Numerical Prediction of The Notch Effect of Riblets on Axial Compressor Blades

Abstract

Riblet structured surfaces can reduce the aerodynamic drag of bodies, which are immersed in fluid flows. A future application of these microscopic grooves with dimensions below 100 μm on axial compressor blades could increase the compressor efficiency and could reduce the fuel consumption and CO2emissions of aircraft engines. In order to reduce the aerodynamic wall shear stress, riblets are aligned with the flow direction. In the case of an axial compressor rotor blade, this means that the riblets are also oriented perpendicular to the radial direction of the centrifugal blade load. Thus, the negative consequence from riblet structuring of an axial compressor rotor blade is a local stress increase by a notch factor between 1.5and 14.0. For the example of an axial compressor rotor blade rotating at a speed of 18,000 rpm, this means, that if static strength requirements must be met, and the blade material does not have any blade internal residual stresses –like in the case of trapezoidal riblet manufactured by contact-free laser ablation –only the upper 20%of the blade span can be structured wit riblets.