Vortex structures and heat transfer in a wall-bounded pin matrix: LES with a RANS wall-treatment

A hybrid LES/RANS simulation is applied to study the velocity, vorticity and thermal fields in flow over a staggered matrix of cylindrical pins bounded by a cold and a heated plane endwall approximating the typical configuration of internal cooling of gas-turbine blades. The hybrid approach considered is in fact a coarse-grid conventional LES coupled with the elliptic relaxation ζ-f RANS model that prevails in the wall-adjacent regions. Two Reynolds numbers have been considered, 10.000 and 30.000, based on the pin diameter and mean velocity between the two pins. First the performance of the hybrid approach was evaluated in comparison with the earlier reported URANS using the same RANS model throughout the whole flow, as well as with wall-resolved LES. The results of the hybrid method, found to recover with acceptable accuracy the dominant large-scale vortical patterns and the averaged flow parameters, were then used to analyse the effects of vortex structures on the velocity and thermal fields and their role in wall heat transfer using graphical visualisation. In addition to the temperature contours, the thermal field is also visualized by heat-flux lines, which make it possible to identify heat “corridors” and distinguish regions dominated by stochastic turbulent transport and those of large-scale vortical convection.