管道中旋流喷嘴雾化流场的速度分布特性

Velocity Distribution Characteristics of Atomization Flow Field in Swirling Nozzle in Pipeline

离心式旋流雾化喷嘴内流场的速度分布决定了喷嘴的雾化性能。利用VOF两相流模型和RNG k-ε湍流模型对管道中减温水通过旋流喷嘴雾化并与过热蒸汽混合的整个流动过程进行了三维数值模拟,获得了喷嘴雾化场的流动过程,着重分析了内外流场的速度分布特性。研究表明：流体通过离心式旋流喷嘴的切向孔后变成旋转流体,从喷嘴出口螺旋喷出后,迅速由液柱变为沿一定的锥角扩散的液膜,液膜逐渐雾化为液滴;在喷嘴内部的旋转流体,其合速度与切向速度沿径向,都是先增加后减小;随着流通截面发生改变,其速度的变化主要发生在轴向分量上,切向速度的变化比较小;流体从旋流喷嘴喷出雾化,会在喷嘴出口中心轴线附近形成回流区;当管道中的流体具有一定的流速时,还会在喷嘴前壁边缘附近形成回流区。

The velocity distribution of the flow field in the centrifugal swirl atomization nozzle determines the atomization performance of the nozzle. With the VOF two-phase flow model and the RNG k - e turbu- lence model, the atomization of the hot water in the pipe through a swirl nozzle and its mixing with the su- perheated steam were simulated, and then the nozzle atomization field flow was obtained. The velocity dis- tributions of internal and external flow field were analyzed. The caculation results come to the following conclusion：After the fluid passes through the tangential hole in the centrifugal swirl nozzle, it becomes a swirling flow, spiraling forward. The liquid, once exiting from the nozzle outlet, rapidly changes from liquid column into liquid film with a certain cone shape, and then the liquid film is gradually atomized into drop- lets. For the rotating fluid inside the nozzle,its combined velocity and tangential velocity along the radial direction have similar distribution pattern, increasing first and then decreasing. As the cross section area of the flow changes, the change in velocity mainly occurs in the axial component, while the change in the tangential component is relatively small. When the fluid is atomized from the swirl nozzle, a recirculation region is formed near the center of the nozzle outlet. When the fluid in the pipeline reaches a certain flow rate, the recirculation region can be formed near the nozzle outer surface.