Aerodynamic character of partial squealer tip arrangements in an axial flow turbine. Part II: Detailed numerical aerodynamic field visualisations via three dimensional viscous flow simulations around a partial squealer tip

The present investigation deals with the numerical visualisation of tip leakage flow from 'partial-length squealer rims' that are constructed separately on the suction side in a single stage turbine rig. After describing the static pressure field on the tip surface with a squealer rim, the vortical flow features around the squealer rim and inside the tip gap are visualised in vertical planes. The leakage flow paths under the control of squealer rims are described in various planes parallel to the blade tip platform on which the squealer rims are attached. Turbine exit total pressure as calculated from the numerical model is presented for the baseline tip and tips with squealer rims. It is clearly shown that a partial squealer rim arrangement can be extremely effective in weakening the tip leakage vortex in a turbine facility provided that the squealer rim height is specified correctly. The study shows that the chordwise length of partial squealer rims near the suction side corner does not significantly affect the desensitisation process. The aerodynamic benefit of using a partial squealer tip arrangement located near the suction side of the tip platform in a turbine stage is demonstrated.