Numerical Study of Flow and Heat Transfer in a Pre-swirl System

Pre-swirl is often used in the internal cooling-air systems of gas turbines to reduce the temperature of the cooling air relative to the rotating turbine blades. In a "direct-transfer" system, the air passes axially across the wheel-space from stationary pre-swirl nozzles to receiver holes in the rotating turbine disc. This paper investigates the effects of inlet flow conditions and rotational speed on the flow and the heat transfer in such system, using a simplified computational model for three-dimensional steady, incompressible turbulent flow based on an in-house solver developed by the author. The computed results are compared with measurements of tangential velocity and Nusselt number and show that there are significant mixing losses near the inlet nozzles, resulting in a reduced “effective” pre-swirl ratio at inlet. The computed tangential velocity distributions suggest free-vortex-type behaviour for the flow between the pre-swirl nozzle radius and that of the receiver holes. There is mainly good agreements between the computed and the measured velocities, although the measured values are generally lower than the computed ones and follow free-vortex behaviour less closely. There is less agreements between the computed and the measured values of Nusselt number, although the correct trends are obtained for the effects of the main flow parameters.