多孔介质燃烧室内湍流气液两相流的数值研究

以多孔介质发动机为背景,用数值模拟方法考察气缸内加入多孔介质蓄热体后对燃烧室内湍流流场及混合气形成的影响.建立了多孔介质随机结构的简化模型,把多孔介质视为随机分布的大量固相单元的集合.在多孔介质区域引入了Antohe和Lage提出的双方程κ-ε湍流模型.为研究喷雾液滴与多孔介质的高温壁面碰撞,引入新的喷雾模型.在模型中考虑了液滴的破碎、碰撞和合并,并且描述了喷雾和多孔介质壁面之间的相互作用.针对燃油喷雾在不同结构多孔介质内流场进行了数值计算.计算表明,喷雾与多孔介质相互作用对燃烧室内燃油液滴的蒸发、混合气的形成过程和均匀化具有重要的影响.     

湍流模型在内流流场数值模拟中的应用

本文将Spalart-Allmaras湍流模型方程推导为守恒形式,并应用于内流湍流流场计算.采用此-方程湍流模型分别对扩压器流场以及NASA 67转子流场进行了数值模拟.结果表明常用在外流计算中的Spalart-Allmaras湍流模型在内流计算中仍具有较高的精度、数值稳定性和效率.     

双温度通道电弧等离子体二维数值模拟

本文对圆形通道内双温度等离子体的传热与流动特性进行了二维数值模拟,研究中假定体系处于局域化学平衡态,但电子温度不等于重粒子温度,需分别用各自的守恒方程求解．采用数值实验的方法对电子-重粒子非弹性碰撞过程进行了研究,计算结果表明,数值模拟中对非弹性碰撞过程不同的处理方法(α的不同取值)会影响计算预测的等离子体特性．α的合适数值,需要在今后的研究工作中进一步将计算结果与实验测量结果比较来加以确定。     

核–核碰撞的独立源模型及中心快度区末态产生粒子横能量分布

将强子-核碰撞的独立源模型推广到核-核碰撞,给出了核-核碰撞末态产生粒子横能量分布方程,将其与CERN的NA35合作组得到的实验数据相比较,模型较好地解释了实验结果.     

固体粒子在直流式除尘器中湍流脉动的数值模拟

本文对直流除尘器涡室内固体粒子的湍流脉动现象进行了数值分析,通过气体速度随机脉动谱,把气相湍流运动对固体粒子运动的影响引入粒子的运动平衡方程中,用拉格朗日法模拟了粒子的轨迹及其扩散运动,应用四阶龙科库塔方法求解粒子的运动方程。计算结果表明对粒子的数值模拟可以较好地预测除尘器的性能,如除尘器的切割粒径。     

中心集体流对带电粒子关联函数的影响

讨论了中心集体流对带电粒子关联函数的影响,采用蒙特卡罗方法研究了热源发射出的单粒子能谱与双粒子关联谱受中心集体流的影响. 利用QMD模型计算了100MeV/u的Ni+Ni系统在b=0fm条件下的双质子关联函数. 在计算中发展了一种交换粒子计算方法并证实了在100MeV/u Ni+Ni的中心碰撞中存在中心集体流. 计算结果表明,在中重系统中关联函数对中心集体流是灵敏的,为在100MeV/u以上能区研究中重系统中心碰撞形成的中心集体流提供了一种可行的方法.     

基于多体经典轨迹蒙特卡罗方法的H+,Li3+,Be4+,O7+与He原子电荷交换过程

经典轨迹蒙特卡罗(CTMC)方法是研究离子-原子碰撞系统电荷交换过程的常用方法,广泛应用于天体物理以及实验室等离子体环境下重粒子碰撞过程的研究.本文利用四体碰撞模型(4-CTMC)研究了包括两个束缚电子的四体碰撞过程,通过数值求解四体碰撞系统的哈密顿运动方程,计算了高电荷态入射离子(Li³⁺,Be⁴⁺和O⁷⁺)同氦原子在大能量范围的单、双电子电离和俘获截面.H⁺+He碰撞截面的计算中,在50—200 keV/amu的入射能区,4-CTMC的结果几乎重复了实验结果.在高电荷态入射情形下,4-CTMC计算的单电子电离和俘获截面值相较于三体碰撞模型(3-CTMC)在100—500 keV/amu的入射能区内与实验符合更好.尽管4-CTMC和3-CTMC忽略了电子关联,均高估了双电子电离和俘获截面(与实验值相比),但4-CTMC的结果更接近实验.     

