非正交曲线坐标S_1流面流函数反问题松弛计算

本文在文献[1—3]工作的基础上,从叶轮机械S_1流面反问题提法之一(给定叶栅吸力面速度分布及叶片厚度分布求解叶型坐标)出发,推导了流函数反问题主方程及有限差分方程.这方程是以计算网格坐标为主变量的二阶偏微分形式的动量方程,解决了文献[4—7]所未能解决的使用有旋的运动方程求解的问题.此方程与有旋的S_2流面流函数方程的一致性保证了叶轮机械三元求解的收敛性.进一步完善了叶轮机械使用两类流面的三元流设计方法.编制了计算机程序对典型的叶型作了计算例子,结果是理想的.     

混流叶轮S2流面的展向掺混模型与应用

本文在S2流面流动方程中加入了"展向掺混"模型,模拟叶栅端部二次流动、湍流扩散等对局部低动量流体的展向输运效应。方法用于混流叶轮内流动分析,结果表明:由于混流叶轮子午流道的大曲率,叶轮端部的低动量流体在展向的扩散远大于轴流叶栅,叶轮出口的展向均匀化趋势更加明显。合理的选择掺混扩散系数,可以获得与三维N-S计算的周向平均值类似的子午面分布,从而提高了S2流面分析和设计的可靠性。     

非正交座标S_1流面流函数跨音松弛计算

本文在吴仲华教授的叶轮机械三元流动理论的基础上,推导了非正交曲线座标系下的叶轮机械流函数方程及有限差分方程的通用形式.这些方程可用于平面、任意迥转面及任意翘曲的S_1或S_2流面的跨音及亚音流场计算。数值求解中采用了混合差分格式线松弛计算方法。采用了密度预测法由流函数值唯一确定了密度值,解决了流函数方程求解跨音流场的困难,用此方法编制了计算机程序并作了计算,所得结果与实验结果比较一致。     

轴流压气机环壁边界层的流量堵塞效应

本文讨论了轴流压气机环壁边界层的计算,它对流量的堵塞效应和在S_2流面计算中对此进行合理修正的方法.首先介绍了一种适合于叶轮机械设计和分析用的边界层的计算方法.在此基础上进行了主流与边界层的迭代计算。对三种迭代方案进行了比较.本文给出了一台单级和一台十级轴流压气机的算例以及计算与激光测量结果的比较.     

使用非正交曲线坐标与速度分量S_2流面跨音速流函数解

基于叶轮机械两类流面迭代计算理论,在非正交曲线坐标上建立了S_2流面上弱守恒型流函数方程.使用人工密度修正方法求解S_2流面跨音流动正问题,用速度积分方法避免了密度双值问题,并编制了相应的计算机程序.     

透平准三元设计中S_2流面计算探讨

一、引言 自从吴仲华教授创立的叶轮机械三元流动理论广泛应用于叶轮机械的气动设计以来,S_1、S_2两类流面的三元迭代求解方法有了迅速发展。在准三元迭代计算中,由于流线在子午面投影是连续的,若给定远方进、出口参数及间隙站环量,就可一次解出多级叶片中心S_1流场,而S_2流面由于动静叶间有相对运动,在稳定流动下只能计算一有前后延伸空段的单排叶片段,且此延伸空段的参数是多级中心S_2流面计算所没有的。因此为S_1流     

轴流式压气机两类流面迭代三元完全解

本文根据文献[1]提出的三元流动通用理论,使用两类流面的交替迭代求解三元流场的方法,在已有的S_1和S_2流面计算机程序的基础上,建立起一个数值求解叶轮机械三元流场的完整体系。本文算例的收敛过程和计算结果充分证明了用两类流面交替迭代方法求解三元流场的有效性。     

叶轮机械内的三元流动解法——“流面坐标”迭代法

从吴仲华教授最早提出的两类流面交叉求解三元流动的理论出发,本文给出一种任意通流截面上的“流面坐标”迭代法,采用适合各类叶轮机械的两组非正交流面坐标,以及沿这两组坐标方向速度梯度方程的迭代求解,得到了叶轮机械内部的完全三元流场。 计算实例给出了均为扭曲的两类流面形状,并与普通的二元流面解进行了比较,在一个试验过的离心压气机叶轮的计算中还与测量结果进行了比较,结果是满意的.     

