HEMODYNAMICS FOR ASYMMETRIC INLET AXIAL VELOCITY PROFILE IN CAROTID BIFURCATION MODEL

The asymmetric inlet velocity profile has been observed in phantom model using LDA and in health subjects using Magnet Resonance （MR）. The effects of asymmetric inlet axial velocity profile on the flow field and the Wall Shear Stress （WSS） of carotid bifurcation were numerically studied herein with the TF-AHCB model, The results show that the Wall Shear Stress Gradient （WSSG） in the front part of the sinus for inward-tilting inlet axial velocity profile is nearly 2 times of that for the symmetric one in the beginning of systole, the end of systole, and diastole, respectively. The area of WSS below 5× 10^-3 Pa at the outer wall of the sinus for outward-tilting inlet axial velocity profile is 1.5 times of that for the inward-tilting one during diastole of the cardiac cycle. The asymmetric inlet velocity profiles can reduce the flow velocity near the inner wall of the sinus, which has been normally considered a high velocity region. It is concluded that besides bifurcation geometry and flow waveform, the asymmetry of inlet velocity profile is probably a factor influencing atherosclerosis.     

壁面粗糙度突变对明渠流速分布的影响

应用激光测速仪在矩形水槽中实测了光滑和粗糙底板以及粗糙度突变情况下的时均流速分布，根据实测资料分析了粗糙度突变以后流速在内区和外区沿程变化情况，得到粗糙度改变后发展过程中的紊流，其流速在黏性底层区比粗糙度改变前和充分发展的紊流小，而在对数律区其流速增长最快。对y／H〉0．2的外区，发展中的紊流与充分发展的紊流在外区流速分布有明显的不同，其不同表现可从尾流强度系数П看出，П值变化从负值到正值，当形成新的均匀流后П值趋于常数。     

Turbulent flow in a machine honed rough pipe for large Reynolds numbers: General roughness scaling laws

An alternate inner wall variable, for flow over a transitional rough pipe surface, is defined as the ratio of normal coordinate measured above the mean roughness level to the wall roughness scale. The Reynolds equations for mean turbulent flow in a transitional rough pipe, in two layers (inner and outer) are considered. The predictions of the mean velocity and friction factor in fully developed turbulent flow in a rough pipe flow, presented here, covers all types of roughness. The data for a particular case of the machine honed Princeton superpipe roughness, analogous to inflectional type roughness of Nikuradse, is presented, as two expressions using our roughness scale. The velocity profile and friction factor, on a transitional rough wall, are shown to be governed by the new log laws, which are explicitly independent of the transitional wall roughness. Further, the inflectional roughness has also been connected with geometric roughness parameters; like, arithmetic mean roughness, mean peak to valley heights roughness, root mean square (rms), roughness based on texture measure; and the friction factor implicit and approximate explicit formulas have also been proposed. In entire transition region between fully smooth and fully rough wall, monotonic roughness of Colebrook (Moody Chart) over estimaton the friction factor when compared with present inlectional roughness.     

NUMERICAL SIMULATION OF TURBULENT FLOW CHARACTERISTICS IN A CURVED PIPE WITH A BAFFLE

A numerical study on the characteristics of developing turbulent flow in a curved pipe with a baffle was carried out in body-fitted coordinates with the k-ε model turbulence. A curved duct of square cross-section was examined first, and the results agree very well with the experimental data. Then two kinds of pipes, a normal curved pipe and that with a baffle were studied. The computational results are presented and compared with each other to illustrate the changes of the flow after adding the baffle. The longitudinal velocity in the pipe with a baffle was characterized by outer velocity bigger than the inner one. The secondary flow was characterized by four-vortex structure with the intensity reduced, which results in the equability of the flow field of the cross-section compared with that without a baffle, and has much more significant meaning in engineering.     

