Computational study on aerodynamic mitigation of wind-induced, large-amplitude vibrations of stay cables with strakes

Modifications of circular cylinder surfaces, such as strakes and helical wires, effectively mitigate Kármán vortex-induced vibrations normal to flow and have been applied to the reduction of large-amplitude vibrations of stay cables in bridges, which occur under wind oblique to a cable with or without rainfall. This aerodynamic control method cannot be fully effective without understanding the behavior of the flow around and the associated forces on oblique cables. To address this issue, flow around a yawed cylinder with various strake patterns was studied using three-dimensional detached eddy simulation (DES) at Reynolds number of 1.4×10⁵. Results demonstrated that strake patterns strongly influence the development of flow structures around a yawed cylinder and therefore the associated forces on the cylinder. The results suggest that particular strake patterns can mitigate large-amplitude and low-frequency vibrations of stay cables induced by oblique wind.     

NUMERICAL SIMULATION AND EXPERIMENTAL STUDY OF THE NEW METHOD OF HORSESHOE VORTEX CONTROL

The horseshoe vortex generated around the sail-body junction of a submarine has an important influence on the uniformity of the submarine wake at the propeller disc. In this article, the horseshoe vortex is simulated by the Detached Eddy Simulation (DES) method, and a new method to control the horseshoe vortex by vortex control baffler is proposed. The numerical simulation shows that a kind of attached vortex, with the rotation direction opposite to that of horseshoe vortex, is generated by the vortex control baffler. With the attached vortex, the strength of the horseshoe vortex is significantly reduced. The wind tunnel experiment on a submarine model is carried out, and the axial velocities at the propeller disc of the submarine with and without vortex control baffler are measured by a hot wire anemometer system. It is shown from the experimental results that the vortex control baffler can enhance the uniformity of the wake at the propeller disc, which helps to improve the propeller performance. The engineering applicability of the vortex control baffler is discussed.     

DETACHED EDDY SIMULATION OF HYDRAULIC CHARACTERISTICS ALONG THE SIDE-WALL AFTER A NEW ARRANGEMENT-SCHEME OF THE SUDDEN LATERAL ENLARGEMENT AND THE VERTICAL DROP

In order to study the cavitation damage in a side-wall when a sudden lateral enlargement and a vertical drop are imposed at the radial gate,a new arrangement-scheme is proposed,where the sudden lateral enlargement and the vertical drop can be imposed at the outlet of the gate chamber.The hydraulic characteristics along the side-wall are simulated by the detached eddy simulation and the Volume Of Fluid (VOF) method.The numerical results agree well with those of experiment.The experimental and numerical results show that the flow condition is smooth with only a weak water-wing appearing behind the lateral cavity,and the length of the lateral cavity becomes longer and is mainly affected by the size of the lateral enlargement and the zone of negative pressure after the water impacts the side-wall would disappear.The hydraulic characteristics of the new arrangement-scheme are beneficial to the prevention of the cavitation damage in the side-wall and the Detached Eddy Simulation (DES) with the VOF method can well predict the hydraulic characteristics after the new arrangement-scheme of the sudden lateral enlargement and the vertical drop.     

分离涡方法模拟浓淡气固射流两相非稳态流动特性研究

利用分离涡模拟(Detached eddy simulation，DES)这一新型湍流模拟技术对撞击式浓淡燃烧器内部和出口射流的气固两相流动结构进行了模拟，获得了浓淡燃烧器出口射流的旋涡拟序结构，模拟了射流出口旋涡生成、发展和脱落的规律。对于颗粒场，应用了Lagrangian方法跟踪颗粒运动，获得了浓淡燃烧器出口射流中不同Stokes数颗粒在射流流场旋涡拟序结构作用下的运动扩散规律。结果表明，射流外边界处的大涡是引起浓淡侧小颗粒相互混合的主要因素，而煤粉气流中Stokes数大于1的颗粒在射流中基本不会发生浓淡混合现象，燃烧器下游的浓淡分离效果可以在较长的距离内得到保持。     

