AN EXPERIMENTAL INVESTIGATION OF THE WAKE SHED FROM A HIGH-LIFT LOW PRESSURE TURBINE CASCADE AT DIFFERENT REYNOLDS NUMBERS

The paper presents the results of an experimental investigation of the wake shed from a high-lift low-pressure turbine profile. Measurement campaigns have been carried out in a three-blade large-scale turbine linear cascade. The Reynolds number based on the chord length has been varied in the range 100000-500000, to differentiate the influence of the boundary layer separation on the wake development. Two Reynolds number conditions, representative of the typical working conditions of a low pressure aeroengine turbine, have been more extensively investigated. Mean velocity and Reynolds stress components within the wake shed from the central blade have been measured across the wake by means of a two-component crossed miniature hot-wire probe. The measuring traverses were located at distances ranging between 2 and 100% of the blade chord from the central blade trailing edge. Moreover, wake integral parameters, at the two Reynolds conditions, have been evaluated and compared. Both velocity and total pressure results show a wider wake occurring at the lower Reynolds number, due to the separation affecting the suction side boundary layer. Furthermore, the momentum thickness has been found to be much higher at the lower Reynolds number, due to the higher losses related to the separation bubble occurring on the blade suction side. The Strouhal number associated with the vortex shedding seems to be influenced by the Reynolds number, due to the different conditions of the suction side boundary layers.