共查询到20条相似文献,搜索用时 187 毫秒
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在水槽中测量了中等雷诺数下平板湍流边界层中的瞬时流向速度的时间序列,验证了Benzi提出的推广的自相似标度律,用子波变换将壁湍流脉动速度分解为多尺度湍涡结构的速度,研究了每一个尺度的湍涡速度结构函数的推广的自相似标度律。主要结论如下:湍流的统计性质是自相似的,这不仅适用于充分发展湍流,而且适用于中等雷诺数和低雷诺数湍流,而且具有相同的标度指数;推广的自相似标度律的适用的尺度范围远远大于惯性子区的范围,可以一直延伸至耗散区的尺度范围;推广的自相似标度律不仅适用于均匀各向同性湍流,也适用于剪切湍流如边界层湍流。 相似文献
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采用基于非等距网格的紧致差分方法对Mach数为0.8,Reynolds数为3300的可压缩槽道湍流进行了直接数值模拟.建立了充分发展的可压缩槽道湍流数据库.该流场的统计特征(如等效平均速度分布,半局部尺度无量纲化的脉动均方根分布)与他人的数值计算结果吻合较好.在此DNS结果的基础上,作者对该流场进行了统计分析和机理研究.得到了可压缩槽道湍流场的高阶统计矩.同时分析了压缩性效应对近壁相干结构的影响机理,认为在可压壁湍流的近壁区,压力在压缩_膨胀上的做功部分吸收了脉动速度的动能,使得可压湍流的近壁速度条带结构更加平整.还对可压缩槽道湍流进行了标度律分析,指出可压槽道湍流中心线附近较宽的区域内存在标度律及扩展的自相似性.认为当Mach数不是很高时压缩性效应对标度指数影响不大.通过数值计算得到可压缩槽道湍流的标度指数. 相似文献
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通过对直接数值模拟的槽道湍流数据库的研究,发现了粘性底层内横向速度的强脉冲现象.分析并研究了这种强脉冲现象的一般特征和对湍流的贡献以及与涡结构的关系. 相似文献
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首先定性地分析了流线曲率效应对流场湍流结构的影响,然后以U型槽道流为典型算例,对多种湍流模型进行了评估.评估的模型包括:线性涡粘性模型,二阶和三阶非线性涡粘性模型,二阶显式代数应力模型和Reynolds应力模型.评估结果表明,性能良好的三阶非线性涡粘性模型,如黄于宁等人发展的HM模型以及CLS模型,可以较好地描述流线的曲率效应对湍流结构的影响,如凸曲率作用下内壁附近湍流强度的衰减和凹曲率作用下外壁附近湍流的增强,并且较好地确定了管道下游的分离点位置和分离泡长度,其预测的结果和实验符合较好,与Reynolds力模型的结果十分接近,因此可以较好地应用于具有曲率效应的工程湍流的计算. 相似文献
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大涡模拟是近十多年来发展起来的湍流研究的重要手段。本文介绍了大涡模拟的基本思想,提出了大涡模拟的代数模型,并详细地讨论了模型的建立。并将它应用于平直槽道和弯曲槽道中湍流的数值模拟,计算的初步结果表明本模型是可行的,并有望在进一步改善后可用于较复杂湍流的数值模拟。 相似文献
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利用从细长体理论出发得到的三维分段积分法和湍流简化方法模拟了大量纤维粒子在圆管湍流内的运动.统计了不同Re数下计算区域内的纤维的取向分布,计算结果与实验结果基本吻合,结果表明湍流的脉动速度导致纤维取向趋于无序,且随着Re数的增加,纤维取向的分布越来越趋于均匀.其后又考虑了纤维速度和角速度的脉动,二者都充分体现了流体速度脉动的影响,且纤维速度的脉动在流向上的强度大于横向,而其角速度的脉动在流向上的强度小于横向.最后统计了纤维在管道截面上的位置分布,说明Re数的增加加速了纤维在管道截面上的位置扩散. 相似文献
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High Accuracy Numerical Simulation of Non-Isothermal Viscoelastic Polymer Fluid Past a Cylinder北大核心CSCD 下载免费PDF全文
采用同位网格有限体积(coupled and linked equations algorithm revised,CLEAR)方法求解黏性和XPP (eXtended Pom-Pom)黏弹性流动的控制方程,基于延时修正方法构造了动量和本构方程对流项的高精度AVLsmart格式。首先,为了验证该文方法的有效性,对不同Reynolds数下不可压黏性流体圆柱绕流问题进行了模拟。随后,对等温及非等温不可压XPP黏弹性流体圆柱绕流问题进行了有效模拟,给出了速度矢量、应力分量、拉升量以及温度的分布规律,分析了We数对水平速度、法向应力及拉升量的影响。该文研究成果能为精确预测复杂型腔纤维增强黏弹性聚合物熔体动态充填过程提供理论基础。 相似文献
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Computational Fluid Dynamics (CFD) simulations of liquid–metal spallation targets, such as MEGAPIE and ESS, which utilize the High Reynolds number k–ε turbulence model, invariably incorporate an implicit law of the wall treatment in which a linear or logarithmic fit to the velocity and temperature profiles is made next to heated, non-slip surfaces. The law is well-established, but has been derived from the assumptions that the wall shear stress and the normal heat flux are constant through the viscous sub-layer and buffer zone, which lie beneath the turbulent boundary layer. However, in the case of the heat flux, this condition will be violated for applications in which there is intense volumetric heating in the near-wall layers. This is just the case for the spallation reactions taking place in liquid–metal targets as a result of proton bombardment. In this article, a modified law of the wall is derived to be used under such conditions. Use of the law is illustrated by means of flow in a flat channel and one application to a spallation target. From the applications considered, it is found that the effect of the modification is small, provided the local mesh resolution is chosen appropriately. Specific recommendations regarding optimum mesh size for liquid–metal heat transfer problems are given, which will be of general interest, with or without volumetric heating. 相似文献
