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旋进射流流动的大涡模拟 总被引:3,自引:2,他引:1
分析了基于流体附壁效应而自激产生的旋进射流的流动特征,采用大涡模拟(LES)方法研究了射流喷嘴内部的流场.数值模拟得到了流场的速度分布和压力分布,比较了膨胀比、长径比等喷嘴结构参数以及雷诺数对旋进射流流动的影响.数值模拟表明旋进射流的轴向流动速度衰减得很快,流场中存在明显的旋流、附壁效应和反向回流现象,所得到的结果与已有的分析结论基本吻合. 相似文献
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采用CFD方法,建立公路隧道纵向射流通风的物理数学模型,对某隧道内一组射流风机通风进行三维数值模拟,以隧道纵向射流通风基本理论为基础,分析了隧道内气流速度和压力分布特性,为进一步优化纵向射流通风设计提供参考。 相似文献
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电弧加热器流场数值模拟研究 总被引:1,自引:0,他引:1
电弧加热器流场特性是影响材料热化学烧蚀的关键因素之一,根据可压缩的轴对称N-S方程,对喷嘴的超声速自由射流、垂直冲击射流进行了数值模拟,采用k-ε湍流模型.计算得到自由射流流场结构的三个区域:射流核心区、射流卷吸区和射流湍流区,射流的速度分布具有不均匀性,其轴线射流速度存在较大变动;冲击射流近壁处存在着滞止区.所获得的喷嘴外部流场的流动状况以及冲击射流参数分布,如压力、温度和速度分布,可用于烧蚀试验和计算优化设计,流场计算结果与烧蚀实验值吻合. 相似文献
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《工程爆破》2022,(5)
为了研究起爆方式对截底椭圆形罩LSC射流成型性能影响的特点和规律,运用ANSYS/LSDYNA对不同起爆方式下截底椭圆形罩LSC射流成型过程进行了三维数值模拟,获得了不同时刻射流横断面和正面的成型图片、射流最大速度时程曲线和射流最大速度及其出现的时刻。结果表明,对于顶部中线均布多起爆点,两端起爆时差在3μs以内时,形成的射流最大速度较大,约为42604290m/s,成型性能较好,当起爆点数量大于4时,可以认为是顶部中线线起爆;对于两侧棱上均布多起爆点,两端4点同时起爆时形成的射流最大速度较大,约4800m/s,当两侧棱上均布起爆点数量大于6时,可以认为是两侧棱上线起爆;就射流最大速度而言,两侧棱上均布多起爆点普遍大于顶部中线均布多起爆点。因此,起爆方式对LSC射流成型性能影响较大,研究结果在丰富LSC射流成型理论的同时,为实际应用LSC时选择合适的起爆方式提供了参考。 相似文献
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针对高压降类调节阀涡激振动现象,设计多通道迷宫盘片和多级套筒组合高压降调节阀。基于计算流体动力学(CFD)和流固耦合模态分析法,计算调节阀内部瞬态流场及结构模态,得到其三种典型开度的流体流动情况,升力系数时域和频域特性曲线,以及模态频率和模态振型。分析结果表明:4s时刻,随调节阀开度减小,流体最大流速相应减小,第四级套筒外部流道区域的大涡逐渐形成小涡。调节阀全开时流体升力系数波动比70%和40%开度时更为剧烈,一阶模态频率、二阶模态频率均随开度的增大而增大。调节阀模态频率没有落在漩涡脱落主频率范围内,调节阀不会发生涡激振动锁定现象。 相似文献
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The Ranque-Hilsch vortex tube is a device by which cold gas can be generated using compressed gas. To understand the cooling mechanism of this device, it is necessary to know the pressure, temperature, and velocity distributions inside the tube. In order to investigate this, a simple vortex tube is built and nitrogen is used as its working fluid. A special Pitot tube is used for the measurement of the pressure and velocity. This Pitot tube consists of a capillary which has only one hole in the cylinder wall. With this Pitot tube, the pressure and velocity fields inside the tube were measured. In the same way, the temperature field was measured with a thermocouple. The results of three different entrance conditions are compared here. With the measurements results, the analysis based on the two thermodynamic laws has been made. It is found that rounding off the entrance has influence on the performance of the vortex tube. The secondary circulation gas flow inside the vortex tube can be enhanced and enlarged, the performance of the Ranque-Hilsch vortex tube improved. 相似文献
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Subhajit Dutta Chanchal Loha Pradip Kumar Chatterjee Anup Kumar Sadhukhan Parthapratim Gupta 《Advanced Powder Technology》2018,29(12):3357-3367
Gas-particle hydrodynamic behaviour inside a vortex chamber fluidized bed is studied numerically with respect to different design and operating conditions. A three-dimensional computational fluid dynamics (CFD) model of a cylindrical vortex chamber is developed. Simulations are carried out with particles and without particles. In order to understand the gas-particle flow behavior velocity distribution, particle volume fraction distribution, radial pressure distribution and axial pressure distribution inside the vortex chamber are analyzed in detail. Particles of different diameters are used and its effect on the gas-particle flow behaviour is studied. Design parameters like the number of gas inlet slots and slot width are varied and their impact on the hydrodynamics of the vortex chamber is investigated. The numerical model is validated by comparing the numerical results with experimental results reported in literature. 相似文献
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Pablo Esquinazi 《Journal of Low Temperature Physics》1991,85(3-4):139-232
This review is concerned with effects in the energy dissipation and elastic modulus of superconductors vibrating in a magnetic field. The physics of superconducting vibrating reeds and reeds made of superconducting suspensions is thoroughly described as well as the main features observed in other oscillators applied to flux pinning studies. It is argued that among the diversity of methods to study superconducting and pinning properties as a function of magnetic field and temperature, the vibrating reed technique is one of the most sensitive due to the accurate measurement of frequency and dissipation with feasible magnetometry applications. Results of the elastic coupling between the flux line lattice and the atomic lattice in high- and low-T
