Unsteady flow and fluid-structure interactions in turbines with full- and partial admission

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Due to the increasing use of renewable energy sources, higher demands on the flexibility and part-load operation of steam turbines arise. Using a control stage, an efficient part-load operation of steam turbines can be realised. During part-load admission of the control stage, high velocity and pressure gradients between admitted and not admitted sections appear, which are responsible for unsteady flow conditions and a strong cyclic stress of the rotor blades. Very limited experimental investigations of these complex fluid- and structure-mechanical phenomena can be found in open literature. Numerical investigations of partial-admitted turbines are an appropriate tool for improving the physical understanding of these phenomena. However, a validation of the numerical codes using experiments is necessary, but restricted due the poor experimental data base available. In this project detailed experimental investigations in a large-scale axial air turbine will be performed. It is planned to combine flow investigations with a laser-optical measurement system, time-resolved measurements within the flow channel and at the sidewalls as well as measurements of the unsteady profile pressures on the rotor blades. Based on these detailed flow measurements the flow conditions will be described with high temporal and spatial resolution. For the first time, the influence of partial admission on the incoming flow field of the control stage, the interaction with the flow field within the blade passages as well as the time-resolved structure-mechanical excitation of the blades can be captured with combined experiment.In addition, transient 3D CFD-simulation using a commercial RANS-solver will be carried out and validated with the experiments. The numerical results will gain insight into flow details, which cannot be captured by the experiments or with too much effort, respectively. Further on, supplementary parameter variations are planned in order to improve the physical understanding and to check the application of the findings to other machines. By coupled fluid-mechanical / structural-mechanical investigations the excitation of the rotor blades due to the partial admission will be investigated.Aim of these investigations is to improve the physical understanding of the 3D time-resolved flow phenomena as well as fluid-structural interactions due to partial admission in steam turbines. In future, the results of this project will contribute to an improved design process of steam turbines for higher operational flexibility and improved efficiency for part-load operation, necessary for forthcoming generations of these turbomachines.