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稠密栅元不同子通道内湍流流动的RANS和URANS模拟 总被引:1,自引:0,他引:1
本工作采用RANS和非稳态雷诺平均纳维斯托克斯模拟(URANS)方法对稠密栅元内典型子通道——中心通道和壁面通道内的湍流流动进行CFD模拟。研究分析了稠密栅元子通道内的不同周向角度的主流速度、壁面剪应力、湍动能等参数。将模拟计算结果和实验测量结果进行对比,结果表明:RANS模拟在采用各向异性的湍流模型的情况下能较好地模拟P/D较大的稠密栅元通道,但对于P/D较小(P/D<1.1)的稠密栅元通道,CFD结果和实验数据存在较大差距。相比之下,URANS方法可模拟紧密栅元子通道间隙区的大尺度、准周期的流动振动,从而和实验数据拟合良好。推荐采用雷诺应力湍流模型(SSG,ORS)进行RANS模拟,而采用SAS湍流模型进行URANS模拟。 相似文献
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采用URANS(UnsteadyReynoldsAveragedNavierStokes)方法对不同棒束结构稠密栅元通道(P/D=1.001~1.2)内的湍流流动进行CFD模拟。研究分析了不同Re(Re=5000~215000)的湍流流动的主流速度、壁面剪应力、湍动能等参数。研究表明:在较稠密的棒束(P/D<1.1)通道内,P/D的变化对子通道内主流速度和剪应力分布均有较大影响。本文的模拟结果也验证了在达到临界P/D前(即使δ/D<0.011),交混因子Y和δ/D成反比关系。对于固定的棒束结构(P/D=1.062),当Re达到一定值(Re=9600)时,子通道内主流速度和剪应力分布对Re的变化不敏感。 相似文献
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The turbulent flow in 37 rod bundles is investigated with CFD code FLUENT. The calculation results were validated with experimental data at first. Then the effects of diminishing rod-rod gap size on local flow, heat transfer and coherent structure in tight lattice are analyzed. The critical pitch to diameter ratio is next to 1.03. As the pitch to diameter ratio decreases from a high level to 1.03, the coherent structure and flow oscillation increase gradually. However, as the gap size continues decreasing, the coherent structure and flow oscillation decay very quickly. In the very narrow gap, the coherent structure is so weak that it could be neglected. The oscillations of velocity, wall shear stress and wall temperature are also very weak. But the spatial variation of the parameters in this gap is very significant. 相似文献
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Using laser-Doppler anemometry and calibrated Preston tubes, experiments were performed in water (80°C, 0.6 MPa) to obtain information on the distributions of wall shear stresses, mean axial velocities and turbulence intensities for fully developed adiabatic flow through a six-rod bundle at a Reynolds number of 5 × 105. The rods were arranged in a square array with a pitch to a diameter ratio of 1.15 and a wall-distance to diameter ratio of 0.62. The core flow in the central subchannel appears to be similar to pipe flow, but in the gap regions much higher turbulence intensities are encountered. The skewed wall shear stress profiles together with the deformed constant-velocity lines suggest the presence of secondary flows in the corner subchannels. 相似文献
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Measurements of frequencies and spatial correlations of coherent structures in rod bundle flows 总被引:2,自引:2,他引:0
Cross-wire anemometry was used to identify and characterize coherent flow pulsations in isothermal air flow near the gap regions of a five-rod bundle with a design pitch-to-diameter ratio of 1.149 and contained in a quasi-trapezoidal duct. It was confirmed that such pulsations are quasi-periodic and contribute significantly to the velocity fluctuations across the gap. The frequency of pulsations was found to decrease with diminishing rod–wall gap size in the range between 0.015D and 0.250D, where D is the rod diameter. The pulsations in a rod–wall gap and an adjacent rod–rod gap were strongly coupled and occurred at the same frequency as one rod was displaced towards the duct wall. 相似文献
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The present study deals with the effects of wall geometry on the fluid flow and heat transfer in an annulus. Rectangular-rib structural wall roughness on the inner wall is considered. This roughness is characterized by rib height, width and pitch. A detailed parametric investigation of the effect of rib width-to-height ratio on the friction coefficient is performed for different rib pitches. This ratio varies from 0.125 to 6.0. Various rib pitches are considered, from those corresponding to a smooth wall, and up to the pitch-to-rib-height ratio of 16. Examples of various rib heights are also shown. The hydraulic diameter and the flow Reynolds number serve as additional parameters.Numerical simulations are performed using a modified k-? turbulence model, which makes possible the prediction of flow separation, reattachment and adverse pressure gradients. The model is validated by comparing its results with experimental and numerical results for overall and local flow parameters reported in the literature. The results of the present study indicate that for the given hydraulic diameter of the annulus and flow Reynolds number, the pitch that corresponds to maximal flow resistance depends on the rib width-to-height ratio. It appears that when the width-to-height ratio decreases, this optimal pitch approaches an asymptotic value. On the other hand, the optimum rib distance-to-height ratio remains almost constant. These findings are discussed in context of the available literature.Generalization of the results is attempted through the use of dimensionless groups based on the flow and geometrical parameters of the systems. A correlation for the friction factor is suggested. 相似文献
