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利用加权本质上无振荡(WENO)方法模拟超声速流体Kelvin-Helmholtz(KH)不稳定性,研究速度梯度对KH不稳定性线性增长率和后期非线性演化的影响.模拟发现超声速流体中的速度梯度对KH不稳定性具有较强的致稳作用,给出了包含速度梯度致稳的线性增长率经验公式.数值模拟和经验公式符合得很好.模拟给出了清晰的流场密度等值线,这说明WENO方法模拟超声速流体KH不稳定性具有较好的界面变形捕捉能力.模拟结果表明速度梯度影响KH涡的演化,在给定密度梯度的情况下速度梯度越大KH涡的横向尺度越小.
关键词:
Kelvin-Helmholtz不稳定性
超声速流体
速度梯度 相似文献
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通过将扰动速度势展至三阶,提出了Kelvin-Helmholtz(KH)不稳定性的弱非线性理论.在模耦合过程中观察到一个重要的共振现象,共振使得模耦合过程变得相当复杂,单模扰动很快进入非线性区,产生大量高次谐波,共振加强了非线性作用.分析了单模扰动中二次和三次谐波产生效应,以及对基模指数增长的非线性校正.模拟结果支持了解析理论.利用该理论,分析了KH不稳定的非线性阈值问题.
关键词:
Kelvin-Helmholtz不稳定性
弱非线性理论
非线性阈值 相似文献
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使用离散Boltzmann模型模拟了可压流体系统中多模初始情况下的Rayleigh-Taylor不稳定性.该离散Boltzmann模型等效于一个Navier-Stokes模型外加一个关于热动非平衡行为的粗粒化模型.通过模拟Riemann问题:Sod激波管、冲击波碰撞和热Couette流问题验证模型的有效性,所得数值结果与解析解一致.利用该模型对界面间断随机多模初始扰动的可压Rayleigh-Taylor不稳定性进行数值模拟研究,得到不稳定性界面演化过程的基本图像.由于黏性和热传导共同作用,一开始扰动界面被"抹平",演化较慢;随着模式互相耦合而减少,演化开始加速,并经历非线性小扰动阶段和不规则非线性阶段,而后发展成典型的"蘑菇状",后期进入湍流混合阶段.由于扰动模式的耦合与发展,轻重流体的重力势能、压缩能与动能相互转化,系统先是趋于热动平衡态,而后偏离热动平衡态以线性形式增长,接着再次趋于热动平衡态,最后慢慢远离热动平衡态. 相似文献
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应用匹配渐近展开法和多变量展开法研究各向异性表面张力对定向凝固中深胞晶界面形态稳定性的影响, 通过寻找定向凝固系统的模式解获得了深胞晶界面形态满足的量子化条件. 结果表明, 与各向同性的定向凝固系统中深胞晶界面形态稳定性比较, 考虑各向异性表面张力的定向凝固中深胞晶生长界面形态也有两种整体不稳定性机制: 整体波动不稳定性和低频不稳定性. 随着各向异性表面张力的增加, 中性模式产生强振荡的枝晶结构的整体波动不稳定性的不稳定区域减小, 中性模式产生弱振荡的胞晶结构的低频不稳定性的不稳定区域增加. 相似文献
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液体雾化被广泛应用于工业、农业等领域,雾化过程中液体首先形成液膜,液膜在气液边界层内出现不稳定,导致液膜破碎。因此液膜的不稳定性对液体雾化起着非常重要的作用,有必要对液膜的不稳定性进行研究。采用数值计算的方法对可压缩气体中黏性平面液膜的不稳定性进行了研究,首先对黏性平面液膜和气体的速度分布进行推导,在此基础上采用谱方法对黏性平面液膜的不稳定性进行了研究。研究发现:在正弦和曲张模式下,施加电场会加速平面液膜的破碎;正弦模式比曲张模式更加不稳定,说明正弦模式在平面液膜不稳定中起主导作用;气体Mach数、电Euler数、气体Reynolds数、 Weber数和动量通量比的增加会加速液膜的破裂;随着气体边界层与液膜厚度比和液体Reynolds数的增加,扰动波的增长速率降低,液膜变得更加稳定。 相似文献
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This work focuses on the characteristics of the Rayleigh-Taylor Instability (RTI) of the interfaces formed by two semi-infinitely distributed fluids and one interlayer. In consideration of the coupling effects between the interfaces, the expression of the growth rate is obtained. The result reveals that the instability growth rate depends on the density and thickness of the interlayer. It is found that /f the interlayer thickness is less than 0.6 times of the disturbing wavelength, the coupling effects should be considered. 相似文献
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E.N. Zubarev V.V. Kondratenko V.A. Sevryukova S.A. Yulin T. Feigl N. Kaiser 《Applied Physics A: Materials Science & Processing》2008,90(4):705-710
The influence of a negative substrate-applied bias potential on the structure of periodic Mo/Si multilayer compositions has
been investigated by means of cross-sectional electron microscopy, small-angle X-ray reflectivity, X-ray diffraction and by
modeling the small-angle spectra. It is known that the crystalline structure of molybdenum layers is the main source of interface
roughness. In the absence of a bias potential application, the interface roughness tends to develop from the substrate towards
the surface of a Mo/Si multilayer composition. A negative bias potential (up to -200 V) applied to a substrate during silicon
layer deposition leads to smoother interfaces and improves the layer morphology. After increasing the bias potential over
-200 V a considerable growth of an amorphous interlayer transition zone can be observed at Si-on-Mo interfaces. By raising
the bias potential during the deposition of Mo layers a development of roughness at Mo-on-Si interfaces as well as growing
interlayer thicknesses were found.
PACS 61.10.Kw; 68.37.-d; 68.65.Ac 相似文献
