Experimental Study of the Endwall Heat Transfer of a Transonic Nozzle Guide Vane With Upstream Jet Purge Cooling Part 2—Effect of Combustor-Nozzle Guide Vane Misalignment

Abstract

A misalignment between the combustor exit and the nozzle guide vane (NGV) platform commonly exists due to manufacturing tolerances and thermal transience. This study investigated, experimentally and computationally, the effect of the combustor-turbine misalignment on the heat transfer for an axisymmetric converging endwall with a jet purge cooling scheme at transonic conditions. The studies were conducted at engine-representative Maexit = 0.85, inlet turbulence intensity of 16%, and Reexit,Cax = 1.5 × 106. A film cooling blowing ratio of 2.5 (design condition) and 3.5 and an engine-representative density ratio of 1.95 were used in the study. Three various step misalignments, combustor exit being 4.9% span higher than turbine inlet (backward-facing), no step (baseline), and combustor exit being 4.9% span lower than turbine inlet (forward-facing), were tested to demonstrate the misalignment effect on endwall heat transfer. Results indicated that the step misalignment affects the cooling performance by altering the interaction between the coolant and the cavity vortex, horseshoe vortex, and passage vortex. At the design blowing ratio of 2.5, the backward-facing step leads to increased coolant dissipation, causing the coolant to be later dominated by the passage vortex and leading to poor cooling performance. Meanwhile, a forward-facing step induced more coolant lift-off. At the blowing ratio of 3.5, the additional momentum ensures that enough coolant enters the passage to form a stable boundary layer. Therefore, the step misalignment no longer has a first-order effect.