Numerical Investigation of Three‐Dimensional Bubble Column Flows: A Detached Eddy Simulation Approach

Numerical simulations were performed employing detached eddy simulation (DES) in a three‐dimensional transient Euler‐Euler framework for bubble columns, and all the computational fluid dynamics results were compared with a k‐? model and available experimental data. The numerical results are in good agreement with the experiments in predicting the time‐averaged axial velocity and turbulent kinetic energy profiles. The flow‐resolving capabilities of the DES model are highlighted, and it is shown that the DES turbulence model can be efficiently used for simulating flow field and turbulent quantities in the case of bubble columns.     

Unsteady RANS and detached eddy simulation of the multiphase flow in a co-current spray drying☆

A detached eddy simulation (DES) and a k-ε-based Reynolds-averaged Navier–Stokes (RANS) calculation on the co-current spray drying chamber is presented. The DES used here is based on the Spalart–Al maras (SA) turbu-lence model, whereas the standard k-ε(SKE) was considered here for comparison purposes. Predictions of the mean axial velocity, temperature and humidity profile have been evaluated and compared with experimental measurements. The effects of the turbulence model on the predictions of the mean axial velocity, temperature and the humidity profile are most noticeable in the (highly anisotropic) spraying region. The findings suggest that DES provide a more accurate prediction (with error less than 5%) of the flow field in a spray drying chamber compared with RANS-based k-εmodels. The DES simulation also confirmed the presence of anisotropic turbulent flow in the spray dryer from the analysis of the velocity component fluctuations and turbulent structure as il us-trated by the Q-criterion.     

Numerical study on supersonic combustion of hydrogen and its mixture with Ethylene and methane with strut injection

In this paper, supersonic combustion and flow field of hydrogen and its mixture with ethylene and methane from strut injections in a Mach 2 supersonic flow are studied numerically. The fuel mixture of hydrogen, methane and ethylene represents the major products of pyrolysis of hydrocarbon fuels with large molecules such as kerosene as it acts as coolant and flows through cooling channels and absorbs heat. Detached Eddy Simulation with a reduced kinetic mechanism and steady flamelet model are applied to simulate turbulent combustion. The calculated temperature profiles of hydrogen are compared to the experimental results of DLR supersonic combustor for validation of the present numerical method. The supersonic combustion flows associated with shock waves, turbulent vortices and flame structures are studied. With addition of methane and ethylene, the flame zone moves further downstream of the strut and the maximum flow temperature at chamber exit decreases by 200 K. With analysis of total temperature ratios, it is found that combustion efficiency for hydrogen combustion is 0.91 and it decreases to 0.78 for the fuel mixture. The calculation of ignition delay time and flame speed reveals that fuel mixture of hydrogen and hydrocarbons has considerably larger delay time and smaller flame speed, that contributes to the weakened flame zone and lower combustion efficiency.     

Influences of various vortex structures on the dispersion and deposition of small ash particles

Numerical simulations were conducted to study the influences of various vortex structures on the dispersion and deposition processes of 1 μm to 10 μm diameter fly ash particles on the rear side surface of a boiler tube. Turbulent gas flow was simulated with detached eddy simulation (DES) method and vortex structures in the wakes were modeled. Results suggested that the motions of particles in the near wake region were controlled by different vortex structures, and the impact efficiency and deposit concentration on the rear side surface induced by the vortices varied considerably at different velocities. The results of volume percentages distribution of the deposited particles with various diameters simulated were in good agreement with the experimental data.     

日本木结构独立住宅的建造及其人性化特点

日本具有很久远的木结构建造传统,在建造木结构独立住宅过程中善于总结经验,开发新技术。日本独立住宅具有人性化、舒适,抗震性强等优点,对我国独立住宅的建造具有借鉴意义。该文从建筑的构造类型、建造方式、主要防护措施、抗震措施四个方面介绍日本木结构独立住宅的建造及其体现的人性化特点。