| 自由落体下落速度振荡现象的研究 |
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| 引用本文： | 李轶明.自由落体下落速度振荡现象的研究[J].实验流体力学,2014,0(5):7-12. |
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| 作者姓名： | 李轶明 |
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| 作者单位： | 中国石油大学 北京 石油工程学院,北京,102249 |
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| 基金项目： | 中国石油大学(北京)科研基金资助 |
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| 摘 要： | 为了研究自由下落物体的速度震荡现象,基于相对运动原理,应用立式风洞研究了5种典型形状的物体在上升气流中的悬浮特性。模型包括球形、正方体、长方体、短圆柱体和碟形等刚体。风速的平均值由皮托管风速计测得,同时通过CCD相机记录了物体达到悬浮状态前后的运动状态并进行了定量分析。实验结果表明:对称性较好的物体具有较稳定的悬浮特性;而非对称性物体,由于不同姿态角下的阻力系数和扭矩系数不同,很难维持一个稳定的悬浮状态,将伴随姿态的变化不断发生振荡运动。从而说明,空间形体对称的物体自由下落过程中可以达到较稳定的最大下落速度,而形体非对称的物体则难以达到确定的最大速度。除实验研究之外,还采用动态网格数值模拟手段计算了二维方形模型下落过程中的姿态角及运动轨迹,同时得到模型不同姿态角下的阻力和扭矩,计算结果也进一步解释了物体下落速度会发生振荡的原因。
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| 关 键 词： | 振荡现象 自由落体 下落速度 |
Study on velocity oscillating phenomenon of free falling bodies |
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| Li Yiming.Study on velocity oscillating phenomenon of free falling bodies[J].Experiments and Measur in Fluid Mechanics,2014,0(5):7-12. |
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| Authors: | Li Yiming |
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| Abstract: | In order to study the falling velocity oscillating phenomenon,the characteristic of suspending obj ects of five typical rigid bodies inside up-flow were experimentally studied by using a wind tunnel with vertical test section based on the principle of relative motion.The rigid objects include ball,cube,cuboid,cylinder and disc.The mean wind velocities inside the wind tunnel test section were measured by Pitot-Tube and the dynamic status of the obj ects before and after its suspension were recorded by CCD camera and quantitatively analyzed.The experimental re-sults show that the obj ects of symmetrical bodies can maintain a comparatively stable suspension state,while those of asymmetrical bodies continuously oscillate with changing attitude angle due to different drag coefficient and pitch coefficient on the asymmetrical objects.In other words,the symmetrical objects can reach a stable maximum falling speed during free fall,while the asym-metrical bodies are hard to reach expected maximum falling speed.Besides experimental study,a 2-D Computational Fluid Dynamics (CFD)model combined with dynamic mesh technology was also performed,from which the drag coefficient,pitch coefficient and the trajectory of the square inside the flow were obtained.The simulation results can be used to quantitatively explain the falling velocity oscillation of the asymmetrical free falling bodies. |
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| Keywords: | oscillating phenomenon free falling bodies fall velocities |
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