共查询到18条相似文献,搜索用时 343 毫秒
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本文设计了具有相同平均沟槽密度的三种排列类型的一维沟槽结构: 密排列、周期间隔排列和两种准周期间隔排列, 并采用数值模拟和实验验证相结合的方法研究了一维沟槽结构在不同排列下的流体减阻特性. 模拟计算分析流场特征和总阻力, 发现相对于密排列和周期间隔排列的沟槽结构, 准周期间隔排列具有更好的减阻特性, 并且这一结果得到减阻实验的验证. 通过流场分布特性进一步分析沟槽结构的减阻机理. 机理分析发现高速流在经一维准周期结构的扰动波调制后形成了准周期间隔排列的速度条纹相, 这有效地抑制了大涡在流向和展向上的形成, 从而实现较大幅度的减阻. 同时对比分析沟槽排列结构调制展向涡和流向涡各自对流动减阻的贡献, 结果表明, 调制流向涡对减阻的作用更大.
关键词:
流体减阻
沟槽结构
准周期 相似文献
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设计构建了一排和三排阵列的八重准周期短条纹沟槽减阻结构,以及作为对比研究的无序和周期结构,并采用雷诺Navier-Stokes方程和RANGκ-ε湍流模型,系统计算了这些结构表面的湍流边界层状态和总应力,模拟结果显示:八重准周期沟槽结构相对于周期和无序结构具有更优的减阻效应,且为三排阵列时的减阻效果明显优于单排阵列,这一结果得到了减阻实验的验证,通过分析比较不同结构的流体边界层特性发现,八重准周期结构可有效抑制附面层的涡强度,减小湍流耗散速率,保持流体条纹相的稳定性,结合二维光栅的夫琅禾费衍射波模型分析表明,八重准周期结构可减弱衍射谱在大角度方向上的谱强度,揭示出该结构抑制流体相干扰动波扩展的物理机制,并与流场分析结果相符合。 相似文献
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采用旋转锥板式剪切力测试系统,测试了人工构建的具有五次、八次、十次、十二次对称性的二维准晶结构对甘油和水混合液的减阻性能,并与随机排列结构和周期排列结构的流阻进行了对比.对比试验发现:准晶结构具有显著的减阻效果,其中具有十二次对称性的二维准晶结构减阻效应最大,在剪切率为200—2000 s-1时,剪切力减小的幅度从15%—9%,其最大减阻量可达到15.4%.进一步在所构建的大尺度二维准晶结构的表面,再复合制备微/纳米粗糙结构,这两种尺度的结构协和作用,可实现减阻效果明显提高.
关键词:
准晶结构
粗糙结构
十二次对称性
减阻 相似文献
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提出了一维广义Fibonacci准周期结构的声子晶体模型. 对弹性波通过该一维准周期结构声子晶体的透射系数进行数值计算,并与周期结构和标准Fibonacci准周期结构声子晶体的透射系数进行比较. 结果表明,利用一维广义Fibonacci准周期结构的声子晶体可获得比周期结构和标准Fibonacci准周期结构声子晶体更大的带隙范围,同时在带隙内有更丰富的局域模式存在. 对局域模性质的研究有助于声波或弹性波滤波器的制作.
关键词:
广义Fibonacci准周期结构
声子晶体
局域化 相似文献
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利用高时间分辨率粒子图像测速(time-resolved particle image velocimetry, TR-PIV)技术,在不同雷诺数下对光滑壁面和二维顺流向、三维正弦波(two/three dimensional, 2D/3D)沟槽壁面湍流边界层流场进行了实验测量,从不同沟槽对湍流边界层相干结构影响的角度分析了其减阻的机理.对比不同壁面的各阶统计量结果发现:沟槽降低了壁面摩擦阻力,存在减阻效果,正弦波沟槽的减阻率增大.运用相关函数、λ_(ci)检测准则等方法提取了不同壁面湍流边界层发卡涡和低速条带等典型相干结构的空间拓扑形态,结果表明:两种沟槽壁面的相干结构在流向和法向上的空间尺度均有不同程度的减小,且相干结构与主流之间的倾角趋于更小,流体在法向上的运动及结构的抬升受到明显抑制,发卡涡诱导喷射和扫掠的能力降低,从而影响了湍流中能量与动量的输运过程及湍流的自维持机制,且相比于2D沟槽, 3D正弦波沟槽作用效果更为明显.在同一雷诺数下,随着距离壁面法向位置的增加,不同壁面湍流边界层低速条带的展向间距都变宽;但同一法向位置处2D/3D沟槽壁面湍流边界层低速条带的间距与光滑壁面的相比更宽,沟槽的存在有效抑制了低速条带在展向上的运动,使得低速条带更稳定. 相似文献
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D. V. Olenev É. I. Isaev Yu. Kh. Vekilov 《Journal of Experimental and Theoretical Physics》1998,86(3):550-558
Electron spectra and wave functions of icosahedral quasicrystals have been investigated in the tight-binding approximation
using the two-fragment structural model (the Amman-MacKay network) with “central” decoration. A quasicrystal has been considered
as a limiting structure in a set of optimal cubic approximants with increasing lattice constants. The method of level statistics
indicates that the energy spectrum of an icosahedral quasicrystal contains a singular (nonsmooth) component. The density of
electron states has been calculated for the first four optimal cubic approximants of the icosahedral quasicrystal, and the
respective Lebesgue measures of energy spectra of these approximants have been obtained. Unlike the case of a one-dimensional
quasiperiodic structure, the energy spectrum of an icosahedral quasicrystal does not contain a hierarchical gap structure
typical of the Cantor set of measure zero in a one-dimensional quasicrystal. Localization of wave functions in an icosahedral
quasicrystal has been studied, and their “critical” behavior has been detected. The effect of disorder due to substitutional
impurities on electron properties of icosahedral quasicrystals has been investigated. This disorder makes the electron spectrum
“smoother” and leads to a tendency to localization of wave functions.
