Flow field in a single-stage model air turbine rotor-stator cavity with pre-swirled purge flow

The present work applies a combined approach of experimental measurement and numerical simulation of the flow in a single-stage model gas turbine. Mainstream gas ingestion into the cavity is reduced by utilizing two axially overlapping seal rings, one on the rotor disk and the other on the stator wall. Additionally, pre-swirled purge air is injected into the rotor-stator cavity through the stator radially inboard of the two seal rings. Flow field predictions from the simulations are compared against experimental measurements of static pressure, velocity, and tracer gas concentration acquired in a nearly identical model configuration. The experiment chosen for simulation was performed for a main airflow Reynolds number of 7.86×10⁴ at a rotor disk speed of 3000rpm with a rotational Reynolds number of 8.74×10⁵, and purge air nondimensional flow rate c_w = 4806. The simulation models a 1/14 sector of the cylindrical geometry consisting of four rotor blades and four stator vanes. Gambit 2.4.6 was used to generate the three-dimensional grids ranging from 10 to 20 million elements. Effects of turbulence were modeled using the single-equation Spalart-Allmaras as well as the realizable k-epsilon models. Computations were performed using FLUENT 6.3 for both a simplified frozen-rotor formulation (steady) and a subsequent time-dependent (unsteady) computation. The simulation results show symmetry in the pressure and velocity distributions across each pitch of the stator vanes, but larger scale structures across all four blade pitches are also realized. Velocity distributions were scrutinized in the rotor-stator cavity and are in reasonable agreement with the measurements. Static pressure and tangential velocity components are accurately predicted.