Gradient-based optimization of a 3D Turbine Vane Frame

Authors

Luca Zampini  - Von Karman Institute for Fluid Dynamics, Belgium
Lasse Mueller - Von Karman Institute for Fluid Dynamics, Belgium
Sergio Lavagnoli - Von Karman Institute for Fluid Dynamics, Belgium
Gregory Coussemont - Von Karman Institute for Fluid Dynamics, Belgium
Tom Verstraete - Von Karman Institute for Fluid Dynamics, Belgium

Abstract

The paper presents the optimization of a 3D, multi-body turbine vane frame (TVF). The TVF is a particular S-shaped duct that puts into communication the High-Pressure Turbine (HPT) and the Low-Pressure Turbine (LPT). The Turbine Vane Frame extends considerably in the radial direction and this allows for the shortening of the shaft of the machine, with a consequent reduction in weight. A classical design is characterized by the presence of a mid turbine frame equipped with non-lifting bodies that serve structural and service functions. In multi-body configurations, the bulky pylons are replaced by low-aspect-ratio struts and a series of splitter blades. The low-aspect-ratio struts are aerodynamically shaped to guide efficiently the flow, while having large airfoil thickness to serve mechanical and service functions. The splitter blades are equally loaded and guide the flow and act as a replacement of the LPT stator. The large struts are characterized by a very low aspect ratio that generates large secondary flow structures responsible for significant aerodynamic losses. In addition to that, they also alter the flow approaching the nearby splitter blades, modifying the incidence angle and penalizing their aerodynamic performance. The struts must respect strict mechanical requirements that in the present work are represented as geometrical constraints on the minimum airfoil thickness. In this paper, it is presented the numerical optimization of a Turbine Vane Frame with a very large number of design parameters (~300). The multi-body turbine vane frame geometry is optimized using a gradient based algorithm with the adjoint method for a cheap computation of the gradient. Steady-state CFD simulations are performed for the functional evaluation and a single objective function is considered: the total pressure loss. The parametrization of the TVF geometry includes the airfoil definition along the radial span, lean, and sweep of the blades. Bezier curves are used to enhance the regularity of the CAD geometry. The study explores the huge design space in order to understand which parameters affect the overall performance and the initial design is improved with a reduced number of RANS iterations.