胶体微泵的耗散粒子动力学模拟

应用耗散粒子动力学方法研究了胶体微泵.每个胶体小球按照既定的运动规律相继运动,从而可驱动流体.首先利用耗散粒子动力学方法计算了泊肃叶流动,验证了模拟的正确性.然后模拟了由六个胶体小球组成的周期性胶体微泵的工作过程.胶体颗粒与周围流体粒子之间采用了弹性碰撞模型;模拟中选择了合适的参数,从而可提高流体的粘度并保证DPD流体的不可压缩性.模拟结果与他人的实验数据进行了对比,两者很好吻合.模拟结果显示,胶体微泵的无量纲流量的绝对值随着小球运动ω的变小而增大;而随着ω的减小,无量纲流量的振幅也相应变大.     

SPH方法的运动边界条件研究Research on the moving boundary condition in SPH method

提出一种设置运动边界条件的方法,研究边界附近流体粒子积分截断和非物理穿透边界的问题。边界外的虚粒子在每个时间步由边界附近流体粒子对称生成,赋予相应的物理量,并在虚粒子中引入排斥力,利用拉格朗日形式的N‐S方程自编SPH程序,参考一维激波管的精确解验证边界方法的适用性,研究运动边界条件在计算模型中应用。激波管的模拟结果与精确解基本一致,且在运动边界模型中也计算获得合理的结果。文中提出的运动边界条件,避免了边界附近流体粒子积分截断问题,阻止流体粒子在边界处发生非物理穿透的现象。     

SPH方法的运动边界条件研究

提出一种设置运动边界条件的方法,研究边界附近流体粒子积分截断和非物理穿透边界的问题。边界外的虚粒子在每个时间步由边界附近流体粒子对称生成,赋予相应的物理量,并在虚粒子中引入排斥力,利用拉格朗日形式的N-S方程自编SPH程序,参考一维激波管的精确解验证边界方法的适用性,研究运动边界条件在计算模型中应用。激波管的模拟结果与精确解基本一致,且在运动边界模型中也计算获得合理的结果。文中提出的运动边界条件,避免了边界附近流体粒子积分截断问题,阻止流体粒子在边界处发生非物理穿透的现象。     

水底管道抛石加固过程的DEM-SPH耦合分析

水底管道的抛石加固过程是典型的颗粒-流体耦合问题.采用DEM-SPH耦合方法模拟颗粒-流体系统,其中离散元方法(DEM)用于模拟落石,光滑粒子流体动力学方法(SPH)用于模拟流体.通过三维Voronoi切割算法生成不规则形状的多面体,并基于闵可夫斯基原理构造扩展多面体形态的落石单元.通过SPH的边界排斥力模型计算颗粒与流体间的作用力,从而建立DEM-SPH耦合方法.采用该方法模拟溃坝与楔形块入水的过程,将计算结果与试验结果及其他数值结果进行对比分析,分别验证了 SPH与DEM-SPH耦合方法的合理性.建立锥形结构模拟卸料斗和水底管道,采用DEM-SPH耦合方法模拟落石通过卸料斗入水并与水底管道相互作用的过程,确定了落石和水对管道的作用力,并分析了卸料斗静止与运动时的落石堆积情况.以上研究表明,DEM-SPH方法可有效模拟颗粒材料、水和工程结构的相互作用,可进一步应用于水下抛石过程的结构和参数设计.     

外啮合齿轮泵随机内泄漏模型的研究

为了获得更加精确的外啮合齿轮泵内泄漏数学模型,将不确定性理论引入齿轮泵传统内泄漏模型中进行研究。将齿轮泵的轴向间隙、径向间隙、液压油温度、工作压力和输入转速作为随机变量,运用随机因子法和代数综合法建立齿轮泵随机内泄漏模型,进而获得在不确定性下的齿轮泵容积效率。将随机内泄漏模型研究结果和传统模型的计算结果分别与实验结果进行比较,证明随机内泄漏模型的正确性和优越性。     

