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1.
在非结构混合网格上对化学非平衡粘性绕流进行了数值模拟。控制方程为考虑了化学非平衡效应的二维Navier-Stokes方程,化学动力学模型为7组元、7反应模型。控制方程中的对流项采用VanLeer逆风分裂格式处理,并应用MUSCL方法及Minmod限制器扩展到二阶精度,粘性项用中心差分格式处理。时间推进采用显式5步龙格-库塔方法。为了适应高超声速流场计算,对VanLeer通量分裂方法进行了改进,并引入了化学反应时间步长。对RAMC-II模型的飞行试验流场进行了数值模拟,计算结果与试验测量数据符合较好,并与参考文献中的数值模拟结果吻合。 相似文献
2.
SUMMARY The influence of the choice of transport and chemical models on the numerical simulation of hypersonic flows in chemical non-equilibrium is investigated. A coupled Euler/boundary layer method is employed, which facilitates the incorporation of different models and simplifies the calculation of the resulting flowfields. By considering hypersonic flows with different freestream conditions, it is shown that for flows dominated by chemical reactions, the computed flowfields can be sensitive to the choice of model. This sensitivity must be taken into account when defining test cases for the validation of numerical simulations of hypersonic re-entry flows. 相似文献
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4.
M. G. Khramchenkov 《Fluid Dynamics》2001,36(1):166-168
The effect of chemical reactions on the process of admixture transport by a flow through a porous medium is considered. On the basis of a number of examples it is shown that the dispersion coefficient depends on the chemical reaction rate constant. 相似文献
5.
The Navier-Stokes equations for a laminar flow of a compressible multispecies gas have been used to model numerically the
heat and mass transfer processes in high-temperature chemical reactions of methane in water vapor with activation of reactions
on the microchannel walls and external heat supply. The temperature and concentration fields are obtained, as well as the
distributions of heat fluxes, reacting species, and local coefficients of heat and mass transfer along the channel. It is
shown that a high degree of chemical conversion leads to nonmonotonical changes in reaction rates and velocities of transverse
heat flows, and species along the microchannel, considerably affecting the local coefficients of heat and mass transfer. 相似文献
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7.
Study on the numerical schemes for hypersonic flow simulation 总被引:1,自引:0,他引:1
Hypersonic flow is full of complex physical and chemical processes, hence its investigation needs careful analysis of existing
schemes and choosing a suitable scheme or designing a brand new scheme. The present study deals with two numerical schemes
Harten, Lax, and van Leer with Contact (HLLC) and advection upstream splitting method (AUSM) to effectively simulate hypersonic
flow fields, and accurately predict shock waves with minimal diffusion. In present computations, hypersonic flows have been
modeled as a system of hyperbolic equations with one additional equation for non-equilibrium energy and relaxing source terms.
Real gas effects, which appear typically in hypersonic flows, have been simulated through energy relaxation method. HLLC and
AUSM methods are modified to incorporate the conservation laws for non-equilibrium energy. Numerical implementation have shown
that non-equilibrium energy convect with mass, and hence has no bearing on the basic numerical scheme. The numerical simulation
carried out shows good comparison with experimental data available in literature. Both numerical schemes have shown identical
results at equilibrium. Present study has demonstrated that real gas effects in hypersonic flows can be modeled through energy
relaxation method along with either AUSM or HLLC numerical scheme. 相似文献
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9.
Differentially heated enclosure with heat-generating porous layer on inner walls is studied computationally for non-Darcy flow and thermal non-equilibrium models. In this study, this problem is investigated for different internal and external Rayleigh numbers, Darcy numbers, porosity-scaled thermal conductivity ratio, solid-/fluid-scaled heat transfer coefficient and dimensionless thickness of the porous layer. The results indicate that the dimensionless thickness of the porous layer has an important effect on the heat transfer in the enclosure. It was found that the thermal non-equilibrium model is needed for small values of the porosity-scaled thermal conductivity ratio and the solid-/fluid-scaled heat transfer coefficient. It is shown that the convection of heat due to internal heat generation is increased in the enclosure when the ratio of internal Rayleigh number to external Rayleigh number is larger. 相似文献
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11.
