基于本征正交分解的动边界环形缝隙流场诊断分析

Diagnostic analysis of moving-boundary annular gap flow by Proper Orthogonal Decomposition

缝隙流动的流体应力脉动、流致振动等瞬态现象往往会对水力机械的稳定运行产生一定影响,以往的缝隙流动层流近似求解与边壁脉动压力测量无法对瞬态现象进行全场的定量描述。本文以有压有限域内的动边界环形缝隙为研究对象,对该流场在完全湍流状态下的物理试验结果进行了基于本征正交分解的全场诊断分析。结果表明:流体应力方面,流场前部的雷诺应力迅速增长,在流场中部维持一定幅值,在流场后部迅速沿程递减。主流沿径向的平均对流输运强度,高出同一工况时径向流沿周向的对流输运强度4~7倍,高出主流沿周向的对流输运强度6~14倍;流致振动方面,功率谱密度函数表示的流场流致振动频谱在同一流量时有着较为明显的分区趋势,对于低频段(0~10 Hz)与高频段(120 Hz以上)环隙宽度较小时功率谱密度较大;对于中频段(10~120 Hz)则是环隙宽度较大时功率谱密度较大。对于环隙流场,环隙宽度的减小对于其较大尺度的流致振动抑制作用较强。此外,使用本征正交分解识别出了流场的拟序结构,并且使用低阶模态对雷诺应力进行重构可以较好的估计流场的雷诺应力。

The fluid stress of gap flow,flow induced vibration and other transient phenomena tend to have some influence on the stable operation of hydraulic machinery.The transient phenomenon of the entire gap flow cannot be quantitatively described by laminar approximation or pressure measurement near the wall.So the annular gap flow with moving inner boundary of pressured pipe flow was diagnosed by Proper Orthogonal Decomposition(POD)while the flow was fully turbulence.As the result of fluid stress,the Reynolds stress increases rapidly in the front of the flow field,maintains a certain value in the middle,and decreases rapidly in the rear of the flow field.The strength of convective transport in the radial direction of the main flow is 4-7 times higher than that the radial transport in the circular direction,and 6-14 times higher than the main flow in circular direction.About the flow-induced vibration,the Power Spectrum Density(PSD)function has three subzones in frequency domain.For the low-frequency domain(0 to 10 Hz)and high-frequency domain(more than 120 Hz),the PSD value is larger while the gap width is minor;but the middle-frequency domain has an adverse trend.The limitation effect on larger-scale vibration is more significant while the gap width get smaller.Besides,the coherent structures of the flow are identified by POD method,and the reconstruction of Reynolds stresses by the lower-order modes can be a better estimation for the total Reynolds stresses of flow.