水中激波聚焦的数值模拟

本文利用修正的ＣＣＷ方法，计算了在椭球反射腔中的水激波聚焦行为，并与实验进行比较，所得结果与实验很好地吻合。     

水中激波聚焦的数值模拟

本文利用修正的ＣＣＷ方法,计算了在椭球反射腔中的水激波聚焦行为,并与实验进行比较,所得结果与实验很好地吻合。     

叶栅内部粘性流场的数值模拟

提出了一种求解叶栅内部粘性流场的新方法,并用该方法求解了任意曲线坐标系下的时间相关Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程,该方法采用有限体积离散,对无粘通量采用Ｃｈａｋｒａｖａｒｔｈｙ－Ｏｓｈｅｒ的三阶精度ＴＶＤ格式,对粘性通量采用中心差分格式;并且在边界处理上采用直接将边界条件施加于物理边界上的方法,使得边界条件更加符合真实情况,对叶栅内部粘性流场的计算表明,该方法能够反映叶栅内部的流动情况。     

带活门轴对称变截面管道中强激波的传播特性

研究了核爆炸环境下带活门轴对称变截面管道中非理想气体激波的传播特性,并讨论了在其传播过程中电离和离解效应的影响．通过利用TVD格式和时变非均匀网格对模型进行的数值模拟表明,在理想模型中波前压强的变化不会对无量纲结果产生影响,但在非理想模型中却会导致无量纲结果的较大变化,而且入射激波的波峰越陡,到出口处波峰被抹平的幅度越大,活门的消波效果理想．通过对一维和二维计算结果的比较指出了一维计算的缺陷所在,而数值计算和近似估算结果的比较验证了近似估算公式的正确性．     

含脱体激波流场的数值模拟仿真

利用经典的质点网格法进行了含脱体激波的超音速流动的数值模拟，绘出了形象直观的超音速流动图画，且模拟流场中的各项参数与实验符合较好，为今后进一步探讨复杂形状物体的超音速运动提供了基础．     

基于分块网格技术的潜艇粘性绕流场数值计算研究

文章首先建立了全附体潜艇的几何模型,基于分块网格技术耦合生成了全附体的SUBOFFAFF-8潜艇外流场高质量结构化网格,采用RANS雷诺时均方法和SST k-ω湍流模型,并基于有限体积法(FVM),对潜艇粘性绕流场进行了数值计算研究.给出了潜艇纵中剖面线上压力系数、壁面剪应力系数,指挥台围壳和上尾翼表面三个不同高度处压力系数的纵向分布,以及模型总阻力的数值计算结果;并与DTMB水池试验结果进行了对比.结果表明,文中采用的数值模拟方法精度较高,合理有效,为深入研究全附体潜艇粘性绕流场奠定了基础.     

复杂边界水流高分辨率数值模拟

将基于流向量分裂技术的两步有限体积分量方向TVD格式应用于求解浅水方程的控制方程,建立了高分辨率的计算模型.实际算例表明,该模型能较好地计算浅水流动问题,为浅水流动数值模拟提供了精度高、稳定性好的数值计算模型.     

用PLM格式进行喷管内瞬态激波的数值模拟

在喷管流动问题的数值模拟中,激波的捕获一直是一个研究的重要方面.本文应用二阶精度Godunov型的PLM格式来求解Euler方程,采用非结构化网格,对喷管内瞬态激波的运动及发展进行了研究,并分析激波运动、反射、衍射及相互作用的规律.计算结果表明,PLM法可以用于非结构网格的喷管流场计算中,所得到的数值解较好地反映了瞬态激波结构的有关特征和信息.     

间断洪水波高精度数值模拟与应用

基于守恒型浅水二维方程,采用三单元模板的加权本质无震荡(WENO)格式插值界面两侧守恒变量,并采用Roe方法计算界面处数值通量,建立了平面二维溃坝水流数学模型.为使模型总体精度不致因为时间离散而降低,源项采用三阶Runge-Kutta方法进行处理,时间步进采用自适应步长法.验证结果表明数学模型计算结果与精确解基本一致,间断处数值解无明显震荡,具有高分辨率和高精度.数学模型应用于坝体溃决后水流在干河床上运动、河道部分堤防溃决后水流同时在河道以及洪泛区的演进过程以及天然复杂地形条件下实际工程溃堤方案的比选等预测计算.     