接触式机械密封端面摩擦系数影响因素分析与试验

通过理论模拟计算和试验,研究并分析工作参数和端面形貌分形参数对接触式机械密封端面摩擦系数的影响.依据接触式机械密封端面摩擦系数分形模型,并考虑端面摩擦系数与端面平均温度的相互耦合关系,通过模拟计算,对B104a-70型机械密封端面摩擦系数的影响因素进行分析.计算结果表明,端面摩擦系数随着弹簧比压的增大而增大,随着密封流体压力的增大而减小;当转速较小时,端面摩擦系数随着转速的增大而增大,当转速增大到一定数值后,端面摩擦系数则随着转速的增大而略有减小;端面摩擦系数随着软质环端面分形维数的增大和特征尺度系数的减小而增大,且端面越光滑增大的幅度越大.通过在不同的弹簧比压、密封流体压力和转速下的试验对理论计算结果进行了验证,试验密封流体为15℃清水.结果表明:随着弹簧比压、密封流体压力及转速的变化,摩擦系数理论计算值与试验值的变化规律相同;当转速和密封流体压力均较小时,最大相对误差为21.74%;而当转速达到正常工作转速2 900 r/min时,最大相对误差为5.08%.     

粒子法中自由表面粒子识别

针对移动粒子半隐式法MPS（Moving Particle Semi-implicit Method）基于粒子数密度来判断自由表面会出现将内部粒子误判为自由表面粒子的问题,提出了一种结合几何法和体积法的自由表面粒子判定方法。通过对溃坝问题进行数值模拟,结果表明,全新的自由表面粒子判定方法对流体平稳运动以及剧烈运动两种工况,都能准确地判断出自由表面粒子,解决了基于粒子数密度判断方法因粒子分布稀疏产生误判的问题。[JP2]这种全新的自由表面粒子判定方法对今后采用MPS方法计算两相流问题时,两种介质在界面处的传热传质计算有重要意义。     

基于数据驱动的大气压射频放电等离子体数值模拟研究

随着人工智能技术的进步,结合低温等离子体的物理特点,数据驱动技术由于其独特的优势在低温等离子体的研究中正逐渐兴起.本研究以深度神经网络(DNN)模型在大气压射频放电中的计算研究为例,讨论了数据驱动方法在低温等离子体模拟研究中的应用.对于低温等离子体的研究而言,数据驱动研究所需要的数据可以来自于实验诊断和数值计算,根据等离子体物理特性的不同也可以选择不同的数据驱动模型.粒子模型与流体模型是低温等离子体研究中常用的两类计算模型,基于这两者的模拟数据组成的训练集, DNN可以实现对大气压射频放电的动理学特性等各种特性的实时预测.首先通过将流体模型与粒子模型计算结果与DNN模型的预测结果相比较,验证了DNN模型在给定精度下的有效性.然后基于流体模拟数据,利用DNN探究了α和γ模式下输入电流密度和放电间隙对大气压射频放电特性的影响,最后借助于粒子模拟数据构建的训练集,讨论了大气压射频微放电的频率效应,特别是电子能量分布函数(EEDF)的演化.预测结果表明,经过大约1 h的训练后, DNN只需要耗时0.01 s左右就能以极高的计算精度(与数值模拟之间的相对误差小于0.5%)获得电子密度、电场强度和...     

粒子法中自由表面粒子识别

针对移动粒子半隐式法MPS(Moving Particle Semi-implicit Method)基于粒子数密度来判断自由表面会出现将内部粒子误判为自由表面粒子的问题,提出了一种结合几何法和体积法的自由表面粒子判定方法。通过对溃坝问题进行数值模拟,结果表明,全新的自由表面粒子判定方法对流体平稳运动以及剧烈运动两种工况,都能准确地判断出自由表面粒子,解决了基于粒子数密度判断方法因粒子分布稀疏产生误判的问题。这种全新的自由表面粒子判定方法对今后采用MPS方法计算两相流问题时,两种介质在界面处的传热传质计算有重要意义。     

