共查询到17条相似文献,搜索用时 213 毫秒
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建立窄矩形通道在摇摆条件下湍流流动的物理数学模型,应用数值分析方法模拟窄矩形通道的三维非稳态流动的传热过程;考察摇摆条件下通道内流动阻力和换热性能及其随雷诺数Re、摇摆周期T及摇摆幅度max影响的变化规律。结果表明,摇摆状态下窄矩形通道内速度场呈周期性变化;时均摩擦系数favg和时均努塞尔数Nuavg比非摇摆工况下的结果大,Nuavg满足拟合公式0.851 0.4Nu 0.023Re Pr;在相同Re和摇摆周期T下,通道内流体摩擦压降和Nu的变化幅值随max的增大而增大,其变化周期等于T;在相同Re和max下,摩擦压降pf和Nu的变化幅值随T的增大而减小,其变化周期等于T。 相似文献
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对冷却流体在球床模块堆内燃料颗粒填充区域中的流动和传热过程进行了研究.数值模拟突然停堆后燃料颗粒区在温差作用下的自然对流过程,分析了瑞利数Ra对燃料填充区域内流场、温度场和局部努塞尔数Nu以及壁面摩擦阻力系数的影响.计算结果表明:当球床模块堆突然停堆时燃料填充区域可形成加热壁面流体上升流动、冷却壁面下降流动的自然循环流动;随着Ra数增大,回流中心向上移动;沿轴向壁面局部Nusselt数和摩擦阻力系数存在极值,并且极值点随Ra数增大而向上移动;与氮气相比,氦气作为冷却介质停堆后具有更均匀的堆芯轴向温度分布. 相似文献
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The laminar pulsatile flow in tubes in rolling motion is investigated theoretically. The theoretical model of laminar flow in rolling motion is developed and the velocity correlation is also derived. The effect of rolling motion on velocity and frictional resistance factor is analyzed. The rolling motion mainly affects on the laminar flow by the tangential force. The centrifugal force does not affect on the flow. The tangential force affects on the flow in axial direction, its radial effect is very weak and could be omitted. There are two critical rolling points in rolling motion. After the first critical rolling point, the flowing velocity next to the wall reverses. Moreover, the flow rate at the tube cross-section becomes negative after the second critical rolling point. The buoyancy force is only one part of the effects that affects on the average velocity of a natural circulation system in rolling motion. The effect of Womersley number on the velocity is significant, which can not only affect on the average velocity but also on the oscillating period and velocity amplitude. The rolling motion does not affect on the average frictional resistance of laminar pulsatile flow. If the rolling motion is very serious, the flow is at a transitional or turbulent flow state, in this case the effect of rolling motion on the average frictional resistance is considerable. 相似文献
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The flowing and heat transfer of turbulent flow in typical 4 rod bundles in rolling motion is investigated with LES and URANS. As the rolling period decreases, the average wall shear stress increases, and the frictional resistance increases. The wall shear stress solved by LES is not good enough, while that of URANS is consistent with experiments. The variation of frictional resistance coefficient, Nusselt number and Reynolds stress with rolling amplitude is very weak. In rolling motion, the biggest frictional resistance coefficient is not located in a constant time. 相似文献
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Because of the periodic effects of ocean waves, there are great discrepancies between the operational characteristics of nuclear power systems in ocean environment and that of land-based nuclear power systems. In some special operational status, like natural circulation, the additional forces due to ocean environment may impose so great disturbance on the coolant flow that theatres the safety operation of the systems. In the present paper, the turbulent flow in rectangular channels in ocean environments is investigated theoretically with CFD code FLUENT. The effects of several parameters on turbulent flow are analyzed. The effects of rolling motion includes two parts, the first part is the additional force parallel to flowing direction, which can affect on the pressure drop of the flow and change the flowing velocity, and the other part is the additional force perpendicular to flowing direction. In ocean environments, the flowing characteristics of turbulent flow are dominated by the additional force parallel to flowing direction. The effect of additional force perpendicular to flowing direction is very limited. In rolling and heaving motions, if the flowing velocity is the same, the flowing characteristics of turbulent flow are nearly the same, too. The bigger the Reynolds number is, the more serious the oscillation of turbulent kinetic energy and frictional resistance coefficient is, and the more the oscillation of turbulent flow is. The relationship between average frictional resistance coefficient and velocity oscillating amplitude is quadratic. And the oscillating amplitude of frictional resistance coefficient is in direct ratio with velocity oscillating amplitude. 相似文献
