On the Aerodynamic Design of Compressor Airfoils for Robustness Under Geometric Uncertainty

This paper considers the aerodynamic design of compressor blade sections for improved performance robustness in the face of geometric uncertainty caused by noisy manufacturing processes. A probabilistic, gradient-based optimization method was used to redesign subsonic and transonic compressor airfoils subjected to geometric variability. Three different design goals were considered: Minimizing the deterministic profile total pressure loss coefficient, minimizing the mean value of loss coefficient, and minimizing the loss variability. In both transonic and subsonic applications, deterministic minimization of loss coefficient produced essentially the same airfoils as the probabilistic minimization of mean loss. However probabilistic minimization of loss variability produced clearly different airfoils which achieved reductions of 20% or more in standard deviation of loss compared to the minimum-loss designs. For the subsonic application, the improved robustness of the minimum variability design was achieved through a reduction in diffusion immediately downstream of the leading edge on the pressure side. This reduction in diffusion resulted in less sensitivity of the boundary layer to geometric variability in the leading edge region. For the transonic application, the robustness improvement was achieved by redesigning the suction side to produce a constant pressure region immediately downstream of the passage shock, which had the effect of desensitizing the boundary layer to variability in shock strength and position. A meanline model was used to assess the impact of probabilistic airfoil section optimization on overall compressor performance. While the mean efficiency was found to be nearly the same for all designs, the robust blade designs produced a decrease in compressor efficiency variability of 50% compared to the minimum-loss designs.© 2004 ASME