无网格算法在多段翼型流动计算中的应用

研究了一种求解欧拉方程的无网格算法，发展出了一套布点及点云自动生成的方法；在点云离散的基础上，采用最小二乘法求解矛盾方程的方法来求取空间导数，进而获得数值通量；采用四步龙格-库塔方法进行时间推进，并引入当地时间步长和残值光顺等加速收敛措施。通过对NA-CA0012翼型的跨音速流动和多段翼型复杂绕流的数值模拟，验证了上述无网格算法的正确性和实用性。     

预处理方法在低速弹箭流场计算中的应用

基于Weiss-Smith预处理矩阵和全局截断预处理参数,采用有限体积方法对雷诺平均Navier-Stokes方程进行离散。对流项离散采用二阶线性重构和AUSM ＋-up格式,时间推进方法采用多重网格下的LU-SGS方法。结合M PI消息传递方法,建立了一套计算低速流动的并行数值方法。计算了低速椭球体的流场和气动力,压力系数和切应力系数计算结果与文献实验结果对比吻合度较好。生成了末敏弹的流场计算网格,对绕末敏弹流场进行了数值模拟。对多重网格下多进程的加速比和并行效率进行了测试,显示了程序良好的并行效率。计算的气动力结果与实验结果吻合。综合结果表明：本文的数值方法能够用于低速弹箭流场和气动力计算,为新型弹箭的设计和定型提供保证。     

翼型与风洞侧壁交接角区分离流动研究

运用Navier-Stokes数值模拟对翼型模型试验时风洞侧壁和翼型模型结合部拐角区黏型分离流动进行模拟,并将简单代数湍流模型扩展用于机翼/风洞侧壁拐角区流动.计算格式在空间上采用中心有限体积离散,在时间上采用多步Runge-Kutta时间步长格式进行积分.结果显示,在翼型模型风洞试验时,模型/侧壁拐角区、模型表面、侧壁表面和模型后形成复杂的黏性分离流动和二次分离,对实验结果产生很大的影响.     

数值模拟方法在体液流动研究中的应用与展望

计算流体力学的数值模拟技术产生于20世纪60年代,现已成功地应用到众多科学研究与工程设计领域. 从20世纪80年代开始,虽已有不少研究工作开始利用CFD方法与计算机技术对人体的血流、气管中的气流、胆汁流等流动进行数值模拟与分析,但并没有与器官功能分析和病理分析及临床应用紧密联系. 近十几年来,这方面的工作已经取得了长足的进步和发展,模拟出了譬如脑血管、颈动脉、心血管等复杂血管流动,甚至整个肺泡的活动,得到了非常有病理意义和临床价值的图像.本文介绍和评述计算人体流体动力学的历史,发展和已经取得的成果.      

液体双折射方法及其在流场测量中的应用

本文研究了流体双折射的实验方法及双折射液体的基本性质。计论了两种力学—光学关系式之间的一致性。从理论及实验上证实了用流体双折射方法进行二维流场测量的优越性。提出了实验数据的处理方法。给出了几种流场的等色线图。定量分析了两个流场。     

天然河流流场数值模拟的预处理方法

提出了求解一种二维原始变量湍流模型方程组的预处理方法。应用此方法对驱动方腔内的涡流及天然河流流场作了数值模拟计算，结果表明预处理方法具有较好的稳定性及较快的收敛速度，对天然河流流场的计算只有实用价值。     

多段翼型吹气流动分离控制研究

基于雷诺平均Navier-Stokes粘性流动方程,采用数值模拟方法,分析了吹气控制对多段翼型气动性能的影响,阐述了吹气改善多段翼型流动的机理。采用有限体积法对雷诺平均Navier-Stokes方程进行空间离散,时间方向推进采用二阶迎风格式,湍流模型采用SST k-ω模型。结果表明:在多段翼型基础上采取吹气控制可以获得很好的气动增升效果,三段翼型的最大升力系数可达4.98;吹气可改善多段翼型表面流动,减小其流动分离,增加升力;在同样的吹气口几何参数条件下,在一定范围内增大吹气动量系数可以提高多段翼型的升力系数;在多段翼型主翼后段和襟翼同时施加吹气流动控制可以获得更好的效果,升力系数比基本三段翼型(基本构型A)增加30.05%。     

