High-fidelity computational study of roughness effects on high pressure turbine performance and heat transfer

While blade surface roughness arising from in-service wear and/or the manufacturing process greatly affects aero-thermal performance, the detailed underlying physical mechanisms remain far from fully understood. In this study, a series of highly-resolved Large-Eddy Simulations of compressible flow past a high-pressure turbine vane with systematically varied levels of blade surface roughness have been performed, along with a smooth-blade simulation at matched flow conditions for comparison. Three non-dimensional roughness amplitudes have been investigated, namely, k(s)/c = {1.0, 2.0, 3.0} x 10(-3), where k is an equivalent value of Nikuradse's sandgrain roughness for an irregular, multi-scale near-Gaussian height distribution, and c is the axial blade chord. All simulations have been performed at an axial chord Reynolds number of 0.59 x 10(6) and a Mach number of 0.9, based on the exit conditions of the reference smooth vane, and with synthetic inflow turbulence to mimic unsteady, three-dimensional disturbances from an upstream combustion chamber. The present investigation highlights the profound impact that blade surface roughness can have upon boundarylayer transition mechanisms, wall shear stress and blade surface heat flux, as well as the levels of turbulence kinetic energy and total pressure losses incurred in the wake. While blade surface roughness leads to major aero-thermal differences between the suction-side of the smooth and rough vanes, the pressure-side surface remains relatively unaffected - even for the largest roughness amplitude investigated here.

Automated summary

This study investigates the impact of blade surface roughness on the aero-thermal performance of a high-pressure turbine vane using highly-resolved Large-Eddy Simulations. The study reveals that blade surface roughness affects boundary layer transition mechanisms, wall shear stress, blade surface heat flux, and turbulence kinetic energy and total pressure losses in the wake. However, the pressure-side surface of the blade remains relatively unaffected, even for the largest roughness amplitude.