Project Leader:	Professor Dr-Ing Otto Geisler
Research Assistant:	Dipl-Ing F Ehlers
Duration:	01.11.1992-31.10.1994

 

To improve the partial load behaviour of steam turbines the so-called regulating stage is provided upstream of the steam-laden rotor blading. This stage responds with reduced reaction times and can be build with one or two crowns. Especially under partial load conditions a large part of the enthalpy gradient available is dissipated in the regulating stage (e.g., 40 %) resulting in supercritical pressure conditions inside the ejectors. Furthermore, the blading height in the regulating stage is often too small (e.g., 10 mm), which can lead to relatively large edge and gap losses due to increased secondary flows.

Aim of the project was to develop a new calculation foundation for modelling the operating behaviour of the regulating stage under nominal and partial loads, obtained through targeted measurements and theoretical investigations. In the experimental studies an experimental single-stage constant-pressure steam turbine (VT II) of the Institute located at the steam turbine test rig of the University of the Federal Armed Forces Hamburg has been used. During operation stationary partial loadings were obtained by retaining the steam pameters before the ejectors constant and varying the exhaust steam pressure instead. In this process both under critical and supercritical steam conditions were present in the ejectors. During the test campaign ejectors were also used which were milled either tangentially or along the periphery. Various rotor blade profiles were also tested, combined with different heights for the ejectors and the rotor blades.

In parallel to the experimental investigations a numerical study was also performed, by simulating the jet stream under undercritical and supercritical pressure conditions. Using a computer model which was developed for this purpose it was possible to compute the operating behaviour of the turbine while considering the losses occurring during energy conversion in the turbine stage. This was extended also tooperating conditions deviating from the design point. The flow simulation was based on the median stream filaments theory.