Effects of oscillating mean spanwise pressure gradient on unstably stratified turbulent Poiseuille flow

Abstract

The effects of oscillating mean spanwise pressure gradient (OMSPG) are imposed on unstably stratified turbulent channel flow under a constant mean temperature gradient. First, an unstably stratified turbulent channel flow without OMSPG is performed under a constant mean vertical temperature gradient. The mean temperature gradient and gravity acceleration are imposed simultaneously in the same direction. Our results show that with an increase in the buoyancy, the skin friction coefficient first decreases, and then bounces back to increase, which non-monotonic behavior is related to the interaction between near-wall turbulence and thermal plumes generated by the buoyancy. Then, the effects of OMSPG are investigated and it is found that imposing OMSPG disrupts the generated thermal plumes, and hence decreases the effects of buoyancy, which increases the skin friction coefficient. In contrast, a decrease in heat transfer and Nusselt number is observed compared to cases without imposing OMSPG.