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Numerical investigation of secondary flows in a high-lift low pressure turbine

DOI: 10.1615/ICHMT.2015.THMT-15.1920
pages 847-850

J. Cui
Department of Engineering, University of Cambridge

V. Nagabhushana Rao
Whittle Laboratory, University of Cambridge, Cambridge, CB3 0DY United Kingdom

Paul G. Tucker
Fluid Dynamics Research Centre, School of Engineering, The University of Warwick, Coventry; Whittle laboratory, University of Cambridge, UK

Sinopsis

The secondary flow, also termed endwall flow, usually introduces additional losses into the system thereby decreasing the work output and changes to the flow incidence of downstream blade rows. Using a range of high-fidelity large eddy type simulations, the current study attempts to provide an improved understanding of the complex flow physics over the endwalls of high-lift Low Pressure Turbines (LPT). Simulations are made with both laminar and turbulent endwall boundary layers. Also, the incoming wakes and endwall flow from a precursor eddy resolving simulation is used as inflow. For all simulations, both the dissipation of mean flow energy due to turbulence and viscous effects are noticeable in the passage. The loss generation rate at the midspan increases significantly after the separated shear layer transition. This generation rate decreases to almost zero soon after trailing edge, while at the endwall it stays at a relatively high level. The resistance of the passage vortex to the mixing downstream from the trailing edge is the cause of the higher loss generation rate at the endwall. The turbulent endwall boundary layer increases loss in the aft-portion of passage where it enhances the mixing on the endwall and suction surface. Incoming wakes and endwall flow from upstream rotor representation increase loss generation both on the midspan and endwall in the front portion of passage. However, it suppresses the separation bubble and thus decreases the loss generation rate after the transition point at midspan.

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