旋转变径圆管内螺旋流的LDV流速测量

Flow velocity measurement of spiral flow in a reducing pipe under rotating wall based on LDV

针对旋转变径圆管内螺旋流场激光多普勒测速(laser Doppler velocimetry,LDV)存在的窗口振动、光束难聚焦与旋转多普勒效应等问题,设计了同轴双带驱动LDV实验装置。采用折射率匹配和光路计算相结合的方法,实现了其速度场的二维LDV测量,得到了不同壁面旋转率下变径圆管内螺旋流的切向、轴向速度分布。实验结果表明:旋转与螺旋流同向时,切向速度明显增加,最大切向速度随旋转率的增加率约为10%/N,最大切向速度点向边壁移动;当旋转率与螺旋流自身旋转率接近时,外涡流区几乎消失;旋转与螺旋流反向时,切向速度随之减小,最大切向速度随旋转率的减小率约为8%/N,最大切向速度点向轴心移动;不论壁面正反旋转,近壁区轴向速度都产生了层流化的趋势。

Aiming at the problems of window vibration,beam focusing difficulty and rotating Doppler effect in laser Doppler velocimetry (LDV) of helical flow field in a rotating variable diameter circular tube,a coaxial two-band drive LDV experimental device was designed.The two-dimensional LDV measurement of the velocity field was realized by combining refractive index matching with optical path calculation.The tangential and axial velocity distributions of helical flow in a variable diameter circular tube were obtained with different wall rotation rates.The experimental results show that the tangential velocity will increase remarkably when the rotation is in the same direction as the helical flow.The maximum tangential velocity will increase by about 10%/ N with the rotation rate,and the maximum tangential velocity point will move towards the side wall.When the rotation rate is close to the rotation rate of the helical flow itself,the outer eddy current region will almost disappear.When the rotation and the helical flow are reversed,the tangential velocity will decrease.The maximum tangential velocity will decrease with the rotation rate by about 8%/ N,and the maximum tangential velocity point will move toward the axis.Regardless of the positive and negative wall rotation,the axial velocity near the wall has a trend of laminar fluidization.