预平衡发射研究中的记忆粒子模型

高能的复合系统的激子被分成记忆粒子m与非记忆粒子r两部分.在引入n态m粒子碰撞比a_n后,建立了m与r粒子态-角占据几率的耦合主方程,给出了区分m、r粒子的态密度与发射几率公式.计算结果表明本模型对实验的拟合较广义激子模型有明显改进.     

正冲击波后固壁表面颗粒的上升运动

为揭示固壁表面颗粒的冲击波夹卷本质,模拟垂直于固壁表面的正冲击波后单个颗粒的上升运动.假定颗粒初始时刻处于气载状态(因波的反射或碰撞离开壁面),受Saffman升力、气动阻力和重力作用.模型方程为波后定常气流边界层方程和颗粒运动常微分方程,分别用单参数法和四阶龙格库塔法求解.计算颗粒速度与轨迹表明:颗粒的冲击波卷扬动力...     

边界层转捩对风力机气动性能模拟结果的影响

本文采用CFD软件包FINETM/Turbo,选用结合AGS转捩模型的S-A湍流模型,研究边界层转捩对NORD-TANK 500/41型风力机LM19.1叶片三维流场的影响,并与采用-方程S-A和两方程k-ω(SST)模型获得的全湍流计算结果比较.在计算结果与实验数据进行对比的基础上,分析了三维粘性流场的流动细节,探讨了边界层转捩对风力机叶片气动性能和载荷预估的影响,获得了叶片转捩线随风速和沿展向的变化趋势.结果显示边界层转捩使数值计算的叶片性能和载荷增大、边界层分离推迟,为风力机叶片的优化设计提供参考.     

Modeling of stochastic forces in turbulent space plasmas

A model of a Langevin equation for electrons in turbulent, almost collisionfree magnetoactive plasmas is developed, which can form the starting point for particle simulations, especially in regions with reconnection of magnetic-field lines. The mean wave force is expressed by a friction force and a velocity derivative of the intensity of the stochastic force. The obtained expression for the Langevin force is consistent with the kinetic theory in a polarization approximation. The intensity of the stochastic force corresponds to the velocity diffusion tensor of the electrons, which is estimated for plasmas with ionacoustic turbulence using two different methods. One method is based on direct calculation of the space-time spectral density of the wave energy. The second method uses approximations of quasi-linear plasma theory. The estimates for the intensities of the stochastic forces found by the two methods differ by orders. A table of parameters of ion-acoustic waves, electron-wave collision frequencies, and intensities of stochastic-wave forces on electrons in solar flares, in the solar wind, as well as in different regions of the earth's magnetosphere is presented. Results are given for the entire ranges of available experimental data for the mean magnetic induction, mean plasma temperatures, and mean particle densities.Published from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 1, pp. 93–107, January, 1996.     

喷动床气固流动特性的三维CFD-DEM数值模拟

开展了柱锥形气固流动特性的CFD-DEM耦合三维数值模拟研究。气相场采用基于欧拉坐标体系的k-ε双方程湍流模型,固相场采用基于拉格朗日坐标体系的DEM直接数值模拟方法,跟踪离散颗粒场的每一个颗粒,考虑颗粒与颗粒(壁面)之间的碰撞力、曳力、重力、Magnus升力、saffman升力。颗粒之间的碰撞采用Hertz-Mindlin无滑移模型计算。模拟对象为柱锥形喷动床,其直径为0.152 m,喷口直径为0.019 m,模拟颗粒数22万,探讨了喷动床中射流随时间的发展,不同气速下床内气固流动结构,以及颗粒速度与颗粒浓度的分布,并与实验数据进行了对比。     

Experiments and low-order modelling of intermittent transitions between clockwise and anticlockwise spinning thermoacoustic modes in annular combustors

Annular combustion chambers of gas turbines and aircraft engines are subject to unstable azimuthal thermoacoustic modes leading to high amplitude acoustic waves propagating in the azimuthal direction. For certain operating conditions, the propagating direction of the wave switches randomly. The strong turbulent noise prevailing in gas turbine combustors is a source of random excitation for the thermoacoustic modes and can be the cause of these switching events. A low-order model is proposed to describe qualitatively this property of the dynamics of thermoacoustic azimuthal modes. This model is based on the acoustic wave equation with a destabilizing thermoacoustic source term to account for the flame’s response and a stochastic term to account for the turbulent combustion noise. Slow-flow averaging is applied to describe the modal dynamics on times scales that are slower than the acoustic pulsation. Under certain conditions, the model reduces formally to a Fokker-Planck equation describing a stochastic diffusion process in a potential landscape with two symmetric wells: One well corresponds to a mode propagating in the clockwise direction, the other well corresponds to a mode propagating in the anticlockwise direction. When the level of turbulent noise is sufficient, the stochastic force makes the mode jump from one well to the other at random times, reproducing the phenomenon of direction switching. Experiments were conducted on a laboratory scale annular combustor featuring 12 hydrogen-methan flames. System identification techniques were used to fit the model on the experimental data, allowing to extract the potential shape and the intensity of the stochastic excitation. The statistical predictions obtained from the Fokker–Planck equation on the mode’s behaviour and the direction switching time are in good agreement with the experiments.     

