Acoustic Transducer of Turbulent Pressure Fluctuations in a Temperature-Stratified Medium

The operation of an acoustic transducer in a temperature-stratified medium is investigated. The formation of a response of piezoceramic transducers of pressure fluctuations under the action of temperature fluctuations in a working medium on the sensor element is considered. The attenuation of the temperature signal of a pressure transducer in a turbulent boundary layer is calculated numerically. The effect of distortions of the spectral levels of pressure fluctuations detected by a sound transducer in the field of temperature inhomogeneities is investigated for the example of measurements of turbulent pressure fluctuations in a boundary layer during vertical ascent of the device to the surface from a specified depth in a deep sea.     

Heat Transfer and Pressure Drop Characteristics in Turbulent Flow Through a Tube

An experimental investigation has been carried out for turbulent flow through a tube with perforated strip inserts. Strips were of mild steels with circular holes of different diameters. Flow varies, with ranging Reynolds numbers from 15,000 to 47,000. Air velocity, tube wall temperatures, and pressure drops were measured for a plain and strip-inserted tube. The heat transfer coefficient and friction factor were found to be 2.80 times and 1.8 times, respectively, that of the plain tube. The heat transfer performance was evaluated and found to be 2.3 times that of the plain tube based on constant blower power.     

Two Phases of Coherent Structure Motions in Turbulent Boundary Layer

Two phases of coherent structure motion are acquired after obtaining conditional phase-averaged waveforms for longitudinal velocity of coherent structures in turbulent boundary layer based on Harr wavelet transfer. The correspondences of the two phases to the two processes （i.e. ejection and sweep） during a burst are determined.     

Pressure Dependence of Wurtzite ZnO Structure

From simultaneous X-ray diffraction and EXAFS experiments, structural properties in the Wurtzite phase of ZnO have been measured up to the transition pressure (9 GPa). These results are compared with first-principles calculations and discussed in terms of wurtzite mechanical stability at high pressure.     

湍流边界层对数律区相干结构的Tomo-TRPIV实验研究

应用层析高时间分辨率粒子图像测速技术（tomographic time-resolved particle image velocimetry,Tomo-TRPIV）,测量了Re_θ=2 460的平板湍流边界层三维3分量瞬时速度场的时间序列.提出湍流空间多尺度局部平均速度结构函数的概念,应用流向脉动速度沿流向的空间多尺度局部平均速度结构函数的正负过零点法,从瞬时脉动速度场中检测相干结构的喷射和扫掠事件,对检测到的喷射和扫掠事件的瞬态局部速度场、速度梯度场、涡量场、速度变形率场进行空间相位对齐叠加平均,获得喷射和扫掠事件的局部速度场、速度梯度场、涡量场、速度变形率场的典型特征.研究发现,相干结构喷射和扫掠时,速度梯度、速度变形率、涡量均表现为空间反对称分布的4极子结构.特别是流向涡量是沿流向、法向、展向均为反对称分布的法向多层4极子结构,表明法向各层相干结构是紧密联系,互相关联的.这种法向多层的4极子反对称结构导致强烈的动量、质量和能量交换,维持了相干结构的演化和发展过程.      

Longitudinal Structure Function F L of Proton from Regge Like Behaviour of Structure Function at Small-x

The evolutions of longitudinal structure function F _L from quantum chromodynamics (QCD) evolution equation in next-to-leading order at small-x is presented using the Regge like behaviour of the structure function. The proposed simple analytical expression for F _L structure function provides the t- and x-evolution equations to study the behaviour of F _L structure function at small-x. The calculated results are compared with the data of H1, ZEUS collaborations and results of Block model, Donnachie–Landshoff model. Our calculated results can be described within the framework of perturbative QCD.     

对流湍流池Fried相干长度的光学结构

利用不同的方法，测量并比较了用自适应光学补偿实验的对流湍流池的相干长度，给出到达角起伏谱和起伏方差的概率分布，结果表明，在对流湍流池中，光束的到达角起伏谱满足“－８／３”幂，由于相位起伏服从正态分布，因此到达角起伏的方差呈Ｘ＾２分布，到达角起伏在水平和垂直方向上的谱完全一致表明了湍流池湍流的各向同性特征，相干长度与对流湍流池上下温差的实验结果，符合以往对流湍流池的流体力学和热力学相心关系。     

Turbulent cascades

Turbulent cascades at high Reynolds numbers are explained briefly in terms of multipliers and multiplier distributions. Two properties of the multipliers ensure the existence of power laws for locally averaged energy dissipation rate: (a) the existence of a multiplier probability density function that is independent of the level of the cascade, and (b) the statistical independence of multipliers at one level on those at previous levels. Under certain conditions described in the paper, the same two properties of multipliers guarantee that velocity increments over inertial-range separation distances also possess power laws. This work is specifically motivated by the need to understand the influence on scaling of the experimental observations that property (a) is true for turbulence, but property (b) is not; and additional motivation is the need to relate cascade models to intermittent vortex stretching (and folding). This effect has been modeled by allowing the multiplier distribution to depend on the magnitude of the local strain rate, and it is demonstrated that this rate-dependent model accounts for the statistical dependence observed in experiments. It is also shown that this model is consistent with the uncorrelated cascade models except for very weak singularity strengths (or for negative moments below a certain order), leading to the conclusion that, for all practical purposes, the uncorrelated level-independent multipliers abstract the essence of the breakdown process in turbulence.     

