Non-Axisymmetric Turbine Endwall Aerodynamic Optimization Design: Part II — Turbine Stage Design and Unsteady Flow Characteristics Analysis

Abstract

Aerodynamic optimization design and experimental validation for the non-axisymmetric endwall profiles of the turbine cascade have been completed in the part I of this research work. Non-axisymmetric endwall profile optimization design of the turbine stage and corresponding steady and unsteady flow characteristics were presented in the part II. Aerodynamic optimization design for the non-axisymmetric endwall profile of the turbine stage was conducted when the maximization of the total-total isentropic efficiency was set as the design objective with constraint on the mass flow rate. The aerodynamic performance of the designed turbine stage was evaluated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solutions. The non-axisymmetric endwall profiles of the stator hub and shroud as well as the rotor hub in the turbine stage were optimized using developed endwall profile method in the part I. A total of 15 design variables were employed in the optimization for the stator and rotor endwalls. The global optimization method of the adaptive rang differential evolution algorithm was used to search the optimal non-axisymmetric endwall profile. The total-total isentropic efficiency of the turbine stage with the optimized non-axisymmetric endwall profile increases 0.26% by comparison of the referenced axisymmetric endwall design when the effects of the rotor tip clearance were also considered. The secondary flow losses of the stator and rotor were significantly reduced in the optimized non-axisymmetric endwall stage, as well as the tip leakage flow losses. In addition, the unsteady aerodynamic performance of the turbine stage with the optimized non-axisymmetric endwall profile and referenced axisymmetric endwall were numerically investigated and compared. The numerical results indicate that the fluctuating velocity in the rotor blade passage of the optimized non-axisymmetric endwall stage significantly decreases since the stator wake and secondary flow losses are reduced. Thus, the intensity of the unsteady interaction between the stator upstream flow and the flow in the rotor passage decreases. The time-averaged results indicated that the aerodynamic efficiency and output power of the turbine stage with the optimized non-axisymmetric endwall profile are higher than that of the referenced axisymmetric endwall stage. Meanwhile, the transient results at different time steps show that the periodic fluctuating amplitude of the efficiency and power of the optimized non-axisymmetric endwall stage were smaller than that of the referenced axisymmetric endwall stage due to the weaker stator/rotor unsteady interaction effects.