Secondary flow impact on velocity and thermal fields of a structured turbulent channel flow

Surface structuring in form of streamwise elongated triangular ridges is investigated in a framework of a fully developed turbulent channel flow at Reb = 18000. The ridges generate a strong large-scale secondary motion and hence alter momentum and heat transfer in the channel. A comparison of the obtained skin friction and heat transfer coefficients reveals a 30% enhancement for both quantities relatively to the smooth channel. Tripe decomposition analysis of the total stress and heat flux results in an observation of different mechanisms behind this enhancements: while the skin friction coefficient is mainly increased by the secondary-motion-related contribution, the heat flux is similarly enhanced by the secondary motion and modification of turbulent properties of the flow.