Time Averaged and Time Accurate Aerodynamic Effects of Rotor Purge Flow for a Modern, One and One Half Stage High Pressure Turbine—Part II: Analytical Flow Field Analysis

Abstract

The detailed mechanisms of purge flow interaction with the hotgas flow path were investigated using both unsteady computationally fluid dynamics (CFD) and measurements for a turbine operating at design corrected conditions. This turbine consisted of a singlestage highpressure turbine and the downstream, lowpressure turbine nozzle row with an aerodynamic design equivalent to actual engine hardware and typical of a commercial, highpressure ratio, transonic turbine. The highpressure vane airfoils and inner and outer end walls incorporated stateoftheart film cooling, and purge flow was introduced into the cavity located between the highpressure vane and disk. The flow field above and below the blade angel wing was characterized by both temperature and pressure measurements. Predictions of the timedependent flow field were obtained using a threedimensional, Reynoldsaveraged Navier–Stokes CFD code and a computational model incorporating the three blade rows and the purge flow cavity. The predictions were performed to evaluate the accuracy obtained by a design style application of the code, and no adjustment of boundary conditions was made to better match the experimental data. Part I of this paper compared the predictions to the measurements in and around the purge flow cavity and demonstrated good correlation. Part II of this paper concentrates on the analytical results, looking at the primary gas path ingestion mechanism into the cavity as well as the effects of the rotor purge on the upstream vane and downstream rotor aerodynamics and thermodynamics. Ingestion into the cavity is driven by high static pressure regions downstream of the vane, highvelocity flow coming off the pressure side of the vane, and the blade bow waves. The introduction of the purge flow is seen to have an effect on the static pressure of the vane trailing edge in the lower 5% of span. In addition, the purge flow is weak enough that upon exiting the cavity, it is swept into the mainstream flow and provides no additional cooling benefits on the platform of the rotating blade.