Study on Flow Inside Diffusers for Centrifugal Turbomachines : Report 1, Diffusers Curved in Logarithmic Spiral Form under Uniform Inlet Flow

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Flow inside a diffuser consisting of two curved walls of logarithmic spiral and two parallel flat walls was investigated. Secondary flows and boundary layer growth were measured in detail. A method of calculation for boundary layers and diffuser performance was given. (1) A pair of secondary flow vortices due to flow curvature is recognized. They are intense on the convex wall and very weak on the concave wall. (2) Secondary flows build up typical skewed boundary layers on the side walls. Their velocity profiles are approximately expressed by the formerly known formula for skewed boundary layers of non-decelerating flows. (3) On the side flat wall the boundary layer growth is little, while it is very rapid on the convex wall. It is related with secondary flow conditions. (4) With consideration of these flow phenomena, a method of numerical calculation was given using orthogonal curvilinear coordinates. Effects of inlet boundary layer thickness and Reynolds number were also studied.
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