三维机翼跨音速颤振的分布式并行计算

以多台微机组成分布式计算系统,利用无限插值方法(TFI)生成三维多块贴体运动网格,以Navier Stokes方程为控制方程,求解三维机翼的跨音速非定常气动力,并与颤振方程耦合迭代计算,求解机翼广义位移响应的时间历程,根据广义位移的时间历程的衰减、等幅和发散振荡等情况确定机翼跨音速颤振临界条件.通过算例验证,计算结果与实验结果和理论分析相吻合.     

弹性载机对外挂物动力学响应的影响

在外挂物投放过程中, 载机对外挂物具有气动干扰效应, 产生附加气动力.对于弹性机翼, 在外挂物分离投放时, 相当于给机翼一个初始扰动, 机翼将发生弹性振动, 该振动也会对外挂物带来气动干扰效应.通过耦合求解非定常N-S方程刚体六自由度方程和基于模态法的结构动力学方程, 对考虑弹性变形的载机外挂物分离投放过程进行模拟, 研究了弹性机翼对外挂物的气动干扰效应.研究结果表明:在外挂物分离初期, 弹性机翼的干扰对外挂物气动力响应产生显著影响, 机翼的主要结构模态频率决定了外挂物气动力的变化频率, 并且由载机机翼动弹性变形引起的干扰气动力能占到外挂物总气动力的一半左右.      

振荡机翼跨音速非定常粘性绕流的数值计算

以非定常Ｎ－Ｓ方程为主管方程，采用ＬＵ－ＮＮＤ混合差分格式，Ｃ和Ｃ－Ｈ型贴体运动网格，Ｂ－Ｌ双层代数紊流模型，求解绕振荡翼型和三维机翼的跨音速非定常粘性流场，分别计算了ＮＡＣＡ００１２翼型和Ｍ６机翼作俯仰振荡时跨音速非定常粘性绕流流场。研究了非定常绕流的气动特性，部分计算结果和风洞实验值作了比较。     

温度体动网格模型中控制参数的研究

采用调整导热系数和源项分布的方式,对温度体动网格模型所生成的网格品质进行控制.温度体动网格模型将运动边界的位移虚拟为求解域的温度边界条件,以流体能量方程或固体导热方程作为控制方程,通过选取不同的导热系数或源项分布可以得到适合不同求解问题需要的温度分布,并将求解得到的网格节点的温度作为其动态位移量.采用温度体动网格模型计算平动、三维旋转运动、柔性体运动等流固耦合计算中可能涉及的动网格算例.结果表明,在计算效率和生成网格的品质方面,与已有的动态网格生成方法相比,具有较大的优势,可以有效解决流固耦合数值模拟中存在的动态网格生成难题.     

物体穿越激波非定常流场的统一分区加强解

用数值方法求解非定常可压缩Navier Stokes方程,模拟了物体以超音速穿越与之同向运动激波及逆向运动激波的全过程.为确保数值模拟中的激波和物体的相对运动有足够的网格分辨率,使用了统一分区加强解算法,详细给出了追击穿越和碰撞穿越的流场结构和气动力,并且通过和单区结果的对比,说明统一分区加强解算法是一种处理复杂几何外形和提高网格分辨率的简单有效方法.     

基于CFD/CSD的舵面控制气动弹性数值模拟方法

在动态网格上通过耦合求解流动控制方程和结构动力学方程, 发展了一种舵面控制下飞行器运动响应过程中气动弹性数值模拟研究方法.流动控制方程采用N-S方程, 结构动力学采用线性模态叠加方法, 其中流动控制方程空间离散采用基于非结构网格的有限体积方法, 对流通量采用计算HLLC格式, 非定常时间离散采用基于LU-SGS的双时间步长方法.模拟中, 气动运动和结构变形在双时间步长方法推进过程中采用改进松耦合方法, 气动网格与结构网格之间信息交换采用无限平板样条法实现, 飞行器的运动和变形采用基于重叠网格和Delaunay图映射变形网格相结合的方法进行处理.采用多个考核算例对发展的数值方法进行考核验证, 结果表明该方法可以高效精确模拟舵面开环控制下飞行器运动响应过程中的气动弹性特性.      

