共查询到20条相似文献,搜索用时 21 毫秒
1.
L.I. Zaichik V.A. Pershukov M.V. Kozelev A.A. Vinberg 《Experimental Thermal and Fluid Science》1997,15(4):311-322
The objective of this part of the paper is to summarize the information concerning the authors' works in the field of simulation of two-phase gas-particle turbulent flows with heat transfer and combustion. A kinetic equation had been derived for the probability density function (PDF) of the particle velocity, temperature, and mass distributions in turbulent flows. This PDF equation is used for the construction of the governing conservation equations of mass, momentum, and heat transfer in the dispersed particle phase.The numerical scheme incorporates two-phase fluid dynamics, convective and radiative heat transfer, and combustion. The proposed models have been applied to the calculation of various particle-laden turbulent flows in jets, combustion and gasification chambers, and furnaces. 相似文献
2.
F. Aliev 《Fluid Dynamics》1968,3(2):35-39
We consider turbulent motion of premixed chemically active gases in an infinite system of plane turbulent jets in the presence of diffusive combustion. The proposed calculation method permits determining the distribution of all the parameters in the mixing zone, including the longitudinal pressure. Numerical examples of the calculation of hydrogen combustion in air are presented.The study of heat and mass transfer in jet flows presents major difficulties at the present time. Therefore all the existing methods for calculating jet flows with heat and mass transfer and chemical processes [1–5] are based on an extension of the known semiempirical theories of free turbulence to the more complex cases of flow with chemical reactions. The present study is no exception in this sense; it covers an investigation of the motion in an infinite system of plane turbulent jets with diffusive combustion. 相似文献
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This paper proposes a combustion model based on a turbulent flame speed closure (TFC) technique for large eddy simulation
(LES) of premixed flames. The model was originally developed for the RANS (Reynolds Averaged Navier Stokes equations) approach
and was extended here to LES. The turbulent quantities needed for calculation of the turbulent flame speed are obtained at
the sub grid level. This model was at first experienced via an test case and then applied to a typical industrial combustor
with a swirl stabilized flame. The paper shows that the model is easy to apply and that the results are promising. Even typical
frequencies of arising combustion instabilities can be captured. But, the use of compressible LES may also lead to unphysical
pressure waves which have their origin in the numerical treatment of the boundary conditions. 相似文献
5.
A tabulated, pseudo-turbulent Probability Density Function (PDF) model for premixed combustion is proposed. The Linear-Eddy Model (LEM) is used to construct the PDFs for a temperature-based progress variable in a premixed, turbulent methane/air V-flame produced by the Cambridge slot burner. As a second case study, the LEM PDFs are similarly compared to PDFs extracted from Direct Numerical Simulations (DNS) of a turbulent premixed flame. LEM demonstrates the ability to reproduce the salient features from experimental and DNS PDFs; moreover, it is able to better capture turbulent effects than previously suggested laminar flamelet PDF models. The Scalar Dissipation Rate (SDR) for premixed combustion is likewise investigated. The stochastic nature of LEM enables it to mimic the overall behaviors of turbulent reactions inexpensively and qualitatively. Crucially, LEM appears to be well suited for the preprocessing tabulation of PDF and SDR models for a number of premixed combustion simulation strategies. 相似文献
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通过将密闭空间内爆燃泄放过程进行微分,假设各微分时段内爆燃泄放过程均按照先燃烧、再泄放、最后压力平衡的过程独立分步进行,最终得到泄爆压力分步计算模型。同时,在尺寸为2 m×1.2 m×0.6 m的爆炸腔体一端安装击穿压力相同、泄放面积不同的泄爆构件进行泄爆实验,对分步压力计算模型进行验证。对比发现:大面积泄放条件下,2个传感器测得的压力曲线基本重合,均为单峰值曲线,此时模型计算值与实验结果吻合较好;小面积泄放条件下,腔体内压力曲线均为双峰值曲线,由于泄放截面改变加剧口部湍流扰动,使得腔体内部产生压力梯度,近泄爆口处传感器测得的第2个压力峰值要大于腔体内部传感器相应的测量值,经湍流速度修正后的压力计算模型可以较好地描述近泄爆口处的压力变化情况。 相似文献
9.
为避免密闭空间内可燃预混气体爆炸事故造成的伤害,对其进行较为准确的爆炸超压预测是抗爆设计和日常安全管理的关键。结合已有文献实验数据,利用光滑层流火焰传播理论模型建立了爆炸超压模型;对比发现,当体积较大时,光滑层流火焰传播理论模型存在较大的误差。较大体积密闭空间爆炸火焰传播过程中的不稳定性造成火焰前锋面褶皱并引起湍流燃烧,导致火焰前锋面表面积大幅增加,且在火焰传播过程中表现出自相似分形特征。依据褶皱及湍流火焰传播过程中的自相似分形特征,基于分形燃烧理论和相关经验数据,进一步建立了考虑可燃预混气体爆炸火焰褶皱及湍流火焰传播的爆炸超压预测模型,并与实验所得结果进行了对比。结果表明:当密闭空间体积较大时,利用褶皱及湍流火焰传播理论建立的爆炸超压模型进行峰值压力估算时,两种工况下实验所得和理论计算所得相对误差分别为10.4%和11.1%,较光滑层流火焰传播理论爆炸超压模型相比,误差分别减少了72.3%和50.6%。本文所建立理论模型与实验所得结果具有较好的一致性,在一定程度上可满足结构抗爆设计或日常安全管理的需要。 相似文献
10.
