变截面谐振管内驻波非线性研究

基于整体轴向谐振激励下求解变截面谐振管内非线性驻波的间断Galerkin方法,研究了圆锥形谐振管内非线性驻波稳态时的瞬态特性。在圆锥形谐振管中,能够获取到无冲击的非线性驻波,验证了本方法计算圆锥形谐振管内非线性驻波的正确性,并通过提高局部逼近阶N,改善了压力波形两端的数值振荡;研究了加速度幅值a0、频率f、初始压力P0对非线性驻波压力波形和谐振管内流体流速的影响,为实现谐振管内非线性驻波应用于强声密封提供了有益思考。     

谐振管内非线性驻波的二维间断Galerkin计算方法

基于柱坐标下的二维瞬态可压缩Navier-Stokes方程、理想气体状态方程以及保强稳定的Runge-Kutta方法,提出了求解谐振管内非线性驻波的二维间断Galerkin计算方法。通过处理边界条件以及采取局部时间步长,利用所提出的二维间断Galerkin计算方法对圆柱形谐振管内非线性驻波进行求解,得到了谐振管内压力空间分布以及压力波形、速度波形、密度波形等物理特性,证明时间域、空间域内均产生激波,从而使压力幅值和密度幅值无法进一步提升;同时研究了激励加速度幅值对谐振管内非线性驻波压力波形及非稳态进程的影响。     

圆柱形谐振管内非线性驻波的有限体积计算方法

提出一种用于求解圆柱形谐振管内非线性驻波的有限体积计算方法。谐振管内初始为自由状态的流体被整体谐振激励,当激励频率与谐振管内声场固有频率一致时,谐振管内将产生非线性驻波。建立整体振动条件下谐振管内瞬态可压缩热粘性牛顿流体的一维Navier-Stokes模型方程的积分方程;在时域上,通过SIMPLEC方法(以压力为基础的有限体积法)和交错网格技术推导出离散化代数方程组,并进行求解。当谐振管内的流体为R-12气体,在整体振动的条件下,利用提出的方法对谐振管内的非线性驻波进行求解,通过与现有文献中伽辽金方法的计算结果进行对比,所得到的非线性驻波声压在波形和幅值方面都与这些结果非常吻合,从而验证了该方法的可行性。得到谐振管左端处的绝对压力波形、温度波形和声压频谱响应等物理特性分布;同时得到谐振管内不同位置处的速度变化,发现在谐振管两端出现了速度钉状波形;有限体积计算方法为解决强声密封的非线性驻波的数值计算奠定了良好基础。     

谐振管内非线性驻波的二维有限差分计算方法

谐振管内非线性驻波的数值计算方法是目前强声密封研究的关键技术。基于三个气体动力学方程推导得出一个关于无旋可压缩牛顿流体的非线性波动方程,并通过对非线性波动方程进行有限差分离散化处理,提出求解谐振管内非线性驻波的二维有限差分计算方法。通过边界条件的处理,使所推导的二维有限差分计算方法能够在整体谐振激励作用下计算谐振管内非线性驻波。在圆柱形谐振管内部填充Refrigerant-12作为工作媒质以及整体谐振激励的条件下,利用所提出的二维有限差分计算方法对圆柱形谐振管内的非线性驻波进行求解,并得到圆柱形谐振管内绝对压力波形、声压频谱响应以及谐振管内的声压空间分布。通过与现有仿真方法的计算结果和现有试验结果进行对比,所得到的计算结果无论从波形还是数值上都能与这些结果吻合,从而验证了该方法的可行性。该方法为强声密封的非线性驻波计算研究奠定了良好基础。     

热声制冷机谐振管形状对管内声场分布的影响

热声制冷机中谐振管截面的几何尺寸是比较重要的参数,因此通过建立各截面形状谐振管内三维声场模型,分析不同形状谐振管内声场的声压分布,对于提高热声制冷机的性能具有重要意义。利用声学有限元分析软件ACTRAN(学生版)与Ansys Workbench,分别对长度相同的圆柱形、圆锥形、渐缩变截面管、凹曲线回转体以及凸曲线回转体内声场进行分析。比较当入口口径与出口口径比例相同情况下,截面曲线变化对谐振管的活塞振动模态频率、声压幅值产生的影响,以达到实现提高活塞振动频率和声压幅值最大化的目的。结果表明:对于热声制冷机结构微型化的需求,在相同激励条件下采用圆锥形谐振管,活塞振动模态幅值最大,同时能产生较高声强。     

