Elucidation of surfactant effect on macroscopic structure of bubbly flows

为了对垂直通道内上升泡状流进行三维测量，研制了扫描立体PIV系统。采用电流镜沿展向扫描激光片，测量范围为流向（x-）30 mm，壁面法线（y-）40 mm，展向（z-）20 mm，成功地测量了三维非定常速度场。在时间分辨率为30 Hz，空间分辨率为0. 001的条件下，每个时间步得到约10，000个速度矢量。5mm，0. 5毫米，1。在x、y、z方向上分别为0 mm。使用开发的PIV系统，单相湍流流动进行了测量和定量与以前的结果（包括实验和数值）取得了良好的一致性。然后，利用该系统，在几十个气泡的集群沿壁面附近沿着向上滑动的情况下，测量液体速度。我们成功地测量了这种泡状流中雷诺应力的急剧减少，这是以前只能通过LDV测量获得的。此外，我们还成功地可视化了气泡团在通道中心区域引起的湍流结构的变化。

To conduct 3-dimensional measurement of upward bubbly flows in a vertical channel, Scanning Stereo PIV system was developed. By scanning the laser sheet in span-direction using galvano-mirror in the measurement area of 30mm in the streamwise(x-), 40mm in the wallnormal(y-) and 20mm in the spanwise(z-) directions, we succeeded to measure the 3-dimensional time-dependent velocity fields. Approximately 10, 000 velocity vectors was obtained at each time step with the time resolution of 30Hz and spatial resolution of 0. 5mm, 0. 5mm, and 1. 0mm in x, y, z directions, respectively. Using the developed PIV system, single phase turbulent flow was measured and the quantitatively good agreement with previous results(both experimental and numerical) was achieved. Then, using this system, the liquid velocity was measured under the situation that the clusters of a few tens of bubbles were sliding up along the vicinity of the wall. We succeeded to measure the drastic reduction of Reynolds stress in this type of bubbly flow which was previously obtained only through the LDV measurement. Furthermore, we succeeded to visualize the change of turbulent structures in the center region of channel which is caused by bubble clusters.