Buoyancy effects on a turbulent shear flow

The effects of buoyancy on the structure of a turbulent flow with uniform velocity, temperature, and concentration gradients in the vertical direction are studied theoretically on the basis of a statistical turbulent-flow model. The study shows that the three components of the turbulent kinetic energy, the mean square temperature fluctuation, the Reynolds stress, the turbulent heat transfer, and the turbulent mass transfer are all enhanced under unstable conditions and suppressed under stable conditions. The turbulent heat transfer is more strongly affected by the buoyancy than the Reynolds stress, so that the ratio of the eddy conductivity to the eddy viscosity decreases at increasing Richardson numbers. The buoyancy affects the turbulent heat transfer and the turbulent mass transfer in the same manner. Comparison with experimental data shows satisfactory agreement for most of the turbulent properties.