Numerical investigations of a 1.5 stage axial flow turbine geometry were performed to determine the effects of a variation of the inter-blade row axial gap on turbine efficiency. In order to study the influence of blade row spacing, both steady and unsteady RANS simulations were conducted. State of the art meshing including fillet radii and high grid density was used. In addition to an overall improvement of the aerodynamic efficiency with a decreasing axial distance between the rows, the numerical results showed differences in radial distribution of efficiency downstream of the trailing edges. Furthermore, transition on the blades’ suction side was investigated and compared to former fully turbulent numerical results [1]. The intermittency distributions showed that the laminar fraction of the boundary layer on the rotor, as well as on the second stator suction side, decreases with increasing gap.

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