真空管道超级列车激波簇结构研究

真空管道列车高速飞行时产生的激波簇对于车辆结构气动外形设计具有重要的指导作用。鉴于真空管道超级列车现有试验设备及方法的局限性,根据可压缩N-S方程和SST k-w湍流模型,基于计算流体动力学(Computational fluid dynamics,CFD)流体分析软件,结合动网格和动态自适应网格两种方法,对超级列车在高真空度管道中高速运动时产生的流场结构进行数值仿真,主要研究列车以1 250 km/h的速度在阻塞比为0.2、环境压力为10.132 5 Pa(0.000 1 atm)的管道中飞行时所产生的一系列激波簇结构及管内流场变化规律。研究结果表明,管内列车在管内飞行时产生弓形激波、正激波、反射激波、Lamda激波、菱形激波等激波簇结构;头车附近区域会出现弓形激波、反射激波向正激波转化的过程,中间车附近区域会出现反射激波、菱形激波产生、发展与消失的过程,尾车附近区域会出现Lamda激波、反射激波、菱形激波、正激波的发展过程。     

基于Fluent的指数管内二维声流场特性研究

采用Fluent软件模拟研究了m=2.2的指数型热声谐振管内二维非线性声流场特性。通过与两种圆柱型直管的比较,验证了指数管具有提高声压和抑制高次谐波的能力,并对指数管内声场流场特性进行了分析。研究发现:指数管能显著提高管内压力,获得较大压比,能有效地抑制高次谐波;同时,指数管内声场的压力节点偏离了中心位置并存在可观的二次谐波,表现出非线性声振荡特征,并且流场中会发生"速度环形效应"。     

高压水射流清洗设备异形喷嘴内部流场的性能研究

喷嘴是高压水射流清洗设备终端的重要执行元件,针对圆锥形和棱锥形两种不同结构形式的喷嘴,利用流体力学的计算方法对其高压水射流流场的压力、轴向速度、及孔口出口处的湍流动能进行了数值模拟分析,并对两种喷嘴进行了比较。结果表明,虽然棱锥形喷嘴具有较好的聚集流束的作用,但在同样流量的情况下,其内部流场的压力变化梯度较大,出口速度远大于圆锥形喷嘴,且出口湍流动能较大,流动稳定性弱于圆锥形喷嘴。     

基于ANSYS的热声制冷机谐振管内声场仿真分析

利用有限元数值模拟分析方法,分别对长度相同的圆柱形、圆锥形、渐缩变截面管、凹曲线回转体以及凸曲线回转体内声场进行分析。结果表明:对于热声制冷机结构微型化的需求,在相同激励条件下采用圆锥形谐振管,活塞振动模态幅值最大,同时在小端能产生较高声强。     

壁面边界温度对指数管内声场的影响

采用计算流体力学软件Fluent对10组不同壁面边界温度情况的谐振管的形状参数m=2.2型指数管内二维非线性声场进行了模拟研究,探索了壁面边界温度对指数管内声场的影响。研究分析了不同壁面边界温度下管内声压和压比的变化规律,发现管内声压最大和压比最大的情况分别出现在不同的壁面边界温度条件下,但当上、下壁面边界温度均为328K时,指数管封闭端能同时获得较大声压幅值和压比。     

Thermoelastic damping in cylindrical shells with application to tubular oscillator structures

Thermoelastic vibration and damping of cylindrical shell structures is studied in this paper. The general thermoelastic coupled equations for cylindrical thin shells are presented first. Since the general governing equations are quite complicated, they are then simplified with Donnell–Mushtari–Vlasov approaches for the cylindrical shells under transverse deflection-dominated vibrations. By solving the simplified thermoelastic equations with Galerkin method, the approximate solutions for thermoelastic damping in a cylindrical shell structure are obtained. The solutions are suitable for the predictions of thermoelastic damping of tubular oscillator structures. Some numerical examples for micro- or nano-tube resonators are provided to illustrate the results.     

Assessment of a high-order discontinuous Galerkin method for vortex convection and wave propagation on unstructured meshes

A high-order accurate flow solver based on a discontinuous Galerkin method has been developed for the numerical simulation of vortex convection and wave propagation on unstructured meshes. To assess the performance of the present flow solver, a vortex convection problem in freestream and an acoustic benchmark problem were tested. An airfoil-vortex interaction problem was also simulated by coupling the flow solver with a dynamic mesh adaptation technique. From the mesh resolution test, the present fourth-order discontinuous Galerkin method almost perfectly preserves the vortex and also accurately resolves the acoustic waves on a mesh with an element size of half of characteristic length. It was also observed that the fourth-order method is more than ten times efficient, in terms of the number of degrees of freedom and the elapsed CPU time, compared to the second-order method.     

