ADDITIVE CONCENTRATION MODEL TO AID UNDERSTANDING OF NOZZLE GUIDE VANE EXIT TEMPERATURE DISTRIBUTIONS

Abstract In the turbine design process, the high-pressure (HP) nozzle guide vane (NGV) exit thermal field (or rotor inlet temperature distribution) is sympathetically designed with the aerodynamic and thermal design of the HP turbine rotor. For heavily cooled stages, the vane-exit temperature distribution is strongly influenced by the vane surface film cooling, the vane endwall film cooling, and the vane inlet thermal field (combustor outlet temperature distribution). By analogy with concentration-based superposition models, we can represent the vane-exit thermal field as an equivalent coolant concentration, allowing us to treat the problem as three mixing coolant streams. By performing experiments on heavily cooled engine parts, we investigate the impact of these three cooling streams—both individually and in combination—on the vane exit temperature distribution. Tests are performed across a wide range of coolant-to-mainstream pressure ratios (CMPRs) to investigate cooling performance across the engine design space. An additive concentration model is developed to separate the individual contributions of different coolant streams to the vane-exit thermal field. We gain confidence in the additive concentration model by making comparisons to CFD simulations in which individual contributions were determined by using the passive scalar tracking method. We show that superposition-based models can not only be used to gain understanding of individual cooling contributions to an overall flow effectiveness distribution, but can also be used to predict the performance of new (untested) cooling configurations. This is potentially a powerful technique.