The effect of hub platform misalignment in the first vane of a 1.5 stage axial test rig turbine on the efficiency is numerically analyzed. An investigation is made into how this misalignment, as caused for example by manufacturing deviation, impacts the intended 3D flow in an endwall-contoured design and how robust the design is compared to a uncontoured turbine. Axial misalignment was created by extending all platforms within the blade row in radial direction by up to 5.5 % of the channel height. In order to create circumferential steps, only every third platform was elevated. The results are based on steady and unsteady simulations with the DLR RANS solver TRACE. In general, both axial and circumferential steps alter the static pressure field and lead to flow separations bubbles. These effects lead to the creation of new vortices which interact with the classic turbine secondary flow. It turns out that increasing the step height generally reinforces the secondary flow intensity. In addition to local detrimental effects, these processes significantly alter the inflow conditions to the subsequent blade rows, leading to increased losses there. A comparison of the results for the uncontoured and the non-axisymmetric endwall shows that the beneficial effects of the latter, which are based mainly on radial homogenization of the outlet flow yaw angle in the first vane, still continue to exist in the presence of platform steps, although the overall efficiency is significantly reduced. An experimental validation of the platform effects is not included in this paper but will follow in the near future.

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