【作者】 余俊；

【导师】 刘应征；

【作者基本信息】 上海交通大学 ， 动力机械及工程， 2010， 硕士

【摘要】 本文利用激光粒子图像速度场PIV(Particle Image Velocimetry)测试技术对类仙人掌圆柱绕流的定常及非定常特性进行了细致的实验研究。通过对实验数据进行了一系列的处理分析,阐述了类仙人掌圆柱表面齿槽结构对绕流流动的影响,揭示了类仙人掌圆柱的减阻机理。首先,作者根据实验要求改进了用于湍流实验的低速循环水槽,并建立和完善了用于获取高空间分辨率绕流平均速度场的PIV(High-Resolution PIV)系统,以及用于流场非定常特性测量的时序PIV(Time-Resolved PIV,TR-PIV)系统。通过对高分辨率PIV测量所得到的海量速度场进行统计分析,得到了圆柱周围及尾迹流场的时均分布特征。通过对比类仙人掌圆柱及光滑圆柱的时均尾流场结果,揭示了类仙人掌圆柱齿槽结构对其周围及尾迹的影响。通过对时序PIV系统的测试结果进行频谱分析、相关分析、相干分析及条件平均分析,获取了圆柱尾迹中旋涡脱落的频率及其演化过程。此外,为了更清晰的理解类仙人掌圆柱的减阻机理,本文对PIV速度场测试结果进行了深入的处理分析:作者提出了使用涡强度场代替涡量场用于旋涡识别,并推导了湍流尺度计算方法;建立了基于PIV速度场互相关分析的相位平均方法,以精确识别尾流中大尺度相干结构随时间的演变过程;引入小波降噪方法用于速度场空间和时间序列降噪;改进了基于PIV速度场测试结果的压力场预测方法。更多还原

【Abstract】 Because of the practical importance and the wealth of interesting fluid flow phenomena, lots of progress has been made in understanding of the flow around a cactus-shaped cylinder. However, due to its physical complexity, the experimental results of unsteady characteristics and a complete and conclusive explanation of the physics are still lacking. The use of advanced techniques in experiments and data post-processing methodologies has made it possible to enhance our knowledge of the drag reduction phenomenon.In the present work, detailed results of time averaged flow properties as well as unsteady flow characteristics in the wake of a cactus-shaped cylinder were measured in a low-speed water tunnel. Particle image velocimetry(PIV) and time-resolved particle image velocimetry(TR-PIV) measurements were conducted for both smooth cylinder and cactus-shaped cylinder. The PIV measurements obtain some time-mean results such as velocity field, streamlines, reverse-flow distribution, shear stress distribution and swirl strength distribution. According to the comparison of these results in different shape of cylinders, the influence of cavities on vortex shedding and flow characteristics in the wake is clarified. The results obtain from TR-PIV measurements such as velocity spectrum, cross-correlation analysis and coherence analysis show the vortex shedding and transformation process, by which the different periodic character of the vortex shedding between smooth and cactus-shaped cylinder is revealed.Some new methods of PIV velocity data post-process were discussed in the present work. The swirling strength method was used to investigate the vortex structure instead of vorticity field. The turbulent integral length scale was also calculated. A revised phase averaging method based on cross-correlation of the instantaneous velocity field determined by TR-PIV measurement was proposed to extracting the quasi-periodic flow patterns related to the shedding coherent structures. At last, a revised method of calculating pressure field on the basis of the PIV data was developed.更多还原