平板收缩流的对数构象模拟?

本文采用对数构象方法,结合同位网格有限体积离散,对由 Oldroyd-B 本构模型描述的粘弹性流体流动的高 We 数问题(High Weissenberg Number Problem, HWNP)进行了研究,对等温不可压条件下的平面 Poiseuille 流和4:1平板收缩流进行了数值模拟.平面 Poiseuille 流在不同 We 数时的数值结果验证了对数构象方法在简单流动中的有效性.在4:1粘弹性收缩流的数值模拟中,对数构象方法和传统方法在低 We 数时流场中的流线、应力等的对比结果验证了对数构象方法在复杂流动中的有效性.高 We 数时的数值结果表明:对于 Oldroyd-B 模型,对数构象方法可提高求解时的稳定性,并可将临界 We 数由传统方法的2.5提高到5.0.     

叶栅内非定常不可压流动的数值模拟

基于SMAC(Simplified Marker and Cell)方法推导出直接求解二维非定常、不可压N-S方程的隐式数值方法.求解的基本方程是任意曲线坐标系中以逆变速度为变量的N-S方程和椭圆型的压力Poisson方程.采用该方法,对二维叶栅非定常分离流场进行了数值模拟,叶栅表面压力的计算结果与试验结果相比比较吻合,从而验证了这种方法的可靠性.同时对叶栅非定常流场的流场结构和流动机理做了初步的探讨.在均匀来流和定常边界条件下,叶栅内部流动表现出强烈的非定常性;在小冲角和高雷诺数时,叶栅尾部产生类似卡门涡街的周期性流动.     

平板Couette流场中聚合物流变性质及分子构象的数值模拟

通过耦合Brown构形场的有限体积法,对基于FENE(Finite Extension Non-linear Elastic)殊一簧链分子模型的平板Couette流动进行了模拟.不但得到了流动过程中的速度、应力等宏观信息,还得到了分子链的位形、分子链的取向角以及拉伸量等微观信息.另外,还研究了弹簧的最大拉伸长度b和we...     

不同强化管传热特性的数值模拟与实验研究

对横纹槽管、缩放管和螺旋槽管在夹套间进行了传热特性实验,研究了传热效率指标随雷诺数的变化规律.运用FLUENT软件,采用二维轴对称方法和k-ε模型对夹套间流体流动传热进行了数值模拟,并将模拟结果与实验结果进行对比.从场协同的角度研究了速度场与温度场夹角对传热膜系数的影响.     

粉末注射成形喂料充模层状二维流动的基本方程

将粉末注射成形喂料在薄壁模腔中的流动视为层状二维流动,以喂料流动的守恒方程组为基础,建立了描述粉末注射成形喂料充模流动的数学模型。推导了喂料熔体流导率的计算公式,得出压力场的控制方程是一非线性椭圆偏微分方程。使模型的计算成为可能,为进一步对粉末注射成形进行计算机模拟和数值分析奠定了数学基础。     

方柱绕流的二维和三维数值模拟

为了深入研究方柱绕流中流动情况,详细分析方柱受力,通过采用标准k-ε模型和DES模型,运用有限体积法对单方柱绕流进行了数值模拟,着重研究了流场形态、升阻力系数变化曲线,给出了流场中方柱在不同雷诺数下受到的升力和阻力的变化情况.通过与前人的实验和数值结果比较,证明了DES计算模型对于三维钝体绕流计算是可行的.表明三维数值模拟优于二维数值模拟,且随着雷诺数的增加,CD的平均值增加而St数先增大再减小.     

换气扇内部流场的数值仿真和能效分析研究

某种型号换气扇(B型)在使用中,存在能效偏低的问题,应用计算流体力学方法对其三维内部流场进行了数值模拟,预测了最大风量和整体能效曲线,通过与试验数据比较表明了数值计算的可靠性.进而详细分析了换气扇子午平面和回转面的流动情况,出风口与叶轮之间的间隙流动及叶轮流道内的二次流等局部流动特征.上述结果对于对该换气扇进行优化设计和改型有一定的指导和借鉴意义.     

非结构网格上多介质可压缩流模拟的RKDG方法

针对一般方法模拟具有运动界面的多介质可压缩流动问题计算量大、实施复杂的缺点,本文发展了一种基于非结构网格的数值模拟方法.该方法采用RKDG(RungeKutta Discontinuous Galerkin)方法的弱形式求解Euler方程,用强形式求解可压缩流场模拟中的Level Set方程,并用Simple Fix方法耦合两套方程的数值求解.二维多介质可压缩流的模拟表明:该方法成功地抑制了界面附近的非物理振荡,计算量小、实施简单,并可有效求解具有运动界面的多介质可压缩流动问题.     

