人工扰动信号在湍流边界层中的衰减

将人工扰动引入湍流流场,使用功率谱分析方法,研究边界层外层的较大频率范围内的人工扰动信号沿流向和法向的衰减,获得了人工扰动在湍流边界层中的衰减趋势．     

应用共轴型二维激光测速系统测量孔板管流的湍流特性

本文发表了一种共轴型二维激光测速系统,可同时测量由三束入射光组成的平面内的二维速度分量。讨论了主要的测量误差并提出了一种修正共轴分量角度偏差的方法。应用该系统详细测量了单孔板和双孔板管流的轴向和径向平均速度。湍流度和雷诺切应力分布,表明来流条件对孔板下游的湍流特性有强烈影响。     

吹吸扰动对壁湍流相干结构的影响

采用热线风速仪测量受吹吸扰动的壁湍流边界层的流向速度,用傅里叶变换和子波变换研究 吹吸扰动对壁湍流能谱的影响,结果显示施加的低频扰动使边界层内层大尺度结构的能量减 少,小尺度结构的能量有所增强,远离壁面时扰动强度逐步衰减直到在外层中消失;通过VITA 法和子波变换法检测猝发事件,表明该扰动降低了猝发强度,使猝发周期延长,条件平均速 度波形的幅值降低、持续时间变短,说明扰动明显抑制了相干结构的猝发过程. 利用子波变 换可以实现湍谱分析,能有效检测猝发中的湍流结构,是一种客观的分析工具.     

大动脉中血液流动的中性扰动

本文在长波假定下用流体力学线性稳定性理论对大动脉中血液流动求出了一种中性扰动。结果表明，心室或瓣引起的扰动在一定条件下有可能量一种中性扰动，它可以沿着动脉管无变形地传播到动脉远端。这说明也许有可能提供一种通过在远离心脏的某些浅表动脉部位检测这种中性成动以了解心脏的某些功能的新方法。     

管内湍流旋流的数值计算

本文用有限差分法对直管内的湍流旋流进行了数值模拟。计算中采用Ｂｏｕｓｓｉｎｅｓｑ湍流涡粘性假设的基本思想和Ｋ－ε双方程模型来求解雷诺应力各分量。为了反映旋流中湍流转输的非均匀性和各向异性特征，对雷诺应力各分量及与之相主尖的各湍流粘性系数分别进行计算。计算结果表明该模型能较好地反映直管内湍流旋流的流动结构。     

周期性扰动在湍流边界层中沿法向的衰减

在开口式循环水槽底部湍流边界层外区中引入周期性扰动,利用X型热膜探针对下游扰动进行测量。研究了湍流边界层中周期性人工扰动对湍流结构的影响,获得了人工扰动在湍流边界层中沿法向的衰减趋势。     

气固两相流动的湍流脉动扩散数学模型及其应用

本文提出了气固两相流动的湍流扩展数学模型，本模型用k-ε双方程模型求解气相湍流场，并根据气流脉动的频谱、能谱曲线提出了随机富工级数来模拟气相脉动速度，用拉氏方法描述颗粒的运动，故称为脉动频谱随机颗粒轨道模型。本文还给出了本模型在气固多相射流和流化床内应用的实例。     

PANS模型在空化湍流数值计算中的应用

采用一种基于标准k-ε模型改进的局部时均化模型（Partially-Averaged Navier-Stokes Model,PANS）,并应用于空化流动计算。控制不同的模型参数,分别对绕平头轴对称回转体和Clark-Y型水翼的空化流动进行模拟,并与实验结果进行对比。结果表明：PANS模型中未分解湍动能比率fk的取值对预测空化流动的数值计算精度有重要影响,改变fk的取值可实现对不同滤波尺度范围内的求解;随着fk值的减小PANS的预测精度逐步提高,能在相对较大范围内求解较小尺度的湍流运动过程中,预测到湍流运动中强烈的非定常特性;同时可以比较准确地预测空化流场结构和动力特性。     

轴流压气机失速初始扰动的研究进展

在失速主动控制思想的推动下,对轴流压气机失速初始扰动的研究一直是叶轮机械非定常流领域的热点问题之一,同时也是一个尚未认识清楚的难点问题. 本文从失速初始扰动的理论模型、实验研究和机理分析3个方面对轴流压气机失速初始扰动的研究进展进行了回顾.对目前失速初始扰动研究中的集中问题,如低速和高速环境下初始扰动的试验检测方法, 初始扰动类型,以及初始扰动出现的内在流体动力学机理等问题进行了总结. 在此基础上,讨论了叶尖区域的复杂流动特性和失速初始扰动的内在联系,并指出了失速初始扰动研究的发展趋势, 认为今后应进一步深化如下问题:初始扰动形式影响因素的系统研究, 高速压气机中初始扰动新形式研究,初始扰动产生的流体动力学物理机制及其与压气机的设计和运行参数之间的关联性研究.      