振动拔管夯扩桩施工工艺之探讨

振动拔管夯扩桩采用了内外套管的双管法施工，是一种质量好、施工快、造价省的可靠桩型，夯扩桩机械是在原来无振动拔管桩机的基础上，引用了振动碎石桩的振动拔管工艺，即沉管和夯扩大头用导杆式柴油锤施打，而拔管时采用了液压固定振动锤于桩管上，一边振动一边拔管而成桩．采用了振动拔管工艺后，从根本上解决了现场混凝土灌注桩的桩身质量的通病问题，确保了夯扩桩承载能力的可靠性．在广西南宁等地的应用是成功的。     

柔性壁对湍流边界层速度型的变形影响

本文从稳定性的观点出发，研究了粘弹性柔性壁对湍流边界层的影响。由柔性壁边办层稳定性问题的特征值计算结果发同，原刚性充边界层的速度型导致流固耦合系统不稳定，对数区上移后的边界层速度型却可以使耦合系统稳定，这说明，在没有水动力学不稳定发生的情况下，柔性壁会使湍流边界层中速度型的对数区上移。     

圆管壁粗糙度对圆管内流态影响研究

基于尼古拉兹圆管实验思想,利用颗粒流程序中的流体计算模块,实现了对圆管壁粗糙度的模拟,进而分析了不同粗糙度对圆管断面流态分布的影响以及在不同压力差作用下平均流速与圆管壁粗糙度之间的关系。研究结果表明:圆管内流体流速受管壁的扰动影响,在横截面上呈U型分布,而非抛物线型分布;圆管壁对管内流体流态的影响范围随管壁粗糙度变化而变化,圆管管壁相对粗糙度越大,管内受扰动流体范围越大,即管内层流范围越小;在管壁粗糙度一定的情况下,圆管断面流量随上下端面压力差的增大而增大;在相同压力差作用下,圆管断面流量随管壁相对粗糙度增大而逐渐减小,颗粒的阻流作用明显;随着管壁粗糙度的增大,圆管上下端面受压力差作用的影响范围也随之增大,使管内流体流态变得更加复杂。     

EXPERIMENTAL STUDY OF VELOCITY DISTRIBUTIONS IN THE TRANSITION REGION OF PIPES

The accuracy of an ultrasonic flowmeter meaurement depends on the profile-linear average velocity.But this velocity in the transition region is not available at the present.In this article,the velocity in the transition region in pipes is studied by experimental methods.The Particle Image Velocimetry (PIV) is used to measure the flow field in the transition region in pipes,and the measured results from PIV are in good agreement with the Westerwell’s experimental data.Based on the experimental data of PIV,the curves of the profile-linear average velocity in the transition region against the Reynolds number in the range from 2 000 to 20 000 are obtained,and it is shown that the coefficient k is constant when the Reynolds number is in the range of 2 000-2 400 and 6 000-20 000,and the coefficient k is increasing when the Reynolds number is in the range of 2 400-6 000.The results of this article can be used to improve the measurement accuracy of the ultrasonic flowmeters and as a theoretical basis for the research on the transition flow.     

弯曲河道纵向垂线平均流速平面分布的研究

本文以弯道水流运动方程作为分析的基础，根据弯道水流纵向流速沿垂线分布在凸岸区域眼从对数分布律，在四岸区域眼从抛物分布律，导出了分区域变自率动床弯道水流纵向垂线平均流速计算公式，并从理论上对河湾纵向垂线平均流速的横向分布和沿程变化规律进行了分析，同时给出了适用于定半经弯道的纵向垂线平均流速平面分布公式的简化形式。最后采用美国ＦａｌｌＲｉｖｅｒ野外水流观测资料对纵向垂线平均流速计算公式进行了验证计算，结果令人满意。     

风洞边壁对挟沙气流流速分布的影响

鉴于现有挟沙气流流速分布研究中对风洞边壁影响的认识不足，本文通过改变风洞宽度的方法对风洞边壁的影响进行了探索性实验研究。在五种宽高比条件下，对风洞断面挟沙气流流速分布进行了测量。发现风洞边壁对挟沙气流流速分布有较为明显的影响。在风洞宽度比相同的条件下，断面内中垂线上的有效粗糙度系数大于其它垂线上对应的系数。从靠近边壁的垂线到断面中垂线，各垂线对应的跃移层内区及外区流速分布的上界高度、气流摩阻速度均逐渐增大。随着风洞宽高比的减小，断面内中垂直线上的气流摩阻速度与自由流速的比值以及受风洞边壁影响的气流厚度均增大。     

