Investigation of film behaviour and disintegration at trailing edges of blades under turbomachinery-like conditions

• Applicants: Professor Dr.-Ing. Markus Schatz; Professor Dr.-Ing. Bernhard Weigand
• Subject Area: Hydraulic and Turbo Engines and Piston Engines
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 491583807

In order to mitigate the impact on ambient temperature on gas turbine performance and thermal efficiency, water droplets are injected into the intake, where they evaporate, thus cooling the inlet flow. However, as evaporation is not completed until the flow reaches the first blade rows, droplet deposition and film formation on blade surfaces occurs. Water films and their disintegration into the overflowing steam phase also play an important role in steam turbines. Due to the expansion in the low-pressure stages, tiny droplets are formed and grow as the flow continues. These droplets are deposited on the blade surfaces due to turbulent fluctuations or inertial effects. The subsequent phenomena of film formation on blades, accumulation of water and disintegration at the trailing edges and finally reentry of droplets into the main flow are basically the same for gas turbines and steam turbines.The goal of this proposal is to conduct detailed experimental and numerical studies of wavy liquid films and trailing edge disintegration under turbomachinery-like conditions in order to improve the available models for the trailing edge disintegration of turbomachine blades.The numerical treatment of thin, shear-driven fluid films and the trailing edge disintegration will be done by means of direct numerical simulations, thus allowing a detailed insight into the processes. This proposal aims to extend the existing modelling and to widen the scope of application, for example with the prediction of droplet spectra generated through disintegration. To date, existing models only provide rough information about the primary diameter. As the latter determines the inlet conditions for all downstream blade rows, exact modelling is indispensable here. For the time- and spatially-resolved study of film behaviour, a new dedicated test rig will be installed. The measurement method to be used is based on the principle of light absorption. In order to prove the reliability and validity of the approach, reference data will first be collected using well-established point-based methods for flow over flat plates and later compared with the results of the absorption method. The determination of the measurement uncertainty will be supported by multi-component simulations. Based on this measurement technology, extensive observations of the regimes and wave properties of films for flow over flat plates in a velocity range relevant for turbomachinery will then be carried out.

• DFG Programme: Research Grants