GROWING TURBULENT SPOT IN PLANE COUETTE FLOW PROVIDES DISSIMILARITY BETWEEN MOMENTUM AND HEAT TRANSFERS

Direct numerical simulation of a turbulent spot developing in a laminar plane Couette flow was performed to study the dissimilarity between the heat and momentum transfers. The seed of the turbulent spot was a vortex pair, and the initial flow had an absolute similarity state between heat and momentum transfers. The turbulent spot grows gradually in the early stage and rapidly in the latter stage. The effective heat transfer state, which achieves larger heat transfer than momentum transport, was confirmed in the rapidly developing process. The dissimilarity mechanism was investigated by using a FIK identity equation. We clarified that the turbulent contributions in the friction coefficient and the Stanton number provided the effective heat transfer state. The budgets of Reynolds shear stress and heat flux exhibited that the dissimilarity was attributed to the differences in the pressure-strain and dissipation terms, and the difference in the production terms leads to adverse effects on the effective heat transfer. After the developing process, the pressure-strain term causes a decrease of the heat transfer compared to the skin friction.