摩托车液压减震器内部三维瞬态流场的研究

用CFD方法对摩托车液压减震器的内部流场进行了三维数值模拟。在参照某实际减震器结构和参数的基础上进行简化,用GAMB IT建立了三维几何模型并进行了网格的划分、细化。计算采用Re-alizable湍流模型并使用自定义函数UDF定义进口速度,通过仿真,获得了不同时刻下筒内的瞬时速度分布以及对应的总压分布图。结果表明,筒内流体运动速度越大,通过阻尼孔的液体速度也越大,阻尼孔前后两端的压力差也越大,活塞受到的阻尼力也越大。阻尼孔直径的改变对内部流场的影响,表现为随着阻尼孔直径减小,筒内湍流强度增强,减震效果呈指数型增强。

内燃机缸内湍流参数的实验测量

对ＴＹ１１００发动机在倒拖工况下缸内的湍流进行了测量，并用时间平均滤波方法对所测瞬时流动速度进行了数据处理，获取了非定常湍流的各种参数。

热压自然通风室内污染物浓度演变特性

为探究热压自然通风向稳态发展过程室内气态污染物的迁移规律,对不同高度处污染物浓度演化进行了分析.首先结合预测热分层瞬时变化的非均匀三层模型,针对室内不同的下层污染物混合特性,建立了均匀混合和纯置换两种热压自然通风室内污染物输送模型;其次,采用4阶龙格-库塔(Runge-Kutta)方法迭代求解,得到了通风过程室内污染物层高与浓度演变特性;最后,分析了有效通风面积和浮力组合系数对污染物浓度变化的影响.结果表明:垂直速度为0的界面与新鲜空气层界面是两个不同的分界面;有效通风面积越大,两者高度差的峰值越大,到达稳态所需时间越短;浮力组合系数越大,任意时刻两者高度差越大,且随有效通风面积的增大越发明显;下层污染物混合特性会影响污染物分层以及演变特性,但不改变稳定时刻污染物浓度分布,通风过程室内上层污染物浓度均要大于下层;纯置换模型下原有冷空气层污染物浓度随时间不断降低至定值,下层污染物浓度保持恒定,而上层污染物浓度在初始阶段急剧增大,后缓慢减低;均匀混合模型的上下层污染物浓度会缓慢衰减至定值;此外,增大有效通风面积可缩短污染物衰减时间,提高排污效率,而浮力组合系数对污染物浓度变化的影响则可忽略.

Flow characteristics of variable hydraulic transformer

A new kind of hydraulic transformer, called variable hydraulic transformer(VHT), is proposed to control its load flow rate. The hydraulic transformer evolves from a pressure transducer to a power transducer. The flow characteristics of VHT, such as its instantaneous flow rates, average flow rates, and flow pulsations in the ports, are investigated. Matlab software is used to simulate and calculate. There are five controlled angles of the port plate that can help to define the flow characteristics of VHT. The relationships between the flow characteristics and the structure in VHT are shown. Also, the plus-minus change of the average flow rates and the continuity of the instantaneous flow rates in the ports are presented. The results demonstrate the performance laws of VHT when the controlled angles of the port plate and of the swash plate change. The results also reveal that the special principle of the flow pulsation in the ports and the jump points of the instantaneous curves are the two basic causes of its loud noise, and that the control angles of the port plate and the swash plate and the pressures in the ports are the three key factors of the noise.

NUMERICAL ANALYSIS OF A FEM FOR A TRANSIENT VISCOELASTIC FLOW

We present the numerical analysis of a coupled method for the numerical simulation of transient viscoelastic flow obeying a differential constitutive equation with a Newtonian viscosity. The scheme used is based on Euler implicit method in time and maintains at each time step a couple of the velocity u and the viscoelastic part of the stress σ. Approximation in space is made by finite element method. The approximate stress, velocity and pressure are, respectively, P1-continuous, p2-continuous, and p1continuous. Upwinding needed for convection of σ is made by a 'Streamline Upwind Petrov Galerkin' method (SUPG).

Pseudo-Fluid Simulation of Transient Behaviors in a CFB Riser

The kinetic theory of granular flow (KTGF) is modified to fit the Einstein′s equation for effective viscosity of dilute flow. A pseudo-fluid approach based on this modified KTGF is used to simulate the dynamic formation and dissipation of clusters in a circulating fluidized bed riser. The agglomeration of particles reduces slip velocity within particle clusters, and hence results in two reverse trends: discrete particles are lifted by air while particle clusters fall down along the wall. The dynamic equilibrium of these two types of motion leads to the characteristic sigmoid profile of solid concentration along the longitudinal direction. The predicted solid velocity, lateral and longitudinal profiles of solid volume fraction and annulus thickness are in reasonable agreement with experimental results.

Utilization of Different Variables for the Visualization of Fluid Flows: Application to Instantaneous Channel Flows

The results of different numerical algorithms for the computation of unsteady fluid flows are used to visualize different variables of the flow. In particular, the instantaneous vorticity, velocity and pressure fields, along with streamline plots, are presented as a function of time inside a visualization window of the computational domain. The different forms of visualization are used to analyze the flow inside a two-dimensional channel incorporating an obstacle, which can represent several interesting flows such as the flow over electronic components, heat transfer devices and buildings.

Experimental study on the motion of a spherical particle in a plane traveling sound wave

We present an experimental study on the motion of a spherical droplet in a plane traveling sound wave.The experiments were performed in the test section of a tunnel with two loudspeakers at the two ends of the tunnel.By adjusting the amplitude ratio and the phase difference between the two speakers,a plane traveling sound wave field can be achieved in the test section of the tunnel,which we checked by measuring the amplitudes and phases of the sound pressure along the tunnel and by simultaneously measuring the velocity field of the air flow at three different locations in the tunnel.When a liquid droplet was introduced in the test section,the motion of the droplet and the velocity of the air flow around the droplet were recorded by high speed cameras,from which we analyze and obtain the ratio of the velocity amplitudes and the phase difference between the particle motion and the fluid motion.The experimental data confirm the theoretical result from the wave equations in the long-wavelength regime,i.e.,when the particle size is much smaller than the wavelength.Moreover,we showed that in this regime,the theory on particle motion in an unsteady uniform fluid,when the history term is included,also yields the same results that are in agreement with the experimental data and the wave equation.Our result extends the parameter range over which the theory on particle motion in unsteady fluid is checked against experiments,especially to the range of particle-fluid density ratio that is of important practical applications.