Axial Turbines

There are a number of completed and ongoing research projects on axial turbines. In particular, three areas of interest have received particular attention

1. Two-Stage Shrouded Gas Turbines
•    Evolution of unsteady secondary flows.
The interactions of the rotor indigenous vorticies with the downstream blade row are subject of significant loss generation due to the stretching of the vortices as they convect through the downstream blades. It was found that the high loss fluid of the wake is rolled up into the passage vortex and increases loss at the rotor hub section. (Diss. ETH Nr. 15230)
•    Aerothermal investigation of three different rotor shroud configurations.
The shroud configurations included, a classical full shroud, while the other two are variations of partial shroud geometries. It was found that the partial shroud cases are characterized by highly three-dimensional interactions between the tip passage vortex and the reentering tip leakage flow. The enhanced partial shroud was found to reach an optimum between aerodynamic performance and blade life. (Diss. ETH Nr. 17138)

2. Two-Stage Shrouded Steam Turbines
•    Flow interactions between the main stream and the open shroud cavities.
The upstream cavity flow is dominated by two toroidal vorticies, which swirl around the annulus with 82% blade tip speed. The exit cavity compromises three flow features, which interact among each other: the cavity fluid being a toroidal vortex, the leakage jet and the main flow. The highest losses found are the windage effect within the closed cavities and the mixing downstream of the rotor. (Diss. ETH Nr. 15226)
•    Unsteady vorticity-field in highly-loaded bladin of a two-stage axial turbine.
Multi-plane measurements at blade row exit enable the assessment of the full three-dimensional time-resolved vorticity-field. Furthermore, different inlet cavity geometry-modifications are tested to minimize secondary losses.

3. Highly Loaded One-and-Half-Stage Unshrouded Gas Turbines

•    Rotor tip leakage investigations in a one-and-half-stage unshrouded turbine.
This configuration is designed to study the control mechanisms for rotor tip leakage. The turbine models a highly loaded, cooled HP turbine. The same blade count of the vanes enables a clocking investigation. It is found that clocking rather redistributes the loss, while the potential to reduce loss is judged to be minimal. Furthermore, a study with tip injection reveals an efficiency improvement while a power output reduction is found. (Diss. ETH Nr. 17283)
•    A flat tip rotor was used as baseline case for detailed 3D CFD investigation of recessed blade tips. Three-dimensional cavity flow analysis and extensive optimization lead to an improved recess design.
•    Investigation of performance improvements with non-axisymmetric endwalls.
Non-axisymmetric endwalls are a powerful tool to reduce secondary losses. A first profile geometry in the first stage shows a total-to-total efficiency improvement of 1%. Additionally, the interaction of the main flow with hub purge flow is investigated.

Movie: Measurement of unsteady relative total pressure coefficient downstream of rotor row.