关键词: 湍流;旋转流体;流速测量;激光多普勒速度计

Abstract: Detailed mean velocity distribution of a rotating U-bend duct was measured with LDA.The U-bend duct has a cross section of 50 mm×50 mm,and the ratio of the mean radius of the bend to thd hydraulic diameter of the duct is 0 65,the axis of rotation is parallel to the bend axis.Three cases were investigated:a stationary U-bend duct flow,a case with the U-bend duct rotating positively at a rotation number Ro =0 2,and a case with negative rotation at Ro =-0 2.Flow separation occurs in all three measured cases at the inner wall from half way of the bend to certain downstream region.The size of separation region and the velocity distributions of these three cases are significantly different because the direction and the intensity of the secondary flow are different for different rotation condition.

Key words: Turbulent flow;Rotating fluid;Flow velocity measurement;Laser Doppler velocimeter