微喷管流动粒子仿真与Navier-Stokes数值模拟比较研究

运用DSMC（Direct Simulation Monte—Carlo）方法从分子运动论层次对大膨胀比、喉部转角为尖角的微喷管流动现象进行模拟,考察来流总压对喷管性能的影响,并与Navier—Stokes方程运算结果、实验结果进行比较。研究表明：在模拟微型喷管的流动现象时,DSMC方法比N—S方程更加适用。     

一种改进混合迎风格式在翼型流场激波捕捉中的应用

波阻是飞行器超音速飞行的关键设计因素,精确捕捉激波在流场中的位置,是数值模拟含激波流场和精确计算波阻的一个重要研究内容.本文基于网格节点有限体积空间离散方法,采用AUSM格式与FVS格式的混合格式(MAUSM方法)计算对流通量,从而抑制在数值模拟流场出现的激波处振荡和过冲现象,确保AUSM准确捕获接触间断的特性和FVS格式捕捉激波的能力.本文使用MAUSM方法分别计算了在跨声速和超声速条件下的NACA0012翼型流场,并与中心差分格式的计算结果进行比较.结果表明,对于存在激波的翼型流场,MAUSM方法是有效的.     

90°弯管内流动的理论模型及流动特性的数值研究

从三维不可压缩雷诺时均Navier-Stokes方程出发,对90°弯曲管道内湍流流动进行数值模拟。网格划分采用六面体网格,湍流模型为RNGk-ε模型,在近壁区采用两层壁面模型进行修正,流场的计算结果与实验数据吻合较好。在此基础上,本文数值研究了来流方向对流场结构和流动特性的影响。得出在弯管流场中发生了分离现象,且随着来流侧滑角的增大,分离区范围增大。此外,随着来流从同一侧滑角变换至同一攻角时,横截面的二次流图像中也从具有两个对称主涡变成只具有一个主涡的现象。     

Van Leer格式在全速域范围的推广

通过对格式耗散项的修正将Van Leer格式推广至全速域流场求解范围.对格式耗散项的分析表明,在低马赫数流动情况下格式耗散项中不应包含声速项,以此为依据对Van Leer迎风分裂格式提出了耗散项的修正方法.结合对控制方程时间导数项的预处理,修正后的格式能够成功地模拟低速流动问题,同时在其他马赫数范围内也不损失格式的收敛...     

Low-diffusion preconditioning scheme for numerical simulation of low-speed flows past airfoil

The preconditioning technique can address the stiffness of a low Mach number flow, while its stability is poor. Based on the conventional preconditioning method of Roe's scheme, a low-diffusion scheme is proposed. An adjustable parameter is introduced to control numerical dissipation, especially over the dissipation in the boundary layer and extremely in a low speed region. Numerical simulations of the low Mach number and low Reynolds number flows past a cylinder and the low Mach number and high Reynolds number flows past NACA0012 and S809 airfoils are performed to validate the new scheme. Results of the three tests well agree with experimental data, showing the applicability of the proposed scheme to low Mach number flow simulations.     

Low-diffusion preconditioning scheme with linear cut-off parameter

A low-diffusion preconditioning Roe scheme with an adjustable parameter to control the numerical dissipation is proposed. This scheme reflects the real physical dissipation in the extremely low-speed region. The preconditioning parameter in scheme is improved by linear cut-off and correction factor. The numerical results of low-Mach-number/low-Reynolds-number steady solutions of viscous flows past a circular cylinder and past a NACA0012 airfoil show the efficiency of the new scheme.     

