In this paper, the spatial structures of the velocity fields of water flow between two differentially heated vertical plates were measured by using particle image velocimetry technique, with the Rayleigh number varying from 1. 44 X 105 to 5. 76 X 105. The vorticity fields and divergence fields were calculated from the velocity field. The measurement results indicate that large scale vortical structures exist both in horizontal and vertical directions. Both vorticity and divergence were found concentrated at some regions in measured horizontal planes, where the velocity vector fields display evident rotation and source or sink patterns. These mean that the fluid rotates and up-moves or down-moves at the same time, and indicate that the co-existence of vertical vorticity and vertical velocity, I. E. The existence of helicity, and then confirm the existence of spiral structures.%应用粒子图像测速技术(PIV)对竖直平板间水的温差湍流自然对流的流场进行了测量,并由测量所获得的速度场获取了涡量分布和散度分布.测量结果表明,在流场中的竖直展向截面和水平流向截面上都存在大尺度涡流结构,而且在部分涡量集中区域同时具有正的或者负的散度集中,速度矢量分布也表明水平截面上的这部分涡流结构呈现着清晰的源或汇的特征.这些现象都表明这部分旋转着的流体不但有切向速度,还有径向速度.这意味着这部分流体在旋转的同时也有向上或向下的运动,即同时具有在同方向上的涡量和速度,即螺度,而这是螺旋羽流结构的特征.这些涡结构,尤其是水平流向截面上具有径向速度的涡流结构的存在证实了竖直平板之间的湍流自然对流流场中大尺度的螺旋羽流结构的存在.
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