Modelling of scalar transport in homogeneous turbulent flows

The paper describes a second order closure for calculating the flux of passive scalar quantities in turbulent flow. One of the dominant terms appearing in the scalar flux balance equation for which a closure approximation is required is the fluctuating scalar-pressure gradient correlation. For this quantity a new approximation has been developed in terms of a time scale characteristic of the scalar field and linear combinations of the scalar flux and Reynolds stress. The characteristic time scale is obtained from solution of balance equations for the scalar variance and its 'dissipation' rate. The constants appearing in the model have been chosen to reflect scalar turbulence data in a range of flows including strongly sheared nearly homogeneous flows, inhomogeneous equilibrium shear flows and decaying scalar (heated) grid turbulence. The model has been applied to the calculation of the scalar field in nearly homogeneous strongly sheared flow where it is shown to be capable of closely simulating the measured data.