含活塞的管内湍流的数值模拟

应用两方程模式和 SIMPLER 算法对含活塞的管内复杂湍流进行了数值模拟.活塞直径和外管内径之比为0.8,雷诺数为6.05×10~4.数值模拟得到了三个回流区.下游回流的分离-再附长度是活塞直径的1.5倍.间隙段存在流速超越现象,但不存在后台阶流动计算中的核心区现象.文中给出了数值模拟的详细成果.     

圆管过渡流态的间歇因子

用激光测速方法研究圆管流动的湍流间歇现象．实验表明,间歇湍流首先在管壁发生,逐渐向下游扩张．随着雷诺数的增加,间歇因子γ＝０．５的转捩界面逐渐向入口推移,一直到Ｒｅ＝９８８７,整个管流才变成间歇湍流和充分湍流     

Experiments in Turbulent Pipe Flow with Polymer Additives at Maximum Drag Reduction

In this paper we report on (two-component) LDV experiments in a fully developed turbulent pipe flow with a drag-reducing polymer (partially hydrolyzed polyacrylamide) dissolved in water. The Reynolds number based on the mean velocity, the pipe diameter and the local viscosity at the wall is approximately 10000. We have used polymer solutions with three different concentrations which have been chosen such that maximum drag reduction occurs. The amount of drag reduction found is 60–70%. Our experimental results are compared with results obtained with water and with a very dilute solution which exhibits only a small amount of drag reduction. We have focused on the observation of turbulence statistics (mean velocities and turbulence intensities) and on the various contributions to the total shear stress. The latter consists of a turbulent, a solvent (viscous) and a polymeric part. The polymers are found to contribute significantly to the total stress. With respect to the mean velocity profile we find a thickening of the buffer layer and an increase in the slope of the logarithmic profile. With respect to the turbulence statistics we find for the streamwise velocity fluctuations an increase of the root mean square at low polymer concentration but a return to values comparable to those for water at higher concentrations. The root mean square of the normal velocity fluctuations shows a strong decrease. Also the Reynolds (turbulent) shear stress and the correlation coefficient between the stream wise and the normal components are drastically reduced over the entire pipe diameter. In all cases the Reynolds stress stays definitely non-zero at maximum drag reduction. The consequence of the drop of the Reynolds stress is a large polymer stress, which can be 60% of the total stress. The kinetic-energy balance of the mean flow shows a large transfer of energy directly to the polymers instead of the route by turbulence. The kinetic energy of the turbulence suggests a possibly negative polymeric dissipation of turbulent energy. This revised version was published online in July 2006 with corrections to the Cover Date.     

平面粘性流体扰动与哈密顿体系

通过变分原理,将哈密顿体系的理论引入到平面粘性流体扰动的问题中,导出一套哈密顿算子矩阵的本征函数向量展开求解问题的方法。基于直接法求解流体力学基本方程,导出流场一般特征关系,通过本征值的求解及本征向量的叠加,得到波扰动解,继可分析流场端部效应。从而在该领域用在哈密顿体系下辛几何空间中研究问题的方法代替了传统在拉格朗日体系欧几里德空间分析问题的方法。为流体力学的研究提供一条新途径。     

湍流管径问题算法的改进

本文采服无量纲参数（ｇＪＯ＾３／ｖ＾５）及ＫｓＶ／Ｑ）由最小二乘法以指数函数拟合Ｐｒａｎｄｔｌ及Ｋａｒｍａｎ公式，得出分别适用于光滑区和粗糙区的管径算式。再对以上两式作粘性关联偶合，得出适用于湍流过渡区的管径算式。可直接求出管径，避免繁复试算和迭代。计算结果与Ｐｒａｎｄｔｌ，Ｋａｒｍａｎ及Ｃｏｌｅｌｒｏｏｋ－Ｗｈｉｔｅ等经典公式能精确吻合，较Ｓｗａｍｅｅ－Ｊａｉｎ湍流管径算式误差减少一半以上。     

Analysis of Streamwise Velocity Fluctuations in Turbulent Pipe Flow with the Use of an Ultrasonic Doppler Flowmeter

Data collected from several studies of experimental and numerical nature in wall-bounded turbulent flows and in particular in internal flows (channel and pipe flows, Mochizuki and Nieuwstadt [1]) at different Reynolds numbers R ⁺(Ru _*/ν), indicate that: (i) the peak of the rms-value (normalized by u _*) of the streamwise velocity fluctuations (σ _u ⁺|_peak) is essentially independent of the Reynolds number, (ii) the position of the rms peak value (y ⁺|_peak) is weakly dependent of the Reynolds number, (iii) the skewness of the streamwise velocity fluctuations (S _u ) is close to zero at the position in which the variance has its peak. A series of measurements of streamwise velocity fluctuations has been performed in turbulent pipe flow with the use of an Ultrasonic Doppler Velocimeter and our results support those reported in [1]. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Lower Critical Reynolds Number for Flow in a Circular Pipe

