Influence of the surface geometry variations on the flow in a low-pressure turbine outlet guide vane cascade is studied experimentally and numerically. Experiments are performed in a linear cascade facility at Chalmers, and numerical simulations are carried out at the rig conditions using steady RANS equations. Investigated surface nonconformances are specially designed two- and three-dimensional surface roughness elements which simulate a generic welding trace and a surface repair patch. These surface modifications were implemented on the cascade vanes at different surface locations, and the aerodynamics of the cascade with geometry deviations was compared to the baseline case without them. Investigated characteristics include the cascade performance in terms of the total pressure loss and flow turning angle as well as a detailed description of the downstream development of the secondary flow field. It is found that there is a range of locations on the vane surface where even relatively large roughness elements as were investigated (with height up to 20% of the blade maximum thickness) do not affect the OGV performance significantly. Another range of locations, where the effect is critical and the flow separation is triggered, are identified as well. An accurate prediction of the separation margins in the latter case was found a challenging task for turbulence models.

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