一种锥形管内流场LDV测试方案

利用LDV对锥形管(如水轮机尾水管直锥段、逐扩管路)内流场速度进行测试时,由于锥形管外壁曲率大、内壁有一定倾斜度,以及光束折射现象的发生,会使LDV无法对轴向速度进行测量。针对前述问题,提出了一种锥形管流场测速方案。通过理论推导对锥形管内LDV测试光路进行分析,论证了方案的可行性,并推导出该方案下测点位置与LDV光源位置的线性关系式,以及LDV光源位置变化范围,为同类型锥形管内流场LDV测速提供了一种有效可行的方案。     

求解零航速物体水动力的简单Green函数方法

频率域中求解零航速物体水动力的简单Green函数方法的基本原理是将流场分成内场和外场,外场中的速度势通过特征函数展开写成解析表达式,内场周界上的速度势则利用边界积分方程求解,但选用的Green函数是简单的,即无界域中点源的速度势。这意味着在内场的整个周界都要布置奇点。内外场速度势在它们的交界面上用代入法连接。简单Green函数方法已成功地应用于二维、三维物体的一阶和二阶辐射、绕射问题,结果表明该方法具有很多方面的优越性。     

溃口近区二维数值模拟与溃坝洪水演进耦合

基于黏土心墙砂石坝的溃决过程,以及溃坝洪水传播和运动的特性,建立黑河金盆水库大坝溃口近区二维数值模型和下游地区溃坝洪水演进耦合数学模型。使用DAMBRK法计算逐渐溃坝,并应用其结果进行后续模拟。采用Abbott-Ionescu六点隐式有限差分格式求解一维模型,采用单元中心的有限体积法求解二维模型方程。采用侧向连接方式,将黑河两岸计算水位点与二维网格单元相连,实现一、二维模型的耦合。采用所建立的二维模型对溃口近区进行计算与模拟,得到计算区域某一时刻的水深及流速分布。应用所建耦合模型对黑河金盆水库万年一遇入库洪水漫顶致溃坝洪水进行数值模拟,得到一维河道内各断面的水位和流量变化过程,以及二维计算区域内不同时刻的水深分布图、流速矢量图和淹没范围变化过程。溃口的形成过程不仅包括漫顶水流的直接作用,同时包括溃口形成过程中两侧漩涡状水流的反冲刷作用。耦合模型可以同时兼顾河道内的水流变化以及河道外计算区域内的洪水演进过程,从而减少由于计算结果偏大或偏小所带来的防洪资源浪费和防洪措施不利等不良影响。     

NUMERICAL SIMULATION OF FLOWS FOR SECOND-ORDER VISCOELASTIC FLUID COUPLED WITH HEAT TRANSFER BY DIFFERENTIAL QUADRATURE METHOD

The problem of two-dimensional steady flow of an incompressible second-order viscoelastic fluid coupled with heat transfer between parallel plates was considered. A viscous dissipation function was included in the energy equation.When the elastic property of the fluid is weaker, the zerothorder and first-order approximate governing equations were obtained by means of the perturbation method. To understand the behavior of flow near the tube wall, the half-domain was divided into two sub-domains, in which one is a thin layer near the wall called the inner domain and the remainder is called the outer domain. The governing equations in the inner domain and in the outer domain were discretized respectively by using the Differential Quadrature Method (DQM). The matching conditions at the interface between the inner and outer domains were presented. An iterative method for solving these discretized equations was given in this paper. The numerical results obtained agree with existing results.     

轴对称拉伸流动中大表面张力下球形液滴Stokes流动的准确解

本文采用轴对称情形下内外Stokes流动的Sampson级数解求出了轴对称拉伸流动中大表面张力下球形液滴stokes流动的准确解。该准确解表达式简单且为有限形式。文中详细分析了流线谱,粘度比对内外流的影响以及内流的速度分布和压力分布。     

