共查询到19条相似文献,搜索用时 93 毫秒
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流动超材料与变换流体动力学的发展丰富了人们对于流体流动控制的方法.本文基于变换流体动力学,耦合流动旋转与放大功能,设计出了具有张量化黏度的流动旋聚器.从数值模拟层面验证了旋聚器可在蠕动流状态下同时实现对流速的放大和旋转功能.在旋聚器中心流域,流体流速被放大,呈现出文丘里效应;在旋聚器外部区域,流体流动状态不会因旋聚器的存在而受到干扰,保持原有的流动状态.除此之外,本文发现并解释了空间坐标变换的非互易性所造成的旋转滞后现象的本质.本文所研究内容扩展并优化了现有的流体流动聚集功能;提出了文丘里效应相关应用的一种新途径;为超材料的非互易坐标变换设计提供了新的思路. 相似文献
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竖直圆管中超临界压力CO2对流换热实验研究 总被引:5,自引:1,他引:4
本文对超临界压力CO2在竖直加热圆管内的对流换热进行了实验研究,比较了不同流向、不同热流密度等对流动和换热的影响。实验结果表明,管内径为2mm时,在低进口Re条件下,由于浮升力影响导致层流向湍流提前转变, 对流换热增强;与向上流动相比,向下流动更易由层流转变为湍流;向下流动的换热要强于向上流动,表明浮升力对换热有很大影响。对于管内径为0.27 mm的微细圆管,当进口Re高于104时,浮升力的影响可以忽略,对流换热系数的变化完全由物性的变化尤其是cp的变化导致。 相似文献
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本文对超临界压力二氧化碳在内径为1 mm的竖直细圆管中的对流换热进行了实验研究.分析了流体的热流密度、进口温度、质量流量以及流动方向对超临界压力二氧化碳对流换热的影响.实验研究发现,热流密度、进口温度、质量流量以及浮升力对细圆管内对流换热的影响很大,对流换热系数在准临界温度附近存在峰值.在加热的前半段向上流动的对流换热强于向下流动,在加热的后半段则相反.随着热流密度与质量流量比值的不断增加,向上流动与向下流动对流换热强弱转换的交点不断向流体进口方向推移,并且向上流动的壁面温度出现峰值,发生换热恶化,而向下流动则没有出现换热恶化. 相似文献
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用实验室模拟方法研究了径向温度梯度对热对流涡旋的影响,结果表明,径向温度梯度所引起的基流使热对流涡旋的对称性结构被破坏,使涡旋变成非对称结构,并使涡旋向基流下游偏移,其强度随基流的加强而减弱,直至消失.热对流涡旋越强其对称性结构越稳定,基流对它的影响越小
关键词:
转盘实验
基流
热对流涡旋 相似文献
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Aeroacoustical analogies allow one to extract acoustical information from limited information about the flow. In the particular case of low Mach number compact flows, vortex sound theory has been quite successful. In the present paper, different formulations of the vortex sound theory are compared on the basis of their ability to provide realistic results for vortex-pairing sound when approximate flow models are used. In particular, these theories do not perform equally well when applied to a flow model in which the effective conservation of momentum and kinetic energy is not respected, as it should be in the absence of external forces and neglecting viscous dissipation and compressibility effects. A conservative form of the vortex sound theory is obtained by reiterating the assumptions of conservation of these flow invariants. This alternative form of the analogy allows one to obtain more robust results when applied to perturbed analytical flow models and experimental data. 相似文献
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Machida M 《Physical review letters》2003,90(3):037001
We numerically investigate Josephson vortex flow states in layered high-T(c) superconductors motivated by a recent experimental observation for accurate periodic magnetic field dependences of the Josephson vortex flow resistance over a wide range of magnetic field (0.5-4.0 T). We confirm in our mesoscale simulations that dynamical matching of Josephson vortex lattice with sample edge is responsible for the periodic dependence. The present simulations reveal that the Josephson vortex lattice flow speed is particularly suppressed when the moment of vortex entry matches that of vortex escape. Thus, the possible matching situations are taken into account and the observed periodicity is successfully explained. 相似文献
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A possibility of visualizing flows using random inhomogeneities of film thicknesses of different colors as particles for visualization is shown on an example of a vortex flow structure in an oscillating thin liquid film. Formation of vortex flows in a thin liquid film containing surface-active substances is investigated in experiments. The film is fixed horizontally along the edges of the cell vibrating in the vertical direction. Spatially homogeneous oscillations of the liquid film can excite different types of waves that generate two-dimensional vortex flows due to nonlinearity. We present results of experimental investigation of the structure of vortex flows in a thin film (0.5–10 μm) with rectangular boundaries. It has been revealed that, if the horizontal size of an inhomogeneous region is much smaller than the size of vortices, the inhomogeneities are transported by vortices and their interference pattern can be used for visualization of vortex flows. 相似文献
