbulent convection

Direct measurements of the velocity boundary layer in turbulent convection have been carried out using a novel light scattering technique. The experiment reveals that the velocity profile nu(h)(z) as a function of the distance z from the lower surface of a convection cell has an invariant form nu(h)(Z) = nu(m)f(Z/delta(nu)) over varying Rayleigh numbers (Ra). It is found that the scaling velocity nu(m), the viscous boundary layer thickness delta(nu), and the shear rate gamma all obey power laws of Ra, i.e., nu(m), similar to Ra-0.5, delta(nu), similar to Ra--0.16, and gamma similar to Ra-0.66.