Abstract:

The commercial software Fluent 15.0 is employed to carry out the numerical simulation on the internal and external flow fields of the pressure-swirl nozzle. The axisymmetric 3-D flow field is represented by an equivalent 2-D grid. The VOF multiphase flow model and Reynolds stress model (RSM) are chosen. Numerical simulations on flow fields are performed in two different circumstances:① Gas phase is specified as air and there is no heat and mass transfer between phases; ② Gas phase is saturated steam, heat and mass transfer exists between phases. Lee model, a computational model embedded in Fluent 15.0, is specified as the phase-transition model of heat transfer. Comparisons between CFD simulations and experiment are launched. The internal and external flow fields are analyzed based on simulation datum. Results indicate that an air core forms inside the nozzle due to the helical motion of liquid phase, velocity of which increases sharply at the junction of contraction section and orifice's straight pipe section of the nozzle. Furthermore, comparisons are also performed between circumstance ① and ②. Numerical simulation results indicate that when heat and mass transfer exists between phases (i.e. in case of circumstance ②), (1) pressure of the flow fields is slightly lower and peak velocity is larger; (2) heat transfer coefficient of liquid film decreases gradually along the flow direction; (3)the film is thicker due to the vapor condensation, and liquid film breakup length is larger.

Key words: nozzle, fluid mechanics, numerical simulation, mass transfer, Lee model

摘要：

利用Fluent软件对压力旋流式喷嘴的内外流场进行了数值模拟，以等效的二维网格模型模拟圆周对称的三维流动，多相流和湍流模型分别采用VOF和雷诺应力模型。在两种条件下，对喷嘴流场进行模拟：①气相为空气，不发生相间热质传递；②气相为饱和水蒸气，发生相间热质传递。相变模型采取Fluent中内嵌的Lee模型。将数值模拟结果同实验结果进行对比，并以数值模拟的数据对喷嘴内外流场展开分析。模拟结果显示，由于液相在喷嘴旋流室内的螺旋运动，导致喷嘴内部形成“空气芯”，液相速度在喷嘴旋流室与收缩段的连接处变化剧烈；另外，发生相间热质传递条件下，流场的压力要整体稍低且速度场的速度最大值更大；液膜的传热系数沿液膜流动方向不断减小；因气相冷凝使得液膜厚度更大，液膜破碎长度也因蒸气冷凝而变得更长。

关键词: 喷嘴, 流体力学, 数值模拟, 传质, Lee相变模型