A. Brandl M. Pfitzner J. D. Mooney B. Durst W. Kern 《Flow, Turbulence and Combustion》2005,75(1-4):335-350
In order to simulate the turbulent combustion process occurring in spark-ignition (IC) engines, it is necessary to provide
suitable and numerically economical models, the latter being particularly important in the application to industrial problems.
Moreover, these models must deliver sufficiently accurate results for the unsteady operation of spark combustion engines,
concerning variable geometries, temperatures, pressures and charge development in different configurations. In this work different
turbulent combustion models for premixed hydrocarbon combustion are compared with respect to their ability to accurately predict
the propagation of turbulent perfectly premixed flames.
As a first configuration a cylinder of constant volume was studied. Transient calculations were used to simulate the propagation
of the turbulent flame and to evaluate the resulting turbulent burning velocity. These calculations were performed for a perfect
mixture of air and hydrocarbons at stoichiometric mixture and different initial conditions concerning pressure, temperature
and turbulence intensity. As a second configuration a stationary turbulent bunsen-type flame with methane fuel was used to
validate the turbulent combustion model of [Lindstedt and Vaos, Combust. Flame 116 (1999) 461] at different pressures. Calculated results were then compared to experimental data of [Kobayashi, Tamura,
Maruta and Niioka. In: Proceedings of the 26th Symposium on Combustion, 1996, p. 389] and show excellent agreement for the turbulent burning velocity at several pressure levels using only a single
set of model parameters. 相似文献
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Tabulated chemistry models like the Flamelet Generated Manifolds method are a good approach to include detailed information on the reaction kinetics in a turbulent flame at reasonable computational costs. However, so far, not all information on e.g. heat losses are contained in these models. As those often appear in typical technical applications with enclosed flames in combustion chambers, extensions to the standard FGM approach will be presented in this paper, allowing for the representation of non-adiabatic boundaries. The enthalpy as additional control variable for the table access is introduced, such that the chemistry database becomes three-dimensional with mixture fraction, reaction progress variable and enthalpy describing the thermo-chemical state. The model presented here is first validated with a two-dimensional enclosed Bunsen flame and then applied within the Large Eddy Simulations of a turbulent premixed swirl flame with a water-cooled bluff body and a turbulent stratified flame, where additional modeling for the flame structure using artificially thickened flames was included. The results are encouraging, as the temperature decrease towards the bluff body in the swirl flame and the cooling of the pilot flame exhaust gases in the stratified configuration can be observed in both experiments and simulation. 相似文献
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Christophe Duwig 《Flow, Turbulence and Combustion》2007,79(4):433-454
Despite significant advances in the understanding and modelling of turbulent combustion, no general model has been proposed
for simulating flames in industrial combustion devices. Recently, the increase in computational possibilities has raised the
hope of directly solving the large turbulent scales using large eddy simulation (LES) and capturing the important time-dependant
phenomena. However, the chemical reactions involved in combustion occur at very small scales and the modelling of turbulent
combustion processes is still required within the LES framework. In the present paper, a recently presented model for the
LES of turbulent premixed flames is presented, analysed and discussed. The flamelet hypothesis is used to derive a filtered
source term for the filtered progress variable equation. The model ensures proper flame propagation. The effect of subgrid
scale (SGS) turbulence on the flame is modelled through the flame-wrinkling factor. The present modelling of the source term
is successfully tested against filtered direct numerical simulation (DNS) data of a V-shape flame. Further, a premixed turbulent
flame, stabilised behind an expansion, is simulated. The predictions agree well with the available experimental data, showing
the capabilities of the model for performing accurate simulations of unsteady premixed flames. 相似文献
14.
Computed tomography (CT) has the potential to greatly enhance our understanding of the turbulent flow structures, the combustion
chemistry, and the interactions between the two, which challenge us in our attempts to understand and model the details of
turbulent combustion. Here, we present high-resolution and fully three-dimensional measurements of the flame surface of a
turbulent reacting flow. The CT-reconstructed images show the flame front, at a single instant in time, of a turbulent, premixed
propane/air flame. The significance of this powerful experimental tool is to provide new insight into turbulent combustion,
allowing for the development of cleaner burning, higher power, and more efficient combustors. 相似文献
15.
New mechanistic bubble coalescence and break-up models considering turbulent suppression phenomena, which can possibly occur in the high liquid velocity condition of turbulent bubbly two-phase flow, are presented. The energy exchange mechanism between a turbulent eddy and interfacial structure was taken into account in the efficiency terms. Numerical simulations of turbulent bubbly flow were conducted in a CFD code to evaluate the newly developed models, in comparison with other advanced models coupled with a bubble-induced turbulent effect for one-group interfacial area transport equation. Local measurements of the bubble characteristics on the bubble size evolution along a vertical pipe flow were performed at KAERI-VAWL test facility using the five-sensor conductivity probe method to provide database for models validation. Results from the calculation clearly show the improvements of the newly developed models. 相似文献
16.
