圆渐开线型线的涡旋压缩机内部流场模拟分析

涡旋压缩机运行过程中工作腔内部流场状态参数难以通过试验测试获得。为此,以圆渐开线型线的动、静涡旋盘为对象,建立了带有动边界、径向与轴向间隙的动、静涡旋盘啮合的三维流场数值模型。利用CFD动网格技术设置流场边界、内部网格的变形,获得动、静涡旋盘啮合过程内部流场参数,并结合试验对模拟模型进行验证。结果表明:模拟结果与试验结果基本一致,获得了工作腔内流体流动压力和速度的动态分布规律,探索了压缩过程中腔内压力、速度、温度分布不均匀的原因。     

用改进的Paik型Boltzmann机实现图像复原

为解决传统的Boltzmann机方法不仅容易陷入局部最小点,而且收敛速度慢问题,对传统的Boltzmann机进行了改进.将Paik′s算法与Boltzmann机结合,使串行模式推广到并行模式以加快收敛速度;使用亚单位步长增进技术增加计算精度;最后,为折中收敛速度与收敛精度这一对矛盾,采用了自适应步长策略.对算法的改进进行了理论验证、收敛性分析并对残差变化进行了讨论.实验表明,该方法能够收敛到全局最优, 复原结果的峰值信噪比比改进的Boltzmann机法获得的峰值信噪比高0.5～0.8 dB, 且收敛速度仅为该方法的1/3,证明了本文提出的改进的Paik型Boltzmann机对图像复原是有效的.     

界面极限滑移条件下的液膜密封流场平均速度分布规律

为研究液膜密封流场平均速度分布规律,及其与流-固界面剪切应力之间的关系,基于Couette流动模型建立存在边界速度滑移时的密封间隙流场速度计算模型,采用Mixture均相模型和Schnerr-Sauer空化模型,通过数值模拟考察界面无滑移(滑移速度为0)和无剪切(滑移速度最大)2种极限情况下不同转速时液膜轴向不同位置处的微流场径向、切向和轴向速度分布,并建立流体型槽界面剪切力-速度拟合模型。研究结果显示：液膜的切向速度远大于径向和轴向速度,三维合成速度分布规律主要由切向速度决定;流场在槽区内近台阶轴向1μm范围内压力梯度发生突变,但非槽区和槽区流场相对独立,非槽区可视为简单Couette流动,槽区为逆压梯度Couette流动;流-固界面粘附剪切应力的大小与液膜边界速度滑移密切相关,槽区界面剪切应力变小时,边界滑移速度和槽内外流场各方向速度均变大,且转速越高,数值越大;在不高于10 000 r/min时,空化效应对整体平均速度场的影响较小,但速度更高时,需量化空化效应,并对剪切应力-速度拟合模型进行修正。     

污水处理搅拌机的水力设计与试验研究

针对目前国内污水处理搅拌池内流场测试研究空白,为研究污水处理搅拌机性能,选用NACA翼型,应用升力法对污水处理搅拌机叶片进行水力设计,并对搅拌池内流体流场分布进行试验研究。在设计的试验台上,利用流速仪,通过空间布点测量了污水搅拌池内不同位置的流体速度。利用EXCEL软件绘制了污水处理搅拌池内不同位置截面上的流体速度分布图,分析了池内流体速度分布规律。流体速度沿着轴向传递明显,流体径向扩散相对较小,且污水搅拌池内流体的流速基本沿污水处理搅拌机轴对称分布。试验表明:该测量方法可行,且该污水处理搅拌机具有明显的轴向导流和减少池壁边界对池内流体的影响作用。     

基于浸入实体法的双涡轮液力变矩器流场仿真

以双涡轮液力变矩器为研究对象,建立变矩器内流道流体域及叶片浸入实体域三维计算模型,采用浸入实体法模拟液力变矩器叶轮内流道油液运动状态,分析了液力变矩器油液压力及速度分布情况。基于变矩器三维流场分析结果计算其外特性,并与试验结果进行比较。结果表明:双涡轮液力变矩器泵轮及涡轮流道内均存在涡流和脱流,一级涡轮出口处出现射流现象;仿真结果与试验所得双涡轮液力变矩器外特性曲线吻合良好,为液力变矩器流场仿真分析提供计算思路。     

流场牵引轴向运动细丝的动态响应数值模拟

基于格子玻尔兹曼方法和浸入边界法,针对低雷诺数下受不可压流体牵引轴向释放运动细丝的动态响应进行了数值模拟。结合基于动量交换的ME-IB-LB方法,细丝在时域上采用一阶插值方法,空间上采用中心差分法,研究了不同质量密度和不同释放速度下的细丝在流体中的动态特性。证明了该方法对研究轴向运动细丝的可行性,为一类受流体牵引轴向运动变长度柔性体的动力学研究提供了一种数值分析手段。     

