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排序方式: 共有2564条查询结果,搜索用时 156 毫秒
1.
The combustion and emission formation process of liquid fuel in the trapped vortex combustor(TVC)are very complicated.A trapped vortex combustor with replaceable bluff-bodies was designed to investigate these processes.The bluff-body widths varied from 0.021 m to 0.036 m.Experimental tests were carried out.Liquid RP-3 aviation kerosene was used in the tests.Emissions were measured under atmospheric pressure.The combustion process was analyzed theoretically in the viewpoints of relative evaporation time,mixing time and reaction time.Numerical simulations were also conducted to help analyze the formation and depletion processes of pollutants in TVC.The results reveal that atomization was a critical factor for formation and depletion processes of pollutants.By controlling mixing speed of burned and unburned gases and thus fuel-air uniformity,turbulence intensity could also affect emission levels.In addition,residence time also affected the emissions by affecting combustion completeness and the time for NOx formation.All these factors were combined in a complicated way to affect combustion process and pollutant emissions. 相似文献
2.
Benedetto Rocchio Claudio Chicchiero Maria Vittoria Salvetti Stefania Zanforlin 《风能》2020,23(4):915-938
The present study is focused on modeling of dynamic stall behavior of a pitching airfoil. The deep stall regime is in particular considered. A model is proposed, which has a low implementation and computational complexity but yet is able to deal with different types of dynamic stall conditions, including those characterized by multiple vortex shedding at the airfoil leading edge. The proposed model is appraised against an extensive data set of experimental (α,CL) curves for NACA0012. The results of an existing widely used model, having comparable complexity, are also shown for comparison. The proposed model is able to well reproduce not only the classic curves of deep dynamic stall but also the curves characterized by lift oscillations at high angles of attack due to the shedding of multiple vortices. Furthermore, the model appears to be robust to variations of its parameters from the optimal values and of the airfoil geometry. Finally, the model is successfully implemented in a commercial CFD software and applied to the simulation of a vertical axis wind turbine within the actuator cylinder approach. The accuracy of the prediction of the turbine power coefficient in the whole rotation cycle is very good for the optimal working condition of the turbine, for which the model parameters were calibrated. Fairly good accuracy is also obtained in significantly different working conditions without any further calibration. 相似文献
3.
Vector vortex beams (VVBs) possess ubiquitous applications from particle trapping to quantum information. Recently, the bulky optical devices for generating VVBs have been miniaturized by using metasurfaces. Nevertheless, it is quite challenging for the metasurface-generated VVBs to possess arbitrary polarization and phase distributions. More critical is that the VVBs' annular intensity profiles demonstrated hitherto are dependent on topological charges and are hence not perfect, posing difficulties in spatially shared co-propagation of multiple vortex beams. Here, a single-layer metasurface to address all those aforementioned challenges in one go is proposed, which consists of two identical crystal-silicon nanoblocks with varying positions and rotation angles (i.e., four geometric parameters throughout). Those four geometric parameters are found to be adequate for independent and arbitrary control of the amplitude, phase, and polarization of light. Perfect VVBs with arbitrary polarization and phase distributions are successfully generated, and the constant intensity profiles independent of their topological charges and polarization orders are demonstrated. The proposed strategy casts a distinct perception that a minimalist design of just one single-layer metasurface can empower such robust and versatile control of VVBs. That provides promising opportunities for generating more complex vortex field for advanced applications in structural light, optical micromanipulation, and data communication. 相似文献
4.
