Flow Characteristics in Scroll Casing of Sirocco Fan

摘要

The sirocco fan is advanced in compact with high pressure and large flow rate. But the efficiency of it is relatively low. One of the reasons is the complex and large flow in the scroll casing. Then it is expected to clear the influence of the geometry of the casing to the fan performance and to make compact the fan without reduce the performance. This paper presents the flow characteristics in the scroll casing for four types geometries. The flow characteristics are examined in experiments and numerical simulations. The net flow out of the impeller is biased to the hub side and the circulating flow is generated near the shroud in the scroll casing. The pressure is large in the hub side and gradually decreased toward to the shroud. The pressure distributions are different for each scroll casing until the end of the scroll, and then it is emerged the pressure drop near the end of scroll casing. After it, there are a rapid pressure raise in all types. The pressure out of the fan becomes almost the same in all types. That is, the performance of the fan is hardly varied with the scroll casing geometries. This is caused with the very large flow from the impeller that generates near the end of the scroll. The strong eccentric vortex generates near the end of the scroll casing in the impeller and it controls the performance of the fan, So the geometry of the scroll casing is not so important and is able to cut the scroll casing not to reduce the performance.