CAS压气机跨声速流场主流-边界层准三元迭代解

本文在S_2/S_1流面准三元迭代的基础上,建立了S_1流面和S_2流面的主流-边界层迭代汁算方法,以及S_2/S_1流面之间的无粘-粘性准三元迭代系统,首次完成了跨声速压气机流场的中心S_2流面和六个S_1流面之间的主流-边界层迭代计算,得到了无粘-粘性准三元迭代解.本文为进行跨声速压气机流场无粘-粘性准三元迭代提供了工程实用的计算方法,扩大了两类流面理论在叶轮机械粘性流动计算中的应用.     

开式轴流风扇气动噪声预测

本文采用LES/FW-H的匹配方法,研究了开式轴流风扇内部旋涡流动特征及其与叶片表面干涉引起的气动噪声之间的联系,同时进行了远场噪声预测,探讨了叶轮不同表面辐射噪声时的频谱分布特征.研究结果表明,开式轴流风扇吸力面附近形成的叶尖涡和前缘分离涡在吸力面叶片表面相应位置形成大压力波动,形成主要噪声源;叶片吸力面的辐射噪声可以通过改善吸力面附近的旋涡流动来降低;低速轴流叶轮由叶轮壁面辐射的噪声以宽频成分为主.     

Vertical Sediment Concentration Distribution in High-Concentrated Flows: An Analytical Solution Using Homotopy Analysis Method

Transport of suspended sediment in open channel flow has an enormous impact on real life situations, viz. control and management of reservoir sedimentation, geomorphic evolution such as dunes, rivers, and coastlines etc. Transport entails advection and diffusion. Turbulent diffusion is governed by the concept of Fick's law, which is based on the molecular diffusion theory, and the equation that represents the distribution of sediment concentration is the advection-diffusion equation. The study uses the existing governing equation which considers different phases for solid and fluid, and then couples the two phases. To deal with high-concentrated flow, sediment and turbulent diffusion coefficients are taken to be different from each other. The effect of hindered settling on sediment particles is incorporated in the governing equation, which makes the equation highly non-linear. This study derives an explicit closed-form analytical solution to the generalized one-dimensional diffusion equation representing the vertical sediment concentration distribution with an arbitrary turbulent diffusion coefficient profile. The solution is obtained by Homotopy Analysis Method, which does not rely on the small parameters present in the equation. Finally, the solution is validated by comparing it with the implicit solution and the numerical solution. A relevant set of laboratory data is selected to check the applicability of the model, and a close agreement shows the potential of the model in the context of application to high-concentrated sediment-laden open channel flow.     

Measurement of pressure distribution from PIV experiments

In this study, a non-staggered grid SIMPLER pressure solution algorithm, which is able to produce correct pressure distribution directly if correct velocities are given, is proposed to solve the pressure distribution for PIV experiments. The cell face pseudo velocity required in the pressure equation is approximated by a simple linear average of the adjacent nodal pseudo velocities so that the velocity and pressure are collocated without causing the checkerboard pressure distribution problem. In addition, the proposed pressure solution algorithm has the features that upwind effects of the convective terms are considered, boundary conditions are not required, and the pressure distribution obtained can be used to correct the velocity field so that the continuity equation is satisfied. These features make the present algorithm a superior method to calculate the pressure distribution for PIV experiments. The pressure field solved is realistic and accurate. The proposed pressure equation solver is first calibrated with a two-dimensional cavity flow. It is found that the results are almost identical to the exact solution of the test flow. The algorithm is then applied to analyze a uniform flow past two side-by-side circular cylinders in a soap film channel. With the velocity and pressure distributions successfully measured, the structures of the complex shedding flow patterns are clearly manifested.     

