Numerical Investigations of Film Cooling Characteristics of Interrupted Slot and Trench Holes on a Vane Endwall

This paper describes film cooling characteristics of the novel combined configuration employing interrupted slot and trench holes on a vane endwall. Interrupted slot, formed by uneven thermal expansion between combustor and high-pressure turbine vane, can improve adiabatic film cooling effectiveness of the leading edge and pressure side-endwall junction by inhibiting the development of horseshoes vortex. Holes embedded into a straight trench were introduced to improve film efficiency comparing to cylindrical holes on vane passage endwall. The influences of lateral pressure gradient, slot coolant and step on crossflow of the hole coolant in trench were mainly discussed. Three dimensional Reynolds-averaged Navier-Stokes equations with shear stress turbulence model (SST k - ω ) were used to obtain the flowfields and adiabatic film cooling effectiveness of a cascade model. Four hole blowing ratios M =0.5, 1.0, 1.5, 2.0 and two axial positions X / Cax = −0.05, 0 were considered. The coolant crossflow in trench on flat endwall of cascade passage trends to flow towards suction side due to the lateral pressure gradient rather than both sides on flat plate. For combined configuration of interrupted slot and trench holes, the step vortex rolls up hole coolant upstream of trench which changes η distributions comparing to that on flat passage endwall. Comparing to the cylindrical holes, better film cooling performance can still be obtained when arranging trench holes under high blowing ratios. The influence of hole’s axial positions was also discussed.