From Large-Eddy Simulation to Direct Numerical Simulation of a lean premixed swirl flame: Filtered laminar flame-PDF modeling

Large-Eddy Simulations (LES) and Direct Numerical Simulation (DNS) are applied to the analysis of a swirl burner operated with a lean methane–air mixture and experimentally studied by Meier et al. [19]. LES is performed for various mesh refinements, to study unsteady and coherent large-scale behavior and to validate the simulation tool from measurements, while DNS enables to gain insight into the flame structure and dynamics. The DNS features a 2.6 billion cells unstructured-mesh and a resolution of less than 100 microns, which is sufficient to capture all the turbulent scales and the major species of the flame brush; the unresolved species are taken into account thanks to a tabulated chemistry approach. In a second part of the paper, the DNS is filtered at several filter widths to estimate the prediction capabilities of modeling based on premixed flamelet and presumed probability density functions. The similarities and differences between spatially-filtered laminar and turbulent flames are discussed and a new sub-grid scale closure for premixed turbulent combustion is proposed, which preserves spectral properties of sub-filter flame length scales. All these simulations are performed with a solver specifically tailored for large-scale computations on massively parallel machines.     

湍流燃烧NO生成反应率数值模拟的研究现状与进展

利用计算机数值计算来模拟氮氧化物的生成和优选降低氮氧化物的各种措施，已经受到广泛重视．如何建立合理而经济的数学模型，是其中的关键问题之一．本文从热NO和燃料NO两方面着重介绍了近年来湍流燃烧NO生成湍流反应率数学模型及数值模拟的研究现状及发展趋势，对模拟结果进行了分析，并给出了比较详细的模型方程及代数表达式，便于相关研究人员与工程技术人员参考．     

Prediction of friction factors and heat transfer coefficients for turbulent flow in corrugated tubes combined with twisted tape inserts. Part 1: friction factors

A simple mathematical model following the suggestion of Smithberg and Landis has been created to predict the friction factors for the case of a fully developed turbulent flow in a spirally corrugated tube combined with a twisted tape insert. The flow field is divided into two principal regions--a helicoidal core flow modified by secondary circulation effects and a twisting boundary layer flow. The “wall roughness” has an effect simultaneously on the axial velocity, secondary fluid motion and the resulting swirl mixing. The model reflects the influence of the “wall roughness” on the axial and tangential velocity components. The calculated friction factors have been compared with 570 experimental points obtained from 57 tubes tested. Five hundred points (87.7%) have a relative difference of less than ±15%; fifty one points (8.9%) have a difference of within ±(15-20)% and only nineteen points (3.4%) have a relative difference greater than ±20%.     

THREE-DIMENSIONAL SIMULATION FOR EFFECTS OF BED DISCORDANCE ON FLOW DYNAMICS AT Y-SHAPED OPEN CHANNEL CONFLUENCES

Channel confluences are universally present in nature. They can be divided into two types:asymmetrical river confluences and symmetric river confluences. The latter is also called as the Y-shaped confluences. Most of previous work has paid more attention to the asymmetrical river confluences, but few studies have been conducted on the Y-shaped confluences. In this article, the effects of bed discordance on the flow patterns at"Y"shaped open-channel confluences were studied by using a 3-D numerical simulation. It is proved that the model can undertake quantitative assessment of the flow at confluences. The results indicate that there are a lot of differences between the Y-shaped confluence and asymmetrical confluence. The discordant bed height plays an important role at the Y-shaped junction.     

Effects of free stream turbulence on a turbulent boundary layer on a flat plate with zero pressure gradient part IV: Calculation of the flow field

The effects of free stream turbulence on a turbulent boundary layer were calculated by using a k-ϵ two-equation model. The calculations were performed with respect to velocity profiles on a flat plate, wall shear stress, turbulence energy, integral length scales of turbulence, and decay of free stream turbulence, and the results were compared with the experimental results. The energy of the free stream turbulence and the dissipation values at the leading edge of the flat plate were used as the initial calculation conditions. These initial values of dissipation were determined from the integral length scales of the free stream turbulence at the leading edge. The calculated wall shear stress increased with the free stream turbulence and integral length scales of turbulence. The velocity profiles and turbulence energy agreed well with the experimental results, and the effects of free stream turbulence on the wall shear stress agreed fairly well with those observed in experiments. © 1997 Scripta Technica. Inc. Heat Trans Jpn Res. 25 (2): 65–75, 1996     

An Investigation of Turbulent Rectangular Jet Discharged Into A Narrow Channel Weak Crossflow

A computational investigation of the mean flow field of turbulent rectangular jets issuing into a narrow channel crossflow is presented. The length of the jet slot spans more than 55% of the crossflow channel bed, leaving a small clearance between the jet edge and sidewalls. A finite volume code employing the standard k-εmodel is used to predict the mean, three-dimensional flow field. The mean flow field is investigated for two velocity ratios （6 and 9）. Important flow features, such as the formation of different vortical structures and their characteristics owing to different values of the velocity ratio, are discussed. Some predicted results are compared with the experimental data reported in the literature. The predicted mean and turbulent flow properties are shown to be in good agreement with the experimental data.     

A k－ε－PDF Two－Phase Turbulence Model for Simulating Sudden－Expansion Particle－Laden Flows

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动边界其实并不存在

由于启动压力梯度概念的引入,渗流力学便有了动边界的概念。为了深入了解动边界的性质,该文根据理论分析方法对启动压力梯度存在时的地层压力传播问题进行了研究。研究发现,启动压力梯度存在时地层被分成流动区和非流动区,二者之间的界限为动边界。但是,由动边界概念出发,可以得出非流动区的流体既流动又不流动的悖论,因而理论已不能自洽。动边界由启动压力梯度引起,启动压力梯度并不存在,是一个实验假象,因而,动边界也不存在。消除动边界,渗流力学理论则能够自洽。     

Numerical Study of the Effects of the Face Velocity on Ceramic Filter

INTRODUCTIONTheproductsofcoalcombustionsuchasNOx,SOx,COb,andparticulatehavebeenstronglyregulatedtoreducepollutionintheearthenvironment.TherecentlydevelopedCleanCoalTechnologies(CCT)knownasPressurizedFluidizedBedCombustion(PFBC)[']andintegratedGasificationCombinedCycle(IGCC)I"']providetheimprovementofthermalefficiencywithsignificalltlyreducedenvironmelltalimpacts.ThusthePFBCandIGCChaveincreasingattentiontoachievestringentenvironmentalprotection.Advancingthetechnologyofthehotg…