Aerodynamic and Performance Behavior of a Three‐Stage High Efficiency Turbine at Design and Off‐Design Operating Points

Abstract

Address correspondence to M. T. Schobeiri, Texas A&M University, Dept. of Mechanical Engineering, College Station, TX 77843-3123. E-mail: tschobeiri@mengr.tamu.edu the experimental and computational results. The detailed 3-D flow pictures delivered by viscous flow solvers display the source and location of the total pressure losses and entropy distribution within the blade channel, particularly at the blade hub and tip regions. Based on these results, the turbine aerodynamicist is able to reconfigure the blade geometry to reduce the profile and the secondary flow losses. The latter is especially relevant for high pressure (HP) turbine design with relatively small aspect ratios where the secondary flow losses significantly contribute to the reduction of the stage efficiency. In recent years, the power generation turbine manufacturers have been increasingly focusing their efforts on reducing the secondary flow losses of HPturbine blades by implementing the information obtained from the Navier-Stokes flow simulations. To account for the discrepancy mentioned above, the Navier-Stokes codes are frequently calibrated. The calibration process may provide a temporary matching solution for cases in which experimental results are available. However, it is not appropriate for a priori predicting of the efficiency of new designs. The disagreement between the Navier-Stokes based efficiency calculations and the measurements, however, does not allow the engine manufacturer to issue efficiency and performance guaranty without thoroughly testing their new design. Considering the physical aspects of the computation, among other things, two major issues may be considered primarily responsible for the above discrepancy, namely the turbulence modeling and the modeling of the laminar-turbulent boundary layer transition process. The latter directly impacts the accuracy of the loss, efficiency and heat transfer calculations of the blade and thus the turbomachinery stage. BACKGROUND: UNSTEADY BOUNDARY LAYER TRANSITIONTo quantify the effect of unsteady boundary layer transition on turbine efficiency the first author initiated a comprehensive unsteady boundary layer research program at Texas A&M University, where he and his co-workers studied the development