Hot Gas Induction into the Wheel Side Chamber of Axial-Flow Gas TurbinesCopyright: © Bhavnani
For the efficiency of stationary gas turbines as well as of aero gas turbines, the quantities of cooling and sealing air required are important parameters. These so-called secondary air flows protect the components directly exposed to the hot main flow. In addition, they prevent hot gas from entering the area of the mechanically highly loaded rotor disks. Figure 1 shows typical sealing air flows in a gas turbine stage. The cavity between the rotor disk and stationary components due to the design is called the wheel side space.
Cooling and sealing air only partially contribute to power conversion in the turbine. A reduction leads to a significant increase in efficiency. In order to carry out a reduction of the sealing air mass flow while maintaining structural integrity, an understanding of the mechanisms influencing hot gas intake is necessary.
At the IKDG, the hot gas intake is investigated numerically with the aid of CFD and experimentally in order to deepen the aforementioned understanding. The investigations are carried out on a 1.5-stage test turbine. In addition to measuring planes for balancing the stages, the wheel side space in particular is clearly instrumented.
Pressure holes at the hub downstream the first guide vane ring allow conclusions on the main flow field, in particular on the circumferential distribution of the pressure, which is influenced by the wake of the vane ring upstream. Measuring points in the wheel side space are used to detect the flow field in the wheel side space. Either the pressure can be recorded or a CO2 concentration. In conjunction with the admission of a defined CO2 concentration to the sealing air, a hot gas concentration field can be measured. Thus, conclusions can be made on the penetration of the hot gas depending on the operating point.
Numerical simulations, after validation on measured data, are used to predict the three-dimensional flow and hot gas concentration field. In addition, the influence of small geometric variations can be studied more easily. These small geometric variations can include a slight variation of the axial gap.
Construction of the test turbine is scheduled to end in October 2021.
The project is financially supported by the Research Association for Combustion Engines (Forschungsvereinigung Verbrennungskraftmaschinen). MTU Aero Engines is the chairman of the associated project committee.