Numerical simulations of flows in centrifugal turbomachinery

A quasi-three-di mensional Navier-Stokes analysis has been extended and applied to flows in centrifugal turbomachinery blade rows. The numerical procedure was validated using a radial fan geometry typical of those found in fossil fuels plants and air-handling systems. The predicted blade loading and performance characteristics showed excellent agreement with the experimental data. The numerical analysis was then applied to a low AR centrifugal impeller. Inviscid and viscous flow simulations were performed at three operating conditions. While steady solutions were obtained in the inviscid flow calculations, the appearance of an oscillating separation bubble on the pressure surface of the impeller necessitated that the viscous flow simulations be time dependent. By comparing the predicted and experimental circumferential distributions of the relative frame velocity and flow angle downstream of the impeller, it was hypothesized that in the experiments the end-wall secondary flows energized the impeller suction surface boundary layer, making the flow locally behave like an inviscid fluid. The performance curve generated from the viscous calculations showed satisfactory agreement with the experimental data, while the inviscid calculations overpredicted the performance of the impeller. It was concluded that the physics retained in quasi-three-d imensional analysis give a useful first approximation of the flow trends in certain types of centrifugal turbomachinery.