By positioning the completely rough wall locally on the hub side diffuser wall alone in the vaneless diffuser, the flow rate of rotating stall inception was decreased by 42 percent at a small pressure drop of less than 1 percent. This is based on the fact that the local reverse flow occurs first in the hub side in most centrifugal blowers with a backswept blade impeller. The three-dimensional boundary layer calculation shows that the increase in wall shear component normal to the main-flow direction markedly decreases the skewed angle of the three-dimensional boundary layer, and results in suppression of the three-dimensional separation. It is also clarified theoretically that the diffuser pressure recovery is hardly deteriorated by the rough wall positioned downstream of R = l.2 because the increase in the radial momentum change, resulting from reduction in the skewed angle of the three-dimensional boundary layer, supports the adverse pressure gradient.

Issue Section:
Technical Papers
Keywords:
centrifuges, rotational flow, rough surfaces, boundary layers, shear flow, flow separation, pressure control, Centrifugal Blower, Vaneless Diffuser, Rotating Stall, Three-Dimensional Boundary Layer, Separation Control, Rough Wall
Topics:
Boundary layers, Diffusers, Flow (Dynamics), Pressure, Separation (Technology), Surface roughness, Vaneless diffusers, Friction, Impellers
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