基于雷诺应力湍流模型(简称RSM模型),研究了平衡大气边界层风场数值模拟问题.假设流体不可压,且不计雷诺应力输运方程中的对流项、浮力产生项、系统旋转产生项和扩散项,在准各向同性的条件下,推导出RSM模型湍动能k的表达式是标准k-ε模型k常数表达式的0.893倍.考虑k沿高度变化的修正,根据在标准k-ε模型中满足水平均匀性的湍流来流边界条件,提出在RSM模型中产生平衡大气边界层的湍流来流边界条件.基于空风洞的数值模拟结果表明,与工程上常用的湍流来流边界条件相比,基于本文提出的湍流来流边界条件得到的风场水平均匀性更优,且在整个流域内,得到的雷诺应力剖面更合适.从而验证了该湍流来流边界条件的适用性. 相似文献
17.
Roman Keppeler Eike Tangermann Usman Allaudin Michael Pfitzner 《Flow, Turbulence and Combustion》2014,92(3):767-802
A subgrid scale flame surface density combustion model for the Large Eddy Simulation (LES) of premixed combustion is derived and validated. The model is based on fractal characteristics of the flame surface, assuming a self similar wrinkling of the flame between smallest and largest wrinkling length scales. Experimental and direct numerical simulation databases as well as theoretical models are used to derive a model for the fractal parameters, namely the cut-off lengths and the fractal dimension suitable in the LES context. The combustion model is designed with the intent to simulate low as well as high Reynolds number premixed turbulent flame propagation and with a focus on correct scaling with pressure. The combustion model is validated by simulations of turbulent Bunsen flames with methane and propane fuel at pressure levels between 0.1 MPa and 2 MPa and at turbulence levels of $0 < u^{\prime }/s_{L}^{0} < 11$ , conditions typical for spark ignition engines. The predicted turbulent flame speed is in a very good agreement with the experimental data and a smooth transition from resolved flame wrinkling to fully modelled, nearly subgrid-only wrinkling is realized. Evaluating the influence of mesh resolution shows a predicted mean flame surface and turbulent flame speed independent of mesh resolution for cases with 9–86 % resolved flame surface. Additional simulations of a highly turbulent jet flame at 0.1 MPa and 0.5 MPa and the comparison with experimental data in terms of flame shape, velocity field and turbulent fluctuations validates the model also at conditions typical for gas turbines. 相似文献
18.
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
19.
Nicholas J. Georgiadis Dennis A. Yoder Manan A. Vyas William A. Engblom 《Theoretical and Computational Fluid Dynamics》2014,28(3):295-318
This report provides an assessment of current turbulent flow calculation methods for hypersonic propulsion flowpaths, particularly the scramjet engine. Emphasis is placed on Reynolds-averaged Navier–Stokes (RANS) methods, but some discussion of newer methods such as large eddy simulation (LES) is also provided. The report is organized by considering technical issues throughout the scramjet-powered vehicle flowpath, including laminar-to-turbulent boundary layer transition, shock wave/turbulent boundary layer interactions, scalar transport modeling (specifically the significance of turbulent Prandtl and Schmidt numbers), and compressible mixing. Unit problems are primarily used to conduct the assessment. In the combustor, results from calculations of a direct connect supersonic combustion experiment are also used to address the effects of turbulence model selection and in particular settings for the turbulent Prandtl and Schmidt numbers. It is concluded that RANS turbulence modeling shortfalls are still a major limitation to the accuracy of hypersonic propulsion simulations, whether considering individual components or an overall system. Newer methods such as LES-based techniques may be promising, but are not yet at a maturity to be used routinely by the hypersonic propulsion community. The need for fundamental experiments to provide data for turbulence model development and validation is discussed. 相似文献
20.
This contribution is aimed at drawing the attention of the computational fluid dynamics community on the availability of an
experimental database regarding turbulent lean premixed prevaporised (LPP) reacting flows stabilised behind a double symmetric,
plane sudden expansion fed by two fully developed turbulent channel flows of air plus propane. This flow configuration can
be thought of as a relevant benchmark for testing turbulence and/or combustion models aimed at helping for the design of reliable
LPP combustion chambers. This database contains a large amount of raw and processed data regarding essentially the velocity
field for one inert and three different reacting flows configurations. Additional pieces of information are available and
concern the lean extinction properties and the wall static pressure evolution in the feeding channels. For the reacting flows,
the presence of a large scale coherent motion is clearly visible in the velocity spectra and it is shown how a data processing
based on the semi-deterministic approach that decomposes the velocity signal into the sum of its steady time average, its
coherent fluctuations and its stochastic fluctuations can permit to evaluate their respective contribution to the total velocity
fluctuations. 相似文献