Assessment of the Flow Quality of a Transonic Turbine Cascade

Abstract

The assessment of flow quality through a newly constructed transonic turbine cascade is presented. Although the main objective of this research was to investigate the effect of the modification of a vane profile due to repair on pressure loss, only the results for checking the flow periodicity, two-dimensionality of the flow and transonic exit flow condition are described in this paper. The cascade blades were constructed using the profiles of nozzle guide vanes of a low pressure turbine of an in-service turboshaft engine. The assessment of the flow quality in the cascade was carried out using three methods: wall static pressure measurements at the inlet and exit of each flow passage of the cascade to check the flow periodicity, surface flow visualization using blackened paraffin oil to check the two dimensionality of the flow and thirdly, Schlieren flow visualization to verify the periodicity and transonic flow conditions at the exit of the cascade. The cascade inlet and exit wall pressure showed that the flow was nominally periodic in the cascade. The surface flow visualization of the suction surface showed that the flow was two-dimensional on approximately 70% of the central span and also indicated flow separations on the suction surface. The Schlieren flow visualization confirmed the flow periodicity and revealed the existence of shock waves on the suction surface and near the trailing edge of the blades.