Unsteady Flow Phenomena in Centrifugal Fans : 1st Report, Rotating Flow Patterns in an Inlet Duct

Abstract

In order to make clear the unsteady flow in the inlet duct of a centrifugal fan operating in the stare of rotating stall, this paper presents a method of measuring the flow by a capped hot-wire probe whose directional characteristic is very excellent. The following results are obtained. The flow mentioned above is composed of two different flow regions. One of them is a reverse flow region near the duct wall, and the other is a forward one. These flow regions are not axisymmetric and rotate at constant speed which is determined only by flow rate. In a certain range of flow rates a helical stream tuber moving forward is formed at the center of the duct near the impeller, and it rotates around the duct center. Furthermore, time averaged flow is measured by Pitot tube and compared with unsteady flow mentioned above.