Numerical and theoretical study of flow and heat transfer in a pre-swirl rotor-stator system

In a "direct-transfer" pre-swirl supply system, cooling air flows axially across the wheel space from stationary pre-swirl nozzles to receiver holes located at a similar radius in the rotating turbine disc. This paper describes a combined numerical and theoretical study of flow and heat transfer in such a system. As 3D computations involve long computing times and large resources, a simplified axisymmetric model has been used to study the effects of flow parameters on flow and heat transfer in a rotor-stator pre-swirl system. This allows the effects of the main nondimensional parameters on the flow and heat transfer in the system to be studied with computing times reduced by a factor of around 7 compared with 3-dimensional computations. The computed results are compared with available measured data. An expression has been derived for calculating the adiabatic effectiveness of the system, and this has been been compared with computed values. The computations show that, due to mixing losses, there is a significant drop in angular momentum. The computed flow structure is compared with free vortex behaviour between the pre-swirl inlet and the receiver outlet. The computed moment coefficient decreases as pre-swirl ratio increases and increases as non-dimensional flow rate increases. The computed average Nusselt number decreases with inlet swirl ratio up to a critical value and then increases again.