共查询到20条相似文献,搜索用时 281 毫秒
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本文基于计算流体力学软件FLUENT采用大涡模拟方法(LES)及Smagorinsky-lilly亚格子模型,对空冷岛扁平管外翅片空间的流动与换热特性进行了三维瞬态湍流数值模拟。计算结果表明大涡模拟方法能较好地模拟空冷岛扁平管外翅片空间的瞬态流动特性,能够捕获更多的流场细节信息。可得出流场中温度、压力、涡量等各参数的瞬态变化特性以及翅片空间尾流区瞬态三维涡的发展演化过程,更好地预测多尺度湍流。为进一步揭示扁平管温度场和流场的协同关系以及大型空冷系统多尺度输运规律和非线性尺度效应机理打下基础。 相似文献
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《声学学报:英文版》2015,(1)
为了对热声不稳定的发生及控制机理进行研究,对Rijke管内的自激热声振荡现象进行了数值模拟。采用具有低频散低耗散特点的计算气动声学方法,对带有非线性热源项的声波方程进行数值求解,并比较了不同的热源模型及边界条件对非线性效应的影响。结果表明,计算气动声学方法可以成功捕捉到Rijke管内压力的起振过程,而且在速度扰动达到平均流速度的1/3时,振荡会由线性增长转为非线性增长,最终达到有限幅值极限循环。相比热源项,考虑管口辐射耗散的非线性边界条件在振荡幅值和频谱方面对结果的影响都比较小。数值模拟得到的结果与实验符合较好,表明计算气动声学方法适合于热声振荡问题的研究。 相似文献
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圆管层流脉冲流动对流换热数值分析 总被引:3,自引:0,他引:3
对等热流和等壁温边界条件下圆管内层流脉冲流动对流换热问题进行了数值模拟。在等热流边界条件下的数值计算结果与理论解吻合很好。计算结果表明:在等热流和等壁温边界下脉冲流动可引起速度、温度以及努塞尔数随时间波动,振幅越大,脉冲频率越小,波动越大。但它们的时均值均等于在相同雷诺数下稳态流动的值,脉冲流动不能强化换热。 相似文献
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一种三维环流模型及其应用 总被引:1,自引:0,他引:1
本文建立了一种广泛适用于大陆架浅海的三维环流模型。模型的支配方程是具有自由面的三维非线性瞬态Navier-Stokes方程。支配方程经σ坐标变换后与边界条件一起在空间交错网格系统上用差分法求解。为提高计算效率,基于问题的物理性质引入过程分裂概念没计了计算框架:将三维流动过程分成长重力波的传播(外模式)和速度的垂向剪变(内模式)两大组成部分,对每个部分分别选用最适宜各自物理特性和数值行为的数值方法求解。最后做为本模型的应用实例,计算了渤海三维潮流,获得了很好的结果。 相似文献
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为了对热声不稳定的发生及控制机理进行研究,对Rijke管内的自激热声振荡现象进行了数值模拟。采用具有低频散低耗散特点的计算气动声学方法,对带有非线性热源项的声波方程进行数值求解,并比较了不同的热源模型及边界条件对非线性效应的影响。结果表明,计算气动声学方法可以成功捕捉到Rijke管内压力的起振过程,而且在速度扰动达到平均流速度的1/3时,振荡会由线性增长转为非线性增长,最终达到有限幅值极限循环。相比热源项,考虑管口辐射耗散的非线性边界条件在振荡幅值和频谱方面对结果的影响都比较小。数值模拟得到的结果与实验符合较好,表明计算气动声学方法适合于热声振荡问题的研究。 相似文献
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The paper considers surface recombination at the free active region surface as the mechanism of carrier losses which has not yet been discussed with regard to III‐nitride LEDs despite of its evident importance for AlGaInP‐based light emitters. Using advanced thin‐film and triangular volumetric chip designs reported in literature as prototypes, we have demonstrated by simulation a noticeable impact of surface recombination on the wall‐plug efficiency of InGaN‐based LEDs. Various types of LEDs whose efficiency may be especially affected by surface recombination are discussed. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
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A. Pereira P. M.J. Trevelyan U. Thiele S. Kalliadasis 《The European physical journal. Special topics》2009,166(1):121-125
We investigate the interaction of thin films with chemical reactions by using as a model system a horizontal film with a reactive
mixture of insoluble surfactants on its free surface. The reaction is modeled by a bistable/excitable FitzHugh-Nagumo (FHN)
prototype. The chemical reaction can destabilize the film leading to the propagation of solitary pulses on its free surface. 相似文献
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S. H. Park S. N. Rogak W. K. Bushe J. Z. Wen M. J. Thomson 《Combustion Theory and Modelling》2013,17(3):499-513
An aerosol model to simulate soot formation and growth was developed using moving- and fixed-sectional methods. The new model is composed of a set of subroutines that can be easily combined with the Chemkin package. Using the model, we have simulated soot formation and growth in plug flow reactors. Our model was compared with a previously published method of moments model for a simulation of the plasma pyrolysis of methane in a plug flow reactor. Inclusion of the transition correction factor for the condensation coefficient led to the prediction of a smaller condensation rate compared with the method of moments model. The average coagulation rate calculated by the sectional model was much higher than that by the method of moments model for a broad particle size distribution. The two models predicted significantly different soot precursor concentration and rates of aerosol processes, but substantially similar particle mass and number for the pyrolysis process. We have also simulated soot formation and growth in a jet-stirred/plug flow reactor (JSR/PFR) system for which soot size distribution measurements are available in the literature. It is shown that the adjusted-point fixed-sectional method can provide comparable accuracy to the moving-sectional model in a simulation of soot formation and growth. It is also shown that the measured surface growth rate could be much higher than the value used in this study. Soot mass concentrations and size distributions for particles larger than 10 nm were well predicted with a surface reaction enhancement. The primary particle size was underpredicted by only about 30% compared with the measurements, without any model adjustments. As the new model can predict both the particle size distribution and structure, and is suitable for application in complex flows, its application to diverse soot formation conditions will enhance our knowledge on the evolution of soot structures. 相似文献
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This study aims to clarify the relationship between the deformation of a free surface and flow transition in a “switching
phenomenon” process. In a flow driven by a rotating disk in a cylindrical open vessel, the free surface irregularly changes
its shape from axisymmetric to nonaxisymmetric and vice versa with repeating up-and-down motion (so-called “switching phenomenon”).
