The aerodynamic performance of an aggressive axial steam turbine exhaust diffuser is investigated. CFD simulations are carried out with the last stage rotor included. As expected, results reveal that the last stage tip leakage has a significant influence on the performance of the diffuser. A comparison is made with results from calculations of a conservative diffuser. This shows that although the high total pressure in the tip leakage jet helps to prevent casing separation, it can ruin the recovery if the diffusion is too low. Then the high velocity at the casing can reach the outlet of the diffuser, resulting in a more non-uniform exit flow distribution. This in turn reduces the pressure recovery. This effect is of special importance when the non-dimensional length is short, as for the investigated diffusers.

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