The effect of double diffusion on entrainment in turbulent plumes

Abstract

We investigate experimentally the effect of double diffusion in the salt-fingering configuration on entrainment in turbulent plumes. Plumes over a range of source buoyancy fluxes and source density ratios 𝜌 are examined. When the plumes are double diffusive ( 𝜌 ) the entrainment coefficient 𝛼 is not constant, with an up to 20 % reduction from the value found for single-diffusive plumes, that is, plumes with 𝜌 . The scale of reduction is found to be in direct relation to the source density ratio and is inversely related to the distance travelled by the plume, indicating that double-diffusive effects decrease as the plume evolves. We propose an explanation for the observed reduction in the entrainment coefficient on the basis of differential diffusion hindering large-scale engulfment at the edge of the plume.