一种爆破片气液两相流临界泄放计算方法

针对爆破片气液两相流超压泄放难以确定的问题,应用分相模型和流体基本方程,在绝热等熵假设下引入滑速比理论,推导出气液两相流临界泄放量的计算模型。在环境压强为0.2MPa~0.6MPa情况下,计算得到:当含气率从0增加到0.1时,质量流量急剧下降;当含气率从0.1增加到0.96时,质量流量下降比较平缓;工况压力越大,质量流量越大。其中在含气率大于0.1时,计算结果与实验结果基本吻合;含气率小于0.1时,随着含气率趋近0,误差越来越大。含气率小于0.1时,通过与文献中Yoon模型、Fauske模型、实验结果进行比较,验证了绝热等熵模型仍然具有较高的准确性。最后将其与GB567-2012方法、等焓膨胀模型、均相计算模型比较,计算结果基本一致,验证了模型实际应用的准确性。     

喷水推进双级轴流泵流体动力性能CFD分析

采用高质量结构化网格对某喷水推进双级轴流泵整个数值模拟系统的各部件进行区域离散,利用CFD方法预报该泵扬程、功率和效率等外特性,分析其内部流动情况。计算结果与实验数据的较好吻合证明了CFD方法可以作为通过试验求取喷水推进双级轴流泵特性曲线的辅助方法。研究中对有、无轴情况下双级轴流泵外特性的预报和比较结果表明,轴对该泵动力性能预报结果影响不大;通过计算叶片压力分布,验证了该双级泵叶轮叶片设计中采用的线型;通过观察一、二级导叶出口的流动状态,分析了该泵设计中存在的缺陷,并为导叶改进设计提出建议。     

油水两相渗流压力脉动的实验及数值分析

本文用高精度的压差传感器和高速度的数据采集设备同时测量出油水两相流体在多孔介质流动时产生的较大压力降和微小压力脉动,应用自行研制的大型数据处理软件对恒流速水驱油的两相渗流压力脉动实验数据进行了分析,发现不同阶段压力脉动具有明显的频谱特性和时间相关特性的不同,在第三阶段（油为主,水增加阶段）谱能增加最大,时间正相关程度最强。     

Investigation of fluid dynamics within a miniature mixed flow blood pump

An oil dot flow visualization method was utilized in conjunction with a traditional light sheet particle tracer method to investigate internal flow dynamics of a miniature mixed-flow blood pump. The effects of the operating condition and impeller design on the internal fluid dynamics and hydrodynamic performance were studied. The oil dot method enabled analysis of separated and disturbed flow within the highly wrapped rotating-blade passages – previously imperceptible with light sheet methods. The blade wrap was found to be critical to providing a favorable fluid dynamics for blood pumping over a range of off-design conditions. The low flow operating conditions were found to have a detrimental effect on blood flow. Received: 13 september 2000 / Accepted: 3 April 2001     

Application of photogrammetry to surface flow visualization

The construction of three-dimensional surface flow fields is an extremely difficult task owing largely to the fragmented information available in the form of 2D images. Here, the method of photogrammetric resection based on a comprehensive camera model has been used to map oil flow visualization images on to the surface grid of the model. The data exported in the VRML format allow for user interaction in a manner not possible with 2D images. The technique is demonstrated here using the surface oil flow visualization images of a simplified landing gear model at low speed in a conventional wind tunnel without any specialized rigs for photogrammetry. The results are not limited to low-speed regimes and show that this technique can have significant impact on understanding the flow physics associated with the surface flow topology of highly three-dimensional separated flows on complex models.     

干气密封旋转流场的宏观特性与介观速度场的逻辑关系研究

旋转流场中的流体流动比较复杂，特别是在高转速、微尺度工况时，流场中的流体流态及其判断方法缺乏完备的理论模型. 选择干气密封作为高速旋转流场的研究对象，以开启力和泄漏量作为宏观特性表征指标参数，选择剪切(周向)、径向及轴向速度分量对速度流场进行介观表述，通过Fluent软件仿真计算大跨距转速(低转速至超高转速)时的宏观、介观指标参数，研究密封性能指标参数与速度场间的内在逻辑关系. 结果表明:低速旋转流场中的轴向速度分量较小，可忽略不计，转速升高会促使轴向速度分量持续增大，当转速持续增大并超过某一临界值时，轴向速度分量会出现迅速升高的情形；轴向速度分量的变化情形与微尺度流场(开启力和泄漏量)波动密切相关，是影响旋转流场流态的关键性指标参数，也是引起宏观流场特性变化的主要因素；径向速度分量的变化情形与微尺度流场泄漏量的变化规律基本一致，随着转速的增大，泄漏量的宏观性能反馈要早于开启力波动的出现. 基于以上研究，同时根据管道雷诺数、流量因子判定模型及流体力学基本理论，尝试提出了基于三维速度分量的针对旋转流场流态的椭球判定模型.      

