Flow Characteristics of an Optimized Axial Compressor Rotor Using Smooth Design Parameters

Abstract

Blade designs have evolved from NACA series and free vortex assumptions to detailed meanline and forced vortex definitions. A design process is presented with numerous parametric options to explore a large design space. Smoothness in turbomachinery blade shapes is critical to an effective design. A cubic B-spline is used to control spanwise variations in the curvature definition of airfoil camber, thickness distribution, leading edge definition, inlet angles and outlet angles as parameters with a small number of control points. Varying parameters of individual blade sections requires more control variables that increases the parameter space and adds kinks in the 3D blade shape. Benefits of this smooth spanwise capability are demonstrated by linking the blade design tool with an aerodynamic optimization system. A single subsonic rotor (rotor 6 of a 10 stage axial compressor derived from the GE EEE design) has been considered as the baseline for the optimization process. Optimization is performed by varying curvature of the airfoil camberline as well as inlet and outlet angles in the spanwise direction. A single objective optimization was performed to optimize isentropic efficiency. An improvement in efficiency of 0.83% from 91.87% to 92.63% was obtained. The optimized blade geometry has a smooth transition from a traditional airfoil shape at the hub section to an S-shaped airfoil at the mid and tip sections. This unique blade shape was obtained because the airfoil camber curvature definition was allowed to vary smoothly spanwise. An S-shaped blade near the mid and tip section promotes flow to move radially downwards which allows for a reduction in entropy generation due to tip leakage flows. Entropy is used to quantify losses and improvement in efficiency.