共查询到20条相似文献,搜索用时 109 毫秒
1.
本文采用三种不同亚网格尺度模型对带有V型稳定器的模型燃烧室二维瞬态紊流流动进行了大涡模拟。并在交错网格系下用SIMPLE算法和混合差分格式求解离散方程。数值研究拟不同型式入口速度分布和不同亚网格尺度模型下模型燃烧室二维瞬态紊流流场。计算结果表明不同入口速度分布和不同亚网格尺度模型对瞬态流场和出口速度分布有一定的影响。本文通过数值模拟,揭示了V型稳定器后旋涡的产生和脱落过程。通过计算结果及实验数据的比较可知,本文采用的亚网格尺度模型可以用来模拟模型燃烧室紊流流场及稳定器后面回流区的流动情况。 相似文献
2.
3.
湍流燃烧中的概率密度函数方法 总被引:6,自引:1,他引:5
用求解速度和化学热力学参数联合概率密度函数(pdf)输运方程的方法,计算湍流燃烧问题时,湍流输运和化学反应等过程可以精确计算,无须模拟。它还可以提供比统计矩模型方法更多的信息,因此是一个很有潜力的方法。本文给出了湍流燃烧概率密度函数的输运方程,扼要地介绍了目前应用较多的随机过程模型,以及求解概率密度函数方程的Monte Carlo算法。最后引用两个例子说明概率密度函数方法的优越性。 相似文献
4.
高保真度空天发动机数值模拟通常基于快速化学反应火焰面假设,即超声速燃烧反应的特征尺度小于湍流Kolmgorov尺度,该模型方法对于氢气燃料仿真计算结果较好,但对于乙烯等碳氢燃料仍需进一步研究.受限于极端环境特种非接触测量技术,目前尚未见超声速燃烧火焰分区判别的实验研究,导致目前超声速燃烧火焰面模型适用性以及分区燃烧物理模型认识不清,进而也制约了数值发动机技术发展.本工作基于自主研发的MHz发动机内窥光纤传感器,针对单边扩张双模态冲压发动机超声速燃烧火焰分区开展实验研究,通过化学自发光信号的最小香农熵定义超声速燃烧的特征时间τsc,根据理论方法和来流工况估算了超声速燃烧的流动特征时间,结合分区燃烧理论分析了双模态超燃冲压发动机内碳氢燃料燃烧的分区情况.通过燃烧分区情况以及与泰勒尺度的比较结果,验证了碳氢燃料超燃冲压发动机典型飞行条件下燃烧室内超声速燃烧处于旋涡小火焰区域(Re?50 000; Da∈1.80~2.60, B区),多尺度湍流涡结构发挥重要作用,并随着相对于泰勒尺度的不同大小,分别对应了不同尺度的涡结构主导该过程.同时给出了当量比、通量比以及来流马赫数对燃烧特征时间的影响规律... 相似文献
5.
采用大涡模拟(LES)方法,并结合动力学亚格子尺度应力(SGS)模型,通过数值求解柱坐标系下的滤波Navier-Stokes方程,研究了绕管轴旋转圆管内的湍流流动特性.为验证计算的可靠性,以及动力学SGS模型对于旋转湍流的适用性,将大涡模拟计算所得的结果,与相应的直接模拟(DNS)结果和实验数据进行了对比验证,吻合良好.进一步对旋转圆管湍流的物理机理进行了探讨,研究了湍流特性随旋转速率的变化规律.当旋转速率增加时,湍流流动有层流化的发展趋势.基于湍动能变化的关系,分析了旋转效应对湍流脉动生成的抑制作用. 相似文献
6.
7.
利用处理三维可压缩粘性流体流动问题中的沉浸边界法,并结合基于PPM方法的高精度TVD格式,对三维方形管道中部的圆柱火焰绕流及惰性气体绕流问题进行了数值模拟。计算湍流时采用大涡模拟(LES),化学反应速率采用EBU漩涡破碎模型。通过计算结果与实验结果的比较,发现高精度PPM格式能精确模拟两类圆柱绕流问题。计算中还发现,火焰圆柱绕流算例中,在火焰翻越圆柱前,由于燃烧的膨胀作用,使得火焰正面前的未燃气体流动并形成惰性气体绕流,这与无燃烧时的惰性气体绕流类似。但当火焰翻越圆柱过程中及完全翻越圆柱后,两种算例绕流流场出现明显变化。 相似文献
8.
