高分子溶液壁湍流减阻机理的TRPIV实验研究

利用高时间分辨率粒子图像测速技术(TRPIV)对回流式水槽中低浓度高分子溶液壁湍流的减阻机理进行实验研究。通过对比分析高分子溶液和纯水平板湍流边界层在相同来流速度下的平均速度剖面、湍流强度和雷诺应力,发现高分子溶液的壁面摩擦阻力减小了21.77%,并且其缓冲层增厚,按对数律外移,雷诺应力减小;高分子聚合物主要在近壁区起到抑制湍流脉动的作用,而在主流区的作用不太明显。用流向局部平均多尺度速度结构函数和相干结构条件采样方法,检测并对比了高分子溶液和水的壁湍流相干结构“喷射”和“扫掠”事件中的脉动速度、展向涡量、雷诺应力等物理量的二维拓扑形态,发现高分子溶液近壁区相干结构在猝发时的脉动速度减小,涡量受到抑制,雷诺应力明显减小,说明高分子溶液湍流近壁区相干结构“喷射”和“扫掠”的强度变弱,猝发频率降低,动量和能量的输运减弱,揭示出高分子溶液减阻的重要机理。     

飞行器变后掠过程非定常气动特性形成机理

可变体飞行器变后掠过程中的时变气动力与力矩特性对于飞行安全具有重要意义,是亟待深入研究的基础问题.通过风洞实验对其开展了研究,揭示了可变体飞行器变后掠引起的气动特性动态迟滞现象及滞回环大小与方向的影响因素.基于风洞实验结果和力学中一些重要概念,提出了3种物理效应:流场迟滞效应、附加运动效应、固壁牵连效应,以此定性与定量论证了可变体飞行器变后掠过程中非定常气动特性的形成机理.除了能解释实验现象,这一机理研究亦可用于后续可变体飞行器变后掠过程中的气动特性建模.     

15×10~4m~3超大型油罐应力测试与数值模拟分析

兰州原油末站大型油罐群,是我国首次在饱和黄土地基修建的大型储油设施。依托其中一座15×104 m3超大型非锚固油罐,开展了现场充水测试罐壁静态应力的试验研究。通过粘贴在油罐罐壁的应变计,测试充水过程中罐壁应力的变化规律,并采用有限元对15×104 m3超大型油罐进行应力分析。测试结果表明:罐壁的环向应力随充水水位的增加基本呈线性关系。数值模拟计算表明,罐壁环向应力最大值发生在第二圈罐壁和第三圈罐壁相连接的位置。由于罐壁上部设置了抗风圈和加强圈,有效地控制了罐壁的径向位移,使罐壁环向应力和竖向轴向应力在加强圈和抗风圈附近发生波动。将有限元数值模拟计算的罐壁环向应力分布情况与实测应力进行比较,两者总体吻合较好。上述研究结果可为超大型储罐在黄土地基的设计和建造提供技术依据和设计参数验证。     

Study on local topology model of low/high streak structures in wall-bounded turbulence by tomographic time-resolved particle image velocimetry

The relationship between the bursting event and the low/high-speed streak in the logarithmic law (log-law) region of a turbulent boundary layer is investigated. A tomographic time-resolved particle image velocimetry (TRPIV) system is used to measure the instantaneous three-dimensional-three-component (3D-3C) velocity field. The momentum thickness based Reynolds number is about 2 460. The topological information in the log-law region is obtained experimentally. It is found that the existence of the quadrupole topological structure implies a three-pair hairpin-like vortex packet, which is in connection with the low/high-speed streak. An idealized 3D topological model is then proposed to characterize the observed hairpin vortex packet and low/high-speed streak.     

边孔弧形闸门水流脉动压力特性研究

弧形泄水闸是水利枢纽工程中常见的挡水、泄水建筑物,其在关闭或开启过程中或者局部开启运行时,在水流脉动压力作用下会产生振动,容易引起闸门结构破坏。本文针对边孔闸门与中孔闸门不同的水流边界条件特点,制作了带导流墙与无导流墙两个弧形闸门模型。在实验室内开展了不同库水位、不同闸门开度下的物理模型试验,并对两个模型上大量测点的水流脉动压力数据进行比较分析。试验表明,导流墙的存在对脉动压力主频的影响较小,但对脉动压力均方根值影响较大;在较高库水位下相对开度位于0.2至0.3区间内时,导流墙的存在不但不会改善闸门的受力状况,反而还会导致受力增强。     

Vortex shedding around a near-wall circular cylinder induced by a solitary wave

This study developed a two-dimensional generalized vortex method to analyze the shedding of vortices and the hydrodynamic forces resulting from a solitary wave passing over a submerged circular cylinder placed near a flat seabed. Numerical results for validation are compared with other numerical and experimental results, and satisfactory agreement is found. A series of simulations were performed to study the effects of gap-to-diameter ratio and incident wave height on vorticity pattern as well as the forces exerted on the cylinder. The range of the heights of incident waves is from 0.3h to 0.7h, where h is the still water depth. The range of the gap-to-diameter ratios is from 0.1 to 0.8. The results indicate that the flow pattern and the pressure distribution change significantly because of the close proximity of the seabed where the vorticity flux on the seabed-side surface of the cylinder is suppressed. Placing the cylinder nearer the seabed increases the drag and the positive lift on the cylinder. When the gap-to-diameter ratio increases, the pattern of vortices changes because of the interaction between the main recirculation zone and the shear layers separated from the gap. The maxima of drag, lift and total force increase linearly with the height of the incident wave.     

The rheological properties of the arterial wall

Key words The rheological properties of rat arteries were studied in vitro. Using intact arterial segments undergoing large deformations in longitudinal and circumferential direction, both the stress-strain relationship and the corresponding histological changes with deformation are presented. Correlations between the mechanical properties and the histological structure are discussed.     

单壁碳纳米管内流体流动的手性效应

纳米尺度范围内流道分子结构形成的粗糙度将会影响其中的流体流动。本文采用分子动力学方法,以氩为工质,模拟了不同手性的单壁碳纳米管（SWCNT）内流体的流动。结果表明：由于范德瓦耳斯力的作用,流体分子与壁而间有一定的距离。可以看出在壁面附近有两个明显的分层,这是纳米流动中持有的流体密度分层现象。由于不同手性碳纳米管的分子排...     

冠状动脉狭窄情况下的非牛顿血液流动和大分子传质

针对冠状动脉狭窄的情况,采用数值模拟方法求解了牛顿流体与非牛顿流体(幂次律流体和Casson流体)的定常与脉动的流场。在此基础上,求解了LDL(低密度脂肪蛋白)和Albumin(血清白蛋白)的浓度场。根据计算结果,详细讨论了壁面剪应力、非牛顿流效应、分子大小等因素对大分子传质的影响;并对牛顿流体与非牛顿流体、定常流动与脉动流动的大分子浓度场进行了比较,这些结果对于了解动脉硬化成因与流动特性和大分子传质的联系提供了较为丰富的信息。     

The entropy of Garfinkle-Horne dilaton black hole due to arbitrary spin fields

Using the membrane model which is based on brick wall model, we calculated the free energy and entropy of Garfinkle-Horne dilatonic black hole due to arbitrary spin fields. The result shows that the entropy of scalar field and the entropy of Fermionic field have similar formulas. There is only a coefficient between them.