Abstract
This thesis concerns the application of computational fluid dynamics (CFD) to model the flow and mixing inside gas turbine pre-swirl cavities and the application of cooled cooling air (CCA) to improve the performance of the secondary air system. The use of wall-modeled large-eddy simulation (WMLES) to model the flows inside the pre-swirl cavity was evaluated. The work also investigated the application of cooled-cooling air (CCA) in gas turbine pre-swirl systems in order to reduce the amount of cooling air required for turbine blade cooling. The results of these studies are relevant to the design of CCA concepts for future aero-engines. The interaction between cooled and un-cooled cooling air (UCA) pre-swirl jets was studied using various computational models. These included both direct-feed and cover-plate type pre-swirl systems, and various nozzle configurations. The research also included comparison with experimental CCA/UCA pre-swirl rig results and a good agreement between the computational and experimental results was obtained using different turbulence modeling approaches. An engine-scale model of this rig was simulated using engine-representative boundary conditions. The mixing characteristics of the engine model was found to be similar to those of the test rig. Cover-plate type pre-swirl systems were found to be more efficient in mixing the CCA and UCA flows compared with the direct-transfer systems. An alternating CCA-UCA pre-swirl nozzle configuration (nozzles placed at the same radial location) was also found to promote mixing of the two streams due to the relative motion of the preswirl nozzles on the stator and the receiver holes on the rotor disc. The prospects of preferentially feeding the turbine blades using the colder cooling air stream were also investigated. The studied two-row feed CCA/UCA nozzle arrangements were found to be suitable for this purpose with the mixing predictions showing sensitivity to turbulence modeling. A parametric study including various two-row feed pre-swirl system configurations is presented. The CFD simulations were performed using the HYDRA and ANSYS FLUENT CFD solvers. The solutions given by both CFD solvers show an overall good agreement in predictions of mean flow field, and small differences for the prediction of instantaneous flow field. Computational investigations of the unsteady flows inside alternating-feed CCA/UCA pre-swirl systems were also performed using computational models with different nozzle arrangements and non-nozzle passing frequency unsteadiness was observed in these investigations