A Design Optimization Procedure for Efficient Turbine Airfoil Design

Abstract

An optimization procedure has been developed for the efficient design of turbine blade airfoil sections. A shape sensitivity study of the airfoils has been performed considering two leading edge shapes, circular and elliptic. Pressure and suction surfaces are approximated by polynomials. A two-level, nonlinear constrained optimization problem is formulated and is solved using the method of feasible directions. The aerodynamic analysis is performed using a two-dimensional panel code. Since several evaluations of the objective functions and the constraints are required within the optimizer, and exact aerodynamic analysis at each step is computationally prohibitive, a two-point exponential approximation technique has been used. The procedure developed successfully eliminates the sharp leading edge velocity spikes, characteristic of typical blade sections, without compromising blade performance. Circular leading edge airfoils appear to be more effective in eliminating the spikes than elliptic leading edge airfoils. However, the elliptic leading edge sections are more slender than the circular leading edge sections. Optimum results are compared with a reference design.