分子微观热运动对氢氧点火过程的影响研究

本研究采用DSMC方法和TCE化学反应模型,模拟氢氧混合物中大量分子的微观运动和碰撞。研究发现由于分子链式反应和分子热扩散的影响,燃烧产物会集中于局部区域,导致初始均匀反应物在点火过程中的不均匀,明显影响点火的物理过程以及宏观点火时间

稀薄气体效应对高超声速飞行流动的影响分析

高超声速飞行器在飞行过程中,由于黏性耗散和激波压缩,流动一般具有高速、高温和热化学非平衡的特点:同时由于气动热约束,高超声速巡航要求在密度较低的大气环境中进行,稀薄气体效应显现,流动物理更为复杂。本文结合CFD与DSMC方法,分别模拟了平板、圆柱和球头等简单外形在氩气和近真实大气环境中飞行时的流场,分析了稀薄气体效应对高超声速流动的一些影响规律。研究发现,平板前缘存在局部稀薄气体效应,即使对于小

An Investigation of Grid Resolution on Hypersonic Viscous Flow Simulation

The effects of grid resolution on hypersonic viscous flow simulations are investigated in detail. Previous studies have shown that grid plays an important role on the aerothermodynamic predictions for a hypersonic vehicle. We investigate flows over simplified geometry to analyze the behavior of grid resolution when the flow is solved using the Navier-Stokes equations. It shows that grid&nbsp;independent solutions can be achieved with fine meshes where the surface-based cell Reynolds number is in the order of 10. The reason for fine meshes is analyzed using wall functions derived using the boundary layer approximation. It is found that the truncated error of numerical schemes is increased dramatically when the flow approaches the surface, which explains the fact that near-surface cells should be much smaller than faraway cells to maintain the numerical error at a low level.&nbsp;</div

滦县M_L=4.8地震的局部多台数字记录

据中国数字地震台网测定,2004年1月20日16时34分11.9秒在滦县发生了ML=4.8的地震,震中位于东经118.77°,北纬39.71°,震源深度H=10km。尽管地震造成的破坏轻微,但有感范围较大,在秦皇岛市、青龙县、北京市、廊坊市、天津市等地均有震感。这次地震使震中及其附近地区的5台数字强震仪触发,记录了5组3分量数字加速度记录。本文对这次地震事件、地震地质概况作了简要介绍,并就台站(阵)基本背景资料、数字强震仪主要技术指标作了详细说明。最后,对获取的15条数字加速度记录作了初步处理分析,如基线校正、加速度峰值计算、傅里叶谱及反应谱计算等

DSMC碰撞模型参数对高超声速化学反应流的影响

直接模拟蒙特卡罗(DSMC)方法是一种高效、精确的气体流动模拟方法。DSMC方法高效计算的关键在于它处理分子水平上的输运,内能松弛和化学反应过程使用的唯像模型。例如,Bird的变径硬球(VHS)模型是DSMC中处理弹性碰撞最成功的模型,该模型试图只再现气体粘度对温度的指数依赖关系,而不是对粒子之间的相互作用进行详细的建模。唯象模型参数的准确性对DSMC仿真的准确性至关重要。在早期的发展过程中,这些唯象碰撞模型参数通常是根据实验测得的有限温度范围输运系数数据进行校准的。人们已经认识到这些参数在高温范围内可能是不准确的,例如,在再入飞行中遇到的温度大于10000K的情况。因此,最近新的高温空气参数被推荐,通过对广泛使用的碰撞模型,如VHS和可变软球(VSS)模型,基于从头计算的碰撞积分数据进行参数标定。这些基于从头计算的碰撞参数的准确性已经被证明了。本文针对DSMC模拟最常用的唯象碰撞模型,通过拟合基于从头计算的碰撞积分数据对DSMC模型参数进行重新标定。在本文中,我们将通过使用一个最新开发的采用特定碰撞配对策略的DSMC程序研究碰撞参数对高超声速化学反应流动模拟流场特性的影响。圆柱体的高超声速反应流的初步结果表明,不同的DSMC碰撞模型参数,激波位置、表面热流率等流场特性有显著变化。本文将进行分析以确定模型参数影响流动特性的通道(例如扩散或反应过程)

稀薄大气密度涨落对高空超高速飞行器气动性能的影响

地球周围的大气环境特性,随高度的上升,显著变化。对于本文关心的高度100km附近高超声速飞行器气动特性而言,稀薄大气密度涨落影响是一个重要的问题。按照大气层划分,高度100 km属于热层。热层的下界高度约86 km,上界高度与太阳活动有关,在太阳宁静期约为200 km,太阳活动期约500 km。热层下接中间层(高度50～86 km),上连电离层(高度80～1000 km),大气研究已知,中间层主要受重力波和湍流影响,电离层主要受太阳活动和地磁效应影响。高度100 km附近空域,处在热层下界,重力波、湍流、太阳活动和地磁效应等均有影响,理论上需要Navier-Stokes方程和Maxwell方程..

