LATTICE BOLTZMANN SIMULATION OF POWER-LAW FLOW PAST AN ELLIPTIC CYLINDER

基于格子波尔兹曼方法(lattice Boltzmann method) 和幂律流体本构方程, 建立二维流动模型, 将充分发展的速度分布与理论解进行对比, 吻合良好. 对幂律流体的圆柱绕流进行模拟, 采用了反弹格式的无滑移圆柱边界, 并使用应力积分法计算阻力系数, 分析了稳态圆柱绕流时, 阻力系数随幂律指数n 以及雷诺数Re 的变化规律. 分析了椭圆横轴/纵轴长度比和幂律指数n, 对压力系数C_p 和黏度系数C_v 的影响. 得到的变化规律与有限元方法规律一致, 验证了格子波尔兹曼模型的可行性.     

内部爆炸作用下多层钢筒的动态响应

为评估内部爆炸作用下多层钢筒结构的防护效果,考察多层钢筒结构动态响应和变形吸能特征,采用两端开口、总厚度为50 mm的4层圆柱形Q345钢筒,在8.90~18.18 kg TNT药量下进行爆炸实验,并在容器外壁进行应变电测。实验后钢筒结构爆心局部发生塑性变形,内层钢筒变形最大,但未发生破坏。根据研究得到初步认识:采用爆心单位环面变形吸能的设计方法,可以较好地预估给定药量下所需钢筒的厚度;不同药量下,轴向距离超过多层钢筒结构的1/4内径后,其外壁环向变形峰值约减小为爆心截面环向应变峰值的1/2。     

摩擦磨损试验机模拟活塞环-缸套摩擦行为的功能开发

参考活塞环-缸套的实际运行条件,结合SRV-4摩擦磨损试验机自身的性能特点和工作原理,通过开发设计,增加合理的硬件及软件测试条件,实现摩擦磨损试验机模拟活塞环-缸套摩擦行为的功能.系统测试结果表明：功能开发后的摩擦磨损试验机可在较短时间内获得活塞环-缸套摩擦副性能优劣的试验数据,满足快速、直观评价活塞环-缸套的摩擦磨损性能的需要,在活塞环-缸套摩擦副研究中具有重要的应用价值.     

Effects of Thermal Radiation and Slip Mechanism on Mixed Convection Flow of Williamson Nanofluid Over an Inclined Stretching Cylinder

The current investigation highlights the mixed convection slip flow and radiative heat transport of uniformly electrically conducting Williamson nanofluid yield by an inclined circular cylinder in the presence of Brownian motion and thermophoresis parameter.A Lorentzian magnetic body force model is employed and magnetic induction effects are neglected.The governing equations are reduced to a system of nonlinear ordinary differential equations with associated boundary conditions by applying scaling group transformations.The reduced nonlinear ordinary differential equations are then solved numerically by Runge-Kutta-Fehlberg fifth-order method with shooting technique.The effects of magnetic field,Prandtl number,mixed convection parameter,buoyancy ratio parameter,Brownian motion parameter,thermophoresis parameter,heat generation/absorption parameter,mass transfer parameter,radiation parameter and Schmidt number on the skin friction coefficient and local Nusselt are analyzed and discussed.It is found that the velocity of the fluid decreases with decrease in curvature parameter,whereas it increases with mixed convection parameter.Further,the local Nusselt number decreases with an increase in the radiation parameter.The numerical comparison is also presented with the existing published results and found that the present results are in excellent agreement which also confirms the validity of the present methodology.     

两端铰接的细长柔性圆柱体涡激振动响应特性数值研究

目前细长柔性圆柱体涡激振动响应的研究方法主要包括实验方法、计算流体动力学方法以及半经验模型方法. 鉴于实验方法研究成本较高、计算流体动力学方法计算时间较长,本文基于尾流振子模型对线性剪切来流下两端铰接的细长柔性圆柱体涡激振动响应特性进行了半经验模型方法研究. 先建立了柔性圆柱体结构振子以及尾流振子之间的耦合模型,紧接着基于二阶精度中心差分格式对耦合模型先离散后迭代进行求解. 对不同剪切参数下柔性圆柱体涡激振动响应的振动波长、振动频率、振动位移以及响应频率随时间的变化特性等参数进行了分析. 分析结果表明:圆柱体的涡激振动响应由驻波和行波混合组成. 当无量纲弯曲刚度较小时,在圆柱体两端附近,驻波占主导;而在圆柱体中间段附近,行波占主导. 当无量纲弯曲刚度较大时,在圆柱体整个长度区间上均为驻波占主导. 随着剪切参数的增大,振动位移以及振动波长均逐渐减小,而振动频率和频率带宽均逐渐增大.      