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superconductors obtained with the vibrating reed are summarized as well as the behavior of vibrating type II superconductors near their lower critical field. Results from mechanical measurements in high-temperature superconductors are reviewed, which support the model of thermally activated depinning and vortex diffusion. 相似文献
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为准确捕捉小开度流动的瞬态湍流特性,充分了解流场结构,采用滑移网格技术以及基于Vreman亚格子模型的全局动态大涡模拟方法,不仅得到混流式水轮机全流道内速度、压力以及涡量的分布,同时捕捉到了活动导叶周围独特的流动形式和叶道涡的时空演化。计算结果表明:当高转速、小开度工况时,流道内流体的圆周速度占有绝对优势,加强了导叶后尾迹涡的相互影响,致使流道中发生更为剧烈和复杂的漩涡、脱流等各种水力不稳定现象。从蜗壳到转轮室的压力脉动均以低频为主,主要的频率能量成分基本相同,说明小开度低频异常振动与压力波的传递有关。叶道涡是致使叶片疲劳破坏的主要因素。 相似文献
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Makoto Tsubota Tsunehiko Araki Sergey K. Nemirovskii 《Journal of Low Temperature Physics》2000,119(3-4):337-342
Recently McClintock et al. observed the free decay of a vortex tangle in superfluid 4He at mK temperatures. Since the system at such low temperatures is free from normal fluid and usual mutual friction, the mechanism of the free decay is unknown. In order to understand this phenomenon, this work studies numerically the vortex dynamics without the mutual friction. The absence of mutual friction prevents the vortex from smoothing. The resulting kinked structure promotes vortex reconnection, thus making lots of small vortex loops. Such cascade process as breakup of vortices to smaller ones can decay the vortex line density. This paper describes the decay of vortex tangle under the localized induction approximation, and that of four vortex rings under the full nonlocal calculation. 相似文献
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In this study, aerocyclone separators, with five different vortex finder diameters are simulated using commercially available computational fluid dynamics code Fluent 6.3.26 to analyze flow field pattern and the collection efficiency. It is found that a decrease in vortex finder diameter results in an increase in pressure drop by 47.84% and an increase in the collection efficiency by 9.54%, whereas, the increase in vortex finder diameter leads to a reduction in pressure drop by 23.87% and a decrease in the collection efficiency by 7.70% as compared to the Stairmand high efficiency cyclone. It is also observed that a decrease in vortex finder diameter leads to about 33% increase in axial velocity and about 25% increase in tangential velocity, whereas, an increase in vortex finder diameter results in about 23% decrease in axial velocity and about 12% decrease in tangential velocity as compared to the Stairmand high efficiency cyclone. 相似文献
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为拓展声波团聚机理,对声波团聚过程中的声流与声涡作用进行了理论和实验研究。利用声流测试系统,发现在0~1 kHz低频与5 kHz高频时,团聚室内声流现象较为明显;并通过可视化测试,在7 kHz高频时观察到明显的漩涡。结果表明,流场中的声流与声涡对颗粒团聚会产生很大的影响,声流或声涡越强,团聚效果越好。在0~1 kHz低频与5 kHz高频时,声流产生的切应力带动气溶胶颗粒发生碰撞团聚;高频时声涡力矩较大,其产生的轨道角动量带动粒子发生圆周和自旋运动;当声压级大于132 dB时,声涡团聚开始发挥作用,与声流一起促进颗粒团聚,且声压级越大团聚效果越强;与波节相比,波腹处的声流速度更大,声涡现象更明显,团聚效果也更好。 相似文献
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D. Surek 《Forschung im Ingenieurwesen》2000,66(2):79-93
By the turbulent vortex forced by the impeller, strong high-frequency pressure oscillations occur in the side channel. These pressure oscillations result from the temporal modification of the vortex structure and the specific impulse flow transportation in the side channel. They are visible due to the high-frequency character neither at integral static pressures not in the characteristic lines of the pumps. However, they add essentially to the energy transfer to the pumped fluid and to the increase of the static pressure in the side channel. The dynamic pressure oscillations in the side channel with the characteristic exciter frequency by the blade revolution frequency are transmitted to the pump case and a part of it is emitted as effective acoustic pressure to the environment. The blade revolution frequency is by far recognizable as exciter frequency in the pressure oscillations, in the mechanical case oscillation and as effective acoustic pressure in the raised amplitude parts. The pressure oscillations refer to the unsteady flow in side channel pumps. 相似文献