URANS of flow and endwall heat transfer in a pinned passage relevant to gas-turbine blade cooling

This paper presents some results of URANS study of flow and heat transfer in a matrix of wall-bounded 8 × 8 round pins, mimicking internal cooling passage of gas-turbine blades. The focus is on flow unsteadiness, its role in heat transfer and the capabilities of RANS models to reproduce these features in a set-up of industrial relevance. The results for two Reynolds numbers, 10 000 and 30 000, are compared with the available experiments and LES. It is shown that the elliptic-relaxation eddy-viscosity model, ζ-f captures vortex shedding and the consequent gross effects on the flow development. However, a closer look at flow details reveals discrepancies, especially around the first three pin rows, where the unsteadiness reproduced by URANS shows much weaker amplitudes as compared with LES. Only further downstream the succession of forcing from a series of pins produced unsteadiness akin to those captured by LES. The comparison suggests that smaller structures undetected by URANS need to be resolved to capture properly the separation and wake characteristics of each row. At Re = 10 000, the average endwall Nusselt number agrees well with the LES, both being about 20% lower than in the experiment. For Re = 30 000 the URANS Nusselt is within 10% of the experimental value.