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本文采用水洞流谱观测方法,研究了带有涡襟翼的翼—身组合体前缘分离涡及涡系干扰的流动特性,并与普通翼—身组合体情况进行比较;分析了涡襟翼的涡流运动特点及其升阻比增大的机理;讨论了翼—身组合体涡系干扰的主要反映及对涡破碎特性的影响;并对非对称体涡出现的条件以及分离旋涡在稳定发展过程中的抗干扰能力提出了看法. 相似文献
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本言语利用离散涡环方法对三个共轴涡环运动进行了数值模拟,在此基础上,采用非线性动力学中混沌特征量的计算方法,得到了涡环呈规则运动和混沌运动的结论。结果表明,三个共轴涡环在运动时,总是会产主规划与混沌的现象。而这些现象的产生取决于三个涡环的初一文析得出对于利用共轴涡环模拟轴对称射流场涡结构的演变具有重要的参考价值。 相似文献
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波涡相互作用研究的某些进展(Ⅱ) 总被引:4,自引:1,他引:3
<正> 5 波涡共振 从第3节的感受性问题再前进一步,自然要问在什么条件下入射波激发起涡中之波的最大响应.这就导致了入射波与层状或轴状涡中受激波之间共振的概念,简称波涡共振.一般说来,在流体内部若有两个或多个波相会,它们将互相穿透而沿原来的方向离去.但若它们的波矢量和频率满足一定的关系(参见Craik 1985),就会在相会点产生新的波.2阶扰动的振幅可达到1阶扰动振幅的量级,而且流场中会出现一些重要的独特性质.这就是流体内部波共振,波涡共振是其一类情形. 相似文献
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混合层流动拟序结构的大涡模拟 总被引:2,自引:0,他引:2
采用大涡模拟方法对空间发展的二维平面混合层进行了数值模拟 ,动量方程采用分步投影法求解 ,亚格子项采用标准Smagorinsky亚格子模式模拟 ,压力泊松方程采用修正的循环消去法快速求解 ,同时求解了标志物输运方程以实现数值流场显示。模拟结果给出了混合层流动的瞬态发展过程以及流动中拟序结构的发展演变过程 ,成功地模拟了混合层发展中的各种瞬态细节过程 ,如涡的卷起、增长 ,涡与涡之间的配对、合并过程 ,以及大涡破碎为小涡的级联过程 ,为各种以混合层流动为原型流动的射流、尾流等工业流动的控制和优化提供了理论基础。 相似文献
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分别用RANS-SA方法和DES方法对NACA0012翼端梢涡进行模拟计算,分析了梢涡区域网格局部加密对梢涡计算结果的影响,并与实验结果进行了对比.相比于RANS-SA方法,DES方法在梢涡流场计算中具有更好的适用性,能够得到更准确的流动信息和更精细的涡结构;另外,网格局部加密对脉动量的计算影响很大.通过对脉动量的分析发现,在近尾缘处,几股涡的融合产生了比较强烈的脉动,随着梢涡的逐渐稳定,脉动量也逐渐减小;现有的实验结果显示在偏下游处会产生梢涡的振荡现象,使统计脉动量增大,而本文计算中未发现该现象. 相似文献
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本文是在文[1]的基础上,引用Cain等人(1981)提出的映射函数将无穷远的边界变换到有限距离处,用伪谱方法对N-S方程组进行直接数值模拟,研究时间发展的二维混合层的不稳定性,再现了大涡的卷起,涡对的合并与撕裂以及三个涡、四个涡之间的相互作用过程,并将过程进行了动态显示。 相似文献
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时间发展平面混合流的三维演化 总被引:6,自引:0,他引:6
采用高精度差分方法和群速度控制方法,求解三维可压缩N S方程,直接数值模拟了时间发展的平面混合流.研究了平面混合流三维拟序结构的形成及发展.给出了流动失稳后涡的卷起,相邻两涡的对并,激波的形成及发展.指出,涡对并所诱导产生的激波对三维拟序结构的形成及发展过程是重要的. 相似文献
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This paper performs large eddy simulations (LES) to investigate coherent structures in the flows after the Sydney bluff-body burner, a circular bluff body with an orifice at its center. The simulations are validated by comparison to existing experimental data. The Q function method is used to visualize the instantaneous vortex structures. Three kinds of structures are found, a cylindrical shell structure in the outer shear layer, a ring structure and some hairpin-like structures in the inner shear layer. An eduction scheme is employed to investigate the coherent structures in this flow. Some large streaks constituted by counter-rotating vortices are found in the outer shear layer and some well-organized strong structures are found in the inner shear layer. Finally, the influences of coherent structures on scalar mixing are studied and it is shown that scalar in the recirculation region is transported outward by coherent structures. 相似文献
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The dynamic characteristics of the large scale coherent structures in a forced free shear layer are experimentally studied
by means of flow visualization. The quantitative measurements are acquired by the use of a LDV. It is shown that the development
of the coherent structures can be greatly influenced by upstream artificial perturbations and as a result the mixing in the
layer can be controlled. Like vortex merging, vortex splitting is also a common evolution pattern in the development of the
coherent structures. 相似文献
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J.P. Dussauge 《Flow, Turbulence and Combustion》2001,66(4):373-391
Some properties of large-scale structures in supersonic turbulent flows are examined through experiments. The large eddies
considered here include energetic scales, which contribute predominantly to, say, turbulent energy and coherent structures.
