Identifying Inefficiencies in Unsteady Pin Fin Heat Transfer

Internal cooling of the trailing edge region in a gas turbine blade is typically achieved with an array of pin fins. In order to better understand the effectiveness of this configuration for heat transfer, an unsteady Reynolds-averaged Navier Stokes computation is performed on a single row of cylindrical pin fins with a spanwise distance to fin diameter ratio of 2 and height over fin diameter ratio of one. With a locally adapted mesh, the boundary layer is resolved throughout the domain. For validation purposes, the flow Reynolds number based on hydraulic channel diameter Re_DH = 12,800 was set to match experiments available in the open literature. The resulting time-dependent flow field was analyzed using a variation of Proper Orthogonal Decomposition (POD), where the correlation matrices were built using the internal energy in addition to the three velocity components. This enables a flow decomposition with respect to the flow structure’s influence on surface heat transfer. The second and third most energetic modes showed a zero temperature eigenfunction, which means that a considerable amount of energy is contained in flow structures that don’t contribute to increasing endwall heat transfer. It was also found that the vortex shedding frequency changes over time and both lift coefficient and Strouhal number increase compared to experimental values for a single cylinder.