对流湍流池光学湍流的空间和时间结构分析

分析了用于自适应光学波前补偿实验的对流湍流池折射离和光强起伏的空间、时间结构,建立了平均速度很小或等于零时的相关函数,讨论了速度起估对相关的扩散作用。数值计算和实测的结果表明：速度起估不仅使时间相关减小,而且使频谱的内尺度减小。     

Crystal Structure Transformations of Rare-Gas Solids Under Pressure

Pressure-induced structural changes in solid krypton (Kr) and xenon (Xe) have been studied using angle dispersive X-ray diffraction in a diamond-anvil cell (DAC) up to 50 GPa. The analysis of the results shows that in solid Kr (Xe) the phase transition from fcc to hcp starts below 3.2 GPa (1.5 GPa). Albeit the hcp/fcc ratio increases under pressure, both phases coexist up to the highest pressure reached in this study. Room temperature (RT) equations of state (EOS) are determined.     

Heat Transfer and Pressure Drop of Nanofluid with Rod-like Particles in Turbulent Flows through a Curved Pipe

Pressure drop, heat transfer, and energy performance of ZnO/water nanofluid with rodlike particles flowing through a curved pipe are studied in the range of Reynolds number 5000 ≤ Re ≤ 30,000, particle volume concentration 0.1% ≤ Φ ≤ 5%, Schmidt number 10⁴ ≤ Sc ≤ 3 × 10⁵, particle aspect ratio 2 ≤ λ ≤ 14, and Dean number 5 × 10³ ≤ De ≤ 1.5 × 10⁴. The momentum and energy equations of nanofluid, together with the equation of particle number density for particles, are solved numerically. Some results are validated by comparing with the experimental results. The effect of Re, Φ, Sc, λ, and De on the friction factor f and Nusselt number Nu is analyzed. The results showed that the values of f are increased with increases in Φ, Sc, and De, and with decreases in Re and λ. The heat transfer performance is enhanced with increases in Re, Φ, λ, and De, and with decreases in Sc. The ratio of energy PEC for nanofluid to base fluid is increased with increases in Re, Φ, λ, and De, and with decreases in Sc. Finally, the formula of ratio of energy PEC for nanofluid to base fluid as a function of Re, Φ, Sc, λ, and De is derived based on the numerical data.     

Resonance Structure of the Charge-Exchange Strength Function

Physics of Atomic Nuclei - The resonance structure of the charge-exchange strength function S(E) is studied. Three types of isobaric resonances are considered within the self-consistent theory of...     

Nuclear Effect on the Nucleon Structure Function

The overlap and the leakage of the parton was considered so that the nucleon effective mass can be successfully used as the only free parameter to adjust the structure function ratios recently measured by NMC.     

LaB_6 Work Function and Structural Stability under High Pressure

The work functions of the(110) and(100) surfaces of LaB_6 are determined from ambient pressure to 39.1 GPa.The work function of the(110) surface slowly decreases but that of the(100) surface remains at a relatively constant value. To determine the reason for this difference, the electron density distribution(EDD) is determined from high-pressure single-crystal x-ray diffraction data by the maximum entropy method. The EDD results show that the chemical bond properties in LaB_6 play a key role. The structural stability of LaB6 under high pressure is also investigated by single-crystal x-ray diffraction. In this study, no structural or electronic phase transition is observed from ambient pressure to 39.1 GPa.     

Turbulent pair diffusion

Kinematic simulations of turbulent pair diffusion in planar turbulence with a k(-5/3) energy spectrum reproduce the laboratory results of Jullien et al. [Phys. Rev. Lett. 82, 2872 (1999)]], in particular the stretched exponential form of the probability density function of pair separations and their correlation functions. The root mean square separation is found to be strongly dependent on initial conditions for very long stretches of time. This dependence is consistent with the topological picture where pairs initially close enough travel together for long stretches of time and separate violently when they meet straining regions around hyperbolic points. A new argument based on the divergence of accelerations is given to support this picture.     

Development of Experimental Research of Turbulent Surface Pressure Fluctuations: Critical Analysis and Generalization of Accumulated Experimental Data

Acoustical Physics - The article reviews the current state of experimental research into near-wall turbulent pressures. In recent decades, a large number of applied, theoretical, and experimental...