Zh. éksp. Teor. Fiz. 113, 1009–1025 (March 1998) 相似文献
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《Superlattices and Microstructures》1998,24(4):291-293
Mesoscopic conductance fluctuations of a two-dimensional electron gas in a one-dimensional periodic array of antidots have been studied experimentally, for the first time. The fluctuations show a quasiperiodic behaviour on magnetic field, with period corresponding to the quantization of magnetic flux through the area of a unit cell of the one-dimensional array. The existence of the quasiperiodic component is explained by an anomalous area distribution of interfering trajectories. 相似文献
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Structure of the Al---Rh---Cu decagonal quasicrystal has been studied by high-resolution electron microscopy. The high-resolution structure image shows an aperiodic tiling composed of three kinds of subunits, namely flattened hexagon, crown and five star. Therefore, a structural model of the Al---Rh---Cu decagonal quasicrystal has been constructed in a unit-cell approach, in which the atom arrangements in the subunits have been proposed. It is known that the phase has two layers in a period of 0.4 nm along the unique tenfold axis according to the previous study by electron diffraction method. The ideal model of the Al---Rh---Cu decagonal quasicrystal is proposed as periodic stacking of the layers with quasiperiodic tessellation of the three kinds of subunits, in each layer the two-colour Penrose tiling is obtained if different atom decorations for the same shape subunits are distinguished by white and black colours. Calculated images reproduces well the contrast features of the observed images, which means that the present model is basically correct. Structural relationship between the Al---Rh---Cu decagonal quasicrystal and the previously reported Al---Ni---Co decagonal quasicrystal, which has also a period of 0.4 nm, has also been discussed. 相似文献
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Stefanie Thiem 《哲学杂志》2015,95(11):1233-1243
Recently, the occurrence of log-periodic oscillations in the quantum dynamics of electrons was reported for the one-dimensional Fibonacci quasicrystal by Lifshitz and Even-Dar Mandel. We apply a real-space renormalization group approach to show that these log-periodic oscillations are related to the underlying quasiperiodic structure of the Fibonacci quasicrystal. We find that they originate from the superposition of bonding and antibonding states associated to strongly coupled atoms in the chains, and that they show a hierarchical structure closely related to the atomic configurations. 相似文献
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Abstract In this article, light reflection spectrums for different one-dimensional multi-layer structures are obtained. Optical reflectivities for periodic, superperiodic, and quasiperiodic structures have been calculated using the transfer matrix method. PBGs of each structure have been obtained using the optical reflectivity pattern. From a comparison of reflectivity and standard dense wavelength division multiplexing grids, it is demonstrated that narrow and dense band filters can be built from generalized Fibonacci quasiperiodic structures. Reflectivity of these structures contains bands that meet the ITU-T dense wavelength division multiplexing standard. Reflectivity of other multi-layer structures has poor or less potential to be used in dense wavelength division multiplexing systems. 相似文献
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Mechanism of controlling turbulent channel flow with the effect of spanwise Lorentz force distribution 下载免费PDF全文
A direct numerical simulation(DNS) is performed to investigate the control effect and mechanism of turbulent channel flow with the distribution of spanwise Lorentz force. A sinusoidal distribution of constant spanwise Lorentz force is selected, of which the control effects, such as flow characters, mean Reynolds stress, and drag reductions, at different parameters of amplitude A and wave number k_x are discussed. The results indicate that the control effects vary with the parameter A and k_x. With the increase of A, the drag reduction rate D_r first increases and then decreases rapidly at low k_x,and slowly at high k_x. The low drag reduction(or even drag increase) is due to a weak suppression or even the enhancements of the random velocity fluctuation and mean Reynolds stress. The efficient drag reduction is due to the quasi-streamwise vortex structure induced by Lorentz force, which contributes to suppressing the random velocity fluctuation and mean Reynolds stress, and the negative vorticity improves the distribution of streamwise velocity. Therefore, the optimal control effect with a drag reduction of up to 58% can be obtained. 相似文献