Abstract
The purpose of this study is to investigate the effects of the axial gap between stator and rotor upon the performance and secondary flow field of a single axial flow turbine stage. We performed experiments for three axial gaps. In our test rig, it is possible to change the axial gap by moving the stator vane in axial direction. The tests were carried out at two different conditions, that is design and off-design conditions. The unsteady three-dimensional flow field was analyzed by time-accurate RANS (Reynolds-Averaged Navier-Stokes) simulations. The simulation results were compared with the experiments, in which total pressure loss and time-averaged flow field upstream and downstream of the rotor were obtained by five-hole probe measurements. The effect of the axial gap was confirmed in the endwall regions, and obtained relatively at the off-design condition. The turbine stage efficiency was improved almost linearly to reduce the axial gap at the off-design condition.
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