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在充满两种互不相溶粘性流体的多孔固体中,研究弹性波的传播.用3个数性的势函数描述3个纵波的传播,用1个矢性的势函数单独描述横波的传播.根据这些势函数,在不同的组合相中,定义出质点的位移.可以看出,可能存在3个纵波和1个横波.在一个弹性固体半空间与一个充满两种互不相溶粘性流体的多孔固体半空间之间,研究其界面上入射纵波和横波所引起的反射和折射现象.由于孔隙流体中有粘性,折射到多孔介质中的波,朝垂直界面方向偏离.将入射波引起的反射波和折射波的波幅比,作为非奇异的线性代数方程组计算.进一步通过这些波幅比,计算出各个被离散波在入射波能量中所占的份额.通过一个特殊的数值模型,计算出波幅比和能量比系数随入射角的变化.超过SV波的临界入射角,反射波P将不再出现.越过界面的能量守恒原理得到了验证.绘出了图形并对不同孔隙饱和度以及频率的变化,讨论它们对能量分配的影响. 相似文献
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I.G. Brykina B.V. Rogov G.A. Tirskiy 《Journal of Applied Mathematics and Mechanics》2009,73(5):502-513
Hypersonic rarefied gas flow over blunt bodies in the transitional flow regime (from continuum to free-molecule) is investigated. Asymptotically correct boundary conditions on the body surface are derived for the full and thin viscous shock layer models. The effect of taking into account the slip velocity and the temperature jump in the boundary condition along the surface on the extension of the limits of applicability of continuum models to high free-stream Knudsen numbers is investigated. Analytic relations are obtained, by an asymptotic method, for the heat transfer coefficient, the skin friction coefficient and the pressure as functions of the free-stream parameters and the geometry of the body in the flow field at low Reynolds number; the values of these coefficients approach their values in free-molecule flow (for unit accommodation coefficient) as the Reynolds number approaches zero. Numerical solutions of the thin viscous shock layer and full viscous shock layer equations, both with the no-slip boundary conditions and with boundary conditions taking into account the effects slip on the surface are obtained by the implicit finite-difference marching method of high accuracy of approximation. The asymptotic and numerical solutions are compared with the results of calculations by the Direct Simulation Monte Carlo method for flow over bodies of different shape and for the free-stream conditions corresponding to altitudes of 75–150 km of the trajectory of the Space Shuttle, and also with the known solutions for the free-molecule flow regine. The areas of applicability of the thin and full viscous shock layer models for calculating the pressure, skin friction and heat transfer on blunt bodies, in the hypersonic gas flow are estimated for various free-stream Knudsen numbers. 相似文献
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This paper presents a relatively simple numerical method to investigate the flow and heat transfer of laminar power-law fluids over a semi-infinite plate in the presence of viscous dissipation and anisotropy radiation. On one hand, unlike most classical works, the effects of power-law viscosity on velocity and temperature fields are taken into account when both the dynamic viscosity and the thermal diffusivity vary as a power-law function. On the other hand, boundary layer equations are derived by Taylor expansion, and a mixed analytical/numerical method (a pseudo-similarity method) is proposed to effectively solve the boundary layer equations. This method has been justified by comparing its results with those of the original governing equations obtained by a finite element method. These results agree very well especially when the Reynolds number is large. We also observe that the robustness and accuracy of the algorithm are better when thermal boundary layer is thinner than velocity boundary layer. 相似文献
