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 vₕ(z) as a function of the distance z from the lower surface of a convection cell has an invariant form vₕ(z)0ex0ex=0ex0exvₘf(z/δᵥ) over varying Rayleigh numbers (Ra). It is found that the scaling velocity vₘ, the viscous boundary layer thickness δᵥ, and the shear rate γ all obey power laws of Ra, i.e., vₘ~Ra0.5,δᵥ~Ra^-0.16, and γ~Ra0.66.