亚临界雷诺数下圆柱绕流的大涡模拟 总被引:20,自引:0,他引:20
本文应用Smagorinsky涡粘性模式和二阶精度的有限体积法对圆柱绕流的流场进行大涡模拟.求解了非正交曲线坐标系下的N-S方程,对雷诺数为100和20000的工况进行了计算.计算结果与实验及动力涡粘性模式的结果进行了比较,表明计算对于层流及高亚临界雷诺数的湍流流动是合理的 相似文献
9.
对短环形流燃烧室内有较强回流的湍流旋流流动进行了模拟,并从两个方面(燃烧室构型和多点喷射)对燃烧室性能的影响进行了分析。计算中采用Reynoldes应力湍流模型(RSM)、EBU-Arrheniue湍流燃烧模型和离散坐标辐射模型描述其燃烧流动,液相采用Lagrange法处理,气相采用SIMPLE法求解。研究表明:在燃料和空气总流量不变的情况下,燃烧室构型对燃烧室出口平均温度影响不大,对出口温度分布、燃烧室内空气流场有比较大的影响。喷嘴数目的改变对出口处的平均温度和平均速度影响不大,但是对出口截面处的温度分布影响比较大,在局部范围可能产生温度比较高的热斑。 相似文献
10.
本文基于动态分区概念开展了亿级网格的高马赫数全尺寸超燃冲压发动机内外流耦合一体化改进延迟分离涡(IDDES)模拟研究. 研究建立了包括动态分区火焰面湍流燃烧模型(DZFM)、分区自适应化学(Z-DAC)和分区并行自适应建表(Z-ISAT)的完整动态分区燃烧模拟框架, 并通过1.15亿网格的马赫数12 REST标准高超声速燃烧室模型初步验证了分区模拟框架的保真性. DZFM通过分区解耦的思想既准确表征了当地湍流化学交互作用关系, 又有效提升了整场湍流燃烧的计算效率. Z-DAC和Z-ISAT通过在分区框架内对化学反应机理进行动态实时简化和建表查询, 可进一步提升当前分区内化学反应的求解效率. 基于1.25和1.4亿网格动态分区框架对比分析了马赫数10条件下中心支板(strut)和壁面撑挡型(pylon)两类构型氢气高超声速燃烧室特性. 支板或撑挡结构均诱发了明显的边界层分离和头部回流区, 由此两种燃烧室均出现了较长区域的喷注点前部燃烧现象. 基于Borghi图的数值分析表明当前氢气高超声速燃烧室中广泛存在扩散控制为主的火焰面模式, 效率提升的瓶颈在于高效增混. 壁面撑挡燃烧室具有较高的穿透深度和近场混合效率, 因而燃烧效率高于净推力准则80%, 相应的比冲1234 s也远高于中心支板燃烧室的437 s. 分区自适应化学方法在将近一半的计算域上降低了反应求解计算代价, 特别是在无燃料区反应机理的简化幅度更加明显. 相比与传统的有限速率PaSR模型, DZFM模型实现了高达11倍的加速比. 相似文献
11.
Conditional Moment Closure for Large Eddy Simulations 总被引:1,自引:0,他引:1
A conditional moment closure (CMC) based combustion model for large-eddy simulations (LES) of turbulent reacting flow is proposed
and evaluated. Transport equations for the conditionally filtered species are derived that are consistent with the LES formulation
and closures are suggested for the modelling of the conditional velocity, conditional scalar dissipation and the fluctuations
around the conditional mean. A conventional β-probability density distribution of the scalar is used together with dynamic
modelling for the sub-grid fluxes. The model is validated by comparison of simulations with measurements of a piloted, turbulent
methane-air jet diffusion flame. 相似文献
12.
Large-eddy structures of turbulent swirling flows and methane-air swirling diffusion combustion 总被引:3,自引:0,他引:3
Turbulent swirling flows and methane-air swirling diffusion combustion are studied by large-eddy simulation (LES) using a
Smagorinsky-Lilly subgrid scale turbulence model and a second-order moment (SOM) SGS combustion model, and also by RANS modeling
using the Reynolds Stress equation model with the IPCM+wall and IPCM pressure-strain models and SOM combustion model. The
LES statistical results for swirling flows give good agreement with the experimental results, indicating that the adopted
subgrid-scale turbulence model is suitable for swirling flows. The LES instantaneous results show the complex vortex shedding
pattern in swirling flows. The initially formed large vortex structures soon break up in swirling flows. The LES statistical
results of combustion modeling are near the experimental results and are as good as the RANS-SOM modeling results. The LES
results show that the size and range of large vortex structures in swirling combustion are different from those of isothermal
swirling flows, and the chemical reaction is intensified by the large-eddy vortex structures.
