NUMERICAL STUDY OF EFFECT OF STREAMWISE END WALL FENCES ON SECONDARY FLOW LOSSES IN TWO DIMENSIONAL TURBINE ROTOR CASCADE

In a turbine cascade flow losses due to secondary flow are nearly 33% of total losses. In the present study effect of streamwise end wall fence on secondary flow loss reduction is studied numerically with experimental validation. A fence was fixed normal to the end wall and at half pitch away from the blades. Curvature of the fence was the same as that of the blade camberline. Optimization of the fence height for minimum secondary losses is done numerically using coefficient of secondary kinetic energy as the optimization parameter. A fence of height 1/3rd of inlet boundary layer thickness (delta) was found to be optimum and produces a total pressure loss reduction of 15% compared to cascade without fence. This fence trapped the pressure side leg of horseshoe vortex and reduced maximum overturning near the end wall compared to baseline case. A counter-rotating vortex is produced by this fence which weakens the passage vortex and trailing edge vortex. Climbing of passage vortex on suction surface reduced drastically. Fence of height 1/3rd of inlet boundary layer thickness reduced the three dimensionality of the flow and so the losses.