Implicit geometric representation of gas turbine blades for optimal shape design

This work is concerned with the development and integration of two geometric representations of turbine blade profiles that are appropriate for aerodynamic optimization. The first model is the Modified Rapid Axial Turbine Design (MRATD) model where the blade is represented by five low-order curves that satisfy fifteen designer parameters; this model is suitable for a global search of the design space. The second model is based on a Non-Uniform Rational B-Spline (NURBS) parametrization that implicitly represents the MRATD profile and the implied designer parameters; this model can be used for a local shape refinement. The two models are presented and are assessed for flexibility, accuracy and curve smoothness when representing several typical turbine blade profiles. The models are also assessed in terms of their effect on the blades aerodynamic performance as measured by the pressure distribution along the blade surfaces. The usefulness of the MRATD model is demonstrated in the global shape optimization of a subsonic cascade. The NURBS parametrization provides a means to control the blade profile locally, e.g., the blade curvature near a point smoothened by adjusting the NURBS control points and corresponding weights defining the given region. Finally, a 3D blade design model that uses the NURBS skinning technique is developed and assessed in terms of its precision and smoothness. This 3D model sets the foundation towards developing a robust scheme for 3D aerodynamic optimization. (Abstract shortened by UMI.)...