URANS of Flow and Endwall Heat Transfer in a Pinned Passage Relevant to Gas Turbine Blade Cooling

The paper presents some results of unsteady RANS (URANS) study of flow and heat transfer in a matrix of 8x8 round pins connecting walls of a plane channel. The configuration mimics an internal cooling passage of gas-turbine blades. The focus is on flow unsteadiness, its role in governing the overall flow and heat transfer and the capabilities of a selected RANS model in reproducing these features in a set-up of industrial relevance. The results obtained at two Reynolds numbers, 10000 and 30000, are compared with the available experiments and large-eddy simulations (LES). It is shown that the elliptic-relaxation eddy viscosity model, ?-f captures reasonably well the general pattern of the vortex shedding and the consequent gross effects on the flow development. However, a closer look at flow details reveals discrepancies, especially in the initial portion of flow 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, but this was not sufficient to fully recover the flow pattern generated by LES. The comparison seems to suggest that smaller structures that are undetected by URANS need to be resolved to capture properly the separation and wake characteristics of each row. Surprisingly, at the lower Re, the average Nusselt number at the endwalls shows very close agreement with LES, both being about 20% lower from the reported experimental value. On the other hand, for the higher Re (for which LES are not available) the computed Nusselt number is within 8% of the experimental value.