An experimental investigation of secondary flows and loss development downstream of a highly loaded low pressure turbine outlet guide vane cascade

Paper in proceeding, 2006

This paper presents a detailed experimental investigation of the evolution of secondary flow field characteristics and the losses at several measurement planes downstream of a highly loaded low pressure turbine/outlet guide vane (LPT/OGV). The experiments are conducted in a linear cascade equipped with a boundary-layer suction system designed at Chalmers in Sweden. The aerodynamic function of the LPT/OGV's is to turn the swirling flow out from the last low-pressure turbine rotor into an axial direction. This de-swirling gives a diffusive flow with growing boundary layers, strong secondary flows, and risk for separation both on vanes and end-walls. Important parameters that influence the secondary flow-field are the upstream boundary-layer height, the Re-number and the inlet incidence. All these parameters together with the turbulence intensity can be adjusted in the test-facility in order to encounter engine like conditions. In the final paper several upstream realistic incidences and turbulence intensities are investigated for one Reynolds number. Downstream characteristics have been measured by means of a 5-hole pneumatic probe. It allows for the determination of the mean vortical structures, their development and their interactions. The trailing edge vortices, the two branches of the passage vortex and the corner vortex are clearly visible close to the blade trailing edge. They merge and grow into a single large vortical structure further downstream. Their intensity is shown to be strongly dependent on the incidence. The turbulence level seems to play a role on the mixing inside and between the structures. The measurements also show the dependence of the losses and the mean outlet flow angles along the blade span on the vortices development.