Propagation speed of combustion and invasion waves in stochastic simulations with competitive mixing

We consider the propagation speeds of steady waves simulated by particles with stochastic motions, properties and mixing (Pope particles). Conventional conservative mixing is replaced by competitive mixing simulating invasion processes or conditions in turbulent premixed flames under the flamelet regime. The effects of finite correlation times for particle velocity are considered and wave propagation speeds are determined for different limiting regimes. The results are validated by stochastic simulations. If the correlation time is short, the model corresponds to the KPP–Fisher equation, which is conventionally used to simulate invasion processes. If the parameters of the simulations are properly selected, the model under consideration is shown to be consistent with existing experimental evidence for propagation speeds of turbulent premixed flames.     

双稳系统的随机能量共振和作功效率

分析了处于双稳系统中的布朗粒子与外界的周期性外力和热随机力的功、热交互作用,建立了基于Langevin方程的随机能量平衡方程.围绕着受周期力、随机力和阻尼力共同作用的Langevin方程,采用动力学和非平衡热力学相结合的方法,从以"力"为立足点转到以"能量"为研究核心,深入分析了布朗粒子沿单一轨线运动时系统与环境之间的能量交换和作功效率,揭示了双稳系统的随机能量共振现象. 关键词： 双稳系统 随机能量共振 作功效率     

Ergodic Properties of a Model for Turbulent Dispersion of Inertial Particles

We study a simple stochastic differential equation that models the dispersion of close heavy particles moving in a turbulent flow. In one and two dimensions, the model is closely related to the one-dimensional stationary Schr?dinger equation in a random δ-correlated potential. The ergodic properties of the dispersion process are investigated by proving that its generator is hypoelliptic and using control theory.     

快速随机粒子网格法的气动噪声预测方法

耦合随机湍流速度生成模型与线化欧拉方程技术,形成了一套具备模拟噪声在非均匀流场中传播能力的气动噪声混合预测方法。该混合方法的随机湍流速度生成模型采用了快速随机粒子网格法,为声传播模拟提供了可靠的源项。而噪声的传播计算选用线化欧拉方程,其空间离散采用9点5阶的色散保持关系格式,时间推进选用了高精度大时间步长的6级4阶龙格库塔格式,远场边界应用了无分裂形式的理想匹配层边界条件。首先,选用高斯脉冲传播算例对线化欧拉方程的时空离散格式、远场无反射边界条件进行了验证分析。然后,计算分析各向同性湍流的空间相关性验证湍流速度生成模型的可靠性。最后,基于已搭建的气动噪声混合预测方法进行了30P30N三段翼缝翼噪声的计算分析。计算分析可知:监测点处功率谱密度曲线、噪声指向性等计算结果与参考文献结果取得了较好的一致性。数值计算结果表明所建立的气动噪声混合预测方法能有效预测二维复杂构型的气动噪声问题。      

DSM-LPDF两相湍流模型及旋流两相流动的模拟

本文由流体－颗粒速度的拉氏联合概率密度函数（ＰＤＦ）输运方程出发,用Ｓｉｍｏｎｉｎ建议的Ｌａｎｇｅｖｉｎ模型封闭颗粒所遇到流体瞬时速度的条件期望项,并用Ｍｏｎｔｅ Ｃａｒｌｏ方法直接求解 ＰＤＦ输运方程,将其和求解流体雷诺应力方程模型的有限差分方法结合,建立了雷诺应力－拉氏ＰＤＦ（ＤＳＭ－ＬＰＤＦ,简称ＤＬ）两相湍流模型．用此模型模拟了旋流数为０．４７的突扩旋流气粒两相流动,并与文献中ＰＤＰＡ实验和用类似于单相流动湍流模型封闭方法的时平均统一二阶矩（ＵＳＭ）模型的预报进行了对比．