Effect of Radial Location of Nozzles on Performance of Pre-Swirl Systems

This paper investigates the effect of the radial location of the inlet nozzles on the performance of a direct-transfer pre-swirl system in a rotor-stator wheel-space. A commercial code is used to solve the Reynolds Averaged Navier Stokes (RANS) equations using a high-Reynolds-number k-epsilon / k-omega turbulence model with wall functions near the boundary. The 3D steady state model has previously been validated against experimental results from a scale model of a gas turbine rotor-stator system. Computations are performed for three inlet-to-outlet radius ratios, r(p)/r(b) - 0.8, 0.9 and 1.0, a range of pre-swirl ratios, 0.5 < beta(b) < 2.0, and varying flow parameter, 0.12 < lambda(T) < 0.36. The rotational Reynolds number for each case is 10(6). The flow structure in the wheel-space and in the region around the receiver holes for each inlet radius is related to the swirl ratio. The performance of the system is quantified by two parameters: the discharge coefficient for the receiver holes (C-d,C-b) and the adiabatic effectiveness for the System (Theta(b,ad)). As in previous work, the discharge coefficient is found to reach a maximum when the rotating core of fluid is in synchronous rotation with the receiver holes. As the radius ratio is increased this condition can be achieved with a smaller value for pre-swirl rario beta(b). A simple model is presented to estimate the discharge coefficient based on the flow rate and swirl ratio in the system. The adiabatic effectiveness of the system increases linearly with pre-swirl ratio but is independent of flow rate. For a given pre-swirl ratio, the effectiveness increases as the radius ratio increases. Computed values show good agreement with analytical results. Both performance parameters show improvement with increasing inlet radius ratio, suggesting that for an optimum pre-swirl configuration an engine designer would place the pre-swirl nozzles at a high radius.