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Large eddy simulation (LES) of turbulent flow in a bare rod bundle was performed, and a new concept about the flow structure that enhances heat transport between subchannels was proposed. To investigate the geometrical effect, the LES was performed for three different values of rod diameter over pitch ratio (D/P = 0.7, 0.8, 0.9). The computational domain containing 4 subchannels was large enough to capture large-scale structures wide across subchannels. Lateral flow obtained was unconfined in a subchannel, and some flows indicated a pulsation through the rod gap between subchannels. The gap flow became strong as D/P increased, as existing experimental studies had reported. Turbulence intensity profile in the rod gap suggested that the pulsation was caused by the turbulence energy transferred from the main flow to the wall-tangential direction. This implied that the flow pulsation was an unsteady mode of the secondary flow and arose from the same geometrical effect of turbulence. This implication was supported by the analysis results: two-points correlation functions of fluctuating velocities indicated two length-scales, P-D and D, respectively of cross-sectional and longitudinal motions; turbulence stress in the cross-sectional mean flow contained a non-potential component, which represented energy injection through the unsteady longitudinal fluid motion. 相似文献
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《Journal of Nuclear Science and Technology》2013,50(11):1075-1078
The supercritical-water-cooled power reactor (SCPR) is expected to reduce power costs compared with those of current LWRs because of its high thermal efficiency and simple reactor system. The high thermal efficiency is obtained by supercritical pressure water cooling. The fuel cladding surface temperature increases locally due to a synergistic effect from the increased coolant temperature, the expanded flow deflection due to coolant density change and the decreased heat transfer coefficient, if the coolant flow distribution is non-uniform in the fuel assembly. Therefore, the SCPR fuel assembly is designed using a subchannel analysis code based on the SILFEED code for BWRs. The SCPR fuel assembly has many square-shaped water rods. The fuel rods are arranged around these water rods. The fuel rod pitch and diameter are 11.2 mm and 10.2 mm, respectively. Since coolant flow distribution in the fuel assembly strongly depends on the gap width between the fuel rod and the water rod, the proper gap width is examined. Subchannel analysis shows that the coolant flow distribution becomes uniform when the gap width is 1.0 mm. The maximum fuel cladding surface temperature is lower than 600°C and the temperature margin of the fuel cladding is increased in the design. 相似文献
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L. Meyer 《Nuclear Engineering and Design》1994,146(1-3)
Fully developed turbulent air flow in a heated 37-rod bundle with a pitch to diameter ratio of 1.12 has been investigated. Measurements were performed with a hot-wire probe with x-wires and a temperature wire. Besides the distributions of the mean velocity, mean fluid temperature, the wall shear stress and wall temperature, the turbulent quantities such as the turbulent kinetic energy, the Reynolds-stresses and the turbulent heat fluxes were measured and compared with data from isothermal flow and heated flow in pipes. 相似文献
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双弹性管流固耦合振动的数值模拟 总被引:2,自引:2,他引:0
为研究反应堆结构中诸如燃料棒、蒸汽发生器和其他换热器等管束类结构的流固耦合振动问题,利用有限体积法离散大涡模拟的流体控制方程及有限元方法离散结构动力学方程,结合动网格技术,建立了三维流体诱发弹性管束振动的数值模型,实现了计算结构动力学与计算流体力学之间的双向耦合。得到横流作用下单管的振动响应,并与已有的实验数据比较,证明了本文模型的合理性;对横流作用下的两串列管、两并列管的流固耦合振动进行了数值模拟,着重研究了节径比为1.2、1.6、2、3、4的两弹性管在不同流速作用下的动力学响应及流场特性;得到串列管、并列管的临界间距与临界流速。 相似文献