Flow and heat transfer in a rotating and non-rotating wedge-shaped cooling passage with ribs and pin fins

Cooling the trailing edge of a gas-turbine vane/blade typically involves an embedded wedge-shaped duct in a very confined volume, where coolant enters the duct radially and then directed to flow axially by ribs and pin fins to cool the entire trailing-edge region as efficiently and uniformly as possible. CFD simulations based on steady RANS - compressible formulation with temperature-dependent properties closed by the shearstress transport turbulence model - were performed to study the flow and heat transfer in a wedge-shaped duct with ribs and pin fins under rotating and non-rotating conditions. The objective of this study is twofold. The first is to understand the flow mechanisms by which ribs and pin fins turn radially outward flow to flow in the axial direction. The second is to understand what features of the flow and heat transfer obtained under laboratory conditions - where measurements have been made to validate this computational study - can be extrapolated to engine-relevant operating conditions. Results obtained show pin fins judiciously placed around the turn of the wedge-shaped duct to greatly reduce the size of the separated region when the coolant jets radially into the wedge-shaped duct. Also, pin fins provide flow resistance to control the flow direction, and the uniformity of the flow along the cross section of the wedge-shaped duct in addition to enhancing surface heat transfer via horseshoe vortices about each pin fin. The staggered array of ribs along the radial direction of the wedge-shaped duct was found to create up to three sets of recirculating flows that cause the flow entering the duct in the radial direction to spiral towards the axial direction with one created by the stagnation region upstream of each rib, one by the separation at the downstream edge of each rib, and one by the cavity-like flow between the aforementioned recirculating flows. When there is rotation, the staggered array of ribs was found to minimize the adverse effects of centrifugal buoyancy by confining flow separation to be between the ribs on the leading face. On what could be learned under laboratory condition that are meaningful for engine-relevant conditions, all of the aforementioned flow mechanisms are the same and the flow features are qualitatively similar. The exception is the size of the separated region at the tip of the wedge-shaped duct under non-rotating conditions, which is very large for the laboratory condition and very small for the engine-relevant condition.