Flow and Blade Loading in Centrifugal Impellers

Abstract

PHOENICS-81. with body fitted coordinates, has been applied to the simulation of the three-dimensional viscous flow in a centrifugal impeller blade passage. The rotation of the coordinate system is represented by introducing momentum sources corresponding to the centrifugal and Coriolis accelerations. The whole of the blade passage is modelled, including the inducer, and a portion of the vaneless diffuser. This permits a uniform exit pressure boundary condition to be applied. The specification of impeller geometries has been automated, so that surface shapes which can be represented in terms of circular arcs and straight sections can easily be defined and modified by the user.

For the calculations reported a simple uniform-viscosity representation of turbulence is used. The experimental data used for comparison are those of Mizuki et al, in which the flow is, in effect, incompressible. Two impeller shapes are considered, one having no net diffusion in the rotor and the other having very high diffusion. Two flowrates have been considered, representing the design flow and a flowrate 25% greater. For both shapes, the overall pressure rise in the passage is well predicted. For the shape with no net diffusion, the results are in good agreement with experiment. For the more-severe high-diffusion case, the predicted pressure rise is correct, but detailed comparison of the results with experiment shows certain discrepancies in the off-design case. Nevertheless, the predictions are seen to reflect the observed trends in the data.