简单流场中聚合物稀溶液的分子构象

介绍了研究聚合物分子模拟流变性质的Brown动力学模拟方法,提出利用FENE珠-簧链分子模型来确定聚合物稀溶液分子链在简单剪切流场下不同时刻位形的变化,并对分子链与流动方向的取向角和分子链在速度梯度方向上的构象厚度进行了计算。     

单回路液氦脉动热管气液两相流数值模拟

为了探究液氦脉动热管的传热机理,建立了单回路液氦脉动热管的二维数值模型。基于多相流VOF(Volume of Fluid)方法对该模型进行了数值求解,模拟了该液氦脉动热管的初始状态以及运行状态。其中初始状态为气液交替分布的饱和静止状态。运行状态为方向变化的脉动流动状态,流型为塞状流。分析了液氦脉动热管的流动与传热特性。     

Hyperbolic contraction measuring systems for extensional flow

In this paper an experimental method for extensional measurements on medium viscosity fluids in contraction flow is evaluated through numerical simulations and experimental measurements. This measuring technique measures the pressure drop over a hyperbolic contraction, caused by fluid extension and fluid shear, where the extensional component is assumed to dominate. The present evaluative work advances our previous studies on this experimental method by introducing several contraction ratios and addressing different constitutive models of varying shear and extensional response. The constitutive models included are those of the constant viscosity Oldroyd-B and FENE-CR models, and the shear-thinning LPTT model. Examining the results, the impact of shear and first normal stress difference on the measured pressure drop are studied through numerical pressure drop predictions. In addition, stream function patterns are investigated to detect vortex development and influence of contraction ratio. The numerical predictions are further related to experimental measurements for the flow through a 15:1 contraction ratio with three different test fluids. The measured pressure drops are observed to exhibit the same trends as predicted in the numerical simulations, offering close correlation and tight predictive windows for experimental data capture. This result has demonstrated that the hyperbolic contraction flow is well able to detect such elastic fluid properties and that this is matched by numerical predictions in evaluation of their flow response. The hyperbolical contraction flow technique is commended for its distinct benefits: it is straightforward and simple to perform, the Hencky strain can be set by changing contraction ratio, non-homogeneous fluids can be tested, and one can directly determine the degree of elastic fluid behaviour. Based on matching of viscometric extensional viscosity response for FENE-CR and LPTT models, a decline is predicted in pressure drop for the shear-thinning LPTT model. This would indicate a modest impact of shear in the flow since such a pressure drop decline is relatively small. It is particularly noteworthy that the increase in pressure drop gathered from the experimental measurements is relatively high despite the low Deborah number range explored.     

A fully explicit characteristic based split (CBS) scheme for viscoelastic flow calculations

In this paper, an explicit characteristic based split (CBS) scheme is proposed for the numerical solution of incompressible viscoelastic flow equations. The scheme proposed is free from simultaneous solution to the matrices arising from the finite element discretization of the governing equations. The experience gained from the solution of Newtonian fluid dynamics problems has been applied to the solution of viscoelastic flows. The Oldroyd‐B model has been employed to solve two benchmark problems of viscoelastic flow. They are viscoelastic flow past a circular cylinder and viscoelastic flow through planar contraction geometry. The results show that the solutions obtained are stable for the Weissenberg or Deborah number range studied in this paper. The solutions obtained at lower Weissenberg or Deborah numbers are accurate and agree excellently with the majority of available numerical data. However at higher Weissenberg or Deborah numbers, results show some sign of negative influence of the artificial dissipation added to the discrete constitutive equations. Copyright © 2004 John Wiley Sons, Ltd.     

Characteristic based split (CBS) meshfree method modeling for viscoelastic flow

A semi-implicit characteristic based split meshfree algorithm is proposed for the numerical solution of incompressible viscoelastic flow in the paper, in which the governing equations are discretized by element free Galerkin method in spatial space and the characteristic based split method is adopted in temporal space. In order to obtain stable and convergent solution at high Weissenberg number, streamline upwind method is chosen to tackle the convective terms in constitutive equations of viscoelastic flow. Meanwhile, mass lumped technique is adopted to accelerate computational efficiency. The method allows the equal order basis to approximate pressure, velocity and extra stress, especially the linear basis that is easy to implement. The planar Poiseuile flow and 4:1 planar contraction flow for an Oldroyd B fluid are investigated. Through these numerical experiments, we find that the method has good stability and the numerical results are in agreement well with those reported by other papers.     

