Large-eddy simulation and analysis of tip-clearance flows in turbomachinery applications

The tip-leakage flow in axial turbomachines is studied using large-eddy simulation with an emphasis on understanding the underlying mechanisms for low-pressure fluctuations and cavitations downstream of the tip-gap. Simulation results are validated against experimental measurements, and reasonable agreements are obtained. Dominant vortical structures such as the tip-leakage vortex and tip-separation vortices are examined, and their effects on the turbulent flow characteristics as well as on the low-pressure statistics are investigated. Analysis of the velocity and pressure fields suggests a high correlation between cavitations inception and the tip-leakage vortex. To suppress the tip-leakage vortex and the associated low-pressure events, the use of a grooved casing wall is explored, and preliminary simulation results show good promise. Additional simulations to investigate the effects of inflow vortices and tip-gap size are also discussed.