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The flow and heat transfer models of laminar flow and turbulent flow in rolling motion are established theoretically and modified with CFD results and experimental data. The correlations of frictional resistance coefficient and Nusselt number in pipes in rolling motion are obtained. The effect of rolling motion on the flow and heat transfer is mainly affected by the Reynolds number, angular acceleration and channel diameter. As the channel diameter is small, the effect of rolling motion on the flow and heat transfer is weak. The modified correlations of frictional resistance coefficient and Nusselt number in rolling motion could predict the flow and heat transfer in pipes in rolling motion correctly. The average discrepancy between theoretical correlations and experimental data is about 15%. 相似文献
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通过实验研究了摇摆造成的周期性附加惯性力作用下矩形窄通道内空气 水两相流压降特性。按分液相雷诺数将流动分为层流区(Ref <800)、过渡区(800≤Ref≤1 400)及湍流区(Ref >1 400)3个区域,并对各区域内附加压降、重位压降和摩擦压降平均值及瞬态值进行了比较。结果表明,附加惯性力对窄通道内两相流整数倍周期内平均摩擦阻力无明显影响。周期性附加惯性力作用下(摇摆周期16 s,摇摆振幅30°),层流区及过渡区气相表观速度、液相表观速度、质量含气率及摩擦压降随时间周期性波动,波动周期等于摇摆运动周期;瞬时摩擦压降相对于其平均值的波动幅值随气液两相流速的增加而减小。湍流区两相流动参数周期性波动不明显。 相似文献
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Effects of rolling on laminar frictional resistance in tubes 总被引:2,自引:0,他引:2
The laminar velocity distribution in tubes in rolling motion is obtained by properly simplifying the laminar flow equations. The method of 7 and 8 for analyzing the effect of periodic pressure on laminar flow is partly adopted. The influence of initial velocity on the velocity in rolling motion fades away quickly, while the periodic pressure due to rolling motion controls the velocity variation gradually. The effects of several parameters on the velocity profile in the cross-section are investigated. The rolling radius and amplitude only affect the velocity in a specified proportion, and the velocity profile shape remains unchanged. The tube radius, rolling period and fluid viscosity not only affect the velocity peak, but also the profile shape. The tube radius and fluid viscosity could limit the effect of rolling motion on the flow. The laminar friction coefficient in rolling motion is also obtained. The laminar friction resistance and factor for two special cases are investigated. 相似文献
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Research on operational characteristics of passive residual heat removal system under rolling motion 总被引:5,自引:0,他引:5
The operational characteristics of passive residual heat removal system under rolling motion were investigated experimentally. The passive residual heat removal system under rolling motion was simulated with the advanced RELAP5 code. The results are consistent with experiments. The relative discrepancy between calculating and experimental results is less than 10%. The modified condensation heat transfer model can also be used to calculate the condensation heat transfer coefficient with droplet carryover precisely. The fluctuation of condensate temperature and steam pressure is not noticeable. As the power becomes larger for the same rolling motion, the oscillation amplitude of condensate flow rate becomes larger. The effect of rolling motion upon heat transfer coefficient and flow resistance was investigated with experimental results. Rolling motion can increase the flow resistance in a great extent. The more serious the rolling is, the more the flow resistance is. Additional pressure drop does not effect on average flow velocity. The decreasing of average flow velocity is due to the decreasing average gravity pressure drop and the increasing of flow resistance. The contribution of gravity pressure drop on the decrement of average flow velocity is less than 20%. The other is due to the increasing flow resistance. In the present paper, the experimental results are listed first, and then the simulation results comparing with the experimental results are listed in the second part. At last, the effect of rolling motion is investigated theoretically. 相似文献