A Microscopic Analysis of Premixed Hydrogen-Oxygen Auto-ignition

Combustion is a complex problem involving multi-stage chemical reactions and multi-scale physics. The microscopic process of chemical reactions has obvious stochastic character and may bring important influence to combustion phenomena both locally and globally. In this study, we employ a stochastic simulation algorithm (SSA) to simulate the microscopic hydrogen-oxygen auto-ignition process. Statistical result of SSA calculation shows that fluctuation is controlled by both temperature and microscopic volume. The non-homogeneous distribution of radicals caused by local fluctuation may cause the difference between average microscopic quantities and their macroscopic counterparts due to some radical-radical reactions

A unified gas-kinetic scheme for continuum and rarefied flows IV: Full Boltzmann and model equations

Fluid dynamic equations are valid in their respective modeling scales, such as the particle mean free path scale of the Boltzmann equation and the hydrodynamic scale of the NavierStokes (NS) equations. With a variation of the modeling scales, theoretically there should have a continuous spectrum of fluid dynamic equations. Even though the Boltzmann equation is claimed to be valid in all scales, many Boltzmann solvers, including direct simulation Monte Carlo method, require the cell resolution to the order of particle mean free path scale. Therefore, they are still single scale methods. In order to study multiscale flow evolution efficiently, the dynamics in the computational fluid has to be changed with the scales. A direct modeling of flow physics with a changeable scale may become an appropriate approach. The unified gas-kinetic scheme (UGKS) is a direct modeling method in the mesh size scale, and its underlying flow physics depends on the resolution of the cell size relative to the particle mean free path. The cell size of UGKS is not limited by the particle mean free path. With the variation of the ratio between the numerical cell size and local particle mean free path, the UGKS recovers the flow dynamics from the particle transport and collision in the kinetic scale to the wave propagation in the hydrodynamic scale. The previous UGKS is mostly constructed from the evolution solution of kinetic model equations. Even though the UGKS is very accurate and effective in the low transition and continuum flow regimes with the time step being much larger than the particle mean free time, it still has space to develop more accurate flow solver in the region, where the time step is comparable with the local particle mean free time. In such a scale, there is dynamic difference from the full Boltzmann collision term and the model equations. This work is about the further development of the UGKS with the implementation of the full Boltzmann collision term in the region where it is needed. The central ingredient of the UGKS is the coupled treatment of particle transport and collision in the flux evaluation across a cell interface, where a continuous flow dynamics from kinetic to hydrodynamic scales is modeled. The newly developed UGKS has the asymptotic preserving (AP) property of recovering the NS solutions in the continuum flow regime, and the full Boltzmann solution in the rarefied regime. In the mostly unexplored transition regime, the UGKS itself provides a valuable tool for the non-equilibrium flow study. The mathematical properties of the scheme, such as stability, accuracy, and the asymptotic preserving, will be analyzed in this paper as well. (C) 2016 Elsevier Inc. All rights reserved

高超声速平板绕流中的黏性干扰与稀薄气体效应分析

选择高超声速平板绕流问题来分析黏性于扰与稀薄气体效应对流动的影响。采用动理论计算来分析从平板前缘到尾缘的详细流动情况。在平板前缘,稀薄气体效应永远存在,其非平衡影响可以用能量非平衡来表示;当平板表面的速度滑移可以用一阶理论描述时,可以认为流动进入了滑移区。其边界层位移可近似从激波角分析得到,进而可以评估传统的黏性干扰理论。定量上,通过平板表面的摩阻分析

化学非平衡对高超声速流动影响的理论分析

针对钝头体前缘流动的化学非平衡问题,通过构建驻点线上的准一维理论模型,研究不同来流条件下组分离解度的变化及其对流动的影响。考虑到飞行器周围空气中的氧气首先发生离解,在分析氧气离解时可以把氮气视为惰性气体。在理想解离气体(ideal dissociating gas,IDG)模型的基础上,通过考虑空气的有限速率化学反应,得到定常流动的氧气离解度的松弛方程。进一步对驻点线流动作合理假设,联立松弛方程与流动方程,可以快速求解驻点线上的流动参数。不同高度下的理论计算结果显示,氧