Hydrodynamic and heat transfer characteristics of a centrally heated cylindrical enclosure: CFD simulations and experimental measurements

Natural convection in enclosures is of importance in many engineering applications. The stratification arising out of natural convection may be desirable/undesirable depending on applications. In order to control the degree of stratification, understanding of flow pattern and temperature profiles is required. In the present work, transient natural convection in a cylindrical enclosure has been investigated for water with CFD simulations and flow visualization [using particle image velocimetry (PIV) and hot film anemometry (HFA)] over a wide range of parameters namely Rayleigh number (1.08 × 10¹¹ ≤ Ra ≤ 3.76 × 10¹³) and aspect ratio (1 ≤ H/R ≤ 2). The effect of various parameters like pressure, tube diameter and aspect ratio on the extent of stratification has been studied. PIV measurements have been performed to understand the transient flow behavior. Multiple thermocouples were used to measure the temperature profiles. CFD simulations have been performed using SST k–ω model and the results have been compared with the PIV measurements. The CFD simulations have been carried out for 2D axi-symmetric cases and the effect of boundary conditions (free-slip and no-slip) has been investigated. An excellent agreement was found between the CFD predictions and the experimental measurements of flow and temperature patterns. The extent of stratification has been quantified using dimensionless parameters like stratification number and stratification time. The kinetic energy profiles and kinetic energy dissipation profiles show that almost 75% of the enclosure is stratified (after different times depending on Ra number and the aspect ratio). The turbulence parameters were found to weaken with time in the stratified region and these predictions are corroborated with HFA measurements.     

汽车天窗风振噪声分析与优化控制

运用大涡模拟(LES)和FW-H声学模型,对某轿车天窗开启工况下风振噪声特性进行了数值仿真,揭示了天窗风振噪声的产生机理。在对轿车天窗风振噪声特性研究的基础上,引入现代优化算法,设计目标为降低驾驶员右耳及乘员左耳的噪声加权值。首先,选取某轿车的天窗开槽导流板作为优化对象,将导流板安装角度、开槽宽度及开槽深度定义成设计变量,通过设计实验选取20个样本点,采用kriging模型建立近似模型,并利用多岛遗传算法进行优化设计,获得了理想的导流板参数。仿真结果表明,优化后的导流板相比初始导流板,在监测点处其风振噪声的声压级降低了21.6%。     

FORCE REDUCTION OF FLOW AROUND A SINUSOIDAL WAVY CYLINDER

A large eddy simulation of cross-flow around a sinusoidal wavy cylinder at Re=3000 was performed and the load cell measurement was introduced for the validation test. The mean flow field and the near wake flow structures were presented and compared with those for a circular cylinder at the same Reynolds number. The mean drag coefficient for the wavy cylinder is smaller than that for a corresponding circular cylinder due to the formation of a longer wake vortex generated by the wavy cylinder. The fluctuating lift coefficient of the wavy cylinder is also greatly reduced. This kind of wavy surface leads to the formation of 3-D free shear layers which are more stable than purely 2-D free shear layers. Such free shear layers only roll up into mature vortices at further downstream position and significantly modify the near wake structures and the pressure distributions around the wavy cylinder. Moreover, the simulations in laminar flow condition were also performed to investigate the effect of Reynolds number on force reduction control.     

基于分区大涡模拟方法的双角冰翼型气动特性分析

为研究大迎角状态下机翼前缘双角冰诱导产生的流动大分离问题,本文将RANS方法与WMLES方法结合起来,构造了一种分区大涡模拟(ZLES)方法,针对具有双角冰的GLC305翼型进行了数值研究,并与RANS方法、IDDES方法及风洞试验进行了对比,结果表明:ZLES方法够准确预测宏观的升力系数,压力分布、分离范围、再附位置等流场特征参数较之IDDES、RANS及文献结果与试验吻合最好,适用于双角冰诱导大分离流动的数值模拟。     

大涡模拟在水下航行体周围黏性流场计算中的初步应用

在空间过滤得到的不可压缩流动的大涡模拟控制方程基础上,利用基于三阶迎风偏置格式的混合差分及二阶中心差分离散控制方程的对流项及耗散项,离散得到的线性方程组通过无矩阵计算的隐式LU-SGS（Lower-Upper Symmetric Gauss Seidel）分步迭代方法求解.利用大涡模拟（Large Eddy Simulation-LES）方法对水下航行体周围的黏性流场及水动力进行了定常数值模拟,计算得到的速度、压力分布及阻力值与试验吻合较好.     

Large-Eddy simulation of three-dimensional turbulent flow around a circular pier

1. INTRODUCTION The local scouring around a circular pier occurs rather frequently in engineering, which is closely related to the flow field and the movable bed. The flow field is a complex three-dimensional unsteady flow. The complexity is further magnified due to the interaction between the flow and the movable bed during scouring. Hitherto, there have been a number of investigations on the problem, but most of the studies focused on the formation of the maximum scouring depth based on…