二次曝光全息照相干涉仪及其在冲击波观测中的应用

本文简要阐述了全息照相术的原理及会聚冲击波的特点,在此基础上,设计了一种二次曝光全息照相干涉系统,使用该系统对圆柱形冲击波会聚过程的不稳定性进行了观测,得到了清晰的干涉图像,给出了几个重要结论。     

Modelling one-dimensional unsteady flows in ducts: Symmetric finite difference schemes versus galerkin discontinuous finite element methods

The Euler equations for one-dimensional unsteady flows in ducts have been solved resorting to classical symmetric shock-capturing methods with second-order accuracy and to the recent discontinuous Galerkin finite-element method, with second- and third-order accuracy. In particular, the finite difference techniques adopted are the two-step Lax—Wendroff method and the MacCormack predictor—corrector method, with the addition of the flux corrected transport (FCT) or of the Davis nonupwind TVD scheme to suppress the spurious oscillations in the vicinity of discontinuous solutions. The finite-element method adopted is based on the weak formulation of the Euler equations, which are solved by introducing a discontinuous finite-element space discretization. A dissipative mechanism has been considered to supplement the FEM with a “discontinuity capturing” operator, adding a “viscous like” term to damp minor numerical overshoots arising in proximity of steep gradients of the solution. The numerical tests chosen to carry out a comparison between these schemes are the shock-tube problem and the shock—turbulence interaction problem. Both the test cases considered show the superiority of third-order FEM calculations, whereas the comparison between the computer run times points out the greater computational effort required.     

The self-induced oscillations of the under expanded jets impinging upon a cylindrical body

The present study addresses the flow characteristics involved in the self-induced oscillations of the underexpanded jet impinging upon a cylindrical body. Both experiment and computational analysis are carried out to elucidate the shock motions of the self-induced oscillations and to find the associated major flow factors. The underexpanded sonic jet is made from a nozzle and a cylindrical body is placed downstream to simulate the impinging jet upon an obstacle. The computational analysis using TVD scheme is applied to solve the axisymmetric, unsteady, inviscid governing equations. A Schlieren system is employed to visualize the self-induced oscillations generated in flow field. The data of the shock motions are obtained from a high-speed video system. The detailed characteristics of the Mach disk oscillations and the resulting pressure variations are expatiated using the time dependent data of the Mach disk positions. The mechanisms of the self-induced oscillations are discussed in details based upon the experimental and computational results.     

Heat transfer and resistance characteristics of conical spiral tube bundle based on field synergy principle

Conical spiral tube bundle are universally used in heat transfer enhancement in heat exchangers.The heat transfer and resistance of the tube bundle are affected greatly by the conical structure,so the ...     

具有孔道沉槽的滑阀过流面积分析

多路阀以其高集成度被广泛应用于工程机械领域,其中阀口形式对多路阀流量控制特性具有重要影响。对于阀体上开有孔道沉槽、节流面为常见的圆柱面和圆锥面两种滑阀阀口形式的多路阀,根据其结构特征及内部流场压力分布和速度变化情况,利用等效阀口面积理论,推导了圆柱面阀口和圆锥面阀口过流面积计算公式。利用流场仿真对计算结果进行了修正,采用实验手段验证了计算结果的准确性。研究结果对滑阀阀芯的多路阀设计及性能预测具有一定参考价值。     

A new algorithm for solving the multi-indentation problem of rigid bodies of arbitrary shapes on a viscoelastic half-space

In this paper the contact problem between rigid indenters of arbitrary shapes and a viscoelastic half-space is considered. Under the action of a normal force the penetration of the indenters changes and a few contact areas appeared. We wish to find the relations which link the pressure distribution, the resultant forces on the indenters and the penetration on the assumption that the surfaces are frictionless. For indenters of arbitrary shapes the problem may be solved numerically by using the matrix inversion method, extended to viscoelastic cases [1]. But when the problem involves a large number of points the matrix inversion method can become very time-consuming. Here the problem is solved using an alternative scheme, called the two-scale iterative method. In this method the local matrix inversion method is used at the micro-scale for each contact area to compute the pressure distribution taking into account interacting effect (the forces on the other contact areas which can be calculated at the macro-scale) between indenters. Two algorithms were proposed. The first algorithm takes into account the distribution of forces on the other contact areas and the second is the approximation of the first algorithm and takes into account the resultant forces on the other contact areas. The method was implemented for a simple configuration of seven spherical indenters, seven spherical-ended cylindrical indenters and seven flat-ended cylindrical indenters as well as for a more complex configuration of 12 randomly positioned indenters of arbitrary shapes: spherical-ended cylindrical, flat-ended cylindrical, conical and cylindrical indenters (finite cylindrical shape with its curved face). This last case is more difficult as the indenting geometry does not have an axisymmetric profile. For all these cases the two-scale iterative method permits to find the pressure distribution and the contact forces versus the penetration. It can be validated by comparing the numerical results to the numerical results obtained with the matrix inversion method.