Effects of Localized Non-Gaussian Roughness on High Pressure Turbine Aero-Thermal Performance: Convective Heat Transfer, Skin-Friction and the Reynolds’ Analogy

Abstract Compressible direct numerical simulations are conducted to investigate how surface roughness affects the aero-thermal performance of a high pressure turbine vane operating at an exit Reynolds number of 0.59 × 106 and exit Mach number of 0.92. The roughness under investigation here was synthesized with non-Gaussian statistical properties and an amplitude that varies over its chord length — representative of what truly occurs on an in-service vane. Particular attention is directed towards how systematically changing the axial extent of leading edge roughness affects convective heat transfer (Nusselt and Stanton numbers) and aerodynamic drag (skin-friction coefficient) on the pressure and suction surfaces. The results of this investigation demonstrate that moving the larger amplitude roughness further along the suction surface can alter the blade boundary-layer state. In fact, towards the trailing-edge of one of the rough vanes investigated here, the local skin-friction coefficient increases by a factor of twenty-two compared to smooth-vane levels, whereas the local Nusselt number increases by a factor six. The disproportionate rise of drag compared to heat transfer is explored in further detail by quantifying the Reynolds’ analogy and by calculating the fractional contributions of pressure drag and viscous drag to the total drag force. The effect of varying the inlet turbulence intensity and integral length-scale for a fixed roughness topography is also investigated, and the Reynolds-number scaling of heat transfer and drag is examined in the context of the Chilton-Colburn analogy.