应用笛卡尔非结构切割网格进行外挂物投放的数值模拟

描述了一种新的网格生成技术,即笛卡尔非结构切割网格技术,采用叉树数据结构,完成了几种单段和多段翼型以及三维机翼的网格生成.应用中心有限体积法,对其绕流问题进行Euler方程数值模拟,并将计算结果与实验数据进行对比.在机翼绕流数值模拟的基础上,求解出机翼带外挂物的分离投放的流场计算问题.     

带有结构非线性的跨音速翼型颤振特性研究

以非定常N-S方程为主管方程,采用时间推进的方法,计算翼型振荡的瞬态非定常气动力,并与带有结构非线性的颤振方程耦合求解,计算了带有结构刚度非线性(间隙型,三次型刚度非线性)和结构阻尼非线性(三次型阻尼非线性)的结构响应特性和颤振特性.计算研究表明,由于同时具有结构和气动非线性,振荡极限环和气动力极为复杂.     

基于自动微分的线性/非线性谐波方法研究

本文运用线性/非线性谐波方法并结合自动微分开发求解一维非定常欧拉方程组的求解器.线性/非线性谐波方法求解非定常流不仅精度高,而且计算时间短,自动微分方法的应用又极大地减少了谐波方程求解器开发的工作量.在定常求解器的基础上,利用自动微分工具生成求解谐波方程的基本代码,通过手动组合和微调最终得到求解一维非定常欧拉方程的求解器.最后通过准一维拉瓦尔喷管算例和直管算例来验证求解器的准确性.     

非结构混合网格上的NS方程求解方法

提出了一套较为通用的,完全自动化的非结构混合网格生成方法.在物面粘性作用区,采用一种改进的推进层方法生成三棱柱形和金字塔形网格;在其他流动区域采用阵面推进方法生成四面体网格.采用一种改进精度的格心有限体积法对三维NS方程进行了求解,在加速收敛措施方面,提出了一种新的当地时间步长取定方法来减小质量较差的网格单元对流场计算稳定性和收敛速度的不利影响.以M6机翼和DLR/F4翼身组合体外形的粘性流场作为数值算例,验证了上述网格生成和流场求解方法的正确性和实用性.     

三维非均匀不稳定渗流方程的自适应网格粗化算法

将渗透率自适应网格技术应用于三维非均匀不稳定渗流方程的网格粗化算法中,在渗透率或孔隙度变化异常区域自动采用精细网格,用直接解法求解渗透率或孔隙度变化异常区域的压强分布,在其它区域采用不均匀网格粗化的方法计算,即在流体流速大的区域采用精细网格.用该方法计算了三维非均匀不稳定渗流场的压降解,结果表明三维非均匀不稳定渗流方程的三维非均匀自适应网格粗化算法的解在渗透率或孔隙度异常区的压强分布规律与采用精细网格的解非常逼近,在其它区域压强分布规律与粗化算法的解非常逼近,计算速度比采用精细网格提高100多倍.     

Nonlinear dynamic behaviors of a deploying-and-retreating wing with varying velocity

In this paper, the nonlinear dynamical behaviors of deploying-and-retreating wings in supersonic airflow are investigated. A cantilever laminated composite beam, which is axially moving at a known rate, is implemented to model the deploying-and-retreating wing. Associated with Reddy's third-order theory and von Karman type equations of large deformation, the nonlinear governing equations of motion of the deploying-and-retreating wing are derived based on the Hamilton's principle. The nonlinear partial differential equations of motion are transformed into a set of the ordinary differential equations using Galerkin's method. The nonlinear dynamical behaviors of the deployable-and-retreating wing are investigated in the cases of three different axially moving rates during deploying process and retreating process using the numerical simulations.     

网格单元形状对数值计算的影响

实现了二维非结构化网格上的N-S方程的离散,编制了非结构化同位网格上的SIMPLE程序,针对CFD/NHT 中几个有基准解的问题进行了试算考核。结果表明,在步长基本相同的情况下,四边形网格的收敛速度和解的精度都优于 三角形网格,尤其是收敛速度更明显;使用考虑边界贴体特性的边界层网格,解的精度优于均匀网格。     

New Compacton Solutions of Nonlinearly Dispersive R(m, n) Equations

In this paper, we establish exact solutions for the R(m,n) equations by using an sn-cn method. As a result, abundant new compactons, i.e. solitons with the absence of infinite wings, new type of Jacobi elliptic function, solitary wave and periodic wave solutions, of this equation are obtained with minimal calculations. The properties of the R(m,n) equations are shown in figures.     