三维水流的紊动结构特征

矩形断面中流动的水流，在边壁附近其特征表现为三维性。依据试验资料，论证了笔者提出的水力半径分割原则，在角区附近存在一条雷诺应力为零的曲线，二次流不穿越该线，两个方向相反的二次流分别存在于分割线上、下。在此基础上，从流速分布角度论证了水力半径分割曲线的存在；通过整理试验资料发现，同一根垂线上，当高度越过分割线时，其流速分布曲线偏离对数规律，需用另一区域的对数规律描述。并提出了断面流速的计算方法。     

PIV EXPERIMENTAL RESEARCH OF FLOW STRUCTURE IN RECTANGULAR CHANNEL WITH TRANSVERSELY PLACED SPIRAL COIL INSERT

The flow field in a rectangular channel with a transversely placed spiral coil insert is investigated by Particle Image Velocimetry (PIV) measurements in both transverse and longitudinal sections. The experimental results show that multi-longitudinal vortices are induced downstream of the spiral coil and are distributed as a symmetrical vortex array along the horizontal central line of the transverse section. Along the mainstream, due to the spiral motion of the longitudinal vortices, the velocity fluctuates in a manner of the damped sinusoidal curve and the velocity component in the wall normal direction is improved in the channel. Compared with the flow field in a smooth channel it is found that the movement of the longitudinal vortices can cause a continuous disturbance near the channel walls and thus enhances the fluid velocity in the near wall region, which consequently leads to the reduction of the velocity gradient and a more uniform velocity distribution. With the increase of the Reynolds number, the induced longitudinal vortices gain strength and become straighter and closer to the channel walls, thus the turbulence intensity is further enhanced in this area.     

CONCENTRATION DISTRIBUTION OF SEDIMENT IN BED LOAD LAYER

In this paper the concentration profile in bed load layer is derived based on kinetic theory. According to observations, particles moving in near wall region behave differently during ejection and sweeping of turbulence burst, as indicates that they are subject to different influences from turbulence, and therefore, the forces acting on particles are not the same. Consequently, particles moving in bed load layer are classified into two groups, one lifted upward by ejections, the other carried back to bed by sweepings, and the forces corresponding to upward and downward motions are proposed. By solving the basic transport equation of kinetic theory, the velocity distribution functions, upward and downward fluxes of particles in bed load layer are derived. Upon assumption of equilibrium sediment transport, concentration profile in bed load layer is obtained. Verification is also presented in this paper, which shows that the concentration profile produced by the relation proposed in this paper agrees with observations well.     

管壁均匀密集加糙圆管流的新总流机械能方程及流动数值模拟

能量(机械能)方程是水力学的理论基础;能量损失(机械能损失)的计算既是水力学乃至工程流体力学的主要研究内容之一,也是工程实际中颇为关注的问题。以往水力学中的能量方程系以重力场中理想不可压缩流体的伯努利方程为基础而得到,其既不能直接反映紊动对流动的作用,能量损失也无明确的表达式。本文在我们现有研究工作基础上,通过理论分析与数值模拟,得到如下成果:(1)构建了管壁均匀密集加糙圆管流的新总流机械能方程;(2)通过数值模拟,对管壁均匀密集加糙圆管流的机械能损失及其构成进行了研究。构建的方程包含了紊动的作用;研究成果表明,均匀密集加糙圆管流总流机械能损失与雷诺数及管壁光滑度有关,且可分解为与时均流速梯度相关的损失及与紊动耗散相关的损失两部分。     

同轴套管间涡旋流动及强化传热数值模拟

相对旋转两同轴套管间的涡旋流动,能够带来二次流强化传热传质作用,在航空、水处理、生态保护、生物工程和膜分离等领域都具有广泛的应用价值。本文使用Fluent软件,对同轴套管间涡旋流动及传热特性进行数值模拟,考察了内管转速、内外管壁面温差等操作参数变化对同轴套管间流体传热性能的影响,分析了涡旋流动与传热效率之间的关联关系。模拟结果表明:内管转速增加在流场中形成泰勒涡,涡流扰动增大了高温壁面与流体间的热流密度,增强了流体传热效率。增大内外管壁面温差,也可加强流体传热性能,但其强化作用不及内管转速的强化作用显著。受流场中泰勒涡影响,流体速度、温度及热流密度沿轴向的分布都呈正弦状周期性波动,在相邻两涡交界面处,流体传热性能最好,在涡中心处的传热性能最差。