Remo Marini

The Effect of Blade Leading Edge Platform Shape on Upstream Disk Cavity to Mainstream Flow Interaction of a High-Pressure Turbine Stage

This paper presents a CFD study of a transonic highpressure 1-stage turbine that includes the blade upstream disk cavity. The emphasis of the analysis was to understand and quantify the impact of the blade leading edge platform shape on the flow interaction between the upstream disk cavity flow and the gaspath mainstream flow. Two blade platform shapes were analyzed: a recessed and a raised leading edge shape. The results presented include steadystate and transient simulations in order to describe the flow interaction and quantify the impact on stage efficiency. A sensitivity analysis on the amount of cavity flow was performed to investigate the impact on secondary losses (interpreted by entropy generation) and stage efficiency. It was found that the blade leading edge platform shape and cavity flow amount affected the blade hub passage vortex structure and location. At the nominal engine condition, the raised leading edge platform shape showed an improvement in stage efficiency. It also showed a reduced sensitivity of stage efficiency due to cavity flow amount.© 2007 ASME

Simulations of Flow Ingestion and Related Structures in a Turbine Disk Cavity

Preliminary results of unsteady numerical simulations of disk cavity flow in interaction with the main gaspath flow in an axial turbine are presented in this article. A large periodic sector including vanes, blades and disk cavity of approximately 74° has been used in order to allow for the formation of large scale flow structures within the cavity. Three purge flow rates have been tested, namely no purge, low purge and high purge flow rates. Energetic large scale flow structures are detected through flow visualizations for the two lowest purge flow rates. They are found to rotate at an angular velocity slightly less than the rotor speed. The presence of the large scale structures involves important pressure perturbations inside the cavity that may lead to deep mass flow ingress, whereas the unsteady vane-blade interaction seems to cause only shallow ingress. Increasing purge flow rate appears to have a stabilizing effect on the pressure fluctuations inside the cavity and to reduce the intensity of the large scale flow structures.Copyright

CFD Study of HPT Blade Cooling Flow Supply Systems

This work summarizes the results of the CFD analyses to investigate the effect of the geometrical parameters for a typical coverplate-disk cavity and blade broach system also known as the blade cooling flow supply system. A turbofan high pressure turbine was used as the test vehicle for this investigation. The main objective was to explore potential improvements in engine SFC (aerodynamic performance) by reducing the parasitic work while minimizing the impact on the factors that affect the durability of the turbine blades; feed pressure, temperature, and mass flow. Various tangential on-board injection (TOBI) blade cooling flow supply systems were considered: i) Phase 1 compared the radial TOBI and axial TOBI, ii) Phase 2 compared coverplate-disk cavity shapes, and iii) Phase 3 compared blade broach shapes. The in-house CFD code NS3D was used for the analyses. Compared to the radial TOBI, the axial TOBI has a positive impact on the parasitic work (lower) and blade feed temperature (lower) while it has a negative impact on the blade feed pressure (lower). Further, the coverplate-disk cavity shapes investigated had no significant impact on the parasitic work, blade feed pressure, and blade feed temperature. The CFD solutions show that the major portion of the parasitic work is due to flow turning at the broach entrance. Finally, reducing the blade broach cross-section by sloping up the lower wall has no significant impact on the parasitic work and blade feed temperature but a negative impact on the blade feed pressure and mass flow. Modifying the broach pressure side wall shape is preferred among the blade broach geometries investigated. Future work to improve the CFD analysis consists of performing unsteady analyses to better capture the vortex flow in the blade broach, and including upstream stationary components with either iterative boundary condition modeling or an unsteady multi-stage approach.Copyright

Passive Tracer Validity for Cooling Effectiveness Through Flow Computation in a Turbine Rim Seal Environment

This paper reports the first phase of an investigation aiming to determine the validity of using a CO2 marker in cold rig experiments to characterize the thermal performances of turbine rim seals under actual engine operating conditions. For comparison purposes, simulations are carried out for two sets of operating conditions, namely cold rig (with uniform low temperature) and real turbine thermal conditions (high temperature gaspath and cold purge flow). Sealing effectiveness based on the CO2 diagnostic under cold rig operating conditions is compared to sealing effectiveness based on the computed temperature field under real engine temperature conditions. Unsteady RANS simulations with different purge flow rates are performed. Tested geometries include a 180° domain presenting a simplified rim seal geometry with no vanes nor blades in the gaspath, and a 24° sector of a complete turbine stage including 3 vanes and 4 blades. Three-dimensional flow structures known to affect ingestion are found with both geometries but appear to be sensitive to the differences in operating conditions. Indeed, their circumferential number and strength differ between the two scenarios of conditions. Furthermore, it is found that the cold rig predictor tends to slightly overestimate the sealing effectiveness, while providing nonetheless the right trends and reasonably accurate average values in levels of actual sealing. At this stage of the investigation, we conclude that it seems adequate to use a passive tracer in cold rig experiments to compare performances of rim seal designs.Copyright