Different features are presented, such as the level of energy in supersonic free shear flows, the average size of energetic
structures, and their characteristic timescales. It is shown that compressibility affects the level of velocity and the size
of the energetic eddies, but in many common supersonic situations, the estimation of the timescales can be made from rules
valid for solenoidal turbulence. Some implications for compressible turbulence modeling are suggested. Finally, the properties
of coherent structures are considered in the case of mixing layers and in a separated shock/boundary layer interaction. Some
features relative to the organization of the large eddies are given and the importance of the shock motion is discussed in
relation to the shock/layer interaction.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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W.A. McMullan 《International Journal of Computational Fluid Dynamics》2015,29(6-8):333-345
Large Eddy Simulation is used to simulate a series of plane mixing layers. The influence of the spanwise domain on the development of the mixing layer, and the evolution of the coherent structures, are considered. The mixing layers originate from laminar conditions, and an idealised inflow condition is found to produce accurate flow predictions when the spanwise computational domain extent is sufficient to avoid confinement effects. Spanwise domain confinement of the flow occurs when the ratio of spanwise domain extent to local momentum thickness reaches a value of ten. Flow confinement results in changes to both the growth mechanism of the turbulent coherent structures, and the nature of the interactions that occur between them. The results demonstrate that simulations of the two-dimensional mixing layer flow requires a three-dimensional computational domain in order that the flow will evolve in a manner that is free from restraints imposed by the spanwise domain. 相似文献
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The problem of coherent perturbations in a turbulent shear layer is considered for the purpose of developing a mathematical
model based on a triple decomposition that extracts the coherent components of random fluctuations. The governing equations
for the mean and the coherent parts of flow are derived, assuming the eddy-viscosity equivalence for the random part of flow,
and solved by iterations to provide a coupled solution of the problem as a whole. Calculations agree well with experimental
data in the upstream part of the layer where the mean–coherent flow interaction is the most important. In this region, the
interaction changes the mean flow velocity distribution in such a manner that the neutral stability curve is shifted upstream
relative to its position in the undisturbed layer and the perturbation intensity decreases further downstream. Experiments
show that the coherent waves suppress the turbulent Reynolds stress production downstream of this region, but the model fails
to predict the layer spreading correctly probably due to an inadequate turbulence closure of the mean flow. For the case of
a turbulent mixing layer, we suggest a new closure relation that takes into account this coherent-random interaction. 相似文献
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The mixing layer between non-parallel streams 总被引:1,自引:0,他引:1
Compared to the classical two-dimensional plane mixing layer, the mixing layer between non-parallel streams has an additional degree of freedom: the angle between the streams and the direction perpendicular to the trailing edge. Consequently the mean vorticity vector, which depends on these angles, is no longer by necessity parallel to the trailing edge of the flow. The ensuing coherent structures are generally helices with components normal to the trailing edge. They can be controlled by different mechanisms, depending on the velocity vectors. 相似文献
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可压缩燃烧反应转捩混合层直接数值模拟 总被引:1,自引:0,他引:1
针对三维时间发展可压缩氢/氧非预混燃烧反应平面自由剪切混合层,采用5阶迎风/6阶对称紧致混合差分格式以及3阶显式Runge-Kutta时间推进方法,直接数值模拟了伴随燃烧产物生成和反应能量释放, 流动受扰动激发失稳并转捩的演化过程. 在转捩初期, 获得了${\it\Lambda}$涡、马蹄涡等典型的大尺度拟序结构,观察到了流动失稳后发生双马蹄涡三维对并的现象, 大尺度结构呈较好的对称性.在流动演化后期, 大尺度结构逐次破碎形成小尺度结构, 混合层进入转捩末期,呈明显的不对称性. 相似文献
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The equations for fiber suspensions in an evolving mixing layer were solved by the spectral method, and the trajectory and orientation of fibers were calculated based on the slender body theory. The calculated spatial and orientation distributions of fibers are consistent with the experimental ones that were performed in this paper. The relationship between the microstructure of fibers and additional stress was examined. The results show that the spatial and orientation distributions of fibers are heterogeneous because of the influence of coherent vortices in the flow, which leads to the heterogeneity of the additional stress. The degree of heterogeneity increases with the increasing of St number and fiber aspect ratio. The fibers in the flow make the momentum loss thickness of the mixing layer thicker and accelerate the vorticity dispersion.The project supported by the Doctoral Program of Higher Education in China (20030335001) 相似文献