Study on Design Method Considered Circulation Flow and Low Flow Rate Characteristics of a Centrifugal Blower Casing

研究了无扩压器、大舌片间隙的风机壳体内的流动。得出以下结论。(1)在设计点，蜗壳内的压力恢复为45%。其余的55%在涡卷端部和出口管道之间的部分中回收。(2)涡卷端和出口管道之间的部分充当高性能扩散器。二次流产生的离心力和边界层抽吸是高压恢复的主要原因。(3)在出口管道入口处压力突然升高，在壳体的围带侧壁和涡壳壁的上部出现了反向流动，流量Q/Qd = 0.61。该分离区随着流速的降低而增大。(4)蜗壳端部到出口管段的流动状况与风机的低流量特性密切相关。

Flow in a blower casing which has no diffuser and large tongue clearance was studied. The following conclusions were obtained.(1) Pressure recovery in the casing, at the design point, was 45 percent in the scroll. The remaining 55 percent was recovered in the section between the scroll end and exit duct.(2) The section between the scroll end and exit duct acts as a high-performance diffuser. Centrifugal force produced by secondary flow and boundary layer suction are the main cause of high pressure recovery.(3) At the inlet of the exit duct, where the pressure suddenly rose, a reverse flow occurred on the shroud side wall of the casing and the upper part of the scroll wall at the flow rate Q/Q_d=O.61. This separation zone grew with decreasing flow rate.(4) Flow conditions in the section from the scroll end to the exit duct closely related to the low flow rate characteristics of the blower.