基于CFD的气动喷砂机理与喷砂流场特性研究

【作者】 曹玮；

【导师】 贾光政；

【作者基本信息】 大庆石油学院 ， 机械设计及理论， 2006， 硕士

【摘要】 气动喷砂是以压缩空气为动力,磨料通过喷嘴加速后,喷射到零件表面,可用于表面强化、表面清洗等工作,广泛地应用于机械、石油、化工、汽车、船舶等行业。喷嘴是气动喷砂系统中的关键部件之一,其作用是改变气固两相流体的运动和动力特性,对喷砂系统的清理效率影响最大。基于CFD技术,研究气动喷砂机理,对喷嘴内气固两相流动参数之间及其与变截面喷嘴几何参数之间的关系进行分析和研究,为高效喷嘴的设计提供依据;研究气动喷砂流场,对喷嘴出流时气固两相流体的自由喷流颗粒流场进行分析,并对气动喷砂作用表面的冲蚀特性进行研究,得出气固两相流动参数与几何参数对气动喷砂流场特性的影响关系,为气动喷砂系统高效工作提供理论指导;因此,开展气动喷砂机理与喷砂流场特性研究具有重要的实际意义。在气动喷砂机理研究方面,对喷嘴内气固两相流采用遵循欧拉—拉格朗日方法的离散相模型。应用Fluent软件,采用标准的k-ε模型对喷嘴内气体流场进行仿真计算,获得了气体的压力场和速度场的分布;通过对固体颗粒在气体流场中的仿真模拟,得到了固体颗粒的运动轨迹、速度和动力特性的变化规律。研究表明:固体颗粒粒径越小,受气体影响越大;不同粒径固体颗粒通过喷嘴后获得的最大总动量不同,与此对应的喷嘴收缩角也不同,并且粒径越大,固体颗粒获得最大总动量对应的喷嘴收缩角越小。在气动喷砂流场研究方面,应用Spalart-Allmaras模型对气体自由喷流流场仿真,获得喷嘴出口欠膨胀超声速喷流产生的链状流场结构。对平板的冲击流场进行仿真,观察到板激波,驻泡等现象。当气体流场中加入固体颗粒时,得到散射状的颗粒流场结构。比较不同粒径固体颗粒对同一位置的平板的平均冲击动量发现:粒径为0.4mm~0.8mm固体颗粒对平板中心的冲击动量值较大,冲击效果较好。除了由于喷嘴与平板很近时(小于10mm),颗粒的积聚影响了冲刷效果以外,固体颗粒对平板中心的冲蚀程度随着平板与喷嘴出口间距离的增大而减小。更多还原

【Abstract】 The pneumatic sand blasting takes compressed air as motive force, and the abrasive spraysthe part surfaces after the acceleration of the nozzle, it is available in surface strengthen andsurface cleaning etc, it should be extensively applied in machinery, petroleum, chemicalindustry, automobile and shipping etc.The nozzle is one of the critical parts in the pneumatic sand blasting system, and its effectis to change the motion and the motive force property of the gas-solid-two-phase fluid, itgreatly influences the cleaning efficiency. To study pneumatic sand blasting mechanism basedon the CFD technology, analyzing and studying the relation of gas-solid-two-phase fluidparameters and as well as geometry parameters of section changed nozzle, provides the basisfor the design of the high efficiency nozzle. Studying the pneumatic sand blasting flow field,we can find the influence relation of gas-solid-two-phase fluid parameters and geometryparameters to pneumatic sand blasting flow field property by analyzing free jet particles fieldof gas-solid-two-phase fluid and studying impinging corrosion property of effect surface, itprovides theoretical instruction of high efficiency work for the pneumatic sand blasting system.Therefore, the study on the pneumatic sand blasting mechanism and sand blasting flow fieldproperty has important practical significance.The Discrete Phase Model which follows the Euler-Lagrange approach is used to simulategas-solid-two-phase fluid in the nozzle at the aspect of pneumatic sand blasting mechanismresearch. Applying Fluent software, the distribution of the pressure field and the velocity fieldof gas are gained by adopting standard k-ε model to simulate gas flow field in the nozzle;thekinematic trajectory, velocity and dynamic property are gained by simulating solid particlesmovement in the gas flow field. The research indicates: the influence of the gas is more evidentwhen the particles diameter becomes smaller;the solid particles of different diametercorrespond to different maximal momentum in the outlet and the nozzle diminishing-angle, andwhen the particles gain maximal momentum, the nozzle diminishing-angle becomes smallalong with particles diameter becoming big.The Spalart-Allmaras Model is Applied to simulate free jet and impinging jet on flat, thechain form flow field configuration of supersonic underexpanded jet, the plate shock andstagnation bubble of impinging jet in the nozzle outlet are gained;when solid particles areadded in the gas flow filed, its flow field structure is scattering form;we find that the particlediameter between 0.3mm and 0.8mm has great impinging effect in the center of the flat bycomparing the mean impinging momentum of different diameter particles colliding samelocation flat. The level of impinging erosion decreases along with the increasing of the distanceof the nozzle and plate, except the plate greatly close to the nozzle when the accumulation ofparticles affects the efficiency of impinging erosion.更多还原