Flow Control of Vaneless Diffuser Rotating Stall

为了阐明扩散器壁面边界层在扩散器旋转失速中的作用，在不同的径向位置施加了边界层吸力。由于主流量的减小，吸力增加了起始流量，说明目前归因于反向流动的解释是不充分的。对二维无粘非线性扩散器流动进行了分析。在较小的流量下，当来自螺旋桨的涡量构成一定的流型时，出现了与实验中观察到的流型相似的流型。但与实验结果相比，起振条件过于严重，在考虑壁面摩擦影响的情况下，不会发生失稳。从旋转失速主动控制的结果出发，讨论了旋转失速的能量平衡问题。通过在扩散器进口引入与旋转失速成一定相位关系的脉动流量进行控制。旋转、失速引起的离散频率分量在整个扩散器中完全消失，表明控制不是单纯的扰动的线性叠加，而是扰动的加入改变了旋转失速流动本身。脉动流动的位移效应向扩散器流动传递的能量与控制的旋转失速幅度有关。结果表明，当能量为负时，振幅减小。在此基础上，定量讨论了无叶扩张器旋转失速的幅值与能量平衡之间的关系。

In order to elucidate the role of the diffuser wall boundary layers in diffuser rotating stalls, boundary layer suction was applied at various radial locations. The onset flow was increased by the suction owing to the decrease in the main flow rate, showing that the current explanation attributing to the reverse flow is not adequate.A 2-D inviscid, nonlinear diffuser flow anaysis was made. At smaller flow rates, flow patterns similar to that observed in experiments appeared when the vorticity from the inpeller constitutes a certain pattern. However, the onset condition is too severe compared with experiments and the instability did not occur when the effects of skin friction on the diffuser wall was taken into account. Thus, the simulated instability looks to be different from those observed experimentally.Discussions on the energy balance of rotating stall were made from the results of an active control of the rotating stall. The control was made by introducing a fluctuating flow at the diffuser inlet, which is in a certain phase relation with the rotating stall. Discrete frequency component due to rotating, stall completely disappeared in the whole diffuser indicating that the control is not due to a mere linear superposition of the disturbance but the rotation stall flow itself is changed by the addition of the disturbance. The energy transferred to the diffuser flow by the displacement effect of the fluctuating flow was related with the controlled rotating stall amplitude. It was shown that the amplitude decreased when the energy is negative. From this result, the quantitative discussion was made as to the relation between the amplitude and the energy balance of vaneless diffuser rotating stall.