基于时间解析PIV的串列水力转轮尾流特性研究

为研究串列水力转轮组合的下游转轮对上游转轮尾流的影响，采用时间解析PIV系统对2个垂直轴Bach水力转轮之间的流动进行测量。在不同来流速度条件下，研究下游转轮的安放角对上游水力转轮尾流的影响，对比分析受到水力转轮边界影响的尾流特征。研究结果表明:来流速度增大时，速度恢复区向上游转轮延伸，当下游转轮安放角小于108°时，该区域的速度随安放角增大而减小；当下游转轮安放角大于108°时，速度变化趋势相反。尾流中的旋涡涡心位置随安放角不同上下偏移，在部分安放角下，旋涡被拉伸变得扁平，流线也因此呈现出与无下游转轮时不同的非水平偏转状态；高能涡量区域在部分安放角和来流速度增大时，逐渐向下游和尾流中心发展，流场中离散的小尺度涡不断增加；尾流中的大尺度涡结构包含于前3阶的POD模态中，而高阶POD模态主要表征小尺度的流动结构。

Investigation of wake flow characteristics for tandem hydraulic rotors using time-resolved PIV

To study the influence of the downstream rotor on the wake of the upstream rotor, the time-resolved particle image velocimetry (TR-PIV) was used to measure the flow between two hydraulic Bach rotors. For different flow velocities, the influence of the setting angle of the downstream rotor on the upstream rotor wake was considered, and wake characteristics associated with various kinds of rotor boundaries were compared and analyzed. The results indicate that as the upstream velocity increases, the velocity recovery zone extends towards the upstream rotor. As the setting angle of the downstream rotor is smaller than 108°, velocity decreases as the setting angle increases. Such a tendency is overturned as the setting angle exceeds 108°. The positions of the vortex cores in the wake are shifted up and down with the variation in the setting angle, and the vortices are stretched and flattened at certain setting angles. Meanwhile, streamlines are deflected with respect to the main flow, which is significantly different from the situation without the downstream rotor. At some setting angles, with the increase of the upstream flow velocity, high-vorticity regions gradually develop in the streamwise direction and towards the wake center. Meanwhile, the number of sparsely distributed small-scale vortices increases continuously. Large-scale vortex structures in the wake are involved in the first three orders of proper orthogonal decomposition (POD) modes, while the high-order POD modes are featured by small-scale flowstructures.