Axial TurbineCopyright: © RWTH Aachen | IST
The 1.5-stage cold-air turbine has long served as the basis for experimental verification in a wide range of research projects. The knowledge gained from this test rig makes a decisive contribution to improving the efficiency of industrial turbomachinery. The modular design makes it possible to investigate new blading or new measuring techniques without major conversion measures.
Power: 165 kW
Speed: 3500 rpm
Total pressure ratio: 1.29
Total inlet temperature: 56 °C
Mass flow: 8.1 kg/s
Reynolds number up to 810,000
3 total pressure & total temperature rakes at inlet and outlet level
3 measuring planes each behind stator 1 & 2 and rotor for traversing the flow with different probes
The 1.5-stage turbine consists of two guide wheels and the centrally positioned impeller. To determine the efficiency, the total temperature and total pressure upstream of the first stator and downstream of the second stator are measured.
The total temperatures and total pressures upstream of the first guide wheel are determined via four vertical rakes. At the outlet, there are 3 rakes on a ring that can be rotated by 120°. This enables the measurement of a two-dimensional flow field over the entire circumference.
The axial turbine is operated in a semi-open circuit and is supplied with two parallel-connected radial compressors from GHH. The air is cooled down to the desired operating temperature after the compressors in order to set the desired operating points. The inlet and outlet pressure is continuously adjusted via a pressure control and the speed is controlled via an eddy current brake. This control ensures that a constant operating point can be maintained over a driving day, even with changing ambient conditions.
The comprehensive measurement technology allows both the highly accurate determination of global machine parameters and the detailed measurement of the flow within the turbine. For safety, the test setup is surrounded by a burst protection designed to prevent the rotor disc from breaking at 7,500 rpm.
Optimisation of end wall contours
Numerical optimisation algorithms were used to optimise the shape of the end walls on the hub and casing of the first stator and the rotor in order to achieve an increase in efficiency by homogenising the stator outflow and attenuating the secondary flows. Experimental validation of these non-axially symmetric configurations was performed on the axial turbine.
Aerodynamic robustness of optimised end wall contours against sealing air injection
By means of an additionally integrated secondary air system, sealing air can be injected into the main flow through the cavity between rotor and stator. The effects of this sealing air on the mode of action of optimised end wall contours are the subject of ongoing experimental and numerical investigations.
Turbulence development in turbine stages
Many common numerical turbulence models are based on the assumption of isotropic turbulence, which, however, is not always valid for complex flows. With the help of high-precision hot-wire probes, turbulent flow variables in the turbine can be measured in detail. These data are then used to improve and validate the numerical turbulence models.