Turbine stator well CFD studies: effect of upstream egress ingestion

There is a constant demand in the turbomachinery industry to improve engine performance, meet stringent environmental and safety regulations, and reduce the time and cost of new product development. As improvements in component efficiencies become increasingly difficult to achieve and new material development has become more expensive over the years, more attention is focusing on other areas of gas turbine technology. Internal cooling air systems, in particular, have been subject to significant research, in order to reduce the effect of parasitic losses on the overall engine performance. Often, part of the compressor flow passes directly into turbine inter-stage cavities primarily for rotor disc cooling. The advantages such a concept offers are (a) better thermal effectiveness on the rotor disc by having lower wall temperature (b) preventing, to some degree, the ingestion of mainstream hot gases into the cavity. These enhancements have to be integrated into the turbine stage without, of course, sacrificing the overall performance. Detailed knowledge of the flow and heat transfer within these cavities is needed if such improvements are to be further pursued. The material presented in this paper investigates the effect of upstream coolant injection into the mainstream flow being ingested into a turbine stator well. The coolant injection comes from an upstream rim seal, and so called egress. The CFD domain modelled includes both the main gas path and stator well. CFD studies have been performed to predict the flow physics in the cavity, and this has included an investigation of both steady and unsteady effects. This study is extended beyond the cavity flows, and it gives an insight of the mainstream flow particularly behind the blade rows. The CFD results are compared with dedicated aerodynamic 3D-blade design codes. These CFD studies have contributed significantly in understanding the effect on flow and heat transfer of upstream turbine coolant injection being subsequently ingested into a downstream stator well. Most importantly, these CFD studies enhanced the optimisation of turbine stator well design and limited the coolant flow ingested into the rotating cavities whilst maintaining overall performance.