KüpLe WP 1.2
Analysis of the flow in rotor-stator cavities in turbinesCopyright: © Rolls Royce
To achieve higher thermal efficiencies both, in stationary gas turbines and in aero gas turbines, higher turbine inlet temperatures are necessary. For safe operation, the maximum permissible material temperatures of the fast-rotating turbine components must always be monitored. Due to conductive heat transfer and hot gas ingestion into the wheel cavities, not only the turbine guide vanes and rotor blades but also the turbine disks, which are required to carry the rotor blades, are exposed to high thermal stress. In order not to exceed the permissible material temperatures of these turbine disks, cooling air from the compressor is used. As a result, the cooling air mass flow from the compressor used for this purpose does not participate in the actual gas turbine process and therefore has a negative influence on the thermal efficiency. The efficiency of the gas turbine is significantly influenced by the amount of cooling air mass flow required.
For the design of these internal cooling systems for rotor disk cooling within thermal gas turbines, an understanding of the prevailing flow structures in the rotor-stator- and rotor-rotor-cavities is crucial. Furthermore, the flow structures that occur have a major influence on the heat transfer between the injected cooling air and the rotating turbine disk. At the moment, a complete understanding of the prevailing flow and heat transfer phenomena within these cavities is still lacking, so that the design of the required cooling air supply is made more difficult.
The aim of this research project is to set up a new test rig for investigating flow structures and heat transfer phenomena in rotor-stator- and rotor-rotor cavities using a near-engine design of cooling air supply and disk geometry. Subsequently, an extensive measurement campaign will be carried out on this test rig within this research project.
In principle, the configuration of the test rig is based on a first low-pressure turbine stage of a real aero engine. For this purpose, a rotating turbine disk is located inside a closed housing. This creates both a rotor-stator- and a rotor-rotor-cavity. During experimental operation, cooling air is brought in the housing in various inflow configurations at eight circumferentially symmetrical positions on a constant radius. The cooling air impinges on the turbine disk from the front.
By inserting a temperature step in the supplied cooling air, a significant heat flow can in turn be applied in the direction of the turbine disk. By measuring the disk surface temperatures via thermocouples, the heat transfer coefficients between the cooling air and the turbine disk can be calculated. At the same time, stereo particle image velocimetry (PIV) can be used to record all velocity components of the flow in the rotor-stator cavity in different laser light sections.
The resulting data sets from the measurements can the be used to further develop numerical methods that can replace future experimental investigations.
MTU is the chairman of the associated project committee.