Author(s)

K. Kibicho & A.T. Sayers

Abstract

Experimental velocity profiles and static pressure recovery data, which were obtained in a 50° included angle diffuser, are presented. The measurements were carried out at Reynolds numbers between 1.07 x 105 and 2.14 x 105 based on inlet hydraulic diameter and centreline velocity. Separation of the attached flow on the stalled wall occurred at a normalized distance of 0.4 from the diffuser entry. On the unstalled diffuser wall, near the diffuser entry, a separation bubble was observed. The flow in this bubble separated from and reattached to the unstalled wall at normalized distances from the diffuser entry of 0.35 and 1.4 respectively. Finally, a method to predict the distance along the wall, on the stalled side of the diffuser, where reverse flow first occurs (point of stall), is proposed. Keywords: two-dimensional, wide-angled, diffuser, stall, separated flows, subsonic flows, diffuser flow regimes. 1 Introduction Diffusers are found in many fluid-flow systems, such as turbo machines, flow meters, noise suppressors, air-conditioning ducting, wind tunnels etc, and are usually designed to operate in the unstalled condition. However, to meet some design constraints such as the overall size of the fluid flow systems, wide angled diffusers, which undergo stalling, are often tolerated, especially when the area ratios are specified. Whenever stalling in diffuser flows occurs, regions of stalled flow block the normal flow causing poor pressure recovery and severe asymmetry of the flow.

Keywords

two-dimensional, wide-angled, diffuser, stall, separated flows,subsonic flows, diffuser flow regimes.