内置偏心螺旋扭带的管内层流流动特性

采用数值模拟方法,对层流状态下内置偏心螺旋扭带的管内流动特性进行了研究。结果表明:螺旋扭带的偏心放置改变了管内流场的对称结构,轴向速度极值出现在扭带与管壁最大环空间隙中间,径向速度和周向速度极值出现在扭带圆周范围内的扭带两侧;轴向和径向速度极值随着扭带偏心率的增大而提高,而周向速度极值随着扭带偏心率的增大而减小;流体在偏心螺旋扭带作用下会形成一个围绕其轴线同向旋转的强制涡,当螺旋扭带靠近管壁时,该强制涡又会带动其外围流体旋转流动,形成一个与强制涡旋向相反的诱导涡;管内压力降随扭带偏心率及扭率的增大而减小,随扭带宽度及雷诺数的增大而增大;螺旋扭带的偏心放置促进了流体的径向流动,降低了流动阻力,有利于边界层内流体的扰动和更新。

Laminar flow characteristics in a circular tube fitted with an eccentric twisted tape

Using a numerical simulation method, the flow characteristics of a circular tube fitted with an eccentric twisted tape has been studied for laminar flow. The results show that the symmetric velocity field within the circular tube is altered by the eccentric twisted tape. The maximum axial velocity lies in the widest annular gap between the tube wall and the twisted tape, while the maximum radial velocity and maximum tangential velocity both appear near the sides of the twisted tape. The maximum axial velocity and the maximum radial velocity increase with increasing tape eccentricity ratio, while the maximum tangential velocity decreases with increasing tape eccentricity ratio. A forced vortex is formed by the effect of the twisted tape on the fluid, which rotates in the same direction as the hands of the tape. When the twisted tape approaches the tube wall, the forced vortex drives the outside fluid and forms another vortex (the induced vortex) swirling in the opposite direction. The pressure drop along the tube decreases with increasing tape eccentricity ratio or torsion ratio, but increases with increasing Reynolds number or tape width. The radial flow of the fluid is promoted by the eccentric twisted tape and flow resistance is reduced at the same time, which enhances the disturbance and replacement of fluid in the boundary layer.