基于LBM的空腔流动及声传播研究

发布时间：2018-04-24 08:42

本文选题：空腔流 + 格子玻尔兹曼方法　；参考：《华中科技大学》2014年硕士论文

【摘要】：气动噪声在现今工程和生活实际中处处可见，控制噪声无论是对工业实际亦或是日常生活都较为重要。而关于其数值模拟计算也在近几十年来逐渐成为热点，LBM正是其中能够较好模拟声波的产生及传播的方法之一。基于绝热、等熵假设的D2Q9可以将流体视为微可压，这使声传播模拟成为可能。本文研究主要从以下几方面进行：首先模拟多类型空腔流，其中包含方形腔、三角形空腔、半圆形空腔以及梯形空腔。选取含插值的斜边界外推法处理这几类含复杂边界的空腔。改变流速以探究流速变化对各类空腔流场的影响，这些影响主要体现在涡强、涡中心源位置变化及涡数量等方面。总体而言随着入流速度的提高，空腔内涡流状态逐渐向复杂化不稳定化发展，当壁面剪切流达到一定程度时，空腔一般都将于底部或两侧的近壁面处由主涡分化出小涡。其次，为全面了解声波传播特性，对点源、线源的传播、同频率与不同频率点源的合成、不同松弛时间下波的传播特性以及对多普勒效应进行模拟分析。通过将理论分析解与点源、线源在各时刻的LBM模拟结果对比，初步验证其计算可行性。对干涉现象的模拟和多普勒现象的计算分析进一步证明了其模拟声波的准确性，同时，采用不同松弛时间进行模拟，得出松弛时间与流场阻尼正相关，但与声速无关。最后，，本文对矩形腔进行了独立研究，从深长比、入口流速、粘性等角度进行了模拟分析，然后对比相同条件下传统CFD计算结果，统计二者误差，结果显示深长比较大和深长比较小情况下其误差较低，流速方面，二者误差随流速降低而降低。同时，网格技术的模拟说明了其能在一定程度上减少计算耗时。另外，还以LBM监测其内某些点的声压变化，求得其频谱特性并对比文献结果，结果证明其声压计算值对于各个峰值频率计算较为准确，说明了LBM对于预测噪声的准确性。
[Abstract]:Pneumatic noise can be seen everywhere in engineering and daily life nowadays. It is important to control noise both in industry and in daily life. The numerical simulation of LBM has become a hot topic in recent decades, which is one of the methods to simulate the generation and propagation of sound waves. Based on adiabatic, the isentropic D2Q9 can treat the fluid as microcompressible, which makes it possible to simulate acoustic propagation. This paper mainly studies from the following aspects: First, multi-type cavity flow is simulated, including square cavity, triangular cavity, semicircular cavity and trapezoidal cavity. The oblique boundary extrapolation method with interpolation is selected to deal with these kinds of cavity with complex boundary. The effect of velocity variation on the flow field of cavity is investigated by changing the velocity of flow, which is mainly reflected in the vorticity strength, the location change of vortex center source and the number of vortices. In general, with the increase of the inlet velocity, the swirl state in the cavity becomes more and more complex and unstable. When the wall shear flow reaches a certain level, the cavity will generally be separated from the main vortex by the main vortex at the bottom or near the wall of both sides. Secondly, in order to fully understand the characteristics of acoustic wave propagation, the propagation of point source and line source, the synthesis of point source with the same frequency and different frequency, the propagation characteristics of wave at different relaxation time and the Doppler effect are simulated and analyzed. By comparing the theoretical analysis solution with the LBM simulation results of point source and line source at each time, the feasibility of calculation is preliminarily verified. The simulation of the interference phenomenon and the analysis of the Doppler phenomenon further prove the accuracy of the simulated acoustic wave. At the same time, the different relaxation time is used to simulate, and it is found that the relaxation time is positively correlated with the flow field damping, but it is independent of the sound velocity. Finally, an independent study of rectangular cavity is carried out, which is simulated and analyzed from the angles of depth ratio, inlet velocity and viscosity, and then compared with the traditional CFD calculation results under the same conditions, and the errors between the two are calculated. The results show that the error is lower in the case of larger depth ratio and lower depth length ratio, and the error decreases with the decrease of flow velocity. At the same time, the simulation of grid technology shows that it can reduce computational time to some extent. In addition, LBM is used to monitor the variation of sound pressure at some points, and the spectral characteristics are obtained and compared with the results of literature. The results show that the calculated value of sound pressure is more accurate for each peak frequency, which shows the accuracy of LBM in predicting noise.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB53

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