板坯连铸结晶器流场的格子法模拟

给出一种与现有传统数值方法不同的计算流体动力学介观模型。在该模型中,建立描述流体微团运动及碰撞规律的格子Boltzmann方程以及平衡分布函数,并依此求解出流体微团的分布函数,而流场的速度、压力等物理量可直接根据流体微团的分布函数统计求和而得。在此基础上计算了板坯连铸结晶器中心面内的二维流动,模拟出流场在高雷诺数条件下流动模态随时间的变化过程,得到与试验结果一致的流场结构,较真实地反映高雷诺数条件下结晶器内湍流的有漩性、非对称性及非定常性。结果表明随着流场雷诺数的提高,流动中物理量脉动成分的显著增强,打乱了原有对称性的大涡结构,使得流动呈现非对称性及非定常性。     

胶乳分离机高速转鼓内流场的数值分析

为了得到胶乳分离机高速转鼓在离心力场作用下的内部流场规律,建立胶乳物理特征、转鼓结构及转速与流场压力、速度之间的相互关系。基于FLUENT软件,对仿真建模、边界条件设置、计算方法进行了研究;选择混合多相流和层流模型,利用转鼓流场二维模型对内部流场进行了数值模拟,分析得到了流场的压力云图、速度云图以及出流区速度矢量图,定量评价了不同转速下流场压力、速度的变化,提出了一种利用特征参数验证模型的方法。分析结果表明:转鼓内流体压力、速度与流体所处半径成正比,流体速度、压力分别与转鼓转速呈一次、二次正比例关系,在工作转速下最大液体压力为10.4 MPa,重相出流区比轻相出流区存在更明显的漩涡现象,碟片间隙内液体流动状态为层流,仿真结果与理论计算值、文献压力数据及特征参数实测值较一致,验证了分析模型和分析方法的有效性。本研究为胶乳离心分离工艺、转鼓流场及结构优化提供了理论依据和分析方法。     

蒸汽发生器传热管流致振动的数值研究

基于计算流体力学和计算结构动力学,同时考虑流体-结构两个物理场之间的相互作用,利用有限体积法及LES方法离散非稳态、粘性、不可压缩湍流流场的N-S方程,用有限元方法离散结构动力学方程,结合动网格控制技术,建立了横向流体作用下传热管流致振动计算的三维仿真模型。基于建立的模型,首先得到了横流作用下传热管的振动响应,并与已有的实验数据比较,证明了模型的合理性;其次,研究了来流速度和频率比对传热管流致振动特性与流场结构的影响。     

分子动力学模拟研究具有"荷花效应"的微流通道

采用非平衡分子动力学模拟(NEMD)分析了流体在具有"荷花效应"的微流通道中的边界滑移现象.选择不同尺度的纳米级图样、通道管壁厚度、不同的密度和温度分别进行了多次模拟分析,根据模拟结果对比分析了以上各参数对流体流动方向的速度分布、速度最大值及其在通道中流动垂直方向上的位置的影响,确定了适宜的条件,使得通道中流体的速度滑移达到最大,流速这到最快.从对模拟结果的分析可知,流体流动方向的速度在通道上下边界的值及其最大值受到纳米图样高度和通道内径影响显著;在对不同密度的流体的模拟分析中发现,最大速度滑移与最大流速对应不同的流体密度.     

Shape optimization of flow channels based on lattice Boltzmann method

A new optimality criterion algorithm is presented for producing modified shape designs for fluid flow inside channels. To compute the fluid motion in a channel, the lattice Boltzmann method (LBM) was used based on D2Q9 and D3Q15 lattice spaces associated with the Bhatnagar-Gross-Krook (BGK) collision term. An experiential optimality method to design channels with the lowest pressure drop along the passage is introduced. The positions of solid cells and fluid cells are exchanged based on the strain rate tensor at the solid-fluid interface. To obtain the optimized shape, the cells are changed until the optimality condition is obtained with the restriction of constant fluid volume. Examples are presented to validate the algorithm, including an elbow tube as well as symmetrical and nonsymmetrical Tjunction channels. The validation exercises demonstrate that the algorithm is suitable for optimal channel design.     

基于格子Boltzmann方法模拟方腔顶盖驱动流

格子Boltzmann方法是使用时间和空间完全离散的细观模型来模拟流体宏观行为的一种新方法，模型的平均行为符合宏观的Navier-Stokes方程。给出了格子Boltzmann方法详细的求解过程，提出了一种简化的固壁边界条件处理方法。用格子Boltzmann方法对方腔顶盖驱动流进行了数值模拟，并对模拟结果进行了分析和讨论。通过与前人已有的试验及数值研究结果对比，验证了格子Boltzmann方法的正确性。     

Numerical simulation of droplet formation in a micro-channel using the lattice Boltzmann method

This study investigates droplet formation in a micro-channel using the lattice Boltzmann (LB) method. A cross-junction micro-channel and two immiscible, water and oil phase fluids, were used to form the micro-droplets. Droplets are formed by the hydrodynamic instability on the interface between two immiscible fluids when two immiscible fluids are imported simultaneously in a cross-junction micro-channel. The Shan & Chen model, which is a lattice Boltzmann model of two-phase flows, is used to treat the interaction between immiscible fluids. The detailed process of the droplet formation in the cross-junction micro-channel was illustrated. The results of the droplet formation by the LBM predicted well the experimental data by PIV (particle image velocimetry). The effect of the surface tension and the flow rate of water phase fluid on the droplet length and the interval between droplets was also investigated. As the surface tension increased, the droplet length and the interval between droplets were increased. On the other hand, when we increased the flow rate of the water phase fluid under the condition of the fixed oil-phase fluid flow rate, the droplet size was increased while the interval between droplets was decreased.     