Flow in a circular pipe is investigated experimentally at Reynolds numbers higher than that at which the resistance coefficients calculated from the Blasius formula for laminar flow and from the Prandtl formula for turbulent flow are equal. The corresponding Reynolds number based on the mean-flow velocity and the pipe diameter is about 1000. The experiments were performed at a high level of inlet pulsations produced by feeding gas into the pipe through a hole with a diameter several times smaller than the pipe diameter. In our experiments the critical Reynolds number was determined as the value, independent of the distance from the inlet, at which the ratio of the axial to the mean-flow velocity as a function of the Reynolds number deviated from 2. At the maximum ratio of the pipe cross-sectional area to the area of the hole through which the gas entered the pipe, equal to 26, the critical Reynolds number was about 2300. After a fivefold increase in the hole area the critical Reynolds number increased by approximately 4%.At Reynolds numbers below 2000, after at a high level of the inlet pulsations an almost laminar flow had developed in the pipe, a perturbation was introduced by inserting a diametrically oriented cylindrical rod with a diameter 10–20 times smaller than the pipe diameter. In these experiments, at Reynolds numbers higher than 1000, at a distance from the rod equal to 50 pipe diameters the axial to mean-flow velocity ratio was less than 2, approaching this value again at large distances from the rod. The insertion of the rod led to a decrease in the critical Reynolds number by approximately 12%.     

湍流边界层流场与噪声实验研究

在重力式水洞中进行了水翼及半翼湍流边界层流场与噪声的实验研究。测量了水翼及半翼边界层附近的湍流脉动速度场;测量了半翼翼型表面三点处的压力脉动及其辐射噪声,测量了水翼内部测点的噪声及外部辐射噪声,在不同流速、不同攻角、光滑和粗糙翼面的情况下都进行了测量分析。试验结果发现,上述因素对模型的边界层湍流速度场有显著影响,15度攻角时,翼面附近湍流强度要比0度时大得多,粗糙翼面附近的湍流强度比光滑的大,而湍流强度随来流速度的变化不大,u(来流）方向和v方向的湍流强度量级相当;一般地,翼面压力脉动、翼内部噪声及外部噪声都是随来流速度的增大而增大,随攻角的增大而增大,粗糙翼面时的结果要比光滑翼面的大。从压力脉动与噪声测量结果与相应的流场测量结果比较可知,可以从湍流区域的湍流强度来判断出声源强度的定性变化。     

Reynolds Number Dependence of Velocity Structure Functions in a Turbulent Pipe Flow

Low-order moments of the increments δu andδv where u and v are the axial and radial velocity fluctuations respectively, have been obtained using single and X-hot wires mainly on the axis of a fully developed pipe flow for different values of the Taylor microscale Reynolds numberR _λ. The mean energy dissipation rate〉ε〈 was inferred from the uspectrum after the latter was corrected for the spatial resolution of the hot-wire probes. The corrected Kolmogorov-normalized second-order structure functions show a continuous evolution withR _λ. In particular, the scaling exponentζ _v , corresponding to the v structure function, continues to increase with R _λ in contrast to the nearly unchanged value of ζ _u . The Kolmogorov constant for δu shows a smaller rate of increase with R _λ than that forδv. The level of agreement with local isotropy is examined in the context of the competing influences ofR _λ and the mean shear. There is close but not perfect agreement between the present results on the pipe axis and those on the centreline of a fully developed channel flow. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Electric Potential Induced by a Homogeneous Magnetic Field in a Turbulent Pipe Flow

In this paper we study a turbulent pipe flow of a weakly electrical conducting fluid subjected to a homogeneous magnetic field which is applied perpendicular to the flow. This configuration forms the basis of a so-called electromagnetic induction flow meter. When the Hartmann number is small so that modification of flow by the Lorenz force can be neglected, the influence of the magnetic field results only in a spatially and temporally varying electric potential. The magnitude of the potential difference across the pipe is then proportional to the flow rate and this constitutes the principle of the flow meter. In this study the flow and electric potential are computed with help of a numerical flow simulation called Large-Eddy Simulation (LES) to which we have added an equation for the electrical potential. The results of the LES have been compared with experiments in which the electric potential is measured as a function of time at several positions on the circumference of the pipe. Both the experimental and numerical results for the mean potential at the pipe wall agree very well with an exact solution that can be obtained in this particular case of a homogeneous magnetic field. Furthermore, it is found that fluctuations in the electric potential due to the turbulence, are small compared to the velocity fluctuations. Based on the results we conclude that electrical-magnetic effects in pipe flow can be accurately computed with LES.     

Invariant Analysis of Turbulent Pipe Flow

The anisotropy analysis of Lumley provides a useful tool to quantify the degree of anisotropy in turbulent flows. Also included in the analysis are relations which may be used to check if the flow is axisymmetric or two-dimensional. However, the method does not provide any scale information about the structures. The analysis has therefore been extended here to Fourier space, which allows scale information to be derived. The method was applied to fully developed pipe flow and it was shown that the large-scale motion is everywhere close to axisymmetric. The intermediate scales are strongly influenced by the restrictions posed by the pipe walls. At the centre line, the flow structure appears axisymmetric at all scales, but the measurement sindicate that true axisymmetry is lost very quickly away from the centre line. The structure of the smallest scales could not be determined reliably due to a singularity in the analysis which develops as the scales go to zero. This revised version was published online in July 2006 with corrections to the Cover Date.