An Experimental Study of Airfoil and Endwall Heat Transfer on a Linear Turbine Blade Cascade — Secondary Flow and Surface Roughness Effects

The present study is part of a comprehensive heat transfer analysis on a highly loaded turbine blade and endwall with varying surface roughness. In this paper, a smooth airfoil with an endwall of varying surface roughness is considered in order to investigate secondary flow and surface roughness effects on airfoil and endwall heat transfer. The measurements have been conducted in a linear cascade with low pressure blades at several freestream turbulence levels (Tu1 = 1.4% to 10.1%) and varying inlet Reynolds numbers (Re1,c = 50,000 to 250,000). Aerodynamic measurements have been carried out on the airfoil at midspan and complemented by oil paint visualization on airfoil and platform. Heat transfer on both the full-span suction and pressure surfaces of the airfoil and endwall is shown for smooth surfaces. Moreover, rough endwall surfaces are compared to the smooth reference case showing a maximum increase of local heat transfer of up to 240% due to surface roughness.