Applications of scale-adaptive simulation technique based on one-equation turbulence model

A modified scale-adaptive simulation (SAS) technique based on the Spalart-Allmaras (SA) model is proposed. To clarify its capability in prediction of the complex turbulent flow, two typical cases are carried out, i.e., the subcritical flow past a circular cylinder and the transonic flow over a hemisphere cylinder. For comparison, the same cases are calculated by the detached-eddy simulation (DES), the delayed-detached eddy simulation (DDES), and the XY-SAS approaches. Some typical results including the mean pressure coefficient, velocity, and Reynolds stress profiles are obtained and compared with the experiments. Extensive calculations show that the proposed SAS technique can give better prediction of the massively separated flow and shock/turbulent-boundary-layer interaction than the DES and DDES methods. Furthermore, by the comparison of the XY-SAS model with the present SAS model, some improvements can be obtained.     

Point defect states of a hollow cylinder in two-dimensional phononic crystal

Point defect states in two-dimensional phononic crystal of a hollow mercury cylinder in a water host are studied.An improved plane expansion method combined with the supercell technique is used to calculate the band gaps and the pressure distribution at the defect position.The sonic pressure of defect modes shows that the waves are localized at or near the defect.As the filing fraction increases,more defect modes appear in the band gaps.     

Numerical simulation of an axisymmetric separated and reattached flow over a longitudinal blunt circular cylinder

This article presents a numerical investigation of turbulent flow in an axisymmetric separated and reattached flow over a longitudinal blunt circular cylinder. The governing equations were discretized by the finite-volume method and SIMPLER method was applied to solve the equations on a staggered grid. The turbulent flow was numerically simulated using the standard k–ε, Abe–Kondoh–Nagano (AKN) and Shear Stress Transport (SST) turbulence models. The comparisons made between numerical results and experimental measurements showed that the SST model is superior to other models in the present calculation.Computations were performed for three different Reynolds numbers of 6000, 10 000 and 20 000 based on the cylinder diameter. To our knowledge, this study represents the first numerical investigation of the present flow configuration. The computational results were validated with the available experimental data of reattachment length, mean velocity distribution and wall static pressure coefficient in the turbulent blunt circular cylinder flows. Further, other characteristics of the flow, such as turbulent kinetic energy, pressure, streamlines, and the velocity vectors are discussed.The results show that the main characteristics of the turbulence flow in the separation region, such as reattachment length or velocity profiles, are nearly independent of the Reynolds number. The obtained results showed that a secondary separation bubble may appear in the main separation bubble near the leading edge. Furthermore, it was found that the turbulent kinetic energy has a large effect on the formation of the secondary bubble.     

一种改进的夜间数字能见度测量方法

为降低背景光噪声对数字摄像法夜间能见度测量的不确定性影响,对双光源法能见度测量系统进行改进。该系统利用避光筒限制CCD相机视场角,拍摄2个位于不同距离的LED背光源,然后对摄取到的图像进行处理得到光源图像的灰度值,再根据阿拉德定律求得大气消光系数,计算出大气能见度值。通过在无背景光、有背景光未加避光筒和加避光筒3种条件下的比对实验,分析光源图像的灰度信息,并将实验结果进行处理,得出有避光筒和无避光筒时测得的能见度值与无背景光下测量结果的相关系数分别是0.911 3和0.322 7,均方根相对偏差分别是6.87% 和23.38%。结果表明:系统抑制背景光噪声的能力明显增强,能较准确地测量夜间能见度。     

生物油对发动机缸套摩擦学性能的影响

以生物油为研究对象,利用乳化技术对生物油进行提质改性,在发动机缸套-活塞环摩擦磨损试验机上考察了提质前后生物油的摩擦学性能.利用表面轮廓仪,扫描电镜与X-射线光电子能谱仪表征了发动机缸套摩擦表面的微观形貌及化学元素状态,探讨了相关的摩擦磨损机理.结果表明:小球藻生物油比稻壳生物油对缸套-活塞环具有更好的减摩抗磨性能;通过乳化提质方法,可以快速提升生物油的性能;生物油的减摩润滑作用归因于油品中的有机物在缸套表面吸附、摩擦挤压及摩擦沉积形成润滑油膜,局部摩擦熔融形成的"微滚珠",以及在摩擦表面生成的Fe₂O₃及FeOOH氧化膜.此外,小球藻生物油能在摩擦副表面形成含N有机保护膜,这是其具有更好摩擦学性能的重要原因.