Presented is a numerical investigation of the characteristics of the internal flow field of a high-speed low-pressure ratio mixed flow turbine of 95.14mm tip diameter. A commercial computational fluid dynamics (CFD) code has been successfully employed. This has been carefully validated to experimental data taken from a turbine test facility at this institution. A comparison to gated (in phase with the turbine rotation) Laser Doppler Velocimetry measurements at the turbine trailing edge and total to static efficiencies at various operating conditions, was made showing good agreement. Details of the internal flow field from a numerical study using a 393,872 cell density model are presented. These details have been compared to a radial turbine of similar geometry and performance characteristics, also analyzed using the same cell density and analysis and boundary conditions. The flow field was found to be highly three-dimensional with the tip leakage vortex as the dominant secondary flow feature. The tip clearance flow was found to be significantly influenced by the relative motion of the shroud wall, which suppressed the development of a vortex within the mainstream passage particularly in the inducer region. Comparison to the radial turbine has shown noticeable differences concentrated in the inducer region where the greater Coriolis acceleration in the radial turbine is more influential in the development of secondary flows. Considerable loss is observed localized at the blade leading edge tip region along the full length of the blade pitch; this is associated with the increased streamline curvature in the meridional plane.
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