Experiments on steady buoyancy transfer through turbulent fluid layers separated by density interfaces

Abstract

Abstract A laboratory experiment was performed to investigate mixing across a density interface which separates two turbulent fluid layers and coexists with a stabilizing buoyancy flux. It was found that the buoyancy flux ( q 0 ) across the interface and through the turbulent layers (of depth D ) becomes steady and constant in magnitude in the vertical direction, only when q 0 ≅ 1.5 u 3 D , where u is the horizontal r.m.s. velocity at the base of the mixed layers. The results suggest that mixing across the density interface is controlled by a dynamically important buoyancy gradient induced in the turbulent layers and that parameters such as the bulk Richardson number, Ri = ΔbD u 2 , where Δb is the interfacial buoyancy jump, are of secondary importance. Measurements are used to infer the mixing mechanism at the interface, the mixing efficiency of stratified fluids and the entrainment law. Some geophysical applications of the results are also discussed.