【作者】 邵霞；

【导师】 单春贤；

【作者基本信息】 江苏大学 ， 工程热物理， 2007， 硕士

【摘要】 本文对割草机的国内外研究进展进行了大量调研,介绍了PIV技术和叶轮机械内部流场研究的国内外进展;对各种单相气体流动的数学模型进行对比,建立了适合割草机流道气体流动的数值模型;介绍了网格生成技术和不同网格的特点,运用GAMBIT建立流道模型并对其进行非结构网格划分;选用标准κ—ε模型作为流动的数值模型,并作相关假设,采用SIMPLE算法进行方程的求解计算,得到流道内流场的速度、静压强以及湍动能分布规律,分析了刀绳长度、电机转速对流场特性的影响机理;设计并搭建了实验台,完成PIV流场测试实验,并将实验结果与数值计算结果进行了比较分析。数值模拟的结果表明割草机流道内部流动相对于基准面呈基本对称的分布。刀绳长度、电机转速的变化共同影响内部流场。刀绳越长,电机转速越大,割草机切割杂草的能力越强;在速度一定时,应尽量选用长刀绳,这样可获得流场内部尽量大的压差,加强机具抛撒碎草的能力;电机转速一定时长刀绳所引起的速度脉动更强,由速度的脉动产生空气动力噪声更大。试验的结果表明流场的速度分布相对基面呈近似对称分布。实验结果和数值计算比较吻合。数值计算和实验结果比较吻合。由于边缝中的流体除了做回转运动外还可被吸向中心区域的低压区,因而短刀绳时的流道内部流场比长刀绳时更紊乱。更多还原

【Abstract】 In this dissertation, giving a brief research progress of the grass trimmer and a survey of PIV and turbo machine internal flow field technology at home and abroad; comparing all kinds of simulation models of single-phase air flow, establishing the model fitted to grass trimmer’s flow channel; introducing the grid generation and their features, establishing the flow passage’s model and generating unstructured grid by GAMBIT; choosing the k-s model to enclose the rotating flow field, and adopting some hypothesis to the model, using the SIMPLE method to simulate the flow field, giving some results such as velocity, pressure and kinetic energy distribution, analyzing the length of blade and rotating speed velocity of motor how to effect the flow field’s distribution; designing and making a fixable experiment table, completing PIV flow field testing experiment.The result of simulation indicates that the internal flowing in flow field is a symmetric distribution comparing to the basic surface. The length of blade and velocity of motor effect the flow field and grass trimmer’s cutting ability, noise control and the ability of dripping grass. A longer blade and higher motor rotating speed can get a better cutting ability. a longer blade when the rotating speed is fixed can get a bigger pressure drop which can make grass dripping out of the flow field in time. longer blade when the rotating speed is fixed can make a bigger velocity pulse which will make the noise more higher.The experiment indicates that the velocity in flow field is a symmetric distribution comparing to the basic surface. The results anastromose between experiment and numerical simulation. The length of blade effects the flow field’s features. The main reason is that the fluid in the gap may be absorbed to the low pressure area inside in addition to rotating movement, which makes the flow field disorderly.更多还原