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Numerical and experimental investigation is carried out to study the effect of combined vortex generator and nanofluids on turbulent heat transfer and fluid flow characteristics in an equilateral triangular duct. A triangular duct provides a lower heat transfer rate and lower pressure drop compared to other duct configurations. The improvement of heat transfer of these ducts increases their importance for providing higher heat transfer and lower pressure drop. Two different types of nanoparticles, namely Al2O3 and SiO2, suspended in distilled water with two particle concentrations are successfully prepared and experimentally tested. The numerical and experimental results show dramatic heat transfer enhancement by using a vortex generator and nanofluids, simultaneously accomplished with a moderate increase in the friction factor. A low deviation has been seen between the present numerical and experimental results. 相似文献
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直流式旋风除尘器流动特性及性能的试验研究 总被引:5,自引:0,他引:5
1前言近几十年来一些特殊场合的净化除尘问题显得尤为突出,如沙漠地带运行的汽车、坦克和直升机的发动机沙粒磨损所导致的进气中沙粒分离问题,一些电站和锅炉的引风机的固粒磨也会降低其效率和使用寿命,尽管电站一般使用了大型静电除尘装置,但由于烟气的温度较高,使除尘器中电极产生固粒积污现象,降低了其除尘效率。在发动机与风机前装设气固分离装置可降低叶轮机械的磨损,但这要求分离装置必须容积小、压降低及除尘效率高,现有的离心式气固分离设备还不能满足这些要求。本文提出研究发展轴向直流式旋风除尘装置来解决这种除尘问题… 相似文献
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E. V. Thuneberg 《Physica B: Condensed Matter》1995,210(3-4):287-299
It is well known that superfluids respond to rotation by forming vortex lines. It has been recently discovered that a different type of state consisting of a vortex sheet, instead of lines, can be created in the A phase of superfluid 3He. This paper presents an introduction to the vortex sheet. We first discuss 4He, where a vortex sheet is unstable. The way to realize a stable sheet in 3He-A is called a vortex soliton. It consists of a topologically stable domain wall to which nonsingular vorticity is bound. The vortex soliton has been observed by nuclear magnetic resonance, and its most prominent experimental properties are explained. The macroscopic shape of the sheet and the superfluid flow in a rotating container are discussed. 相似文献
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Numerical Investigation and Wind Tunnel Validation on Near-Wake Vortical Structures of Wind Turbine Blades 下载免费PDF全文
Zhenyu Zhang Li Chen & Tongguang Wang 《advances in applied mathematics and mechanics.》2016,8(4):556-572
Computational fluid dynamics (CFD) has been used by numerous researchers
for the simulation of flows around wind turbines. Since the 2000s, the experiments
of NREL phase VI blades for blind comparison have been a de-facto standard
for numerical software on the prediction of full scale horizontal axis wind turbines
(HAWT) performance. However, the characteristics of vortex structures in the wake,
whether for modeling the wake or for understanding the aerodynamic mechanisms
inside, are still not thoroughly investigated. In the present study, the flow around NREL
phase VI blades was numerically simulated, and the results of the wake field were
compared with the experimental ones of a one-to-eight scaled model in a low-speed
wind tunnel. A good agreement between simulation and experimental results was
achieved for the evaluation of overall performances. The simulation captured the complete
formation procedure of tip vortex structure from the blade. Quantitative analysis
showed the streamwise translation movement of vortex cores. Both the initial formation
and the damping of vorticity in near wake field were predicted. These numerical
results showed good agreements with the measurements. Moreover, wind tunnel wall
effects were also investigated on these vortex structures, and it revealed further radial
expansion of the helical vortical structures in comparison with the free-stream case. 相似文献