Experimental Investigation of the Aerodynamic Effect of Local Surface Roughness on a Turbine Blade

Abstract

This paper shows the effect of local surface roughness on the aerodynamic loss behavior of a turbine blade. Non-contact measurements of the surface roughness of turbine blades of a jet engine are conducted. The roughness is quantitatively characterised using a shape and density parameter to parametrise the topology and the average roughness height. An experimental investigation in a linear cascade wind tunnel is conducted in order to identify the contributions of pressure- and friction-losses of the measured surfaces to the overall profile loss increase due to local surface roughness. The results show that the change of profile losses due to local surface roughness is significant. The change in losses is dependent on the roughness height, as well as of the position on the blade of the roughness and the condition of the boundary layer behind. The local pressure gradient at and downstream of the surface roughness is identified as the main influencing parameter besides the roughness height.