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The interaction of iron layers through a chromium spacer in Fe/Cr/Fe trilayers with different roughnesses of interfaces was studied by the Kerr magnetometry and Mandel’shtam-Brillouin light scattering techniques so as to trace the interlayer exchange coupling of the Fe layers depending on the Cr spacer thickness and the sample temperature. It is established that, in a broad range of these parameters, the interlayer exchange in Fe/Cr/Fe structures with sufficiently smooth interfaces is adequately described using the proximity magnetism and half-angle coupling models taking into account the antiferromagnetic properties of chromium. As the interface roughness increases, the well-known biquadratic exchange model becomes valid. This is evidence for the decisive role of the magnetic stiffness of a Cr spacer and the structure of interfaces on the noncollinear exchange coupling in Fe/Cr/Fe trilayers. 相似文献
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The phase transition “polydomain state-single-domain state” with exchange springs in the antiferromagnetic interlayer of the
spin-valve ferromagnet-antiferromagnet-ferromagnet structure, which occurs as the ratio of the interlayer thickness to the
width of atomic steps on the interfaces between the layers increases, has been investigated using mathematical simulation.
The critical value of this ratio, at which the phase transition occurs, and the deflection of exchange springs that appear
at the interfaces between the layers have been determined in a wide range of values of the single-ion anisotropy constant. 相似文献
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The interface-mediated plastic deformation mechanisms of a semi-coherent Cu–Ag bimetal nanolayered structure subjected to out-of-plane tension are characterized by molecular dynamics simulations. Results show that the initially planar Cu–Ag nanolayers abruptly become wavy at a critical tensile strain. This planar-to-wavy interlayer transition is facilitated by the low shear resistance of the Cu–Ag interlayer interface, which slides to accommodate the out-of-plane deformation. The process redistributes misfit dislocations along the interface to reduce the bending energy of the wavy structure. High stress concentrations subsequently develop at the summits and valleys of the wavy Cu–Ag interlayer interfaces, from which micro-twinning partials are emitted. These results demonstrate that the wavelength of the wavy Cu–Ag nanolayer structure forms a critical length scale for the localization of spatially periodic defect sources for twin nucleation. This planar-to-wavy interlayer transition mechanism is only activated in nanolayered metals with interfaces that are amenable to sliding prior to twin or dislocation emissions. 相似文献
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Study on characteristics of a double-conductible channel organic thin-films transistor with an ultra-thin hole-blocking layer
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The properties of top-contact organic thin-film transistors
(TC-OTFTs) using ultra-thin 2, 9-dimethyl-4, 7-diphenyl-1,
10-phenanthroline (BCP) as a hole-blocking interlayer have been
improved significantly and a BCP interlayer was inserted into the
middle of the pentacene active layer. This paper obtains a fire-new
transport mode of an OTFT device with double-conductible channels. The
accumulation and transfer of the hole carriers are limited by the
BCP interlayer in the vertical region of the channel. A huge
amount of carriers is located not only at the interface
between pentacene and the gate insulator, but also at the two interfaces
of pentacene/BCP interlayer and pentacene/gate insulator,
respectively. The results suggest that the BCP interlayer may be