FDTD结合DFT分析宽频高功率微波大气传播

联立麦克斯韦方程与电子流体方程,用时域有限差分法(FDTD)模拟高斯型和阻尼正弦型等宽频高功率微波(HPM)的大气传播.在每个时间网格上,根据窄带脉冲的电子速度,通过离散傅立叶变换(DFT)方法求解出宽频脉冲的等效电场,将等效电场和压强代入电离参数公式,使电离参数随空间网格不断更新,提高计算准确性.结果表明,宽频HPM脉冲幅值、脉宽以及海拔高度等参数对大气击穿有明显的影响;大气击穿导致尾蚀效应;随着传播距离的增加,宽频HPM脉冲的尾部衰减加剧,脉宽缩短,引起宽频脉冲的频谱出现展宽、分裂及中心频率移动等现象.     

A direct-forcing embedded-boundary method with adaptive mesh refinement for fluid–structure interaction problems

In the present work we developed a structured adaptive mesh refinement (S-AMR) strategy for fluid–structure interaction problems in laminar and turbulent incompressible flows. The computational grid consists of a number of nested grid blocks at different refinement levels. The coarsest grid blocks always cover the entire computational domain, and local refinement is achieved by the bisection of selected blocks in every coordinate direction. The grid topology and data-structure is managed using the Paramesh toolkit. The filtered Navier–Stokes equations for incompressible flow are advanced in time using an explicit second-order projection scheme, where all spatial derivatives are approximated using second-order central differences on a staggered grid. For transitional and turbulent flow regimes the large-eddy simulation (LES) approach is used, where special attention is paid on the discontinuities introduced by the local refinement. For all the fluid–structure interaction problems reported in this study the complete set of equations governing the dynamics of the flow and the structure are simultaneously advanced in time using a predictor–corrector strategy. An embedded-boundary method is utilized to enforce the boundary conditions on a complex moving body which is not aligned with the grid lines. Several examples of increasing complexity are given to demonstrate the robustness and accuracy of the proposed formulation.     

The Numerical Algorithm of Secondary Emission Microwave Electron Gun

a tracking algorithm using grid–based space charge fields is studied for the analysis of secondary emission microwave electron gun(semeg). the poisson equations of the space charge forces are determined in the bunchs rest frame with a multi–grid method. the particles equations of motion are solved with a fifth–order embedded runge–Kutta method. the results of the semeg by this algorithm are presented and compared with these by mafia algorithm.     

A low numerical dissipation immersed interface method for the compressible Navier–Stokes equations

A numerical method to solve the compressible Navier–Stokes equations around objects of arbitrary shape using Cartesian grids is described. The approach considered here uses an embedded geometry representation of the objects and approximate the governing equations with a low numerical dissipation centered finite-difference discretization. The method is suitable for compressible flows without shocks and can be classified as an immersed interface method. The objects are sharply captured by the Cartesian mesh by appropriately adapting the discretization stencils around the irregular grid nodes, located around the boundary. In contrast with available methods, no jump conditions are used or explicitly derived from the boundary conditions, although a number of elements are adopted from previous immersed interface approaches. A new element in the present approach is the use of the summation-by-parts formalism to develop stable non-stiff first-order derivative approximations at the irregular grid points. Second-order derivative approximations, as those appearing in the transport terms, can be stiff when irregular grid points are located too close to the boundary. This is addressed using a semi-implicit time integration method. Moreover, it is shown that the resulting implicit equations can be solved explicitly in the case of constant transport properties. Convergence studies are performed for a rotating cylinder and vortex shedding behind objects of varying shapes at different Mach and Reynolds numbers.     

嵌套网格技术中的Collar网格和虚拟网格方法

针对嵌套网格技术中的结合部问题,提出了Collar网格和虚拟网格方法.用双曲型微分方程生成的处于结合部的有两个边界分别处于不同固定曲面上的Collar网格,在保证计算网格的生成方便快捷而且网格质量高的前提下,解决了为物体结合部的内外边界点提供有效插值单元的问题.虚拟网格为紧贴物面的面网格,它的作用是将物面边界条件传递给其它网格的边界面,而其本身不作流场计算.计算实践表明,将Collar网格和虚拟网格结合起来应用在嵌套网格技术中能保证几何外形不发生变化,有效地处理各种复杂组合体外形的结合部问题.