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The present work investigates the effects of the disks contracting, rotation, heat transfer and different permeability on the viscous fluids and temperature distribution between two heated contracting rotating disks. Two cases are considered. For the first case, we neglect the viscous dissipation effects in the energy equation and reduce the Navier-Stokes equations and energy equation into nonlinear coupled ODEs by introducing the Von Kármán type similarity transformations. The effects of various physical parameters like expansion ratio, Prandtl number, Reynolds number and rotation ratio on the velocity and temperature are discussed in detail. The second and more general case is that we consider the viscous dissipation in the energy equation. Under this assumption, the energy equation is reduced to a ordinary differential equation including the Eckert number, whose solution also is solved by HAM. 相似文献
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K. Hutter K. Jöhnk B. Svendsen 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1994,45(5):746-762
A layer of ice and sediment is modelled as a mixture of two nonlinear, very viscous, constant density fluids interacting mechanically via Darcy- and Pick-type forces. An inclined layer of this mixture overlain by a layer of ice modelled as a viscous fluid is considered with boundary conditions of no-slip or viscous sliding at the base and no stress at the free surface. The interface is treated as a singular surface across which the jump conditions of mass and momentum for the constituents are assumed to hold. Furthermore, because the components are viscous fluids, a kinematic condition for the continuity of the tangential velocity is formulated. The momentum jump conditions involve surface production terms requiring additional surfacial constitutive relations.We show that the posed physical problem admits a mathematical solution only in the case that the interface momentum production is non-zero.Dedicated to Hans Roethlisberger on the occasion of his seventieth birthday. 相似文献
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In this paper, we consider a two-stage tandem network. The customers waiting in these two stages share one finite buffer. By constructing a Markov process, we derive the stationary probability distribution of the system and the sojourn time distribution. Given some constraints on the minimum loss probability and the maximum waiting time, we also derive the optimal buffer size and the shared-buffer size by minimizing the total buffer costs. Numerical results show that, by adopting the buffer-sharing policy, the customer acceptance fraction and the delivery reliability are more sensitive to buffer size comparing with the buffer-allocation policy. 相似文献
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Stefan Kopecz Mathias Krebs Andreas Meister Olaf Wünsch 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2010,61(4):673-684
This paper deals with the efficient simulation of polymer melts, as an example of highly viscous non-isothermal non-Newtonian fluids. In flow fields of our interest, which are characterized by small Reynolds numbers and large Prandtl numbers, steep gradients occur in thin boundary layers of the temperature distribution, whereas the boundary layers associated with the velocity field possess a considerable different length scale. In order to benefit from these properties, we introduce a physically motivated multigrid approach by computing velocity and temperature fields on different meshes. This new development is achieved by the modification of a discrete projection method. Numerical experiments are presented which confirm that the method decreases the computational effort considerably, while preserving the numerical accuracy. 相似文献