Progress In Modeling Scalar Transport In ‘Complex’ Turbulent Shear Flows.

Abstract

We are concerned with the development of a mathematical model for the turbulent
scalar fluxes that can be used reliably in the prediction of ‘complex’ shear flows. These flows
are defined as those whose turbulence structure is distorted by the imposition of rates of strain
additional to the usual mean shear, or by body forces arising from buoyancy, streamline curvature
or system rotation. The effects of the extra strain rates or body forces on the turbulent
mixing processes are far greater than what might be expected from inspection of the relevant
terms in the governing conservation equations. Eddy-viscosity models fail badly in predicting
momentum transport unless modified in some ad-hoc way. Similarly, models based on Fick’s
or Fourier’s law have proved inadequate for the case of scalar transport. This paper presents
an alternative to these models; namely an explicit and algebraic model for the turbulent scalar
fluxes that allows them to properly depend on the details of the turbulence and the imposed
strain field. The model is applied to flows involving streamline curvature and is compared with
predictions from other non-linear algebraic closures and with experimental findings.