Flow friction on co-rotating parallel-disk assemblies with forced through-flow

The power requirement for a rotating parallel-disk assembly with through-flow is experimentally studied. The flow velocity at the test core exit is measured using a traverse hot-wire probe, from which the exit kinetic energy is determined. A traverse pitot tube is utilized to monitor the velocity distribution in the inlet duct from which the flow rate is evaluated. The total pressure characteristics, fluid power transmission, rotor efficiency and moment coefficient (i.e. power number) are determined from the measurements of static pressures, rotational speed and torque. It is disclosed that the onset of stall propagation, a unique characteristics of shear pump, can be detected from a total pressure plot.     

A novel experimental facility for measuring internal flow of Solid-liquid two-phase flow in a centrifugal pump by PIV

PIV is one of the most effective flow measurement methods, but for solid-liquid two-phase flow in a centrifugal pump with complex internal structure and high speed rotation, many problems exist in the experimental facility design, such as solid particle releasement, synchronization issues among camera, laser and pump impeller, and methods of avoiding introducing bubbles into flow passage, etc. To solve these critical problems, a new experimental facility without agitation was designed for internal solid-liquid two-phase flow test in a centrifugal pump by PIV. The facility was tested by measuring two-phase flow of water-glass beans and water-rape seeds in a centrifugal slurry pump. The new test facility has many obvious advantages, such as the simpler structure without the agitating device, less noise in the test process, less power consumption, less number of particles to get a certain particle volume concentration, and the decrease of the experiment cost. The result shows that the new facility can realize a stable solid-liquid two-phase flow measurement with high reliability in a centrifugal pump.     

Matrix–Fracture Transfer through Countercurrent Imbibition in Presence of Fracture Fluid Flow

Although a lot of research has been done in modeling the oil recovery from fractured reservoirs by countercurrent imbibition, less attention has been paid to the effect of the fracture fluid velocity upon the rate of oil recovery. Experiments are conducted to determine the effect of fracture flow rate upon countercurrent imbibition. A droplet detachment model is proposed to derive the effective water saturation in a thin boundary layer at the matrix–fracture interface. This effective boundary water saturation is a function of fluid properties, fluid velocity in the fracture and fracture width. For a highly water–wet porous medium, this model predicts an increase in the boundary water saturation with increase in fracture fluid velocity. The increase in boundary water saturation, in turn, increases the oil recovery rate from the matrix, which is consistent with the experimental results. The model also predicts that the oil recovery rate does not vary linearly with the boundary water saturation.     

Energy dissipation mechanism and experiment of particle dampers for gear transmission under centrifugal loads

As a passive means of vibration reduction, particle damping is mainly applied to the horizontal or vertical steady field. However, it is seldom applied to centrifugal fields. Under high speed and heavy loading, the vibration of tooth surfaces of gear transmissions becomes more severe shortening gear service life and augmenting noise. Under centrifugal loading, the particle system exhibits different characteristics, for example, particles are extruded at the end farthest from the center. We investigated gears with drilled via holes filled with damping particles. Using the discrete-element method, we developed an energy dissipation model for the particle system accounting for friction and inelastic collisions. Energy dissipation and damping characteristics of this system were analyzed. Experiments were also conducted with the gear system having different particle filling rates. The results show that this filling rate is an important parameter associated with particle damping in a centrifugal field. An unsuitable filling rate would significantly reduce damping effectiveness. With changes in rotation speed and load, the gear transmission system has different optimal filling rates. The results provide guidelines for the application of particle damping in centrifugal fields of gear transmissions.