Numerical simulation of unsteady cavitating flows around a transient pitching hydrofoil

The objective of this paper is to improve the understanding of the influence of multiphase flow on the turbulent closure model,the interplay between vorticity fields and cavity dynamics around a pitching hydrofoil.The effects of pitching rate on the subcavitating and cavitating response of the pitching hydrofoil are also investigated.In particular,we focus on the interactions between cavity inception,growth,and shedding and the vortex flow structures,and their impacts on the hydrofoil performance.The calculations are 2-D and performed by solving the incompressible,multiphase Unsteady Reynolds Averaged Navier Stokes(URANS)equations via the commercial CFD code CFX.The k-SST(Shear Stress Transport)turbulence model is used along with the transport equation-based cavitation models.The density correction function is considered to reduce the eddy viscosity according to the computed local fluid mixture density.The calculation results are validated with experiments conducted by Ducoin et al.(see Computational and experimental investigation of flow over a transient pitching hydrofoil,Eur J Mech/B Fluids,2009,28:728–743 and An experimental analysis of fluid structure interaction of a flexible hydrofoil in various flow regimes including cavitating flow,Eur J Mech B/fluids,2012,36:63–74).Results are shown for a NACA66 hydrofoil subject to slow(quasi static,6°/s,*0.18)and fast(dynamic,63°/s,*1.89)pitching motions from=0°to=15°.Both subcavitaing(=8.0)and cavitating(=3.0)flows are considered.For subcavitating flow(=8.0),low frequency fluctuations have been observed when the leading edge vortex shedding occurs during stall,and delay of stall is observed with increasing pitching velocity.For cavitating flow(=3.0),small leading edge cavities are observed with the slow pitching case,which significantly modified the vortex dynamics at high angles of attack,leading to high frequency fluctuations of the hydrodynamic coefficients and different stall behaviors compared to the subcavitating flow at the same pitching rate.On the other hand,for the fast pitching case at=3.0,large-scale sheet/cloud cavitation is observed,the cavity behavior is unsteady and has a strong impact on the hydrodynamic response,which leads to high amplitude fluctuations of the hydrodynamic coefficients,as well as significant changes in the stall and post-stall behavior.The numerical results also show that the local density modification helps to reduce turbulent eddy viscosity in the cavitating region,which significantly modifies the cavity lengths and shedding frequencies,particularly for the fast pitching case.In general,compared with the experimental visualizations,the numerical results with local density correction have been found to agree well with experimental measurements and observations for both slow and fast transient pitching cases.     

粘性流体圆柱绕流的有限元模拟

对粘性流体圆柱绕流进行了数值模拟。根据三阶Taylor展开弱解的概念,在二阶分裂步Taylor-Galerkin有限元法基础上,采用时间推进和张量分析的方法推导了对流扩散通用微分方程的ETG有限元离散格式。对Reynolds数为32、102和250的粘性流体圆柱红流流场进行了数值仿真,数值模拟结果与实验结果吻合良好。表明隐含流线迎风耗散作用并具有三阶部分展开的Taylor-Galerkin有限元法稳定性好,精度较高,可用于计算包含对流扩散耦合传递动量的绕流问题及类似的流动问题。     

低速流场中的声传播模拟

为了研究流噪声的产生机理,且考虑介质粘性和流场对声传播的影响,采用分解法对低速流场中的声传播进行数值模拟.基于非结构化网格,采用有限体积法对时域上低速流的声传播问题进行研究.把可压缩N-S方程分解成不可压N-S方程和声扰动方程,并采用SIMPLE算法来求解声扰动方程,吸收边界采用DRP(保持色散关系)无反射边界.对流场...     

微波加热陶瓷动态过程的数值模拟

本文结合中国科学院上海硅酸盐研究所高性能陶瓷开放实验室研制成功的小功率微波烧结陶瓷的实验装置,对微渡加热陶瓷棒的动态过程进行了数值模拟,建立起一个变物性,变内热源的二维传热数学模型,并对模型进行了求解计算。计算结果和实测数据基本吻合。利用本模型可求出不同物性参数和尺寸的陶瓷材料在不同微波加热功率下的升温速率和温度场的变化,为控制微波烧结陶瓷的温度及热应力提供了理论参数。     

Analysis of unsteady supercavitating flow around a wedge

Supercavitating flow around a slender symmetric wedge moving at variable velocity in static fluid has been studied. Singular integral equation for the flow has been founded through distributing the sources and sinks on the symmetrical axis. The supercavity length at each moment is determined by solving the singular integral equation with finite difference method. The supercavity shape at each moment is obtained by solving the partial differential equation with variable coefficient. For the case that the wedge takes the impulse and uniformly variable motion,numerical results of time history of the supercavity length and shape are presented. The calculated results indicate that the shape and the length of the supercavity vary in a similar way to the case that the wedge takes variable motion,and there is a time lag in unsteady supercavitating flow induced by the variation of wedge velocity.     

非定常流中桨后舵附推力鳍的数值模拟

采用基于速度势的面元法计算螺旋桨与其后舵附推力鳍的非定常水动力性能，船体对螺旋桨的影响以桨盘面处的非均匀伴流来模拟．计算了螺旋桨0．7半径处在旋转一周过程中表面压力分布的变化情况，并与试验数值进行对比．在此基础上，计算了处于非均匀来流的螺旋桨后的舵附推力鳍的水动力性能．舵附推力鳍与螺旋桨的互相干扰以迭代处理，分析了采用不同剖面的推力鳍其助推效率的变化，将鱼形鳍剖面引入推力鳍中，并对鱼形鳍随边处进行了一些修改，计算了螺旋桨在旋转一周过程中，鱼形推力鳍助推效率的变化，计算结果与相同展长、弦长的NACA0018剖面相比，鱼形鳍的助推效率增加了约30％．