Characteristics of Rotating stall in High Specific Speed diagonal Flow Fan and Suppression of Rotating Stall

为了弄清比转速为1620的高比转速斜流风机的旋转失速特性，并提出抑制旋转失速的改进设计，从非定常内部流动的观点进行了实验研究。得到的主要结果是：在低流量系数范围内，风扇发生旋转失速，总压曲线呈正梯度的不稳定特性。只有小叶尖间隙的压力特性出现滞后现象。随着叶顶间隙的增大，旋转失速消失，旋转失速单元数为1个，其转速约为转子转速的77%。旋转失速时的进气道流场为：旋转失速时的进气道流场。单元外的流动与高流量区的流动相似，随叶片通过频率的变化而有规律地变化。采用双相位锁定法测量了转子出口总压场。总压力在单元区域中较高，并且其分布使得在叶片的压力侧指示较高的压力。与高压区和叶尖涡的衰减相比，失速单元的衰减非常缓慢。其中一种方法完全抑制了旋转失速，并使风扇特性曲线在低流量区稳定为负梯度。在设计工况下，风机效率仅下降2%。本文从非定常流动的角度，结合内流测量结果，讨论了机匣处理的有效性。

In order to clarify the characteristics of rotating stall in a high specific speed diagonal flow fan with specific speed of 1620, and to propose an improved design for suppressing the rotating stall, experimental investigation has been conducted from the viewpoint of unsteady internal flow. The main results obtained are as follows.The rotating stall of the fan is observed in the range of low flow coefficient where total pressure curve indicates unstable character with positive gradient. Hysteresis appears in the pressure characteristics for small tip clearance only. The rotating stall disappears with increased tip clearance.The number of rotating stall cell is one, its speed is about 77% of the rotor speed. The cell occupies about 3/4 circumference and about 1/3 span at tip region.Velocity fluctuation in the cell is very strong at tip region and it becomes weak with decreasing radius.The inlet flow field with rotating stall is as follows. The flow outside of cell is similar to that of high flow region with regular variation by blade passing frequency. In the cell region flow field is very irregular, flow direction changes positive and negative.Total pressure field at rotor exit is measured with dual-phase-lock method. Total pressure is high in the cell region and its distribution is such that higher pressure is indicated at pressure side of the blade. Decay of the stall cell is very slow compared with decay of high pressure region with tip vortex.Two types of casing treatments with separator ring are developed and tested. With one of them the rotating stall is completely suppressed and fan characteristics curve is stabilized with negative gradient at low flow region. This is realized with little decrease in fan efficiency of 2% at design condition.The effectiveness of the casing treatment is discussed with the results of internal flow measurement from the viewpoint of unsteady flow.