对弹性支撑单圆柱在均匀流作用下的涡激运动特性进行数值模拟,捕捉到"锁定区"、"拍"、"频率变换"等现象。柱体周围流场采用Fluent求解,将4阶Runge-Kutta方法代码写入用户自定义函数(UDF)求解运动微分方程,运用动网格技术更新流场,实现圆柱与流场的非线性耦合作用。发现随着折合速度的增大,涡激运动响应可分为锁定前支、锁定区、锁定后支3个阶段,在进入锁定区前(折合速度Ur=3)横向运动响应发生拍现象,当跨过锁定区后(折合速度Ur=10)发生频率变换现象。结果表明,横向涡激运动有较大范围的频率锁定现象,频率解锁前后圆柱涡激运动轨迹由"右8字"形变换为"左8字"形。 相似文献
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《International Journal of Hydrogen Energy》2022,47(88):37204-37217
This paper was intended to delineate numerical research for hydrogen catalytic combustion over a circular cylinder. The wire/rod-type catalytic reactor is a simple geometry reactor with an economical design with less pressure loss. For the single rod in the reaction channel, the flow characteristic and the difference of conversion efficiency between non-gas-phase reaction and gas-phase reaction have been delineated in the present study. The flow field and the chemical reactions were numerically modeled using 2D Large Eddy Simulation combined with the gas-phase and surface reaction mechanisms. The results show that the current numerical simulation has been validated to precisely predict the vortex shedding and its frequency in the cold flows. Despite the variation trends being dominated by the upstream flow, the vortex shedding phenomena were affected by the flue gas generated from the rod surface. It can be seen from the linear relationship between the vortex shedding frequency of reacting flow and Reynolds Number. It is noted that the vortex shedding vanished if the gas-phase reaction was ignited in the reaction channel. In addition, the geometric modified conversion efficiency was proposed to delineate an indicator that could be potential for the optimization of rod-type catalytic reactor. In summary, the fundamental study of a rod in a 2D flow channel can provide information for optimizing the catalytic design or the rod array arrangement in the reactor. Moreover, the rod can also be a partial catalytic flame holder to ignite and stabilize the gas-phase reaction. The obtained results could be the potential for practical applications of rod-type catalytic combustion, catalytic gas turbine, hydrogen generation, partially catalytic reaction flame holder, and other catalytic reactions that can be appreciated. 相似文献
9.
Jing-wei Zhang Tian-liang Yao Wei-feng Li Mouhammad El Hassan Xin-lei Xu Hai-feng Liu Fu-chen Wang 《American Institute of Chemical Engineers》2020,66(2):e16822
This study follows our previous report (Zhang et al., Phys. Fluids, vol. 31, 2019, 034105) by describing the formation and evolution of the engulfment flow in the cross-shaped channel. First, the flow regimes were studied by planar laser induced fluorescence (PLIF). Results show the formation of a spiral vortex in the center of the chamber and the appearance of a well-mixed zone inside the spiral vortex. Second, we proposed a novel experimental method to analyze the residence time of the fluid in the chamber, and discover an unexpected trapping region inside the well-mixed zone. There is almost no fluid transport into or out of this region. Furthermore, three-dimensional numerical simulation is used to reveal the origination of this trapping region. Simulation results reveal that the fluid recirculates in the trapping region and the flow feature is caused by the bubble-type vortex breakdown. 相似文献
10.
In this study, fluid flow over an array of eight, 0.029 m × 0.029 m, square cross‐section cylinders in an octagonal configuration is studied numerically. The mean force coefficients (drag and lift) and the vortex formation characteristics of the array are calculated numerically by utilizing a three‐dimensional large eddy simulation mathematical model for turbulence. The numerical simulation is performed with commercial software ANSYS Fluent 19R1. To investigate the parametric influences, three spacings between the cylinders (0.07, 0.14, and 0.2 m), two array attack angles (0° and 15°), and two Reynolds numbers (4060 and 45 800) are considered. The results comprise flow patterns and force coefficients' variations with Reynolds numbers. The lift force of the downstream cylinder reaches its maximum at α = 15°, and the drag force of the upstream cylinders finds its peak at α = 0°. It is observed through velocity and viscosity contour plots that vortex formation length near the cylinder increases at higher Reynolds number. Velocity vector plots are also presented to show fluid flow behavior near the cylinder. Furthermore, the predicted mean forces on the cylinders are slightly different for different Reynolds numbers, spacings, and angles of attack. 相似文献