Discrete lattice effect of various forcing methods of body force on immersed Boundary-Lattice Boltzmann method

We investigate the discrete lattice effect of various forcing methods in the lattice Boltzmann method (LBM) to include the body force obtained from the immersed boundary method (IBM). In the immersed boundary lattice Boltzmann method (IB-LBM), the LBM needs a forcing method to involve the body force on a forcing point near the immersed boundary that is calculated by IBM. The proper forcing method in LBM is derived to include the body force, which appears to resolve problems such as multiphase flow, non-ideal gas behavior, etc. Many researchers have adopted different forcing methods in LBM to involve the body force from IBM, even when they solved similar problems. However, it is necessary to evaluate the discrete lattice effect, which originates from different forcing methods in LBM, to include the effect of the body force from IBM on the results. Consequently, in this study, a rigorous analysis of the discrete lattice effect for different forcing methods in IB-LBM is performed by solving various problems.     

Flow around a flexible plate in a free stream

This paper presents a numerical scheme for fluid-structure interaction, especially for flexible structures. The lattice Boltzmann method with an immersed boundary technique using a direct forcing scheme is used for the fluid, and a finite element method with Euler beam elements is used for the flexible plate. The direct forcing scheme of the lattice Boltzmann method was improved for the immersed boundary scheme by introducing the occupation ratio of fluid lattices among the interpolated lattices. We compared the results of our proposed scheme with the known results of conventional schemes. Using the proposed numerical scheme, the flow around the flexible plate in a free stream is simulated for the effect of flexibility. Our results show that the major role of the flexibility of the flexible plate is the reduction of the resistance from flow. From the unsteady flow around a flexible plate, we found that the St of the flexible plate up to Re < 80 increased regardless of plate flexibility, but the St in the range of Re > 120 was dependent on plate flexibility. In the range of Re > 120, the St of very flexible plate increased with increasing Re, while the St of rigid plate decreased with increasing Re.     

铝型材非稳态挤压有限体积法模拟关键技术研究与应用

采用Euler网格和有限体积法(FVM),建立了铝型材非稳态挤压过程的数值模拟模型,研究了相应的关键技术。利用SIMPLE算法迭代计算得到速度场和压力场,继而计算获得等效应变速率、温度等物理场量;根据上述场量,结合铝型材热挤压的本构方程,进行动力粘度的迭代与刷新;利用VOF(volumeoffluid)方法追踪材料的流动前沿;利用“移动网格技术”解决挤压杆移动所造成的边界移动问题;利用时间步长的自动调整保证模拟的稳定性和高效性。开发了铝型材非稳态挤压有限体积法数值模拟程序,并对典型铝型材挤压过程进行了模拟,验证了所建立的铝型材非稳态挤压过程有限体积法模型及其关键技术的可行性。     

Parallel computation of two-phase flow in a microchannel using the lattice Boltzmann method

We present a numerical simulation of two-phase flow in a three-dimensional cross-junction microchannel by using the lattice Boltzmann method (LBM). At first, we validated our LBM code with the velocity profile in a 3-dimensional rectangular channel. Then, we developed a lattice Boltzmann code based on the free energy model to simulate the immiscible binary fluid flow. The parallelization of the developed code is implemented on a PC cluster using the MPI program. The numerical results of two-phase flow in the microchannel reveal droplet formation process, which compares well with corresponding experimental results. The size of droplet decreases with increase of the flow-rate ratio and the capillary number. The movement of a droplet through the microchannel induces three-dimensional circulating flow inside the droplet. This complex flow is thought to enhance the mixing and reaction of reagents.     

基于神经网络软测量的动态流量测量方法研究

文章以圆管中的粘性流体为研究对象,分析了管道中压差、温度、速度的变化对动态流量的影响,设计出了用于软测量建模的RBF神经网络结构;与此同时,还设计了动态流量测量管,并在伺服阀动态性能试验台上采集了相关数据,其间采用超声波类时差法测量了流速信息;利用采集的数据基于NeuroSolution软件对RBF网络进行了学习训练、检验和测试,最后建立了动态流量的软测量模型;通过将流量预测曲线与实测曲线相对比,结果发现该软测量模型具有很高的逼近精度,它可为动态流量的测量提供一条新的途径.     

基于格子Boltzmann方法的分叉微通道内非牛顿流体流动特性研究

为探究分叉微通道内非牛顿流体的流动特性,将非牛顿流体幂律模型引入牛顿流体格子Boltzmann模型,在不同分叉角度矩形截面微通道内数值模拟不同质量分数剪切稀化流体的流动行为;通过分析流动过程中密度随时间的变化趋势以及稳态流动下的密度,得到微通道内压力的分布以及流动区间的压力降;分析溶液质量分数、入口速度与分叉角度对非牛...