Numerical and experimental investigations have been performed to determine the effect of a variation of the inter blade row axial gap on turbine efficiency. The geometry used in this study is the 1.5 stage axial flow turbine rig of the Institute of Jet Propulsion and Turbomachinery at RWTH Aachen University. The influence of the blade row spacing on aerodynamics has been analyzed by conducting steady and unsteady RANS simulations as well as measurements in the cold air turbine test rig of the Institute. Both potential and viscous flow interactions including secondary flow were investigated. The results show an aero-dynamic improvement of efficiency and favorable spatial distribution of secondary kinetic energy by reduction of the axial gap. It is shown that this relation tends to become less pronounced for multistage turbines.

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