Heated injection into turbulent, liquid boundary layers

Since heating and injection have both been shown to reduce the skin friction of turbulent boundary layers in liquids, their combined effects are examined in the present paper with the aid of numerical analyses. Approximate means for predicting the consequent skin friction reduction and its persistence are discussed. An existing two-dimensional finite-control-volume code was extended to account for injection of a heated liquid through a porous surface into a turbulent boundary layer in the same liquid, allowing for viscosity variation. The results predicted that injection can be expected to reduce the skin friction both in the injection region and downstream, but the reduction is much greater at the injection region than downstream. The reduction and its persistence downstream increase with (a) increasing injection rate and (b) increasing temperature of the injected water. Results are sensitive to the wall function of the turbulence model in the injection region but not downstream