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978-3-86853-815-1, Reihe Strömungsmechanik
Experimentelle Untersuchung von Teil- und Schwachlastzuständen in Hochdruckdampfturbinen
141 Seiten, Dissertation Universität Hannover (2011), Softcover, A5
Against the background of declining resources the power generation from renewa- ble sources is promoted by law in the recent past leading to an increased part- and low-load operation of power plants. Therefore research focuses not only on the highest possible efficiency of steam turbines but also on their capability for safe part- and low-load operation. Windage may occur during part- and low-load operation, which is highly dangerous due to power and energy being transfered from the rotor to the steam. The potential catastrophic consequences of windage operation have been widely investigated for low pressure steam turbines. However, the increasing part- and low-load operation is putting high pressure steam turbines at risk of windage damage, too. The main focus of research regarding windage operation of high pressure steam turbines is to determine the flow field during windage and to identify differences to the flow fields of turbines already investigated. The target of these investigations is to de- velop an extended understanding of windage and expand it to the windage operation of high pressure steam turbines.
The investigations on the properties of the flow field of a high pressure turbine in windage operation have been conducted on the 7-stage model air turbine at the Leibniz Universität Hannover, Germany. The results reveal a basic similarity of the flow fields of high and low pressure steam turbines during windage operation. The typical flow field of windage with its main flow meandering in the axial radial plane develops in a high pressure turbine, too. Nevertheless, differences to flow fields measured in the past have been identified. The main differences are the missing vortices in front of the vane rows. The analysis of this effect shows that the vortices in front of blade and vane rows are developing independently. As a result of this analysis, the influence of the shapes of the vane passages is identified as the root cause for the missing vortices in front of these vane rows. As a direct consequence, a turbine without vortices in front of the vane rows produces less windage power than a turbine with these vortices. In addition, the analysis of the vortex development during windage enables a more precise description of the origin of the windage flow field. Measurements of blade material temperatures clearly show the importance of heat conduction through the turbine material for the temperature distribution in the turbine during windage.
Unsteady measurements of the static pressure at the casing of the model turbine during windage operation reveal the existence of rotating pressure perturbations. These per- turbations can be clearly identified as similar to the Rotating Stall of compressors. By using circumferentially distributed pressure sensors, the number of pressure perturbations and their velocities have been determined. The analysis has been performed using a correlation algorithm on the different sensor signals.