Flow and Heat Transfer in a Pre-Swirl Rotor-Stator System

Conditions in the internal-air system of a high-pressure turbine stage are modelled using a rig comprising an outer pre-swirl chamber separated by a seal from an inner rotor-stator system. Pre-swirl nozzles in the stator supply the “blade-cooling” air, which leaves the system via holes in the rotor, and disc-cooling air enters at the centre of the system and leaves through clearances in the peripheral seals. The experimental rig is instrumented with thermocouples, fluxmeters, pitot tubes and pressure taps enabling temperatures, heat fluxes, velocities and pressures to be measured at a number of radial locations. For rotational Reynolds numbers of Reϕ ≃ 1.2 × 106, the swirl ratio and the ratios of disc-cooling and blade-cooling flow rates are chosen to be representative of those found inside gas turbines. Measured radial distributions of velocity, temperature and Nusselt number are compared with computations obtained from an axisymmetric elliptic solver, featuring a low-Reynolds-number k-ε turbulence model. For the inner rotor-stator system, the computed core temperatures and velocities are in good agreement with measured values, but the Nusselt numbers are underpredicted. For the outer pre-swirl chamber, it was possible to make comparisons between the measured and computed values for cooling-air temperatures but not for the Nusselt numbers. As expected, the temperature of the blade-cooling air decreases as the swirl ratio increases, but the computed air temperatures are significantly lower than the measured ones. Overall, the results give valuable insight into some of the heat transfer characteristics of this complex system.