A numerical solution of the first-order homogeneous chemical reaction in an unsteady free convective flow past a semi-infinite
vertical plate is studied. The dimensionless governing equations are solved by an efficient, more accurate, unconditionally
stable, and rapidly converging implicit finite-difference scheme. The effect of various parameters, such as the Prandtl number,
Schmidt number, buoyancy ratio parameter, and chemical reaction parameter on flow velocity and temperature is determined.
The velocity profiles are in excellent agreement with available results in the literature. The local and average values of
skin friction and Nusselt and Sherwood numbers are calculated. The effects of the chemical reaction parameters on these values
are discussed for both generative and destructive reactions. Owing to the presence of the first-order chemical reaction, the
velocity is found to increase in the generative reaction and to decrease in the destructive reaction. 相似文献
12.
碳氢燃料点火燃烧的简化化学反应动力学模型 总被引:3,自引:1,他引:3
基于``准稳态'方法建立了一套复杂化学反应动力学模型简化方法和相应的软件SPARCK.
并以3种典型的碳氢燃料------甲烷、乙烯和庚烷为研究对象,从甲烷点火燃烧的GRI2.11详
细基元反应动力学模型出发简化得出了包含14个组分10步总包反应形式的简化化学反应动
力学模型,从乙烯燃烧的51组分365详细基元反应模型出发简化得出了包含20个组分16
步总包反应形式的简化化学反应动力学模型,从庚烷点火燃烧的160组分1540详细基元反
应模型出发简化得出了包含26个组分22步总包反应形式的简化化学反应动力学模型. 通过
对典型激波管试验的结果对比可以看出:得到的简化反应动力学模型能较为有效地再现
详细基元反应模型的反应机理,具有较高的计算精度. 在工程计算中有较好的应用前景. 相似文献
13.
O. B. Larin 《Fluid Dynamics》1979,14(6):838-844
The ignition of hydrogen blown into a turbulent supersonic boundary layer on a flat plate is investigated numerically. It is assumed that the mixture consists of six chemically active components H, O, OH, H2O, O2, H2 and inert nitrogen N2. The boundary layer is divided into outer and inner regions, for which different expressions for the coefficients of turbulent transport are used. The influence of pulsations on the rates of the chemical reactions, and also the back reaction of the chemical processes on the mechanism of turbulent transfer are not taken into account. The surface of the plate is assumed to be absolutely catalytic with respect to the recombination reactions of the H and O atoms. The influence of the blowing intensity, the Mach number in the outer flow, and the pressure on the ignition delay is analyzed. The possibility of effective porous cooling of the surface when there is combustion in the boundary layer is demonstrated.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 33–40, November–December, 1979.I thank V. G. Gromov and V. A. Levin for their interest in the work. 相似文献
14.
Privatdozent Dr.-Ing. K. Lucas Professor Dr.-Ing. N. Peters 《Heat and Mass Transfer》1977,10(3):211-216
The deviation from local homogeneous chemical equilibrium flow due to non-catalytic heterogeneous reactions in a tubular reactor is analysed by an asymptotic expansion for large Damköhler numbers. Close to the reacting surface a boundary layer is shown to exist where the effects of the homogeneous and the heterogeneous reaction have an influence of the same order of magnitude. The extension of this boundary layer into the equilibrium flow is proportional to the inverse of the square root of the Damköhler number. The boundary layer equation is derived and solved for a particular example. 相似文献
15.
A. D. Polyanin 《Fluid Dynamics》1983,18(5):756-764
A study is made of steady convective mass transfer between a drop and a continuous medium in the case when the resistance to transfer is completely concentrated within the drop, in which an arbitrary bulk chemical reaction takes place. It is shown that the mean Sherwood number Sh on the surface of the drop is uniformly (with respect to the Péclet number Pe) bounded above, Sh ?k const (where the constant depends only on the drop geometry and not on the parameters Pe and K; k is the dimensionless rate of the bulk chemical reaction) and a diffusion boundary layer within the drop cannot be formed merely by increasing the intensity of the circulation of the fluid (i.e., by increasing the Péclet number, Pe →∞). This property of the mean Sherwood number is typical for internal problems and differs radically from the behavior of Sh for the corresponding external problem of mass transfer of a drop, for which, as a rule, the expression Sh = 0(√pe) holds in the limit Pe →∞(k = const). An equation is derived that describes the concentration distribution within the drop at large Peclet numbers for arbitrary rate of the bulk chemical reaction. The dynamics of the behavior of the basic characteristics of the mass transfer of the drop is studied qualitatively as a function of the parameters k and Pe. 相似文献
16.
