EFFECT OF COMBUSTOR-TURBINE PLATFORM MISALIGNMENT ON THE AERODYNAMICS AND HEAT TRANSFER OF AN AXISYMMETRIC CONVERGING VANE ENDWALL AT TRANSONIC CONDITIONS

This paper presents a detailed study on the effect of misalignment between the combustor exit and the nozzle guide vane endwall. The Nusselt number distribution and augmentation on an axisymmetric converging endwall as well as stage pressure losses were studied using experimental techniques and computational analysis. The analyzed endwall configurations are representative of the design intent and average off-design endwall configurations of a land-based high-pressure turbine nozzle guide vane. The studies were carried out at isentropic exit Mach number of 0.85, with an exit Reynolds number of 1.5 x 10(6) based on the true chord, and an inlet turbulence intensity of 16%. The experiment was conducted in a blowdown transonic linear cascade wind tunnel and an infrared camera was used to measure the surface temperature and subsequently the endwall heat transfer coefficient and Nusselt number distribution. Numerical computation analysis using ANSYS Fluent v.16 was used to provide further insight into the near-endwall flow field the predictions compared favorably to experimental data. The findings show that at the two configurations there exist uniquely different endwall secondary flow systems throughout the NGV stage. The interaction of separated flow at the combustor-turbine interface with the vane potential field results in additional secondary flow that is vastly different from that associated with classical endwall flows. This increased secondary flow in the misaligned configuration was marked by a 25% increase in NGV stage losses. The presence of separated flow and additional secondary flows also resulted in flow reattachment inside the vane passage which augmented heat transfer. The region upstream of the vane gage/throat showed heat transfer augmentation of up to 60%, while the endwall region downstream of the throat did not show any considerable heat transfer augmentation.