采用大涡PIV方法研究搅拌槽内湍流动能耗散率

Investigation of Turbulence Kinetic Energy Dissipation Rate in a Stirred Tank Using Large Eddy PIV Approach

在槽径为0.476m的六直叶涡轮桨搅拌槽内,采用粒子图像测速仪(PIV)对桨叶区的流场进行了实验研究,得到了桨叶区的平均流速和湍流动能(k)分布,采用大涡PIV方法对湍流动能耗散率(ε)分布进行了估算,计算了ε与k的相关系数.结果表明大涡PIV方法能有效地估算ε分布;桨叶区的射流向上倾斜,两尾涡分布于射流两侧,射流的倾角和两尾涡中心间距随射流向壁面运动而变化,射流倾角先增大再减小,相位角θ=40o时达到最大值13.2o,两尾涡中心间距先减小再增大,θ=20o时达到最小值0.0387(用槽径T无因次化);湍流动能和湍流动能耗散率峰值均位于尾涡靠近射流的区域;湍流动能和湍流动能耗散率的平均相关系数为0.363,射流核心区相关系数小于周边区域.

The flow field of impeller region in a Rushton impeller stirred tank with a diameter of 0.476 m was measured using particle image velocimeter （PIV）. Average velocity and turbulent kinetic energy k distribution were obtained. Turbulence kinetic energy dissipation rate 6 was estimated by using a large eddy PIV approach. Cross-correlation coefficient of 6 and k was calculated to analyze the relation between them. The results show that the large eddy PIV approach could effectively estimate 6 distribution. Impeller stream inclines slightly upwards, accompanied with two vortices on both sides of the stream. The incline angle of impeller stream and the distance between the centers of two vortices changes as the stream moves towards the tank wall. The incline angle increases before the phase angle θ=40^o, then decreases with the maximal value 13.2^o at θ=40^o. The distance between the centers of two vortices decreases before θ=20^o, then increases with the minimum value 0.0387 （normalized by the tank diameter T） at θ=20^o. The peaks of turbulent kinetic energy and turbulence kinetic energy dissipation are both located in the vortex region near the jet flow. Average cross-correlation coefficient of 6 and k is equal to 0.363, the cross-correlation coefficient in the center impeller stream is larger than that in the other parts of the region.