振荡流混合器流场模拟研究

【作者】 李伟；

【导师】 吴嘉；

【作者基本信息】 浙江大学 ， 化学工程， 2002， 硕士

【摘要】 振荡流混合器(Oscillatory Flow Mixer，缩写为OFM)是一种新型的化工过程设备。它有很好的质量、热量传递性能，并且工艺过程容易控制，可以应用在化工生产中的很多领域中去。如粒子的悬浮分离、絮凝工艺、化工反应器等等。因此引起了人们很大的研究兴趣，并且也产生了一些很有意义的研究效果。 随着计算机技术的飞速发展，计算机模拟技术已经逐渐成继实验之后的又一中有效的研究方法。计算流体力学(CFD)模拟计算越来越受到人们的重视，已经广泛应用到化学工程的各个领域当中，为工程研究做出了很大贡献。本文利用CFD技术，对OFM中的流场分布进行模拟研究，探讨对振荡流场具有决定性影响的两个因素——振荡雷诺数和St准数对振荡流场行为的影响。 本文的工作集中在层流流态下，净流量为零时，OFM流场的分布情况。文中分二维和三维情况来对OFM的流场进行模拟。在振荡雷诺数极低的情况下，OFM的流场分布是轴对称的，在此情况下采用二维模拟可以大大地节约模拟计算时间。随着振荡雷诺数的增大，流场呈非轴对称分布，用二维模拟不能得到正确的结果，这时必须采用三维模拟。 在二维模拟中，主要研究了OFM流场随时间变化情况，结果表明，甚至在小振荡雷诺属下，OFM中也存在尺度不断变化的漩涡，从而使得OFM具有良好径向混合能力；在流场分布为轴对称的情况下，不同周期相同相位，流场的分布状况出现周期性重现。 本文首次实现了对OFM流场的三维模拟，并成功地模拟了OFM流场山轴对称转变为非轴对称的现象。通过研究了三维流场随振荡雷诺数的变化情况，发现当斯特劳数为1、振荡雷诺数在200左右时，OFM流场山轴对称分布转化成非轴对称分布。这一结果与前人的实验观察结果相符。在非轴对称情况下，OFM的流场分布在不同周期的相同相位，没有出现周期性重现。 本文的工作为进一步的研究打下了良好基础。更多还原

【Abstract】 Oscillatory Flow Mixer (OFM) is a new type of devices in Chemical Engineering Process, which has a good performance in heat and mass transport. And the process in an OFM is very convenient to control. It has wide potential usages in many Chemical Engineering Processes, such as particle suspension and separation, flocculation process and chemical reactor. Quite a few researchers have showed great interest in it and many significant results have been achieved.With the rapid development of computer technology, numerical simulation technique becomes an efficient method for scientific research. Computational Fluid Dynamics (CFD) simulation has been widely used in many fields of Chemical engineering and has contributed a lot to the R&D work. In this paper, numerical simulation technique was used to study the oscillatory velocity fields in OFM. The work focus on the influence of two crucial factors梠scillatory Reynolds number and St number on the behavior of OFM.In the study, a series of cases of two-dimensional and three-dimensional velocity field in an OFM was simulated under the conditions of laminar flow and zero net flow were studied. When the oscillatory Reynolds number is very low. the velocity field distribution is axis-symmetric. So the two-dimensional simulation is used to simplify the simulation and to decrease the calculating time. With the increase of oscillator} Reynolds number, the field distribution becomes asymmetric. In this situation, the correct results cannot be obtained by two-dimensional simulation and the three-dimensional simulation must be applied.In the two-dimensional simulation, the work focus on the evolution of velocity field in an OFM. It is found that eddies exist with geometric scale changing continuously even at small Re0 which make OFM excellent in the radial mixing. In the situation of axis-symmetric velocity field, the velocity distributions are periodically similar at the same phase position of different cycles.It is first time that the three-dimensional simulation of OFM velocitv field wasimplemented and that the transition of velocity distribution from an axis-symmetric pattern to an asymmetric one was successfully simulated. By tracing of the variation of the three-dimensional velocity field with Re0, it was found that at St=l, the transition occurs as Re0 is about 200. This result was consistent with the experiment observations reported by others. In situation of asymmetric flow field, the velocity distribution shows obvious different at the same phase position of different cycles. The work presented here will be essentially helpful to the further research.更多还原