应用声测法辨别车流状态的可行性

采用优化速度交通流模型进行数值模拟以捕获每辆车的信息，并根据声学推导出简化的噪声预测公式，进而应用此噪声预测公式计算点噪声声压级。将车流分布特征与噪声声压级变化进行比较，发现在探测路段，车流量－时间曲线与探测点声压级－时间曲线变化特征相吻合，说明在一定条件下可应用声测法来辨别车流状态。     

Steady and unsteady finite element analysis of incompressible viscous fluid

Finite element procedures and related illustrative numerical examples for incompressible viscous fluid motion are discussed in this paper. The steady flow problem is solved by the Newton–Raphson method and the perturbation method. By numerical examples, it can be shown that the combined use of the Newton–Raphson method and perturbation method is suitable. For the analysis of unsteady flow, the perturbation method is employed. Assuming that the basic flow is known, unsteady flow is calculated by accumulating the solution of the linearized equation in which the boundary values are varied by small amounts. Steady flows of temperature dependent free convection are also discretized and analyzed by the same procedure as the conventional finite element Galerkin method. For shape functions, quadratic polynomials are used for velocity and temperature, and linear polynomials for pressure. It is to be noted that the selections of shape functions and solution method are the keys to the analysis of highly non-linear fluid flow problems such as those discussed in this paper.     

Erosion rate correlations of a pipe protruded in an abrupt pipe contraction

Erosion is one of the most serious problems in various gas and liquid flow passages such as flow in pipes, pumps, turbines, compressors and many other devices. Sand presence causes loss of pipe wall thickness that can lead to pipe erosion, frequent failures and loss of expensive production time. The importance of this problem is mainly due to many related engineering applications, viz. heat exchangers. In order to reduce the frequency of such pipe erosions, caps in the form of replaceable pipes are protruded in the sudden contraction regions which are exposed to most of the serious erosion rates. In the present work, numerical investigation of the erosion of a pipe protruded in a sudden contraction is presented. The turbulent, steady, 2-D axi-symmetric flow inside an axi-symmetric abrupt contraction pipe with a pipe protrusion embedded in it was solved by steady-state time averaged conservation equations of mass and momentum along with two equation model for turbulence. Particles are tracked using Lagrangian particle tracking. An erosion model was employed to investigate the erosion phenomena for the given geometry. The influence of the different parameters such as the inlet flow velocity (3–10 m/s), the particle diameter (10–400 μm), the protruded pipe geometry (thickness T=1–5 mm and depth H=2–5 mm) and the pipe contraction ratio (Cr=0.25–0.5) on the erosion of pipe protrusion was investigated. Correlations for the influence of inlet flow velocity, depth and thickness of the protruded pipe on the erosion rate are presented.     

Periodic Galerkin finite element method of tidal flow

This paper presents the finite element method of the analysis of tidal flow. Assuming that tidal flow is periodic, the Galerkin approach is employed as the numerical integration procedure in time using a trigonometric function as the interpolation function. The present method has shown to be suitable for computation especially from the point of computing time and numerical stability.     

Piston-driven laminar flow and heat transfer in a plane channel with a sudden expansion

 This paper presents a numerical study of piston-driven heat transfer and fluid flow in a plane channel containing a sudden expansion. The numerical method employed is based on a control-volume-based finite element method for incompressible flow with a staggered and moving grid and SIMPLER algorithm for pressure-velocity coupling. The numerical results show a good agreement with the experimental data reported in the literature. Results concerning time and space evolution of the thermal and flow fields are presented for different values of the expansion ratio, the initial clearance volume, and the piston velocity. Received: 20 April 2002 / Accepted: 23 January 2003     

水工闸门垂直水动力计算方法

为了解决水工闸门在启闭过程中垂直水动力的计算方法问题,将垂直水动力分为闸门开启过程中的下吸力和关闭过程中的上托力。首先,在闸门开启过程中,闸门底缘水流的压力能会转化为动能,而在同一开度下流过闸孔的流量又是常量,这就造成了过水断面在闸门底缘处的收缩,流体与闸门底缘分离,当外界补气不充足时,在闸门底缘部位将形成一定真空度,这部分真空度则是造成下吸力的主要原因。其次,在闸门关闭过程中,闸门对水流的阻断以及闸门底缘对水流流向的改变是导致上托力产生的主要原因。最后,该文应用下吸力和上托力的作用原理并结合水流的能量和动量方程提出了闸门启闭过程中下吸力和上托力的计算方法。同时,利用经积石峡水电站试验数据验证后的数值模型进行仿真分析,结果表明：下吸力和上托力计算方法所得结果与仿真结果吻合较好。     

变截面管道内流噪声预报与实验测量

应用大涡模拟(LES)时域CFD方法计算变截面管道内的气流噪声,对于突缩和突扩管道,CFD计算结果和实验测量结果吻合较好,进而研究了不同的过渡形式对变截面管道内部流噪声的影响,为变截面管道的低噪声设计提供依据。