一阶不连续光学元件MRF流体动力学分析方法

一阶不连续光学元件的磁流变抛光问题是制约我国高精高效光学制造领域发展的难题之一,其涉及锥形、矩形等几何形貌元件的光学元件加工问题以及常见光学元件的边缘效应控制问题。提出了基于一阶不连续光学元件的磁流变抛光流体动力学方法,建立了该类元件抛光区域流体动力分析的理论方法和数值手段。首先,对磁流变抛光工况下的流场进行了合理假设,其次,从微元流体动力方程出发,建立了适用于一阶不连续面形的流场分析方法,最后,基于有限差分法和数值迭代方法建立了流场控制方程的数值计算方法。通过对切入距离为1~18 mm的抛光过程进行数值仿真,发现该方法所获取的一阶不连续面形的压力分布形态是正确的,产生的不连续压降与实验观测一致。     

轴对称荷电圆盘的静电势

讨论了电荷分布呈轴对称时圆盘的静电势问题。用方程法和延拓法求解了电荷分布为幂函数时的静电势,在原有的延拓法则之外,总结出新的补充法则。     

On the one-dimensional acoustic propagation in conical ducts with stationary mean flow

This paper proposes a direct time-domain calculation of the time-domain responses of anechoic conical tubes with steady weak mean flow. The starting point is the approximated linear one-dimensional wave equation governing the velocity potential for the case of steady flow with low Mach number. A traveling solution with general space-dependent propagation velocity is then proposed from which the inward and outward pressure and velocity impulse responses can be obtained. The results include the well-known responses of conical and cylindrical ducts with zero mean flow.     

Direct numerical simulation of electrohydrodynamic plumes generated by a hyperbolic blade electrode

This paper presents a numerical study of two-dimensional EHD flow occurring between a hyperbolic blade and a plate electrode. The whole set of coupled equations is solved: Navier–Stokes equations, Poisson equation and charge conservation equation. A finite volume approach designed for non-orthogonal structured grid is used to discretize all governing equations. An efficient numerical procedure based on total variation diminishing (TVD) scheme is implemented to compute the distribution of charge density. Two different injection laws are considered: a simple autonomous one and a non autonomous which relates the charge injected by the blade and the local electric field. The flow structure which results in an EHD plume analogous to a thermal plume, has also been successfully characterized numerically by the temporal evolution of the charge density distribution. Preliminary results indicate that the flow is characterized by two different regimes according the value of the applied voltage. The critical Reynolds number for which the transition between the steady and unsteady regimes occurs has been determined to be within the range Re = [1000, 1100].     

一维双流体模型的压力修正算法

针对一维双流体模型，通过推导双流体模型的压力修正方程，及相含率修正方程，将原本应用于单相不可压流动的压力修正系列算法推广至双流体模型求解，提出双流体模型的压力修正算法.在离散过程中运用高阶有界格式，在保证二阶以上精度的基础上克服了由相含率分布的阶跃所造成的数值结果非物理震荡.与公开发表算例进行对比，验证求解的可靠性.     

跨声速流函数方程强隐式解及确定密度场的新方案

基于人工可压缩性对密度的修正,本文用强隐式格式快速求解了非正交曲线坐标系下跨声速流函数方程;在流函数场解出后,通过求解一个由动量方程、能量方程和连续方程组合而成的关于密度的一阶偏微分方程来获得密度场,因此流函数解法中常遇到的密度双值问题在这里已不存在;通常所讲的完成流函数场{Ψ}与密度场{ρ}间的迭代在本文便体现在流函数主方程与这个新推出的一阶微分方程间的迭代计算上;几个典型算例表明了本方法的有效性。     

Numerical Simulations of Unsteady Flows from Rarefied Transition to Continuum Using Gas-Kinetic Unified Algorithm

Numerical simulations of unsteady gas flows are studied on the basis of Gas-Kinetic Unified Algorithm (GKUA) from rarefied transition to continuum flow regimes. Several typical examples are adopted. An unsteady flow solver is developed by solving the Boltzmann model equations, including the Shakhov model and the Rykov model etc. The Rykov kinetic equation involving the effect of rotational energy can be transformed into two kinetic governing equations with inelastic and elastic collisions by integrating the molecular velocity distribution function with the weight factor on the energy of rotational motion. Then, the reduced velocity distribution functions are devised to further simplify the governing equation for one- and two-dimensional flows. The simultaneous equations are numerically solved by the discrete velocity ordinate (DVO) method in velocity space and the finite-difference schemes in physical space. The time-explicit operator-splitting scheme is constructed, and numerical stability conditions to ascertain the time step are discussed. As the application of the newly developed GKUA, several unsteady varying processes of one- and two-dimensional flows with different Knudsen number are simulated, and the unsteady transport phenomena and rarefied effects are revealed and analyzed. It is validated that the GKUA solver is competent for simulations of unsteady gas dynamics covering various flow regimes.