A collocated finite volume method for predicting flows at all speeds

An existing two-dimensional method for the prediction of steady-state incompressible flows in complex geometry is extended to treat also compressible flows at all speeds. The primary variables are the Cartesian velocity components, pressure and temperature. Density is linked to pressure via an equation of state. The influence of pressure on density in the case of compressible flows is implicitly incorporated into the extended SIMPLE algorithm, which in the limit of incompressible flow reduces to its well-known form. Special attention is paid to the numerical treatment of boundary conditions. The method is verified on a number of test cases (inviscid and viscous flows), and both the results and convergence properties compare favourably with other numerical results available in the literature.     

A COMPUTATIONAL METHOD FOR THE NAVIER-STOKES EQUATIONS AT ALL SPEEDS

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A parallel pressure implicit splitting of operators algorithm applied to flows at all speeds

A parallel implementation of the pressure‐based implicit splitting of operators (PISO) method is described and applied to both compressible and incompressible flows. The treatment of variables at the interfaces between adjacent blocks is highlighted, and, for compressible flow, a straightforward method for the implicit handling of density is described. Steady state and oscillatory flow through a sudden expansion are considered at low speeds for both two‐ and three‐dimensional geometries. Extension of the incompressible method to compressible flow is assessed for subsonic, transonic and supersonic flow through a two‐dimensional bump. Although good accuracy is achieved in these high‐speed flows, including the automatic capturing of shock waves, the method is deemed unsuitable for simulating steady state high‐speed flows on fine grids due to the requirement of very small time steps. Copyright © 2001 John Wiley & Sons, Ltd.     

A robust multi‐grid pressure‐based algorithm for multi‐fluid flow at all speeds

This paper reports on the implementation and testing, within a full non‐linear multi‐grid environment, of a new pressure‐based algorithm for the prediction of multi‐fluid flow at all speeds. The algorithm is part of the mass conservation‐based algorithms (MCBA) group in which the pressure correction equation is derived from overall mass conservation. The performance of the new method is assessed by solving a series of two‐dimensional two‐fluid flow test problems varying from turbulent low Mach number to supersonic flows, and from very low to high fluid density ratios. Solutions are generated for several grid sizes using the single grid (SG), the prolongation grid (PG), and the full non‐linear multi‐grid (FMG) methods. The main outcomes of this study are: (i) a clear demonstration of the ability of the FMG method to tackle the added non‐linearity of multi‐fluid flows, which is manifested through the performance jump observed when using the non‐linear multi‐grid approach as compared to the SG and PG methods; (ii) the extension of the FMG method to predict turbulent multi‐fluid flows at all speeds. The convergence history plots and CPU‐times presented indicate that the FMG method is far more efficient than the PG method and accelerates the convergence rate over the SG method, for the problems solved and the grids used, by a factor reaching a value as high as 15. Copyright © 2003 John Wiley & Sons, Ltd.     

A multiblock operator‐splitting algorithm for unsteady flows at all speeds in complex geometries

This paper describes a non‐iterative operator‐splitting algorithm for computing all‐speed flows in complex geometries. A pressure‐based algorithm is adopted as the base, in which pressure, instead of density, is a primary variable, thus allowing for a unified formulation for all Mach numbers. The focus is on adapting the method for (a) flows at all speeds, and (b) multiblock, non‐orthogonal, body‐fitted grids for very complex geometries. Key features of the formulation include special treatment of mass fluxes at control volume interfaces to avoid pressure–velocity decoupling for incompressible (low Mach number limit) flows and to provide robust pressure–velocity–density coupling for compressible (high‐speed) flows. The method is shown to be robust for all Mach number regimes for both steady and unsteady flows; it is found to be stable for CFL numbers of order ten, allowing large time steps to be taken for steady flows. Enhancements to the method which allow for stable solutions to be obtained on non‐orthogonal grids are also discussed. The method is found to be very reliable even in complex engineering applications such as unsteady rotor–stator interactions in turbulent, all‐speed turbomachinery flows. Copyright © 2004 John Wiley & Sons, Ltd.     

Contact problem of rubber rings with large deformation

A contact problem with friction between a rubber ring with large deformation and a linear elastic thin plate is solved by means of the substructuring technique in this paper. A study of the influence of fractional contact, of the influence of plate thickness on rubber ring’ deformation is presented.