Mixing is an essential operation in many microfluidic devices. Droplet-based micromixers utilize droplets for mixing enhancement. In the present study, a novel three-dimensional simulation is conducted which has the ability to capture not only the mixing process, but also the chemical reactions inside liquid droplets. This two-phase model is used for simulating the reacting flow inside a serpentine microchannel and explores the effects of droplet size and reaction rate on the production and consumption of species in droplets. It is observed that the chemical reaction in each droplet, begins from its front area. Furthermore, it is shown that the production of species does not depend on water fraction (ratio of water flow rate to total flow rate) and for all droplet sizes, only depends on the reaction rate. Moreover, different transient generated vortices and secondary flows are studied in the presence and absence of droplets and explained in details based on the position of droplets. It is found that during the passage of droplets through a microchannel bend, the number of cross-sectional vortices changes and the velocity magnitude in these secondary flows increases dramatically. 相似文献
17.
Ⅰ.引言40年代不可逆过程热力学已形成一个新的领域。60年代初对扩散、传热、导电、弛豫以及热电、电磁等不可逆过程的各种唯象处理已被综合为统一的体系——非平衡态热力学。由于热机、气体放电、热核聚变以及天体物理、地球物理等方面的研究和发展,流体力学与非平衡态物理学相结合而形成的非平衡流问题的研究已扩展到广泛的领域,流体力学与非平 相似文献
18.
The unsteady natural convective couple stress fluid flow over a semi-infinite vertical cylinder is analyzed for the homogeneous first-order chemical reaction effect. The couple stress fluid flow model introduces the length dependent effect based on the material constant and dynamic viscosity. Also, it introduces the biharmonic operator in the Navier-Stokes equations, which is absent in the case of Newtonian fluids. The solution to the time-dependent non-linear and coupled governing equations is carried out with an unconditionally stable Crank-Nicolson type of numerical schemes. Numerical results for the transient flow variables, the average wall shear stress, the Nusselt number, and the Sherwood number are shown graphically for both generative and destructive reactions. The time to reach the temporal maximum increases as the reaction constant K increases. The average values of the wall shear stress and the heat transfer rate decrease as K increases, while increase with the increase in the Sherwood number. 相似文献
19.
驻定斜爆轰波并行数值模拟 总被引:1,自引:0,他引:1
采用多组分化学反应Euler方程组对驻定在高速飞行弹丸上的斜爆轰波流场进行了数值模拟。计算中分别采用TVD格式和基元反应模型,并基于并行编程模型MPI(message passing interface)实现了非结构网格上的并行计算,对流项和化学反应项用时间分裂法进行处理。计算结果表明并行计算能有效地提高计算速度,扩展计算规模,为进一步研究超驱爆轰推进技术奠定基础。 相似文献
20.
Effects of Chemical Reaction and Double Dispersion on Non-Darcy Free Convection Heat and Mass Transfer 总被引:1,自引:0,他引:1
In this article, the effects of chemical reaction and double dispersion on non-Darcy free convection heat and mass transfer
from semi-infinite, impermeable vertical wall in a fluid saturated porous medium are investigated. The Forchheimer extension
(non-Darcy term) is considered in the flow equations, while the chemical reaction power–law term is considered in the concentration
equation. The first order chemical reaction (n = 1) was used as an example of calculations. The Darcy and non-Darcy flow, temperature and concentration fields in this study
are observed to be governed by complex interactions among dispersion and natural convection mechanisms. The governing set
of partial differential equations were non-dimensionalized and reduced to a set of ordinary differential equations for which
Runge–Kutta-based numerical technique were implemented. Numerical results for the detail of the velocity, temperature, and
concentration profiles as well as heat transfer rates (Nusselt number) and mass transfer rates (Sherwood number) are presented
in graphs. 相似文献