Characterization of the effect of Froude number on surface waves and heat transfer in inclined turbulent open channel water flows

Interfacial heat transport in open channel turbulent flows is strongly dependent on surface waves that can appear as a result of the interaction of bulk turbulence with the free surface. The paper describes wave/heat transfer phenomena in inclined turbulent open surface water flows. The experiments were conducted in a regime of transition from “weak” to “strong” turbulence, in which the stabilizing influences of gravity and surface tension are relatively small against the disturbing effects of turbulence. A key role of the Froude number, Fr_⊥, built through the surface-normal component of g has been revealed. As Fr_⊥ grows, the wave amplitude grows, and the frequency spectrum shifts towards shorter waves. These changes lead to a heat transfer improvement, enough to double the heat transfer coefficient. The experimental data have been compared with calculations based on a “K-ε” model. As a result, the range of applicability of the standard model has been established as Fr_⊥<2000. The turbulent Prandtl number has been evaluated for Fr_⊥<700.