Measurement and analysis of aerodynamic and thermodynamic losses in pre-swirl system arrangements

In order to separately describe the dominating loss mechanisms in pre-swirled cooling air delivery systems, discharge, temperature and velocity measurements were performed for numerous designs. Whereas pre-swirl nozzles, as first component, were characterized by their discharge coefficients, total pressure losses occurring at the inlet of the receiver holes were correlated depending on the incident angle of the cooling flow. To quantify losses generated inside the rotor-stator gap, flow velocity data, acquired by means of 3D PIV, were compared to total temperature measurements. In addition the influence of wall friction and mixing losses due to the strong velocity gradients inside the pre-swirl chamber was discussed by means of a simple loss model. Finally, dimensionless loss coefficients, discharge behaviour and expected cooling temperature can be predicted for a family of realistic pre-swirl systems. Moreover, this detailed description of the losses provides a methodology to quantify the impact of individual loss sources on the global efficiency of the pre-swirl system, thus allowing improved designs.