湍流混合层流场的PIV测量

PIV MEASUREMENT OF TURBULENT MIXING LAYER

本文使用PIV对在竖直通道内放置一个特殊设计的隔板所形成的湍流混合层流动进行测量,高低侧速比为4:1,基于两股流体速度差和管道水力半径的Re数范围4400～158400。发现混合层中大涡拟序结构的尺度随雷诺数的增加而增大,而后又随雷诺数的继续增大而减小,气泡的加入会延缓或阻碍大涡拟序结构的发展。对雷诺应力、湍流强度、涡量、旋涡强度在混合层流场内随雷诺数的变化和分布规律进行分析,发现混合层内雷诺应力、湍流强度、涡量及旋涡强度均集中分布在隔板下游一个较窄的锥形区域内,雷诺应力和湍流强度随雷诺数的增大先增大后减小,随离开隔板距离的增大而减小.涡量及旋涡强度随雷诺数的增大而增加,随离开隔板距离的增大而减小.

In present paper a turbulent mixing layer with the velocity ratio 4：1 which was produced by a special designed splitter plated placed in a vertical rectangular channel was experimentally investigated by PIV. The Reynolds number based on the velocity difference of two steams and hydraulic diameter of the channel ranges from 4400-158400. It is found that the scale of coherent vortex structure increases with increasing the Reynolds number and then decreases with continuously increasing the Reynolds number. The injected bubble will delay or hinder the evolution of the coherent structures. Afterwards the statistical and instantaneous distributions of Reynolds stress, turbulent intensity, vorticity and swirling strength are obtained. The results show that all these turbulent parameters exist only in a very narrow conical region in the downstream of the mixing layer. The Reynolds stress and turbulent intensity first increase and then decrease with increasing the Reynolds number and decrease with the evolution of mixing layer, while vorticity and swirling strength increase with increasing the Reynolds number and decrease with the evolution of mixing layer.