The flow under the free surface was visualized by anisotropic flakes. When the free surface assumes a parabolic shape, the
flow is distinguished by three regions; local circulation region, rigid vortex region and meridional circulation region. The
flow transition in the switching phenomenon was shown by snapshots and movies of the visualized flow; the flow near the free
surface is laminar even if the shape of the free surface changes to nonaxisymmetric during the time at which the free surface
attaches to the bottom of the vessel. After the free surface detaches from the disk, the flow near the free surface becomes
turbulent. When the free surface changes to axisymmetric while descending to the bottom, the flow changes from turbulent to
laminar flow and the local circulation region reemerges at the center of the vessel. 相似文献
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Near-well ultrasonic processing technology attracts more attention due to its simple operation, high adaptability, low cost and no pollution to the formation. Although this technology has been investigated in detail through laboratory experiments and field tests, systematic and intensive researches are absent for certain major aspects, such as whether ultrasonic excitation is better than chemical agent for any plugs removal; whether ultrasound-chemical combination plug removal technology has the best plugs removal effect. In this paper, the comparison of removing drilling fluid plug, paraffin deposition plug, polymer plug and inorganic scale plug using ultrasonic excitation, chemical agent and ultrasound-chemical combination plug removal technology is investigated. Results show that the initial core permeability and ultrasonic frequency play a significant role in plug removal. Ultrasonic excitation and chemical agent have different impact on different plugs. The comparison results show that the effect of removing any plugs using ultrasound-chemicals composite plug removal technology is obviously better than that using ultrasonic excitation or chemical agent alone. Such conclusion proves that ultrasonic excitation and chemical agent can cause synergetic effects. 相似文献
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应用ANSYS软件建立模型并模拟了ITER诊断插件所处的物理环境,进行了电磁分析,获得了涡流和电磁载荷变化趋势.将电磁载荷耦合到结构模型获得了其对结构的影响.通过计算,获得了结构的应变和应力分布,这可作为评估诊断插件结构可靠性的依据. 相似文献
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Troyer WE Holly R Peemoeller H Pintar MM 《Solid state nuclear magnetic resonance》2005,28(2-4):238-243
The hydration pattern of controlled pore glass, with pore diameter of 237 Å, was investigated using nuclear magnetic resonance. Water proton spin–spin relaxation decay curves were monitored and modeled as two-component exponential decays as a function of hydration. The results are consistent with a geometric model involving a surface water layer and a bulk-like liquid fraction in the form of a plug. The amount of surface water increases as the sample hydrates, until hydration reached approximately a monolayer, at which point a water plug starts to form in the pore, and grow in length at the expense of the surface layer. The results are also analyzed in terms of, and compared to, a recently developed puddle pore-filling model [S.G. Allen, et al. J. Chem. Phys. 106 (1997) 7802–7809]. 相似文献
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I.IntroductionThegenerationofacousticpulsebylaserirradiationofametalsurfacewasfirstsuggestcdbyWhitein1963[1l.SincethatdateLaserU1trasoundtechniquchasbeendcvclopedrapidly.Becausethistechniquehasanumberoftechnicalfcatures,suchasnon-contact,highbandwidth,highhme-spacia1resolution,quantitativeteshng,generationoflongitudinal,shcarandRay1cighwaves(simu1taniously),andsoon,ithasbccnwidelyapp1icdtomcasurementsofmatcrialproperties,detectionofdefects,andcalibrationoftransd.ccrsl'-'o].Inordertodcve1opth… 相似文献
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S. Yu. Dobrokhotov V. E. Nazaikinskii A. A. Tolchennikov 《Russian Journal of Mathematical Physics》2017,24(4):544-552
Consider a liquid in a uniform gravitational field in a horizontally infinite basin of variable finite depth. Assume that the liquid performs a potential motion and its state at the initial time is characterized by a given free surface elevation decaying at infinity and by the zero vertical velocities of the free surface (which, for example, corresponds to the so-called piston model of tsunami generation [1, 2]). The problem is to determine the free surface elevation at the subsequent times. 相似文献
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《Composite Interfaces》2013,20(7-9):731-750
Melt flow instabilities during extrusion of wood polymer composites (WPC) containing 30–60 wt% wood flour (WF) have been investigated. The research emphasized elucidation of the extrudate surface tearing mechanism and its relation to wall slip. This interesting phenomenon has been known in the WPC industry for years; however, it has not received much research interest. It was observed that increasing the wood flour loading up to 50 wt% aggravated the surface tearing; however, addition of 60 wt% wood flour completely eliminated the surface defect due to strong wall slip and plug flow. It was also found that addition of lubricants and increasing the shear rate significantly improved the surface appearance of the filled compounds. Molecular weight and molecular weight distribution of the polymer matrix influence the melt flow properties of the composites. The significance of the entrance pressure measurement and its usefulness for quantitative assessment of filler–matrix interactions in composite materials is also demonstrated in this paper. 相似文献