The project supported by the Special Funds for Major State Basic Research (G-1999-0222-07). The English text was polished
by Keren Wang. 相似文献
13.
14.
15.
Numerical simulation of methane-air turbulent jet flame using a new second-order moment model 总被引:2,自引:0,他引:2
A new second-order moment model for turbulent combustion is applied in the simulation of methane-air turbulent jet flame.
The predicted results are compared with the experimental results and with those predicted using the wellknown EBU-Arrhenius
model and the original second-order moment model. The comparison shows the advantage of the new model that it requires almost
the same computational storage and time as that of the original second-order moment model, but its modeling results are in
better agreement with experiments than those using other models. Hence, the new second-order moment model is promising in
modeling turbulent combustion with NOx formation with finite reaction rate for engineering application.
The project sponsored by the Foundation for Doctorate Thesis of Tsinghua University, and the National Key Project in 1999–2004
sponsored by the Ministry of Science and Technology of China 相似文献
16.
《Particuology》2017
Within the framework of the two-fluid approach, gas was treated with a large-eddy simulation and a sub-grid-scale (SGS) turbulent kinetic energy model while particles were treated with a second-order-moment method to describe the anisotropy of the fluctuating velocity. A modified Simonin model was derived for the gas–solid interphase fluctuating energy transfer. The anisotropic gas–solid flow in a circulating fluidized bed was investigated. Predictions were in good agreement with experimental data. The distributions of the second-order moment of particles and SGS-turbulent kinetic energy of gas were simulated at different solid mass fluxes. The effects of the solid mass flux on the particle second-order moment, particle anisotropic behavior, gas SGS-turbulent kinetic energy and gas SGS energy dissipation were analyzed for the circulating fluidized bed. 相似文献
17.
18.
Ethanol is identified as an interesting alternative fuel. In this regards, the predictive capability of combustion Large Eddy Simulation approach coupled to Lagrangian droplet dynamic model to retrieve the turbulent droplet dispersion, droplet size distribution, spray evolution and combustion properties is investigated in this paper for an ethanol spray flame. Following the Eulerian-Lagrangian approach with a fully two way coupling, the Favre-filtered low Mach number Navier-Stokes equations are solved on structured grids with dynamic sub-grid scale models to describe the turbulent carrier gas phase. Droplets are injected in polydisperse manner and generated in time dependent boundary conditions. They evaporate to form an air-fuel mixture that yields spray flame. Part of the ethanol droplets evaporates within the prevaporization area before reaching the combustion zone, making the flame to burn in a partially premixed regime. The chemistry is described by a tabulated detailed chemistry based on the flamelet generated manifold approach. The fuel, ethanol, is modeled by a detailed reaction mechanism consisting of 56 species and 351 reversible reactions. The simulation results including excess gas temperature, droplet velocities and corresponding fluctuations, droplet mean diameters and spray volume flux at different distances from the exit plane show good agreement with experimental data. Analysis of combustion spray features allows gaining a deep insight into the two-phase flow process ongoing. 相似文献
19.
We compare the space-time correlations calculated from direct numerical simulation(DNS) and large-eddy simulation(LES) of turbulent channel flows.It is found from the comparisons that the LES with an eddy-viscosity subgrid scale(SGS) model over-predicts the space-time correlations than the DNS.The overpredictions are further quantified by the integral scales of directional correlations and convection velocities.A physical argument for the overprediction is provided that the eddy-viscosity SGS model alone does not includes the backscatter effects although it correctly represents the energy dissipations of SGS motions.This argument is confirmed by the recently developed elliptic model for space-time correlations in turbulent shear flows.It suggests that enstrophy is crucial to the LES prediction of spacetime correlations.The random forcing models and stochastic SGS models are proposed to overcome the overpredictions on space-time correlations. 相似文献
20.
本文基于颗粒相的轨道模型,对大速差射流燃烧室中烟煤粉与贫煤粉的二维流动,混合及燃烧进行了数值模拟,模拟结果从两相耦合的角度,阐明了煤粉颗粒在燃烧室中运动的规律,煤粉与大速差射流诱导的中心气体逆流之间的混合及其对煤粉火焰稳定的影响,指出此种燃烧室中煤粉火焰稳定的回流区燃烧机理,气相流场及回流区的预报结果与实验符合良好。 相似文献