Study of Three-Dimensional Internal Flow in Impellers of Centrifugal Blowers with Straight-Radial Blades and Logarithmic-Spiral Blades in Radial Part Only

Abstract

The flow distribution throughout the passages of rotating impeller has been studied in detail about two types of the impellers, one is with straight-radial blades and the other is with logarithmic-spiral blades, and the results are presented in the form of relative velocity and direction of flow. In the former case, the measurments are carried out under various numbers of rotation and flow quantities, and those results are compared with the result of two-dimensional potential theory which has been published. From those results, it is understood that the flow in the impeller cannot be conjectured by the theories. The real flow at the experiment, especially when flow quantity is large, passes through the impeller with nearly the same angle as the incidence angle, and the region of the slowest velocity occurs at the negative side in the passage. In the latter case, the fluid flows comparatively along the blades. The velocity distributions and the direction of flow indicate that the secondary flows in the boundary layer tend to shift the low-energy air toward the negative side within the passage. There is a counter effect at the casing surface apparently caused by leakage flow coming through the blade to casing clearance space. This results in a vortex flow in the passage.