useful to adjust the hole accumulation and transfer, and can
increase the hole mobility and output current of OTFTs. The TC-OTFTs
with a BCP interlayer at VDS=-20~V showed excellent hole
mobility μFE and threshold voltage VTH of
0.58~cm2/(V\cdots) and --4.6~V, respectively. 相似文献
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We present calculations of the non-collinear magnetic structure in Fe/Cr superlattices having imperfect interfaces modeled by considering atomic steps in the Cr layers and Fe/Cr interfacial ordered compounds. The interlayer couplings are obtained directly from self-consistent tight binding band structure calculations. We show that the bilinear–biquadratic expression for the coupling energy fits nicely the calculated interlayer couplings curves. 相似文献
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在微波等离子体化学气相沉积装置中,采用负偏压形核等方法,研究两种不同的W过渡层/基体结合界面对金刚石薄膜与WC-6%Co附着力的影响。采用氢等离子体脱碳、磁控溅射镀W、高偏压碳化等方法,在YG6衬底表面形成化学反应型界面,W膜在碳化时和基体WC连为一体,极大地增加了W膜与基体的附着力,明显优于直接镀钨、碳化形成的物理吸附界面。在高负偏压下碳化,能提高表面粗糙度,增加膜与基体机械钳合,而负偏压形核增加核密度,从而增加膜与基体的接触面积,结果极大地提高了金刚石薄膜的附着力。 相似文献
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The phase of the short-range interlayer exchange coupling oscillations in Fe n Cr m superlattices is expressed in terms of the intermixing at the Fe-Cr as well as at the Cr-Fe interfaces. The interdiffusion is modeled through stochastic algorithms, which presupposes floating of the atoms on the surface of the sample during the epitaxial growth. It automatically leads to the different chemical and magnetic structure of Fe on Cr and Cr on Fe interfaces. Self-consistent calculations of the magnetic moments are performed on the basis of the periodic Anderson model. Although short-range (2 monolayers (ML)) oscillations of exchange coupling were detected for all considered structures, its amplitude and phase strongly depend on the interface alloying. Introduction of the same intermixing at both interfaces does not change the phase as compared to the ideal superlattices with sharp interfaces. However different interdiffusion leads to the ~ -phase shift in accordance with experimental results for the Fe-Cr-Fe trilayers grown on an Fe whiskers. Distribution of magnetic moments on Fe atoms contains several distinct peaks but their position and relative area weakly depend on the alloying and interlayer exchange coupling in the superlattice. On the contrary, magnetic moments on Cr atoms are very sensitive to the intermixing and their behavior determines the strength and the phase of exchange coupling oscillations. 相似文献
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《Composite Interfaces》2013,20(4):321-334
The plasma polymerization technique was used to surface modify glass fibers in order to form a strong but tough link between the glass fiber and the polyester matrix, and enable an efficient stress transfer from the polymer matrix to the fiber. Plasma polymer films of hexamethyldisiloxane, vinyltriethoxysilane, and tetravinylsilane in a mixture with oxygen gas were engineered as compatible interlayers for the glass fiber/polyester composite. The interlayers of controlled physico-chemical properties were tailored using the deposition conditions with regard to the elemental composition, chemical structure, and Young's modulus in order to improve adhesion bonding at the interlayer/glass and polyester/interlayer interfaces and tune the cross-linking of the plasma polymer. The optimized interlayer enabled a 6.5-fold increase of the short-beam strength compared to the untreated fibers. The short-beam strength of GF/polyester composite with the pp-TVS/O2 interlayer was 32% higher than that with industrial sizing developed for fiber-reinforced composites with a polyester matrix. 相似文献