Direct numerical simulation of low-Prandtl number turbulent convection above a wavy wall

• Turbulent convection is investigated in a wavy channel for Re = 18, 880 and Pr = 0.025.
• In the considered Péclet number range, heat transfer is mostly by mean flow advection.
• The Generalized Gradient Diffusion Hypothesis (GGDH) represents with fair accuracy the direction of turbulent heat fluxes.
• Given the time scale in the model depends on mechanical quantities only, Cθ needs to be tuned for Pr ≠ 1.

Turbulent forced convection is investigated by Direct Numerical Simulation in a channel with one sinusoidal wavy wall and one flat wall. Fluid flow and heat transfer are periodically fully developed, the simulated Reynolds number of the bulk velocity and the hydraulic diameter is Re = 18, 880 while three Prandtl numbers are considered, i.e. Pr = 0.025, Pr = 0.2, and Pr = 0.71. The fluid flow is characterized by separation, reattachment and a shear layer downstream the wave peak, these are conditions relevant for turbulent heat transfer and passive scalar transport applications.In the range of Péclet numbers investigated, the most important heat transfer mechanism is by mean flow advection. Accordingly, the peak heat transfer region is in the upslope part of the domain. The separation bubble instead acts as a barrier to convection and the heat transfer rate is minimum close to separation. An a priori analysis is performed in order to assess the accuracy of turbulent heat transfer models based on the Generalized Gradient Diffusion Hypothesis.