共查询到19条相似文献,搜索用时 187 毫秒
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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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为准确评估紧密栅棒束子通道间的搅混现象,采用开源计算流体力学(CFD)软件OpenFOAM 2.0并基于k-ω的显式几何雷诺应力湍流模型对两种子通道内的周期性大尺度涡结构进行模拟,研究了紧密栅子通道间周期性大尺度涡波长、峰值频率等参数的变化规律。结果表明,周期性涡结构存在一个很强的峰值频率,其平均最大频率随雷诺数(Re)呈线性增加,但其平均波长(λ)不随Re变化,只与子通道的结构参数有关;周期性涡结构导致两个子通道间存在很强的周期性的流动震荡,是紧密栅子通道湍流搅浑得到强化的主要原因。 相似文献
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权重窗技术是最常用的降低方差技巧之一,合理运用权重窗技术能大幅提高计算效率。MCNP程序具备基于栅元的伴随权重窗发生器功能,但对一些含重复结构栅元或非对称结构栅元的模型,由于MCNP程序不能计算其中某些栅元体积,伴随权重窗发生器失效。本文在MCNP程序基础上设计了基于MESH技术的伴随权重窗自动生成方法,该方法不改动真实模型,采用一套虚拟的相空间覆盖真实模型。将新方法应用于重复结构算例,计算效率大幅提升。对光子散射基准实验模拟表明,新方法的计算结果与实验值吻合得非常好,相对偏差仅1.2%,计算效率约为直接模拟的8倍。 相似文献
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《中国原子能科学研究院年报(英文版)》2018,(0)
正环形燃料是内外同时通过冷却剂的一种新型燃料形式,较传统燃料在经济性、安全性方面有诸多优势,其结构如图1所示。由于环形燃料栅元的结构与实心燃料栅元存在较大差别,因此其堆芯物理计算分析方法与传统实心燃料栅元存在差异。由于国内外均没有环形燃料堆芯临界实验数据,导致现阶段开展的环形燃料堆芯物理设计都 相似文献
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定位格架夹持结构是保证燃料棒横向与轴向定位的关键。为进一步提高燃料组件中子经济性、简化定位格架生产流程,本文设计了一种可直接从格架条带上冲制而成的拱形且带小刚性凸起的弹簧结构,与刚凸组成新型定位格架夹持系统。针对设计的夹持结构,进行了单条带弹簧、单条带刚凸及格架栅元夹持结构的力学性能试验,获得了弹簧、刚凸、栅元内夹持结构的进程形变量-载荷曲线和回程形变量-载荷曲线,并分析了各结构在100%与120%名义形变量下的载荷、永久形变量等力学性能数据。结果表明:新型全锆夹持结构在名义形变量附近具有较好的力学稳定性;格架栅元夹持结构与单条带弹簧试验所得力学性能相近,表明单条带试验具有较高的代表性和可靠性。 相似文献
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传统的蒙特卡罗粒子输运计算程序在粒子每一步模拟结束后,通过遍历所有计数器来判断当前粒子所在栅元是否需要进行计数,该过程耗时随计数器数量的增加近似线性增长,当计数器数量较大时,计数耗时远高于输运耗时。本文发展了一种基于计数辅助树的大规模计数加速方法,建立了与几何栅元一一对应的树形结构,并在节点中存储了相应栅元的计数信息,通过当前粒子所在栅元的几何信息从树中快速读出对应的计数器。为了验证该方法的有效性,基于Hoogenboom全堆基准例题测量了不同计数器数量下的计算耗时。测试结果显示本文方法能有效地提高大规模计数问题的计算效率。 相似文献
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The heat transfer and friction characteristics in a new lattice with nonuniform wall roughness are simulated using the unsteady Reynolds-averaged Navier–Stokes (URANS) method with the Reynolds stress model (RSM). The applicable test of the turbulent model is made in a rectangular channel with a roughness wall. The roughness element height (e) is specified as a constant, and the influence of the relative roughness pitch (p/e) is analyzed in this work. This new lattice with nonuniform wall roughness is shown to be propitious for raising the quasi-periodic large-scale vortex structure even though the pattern is not as regular as that in the lattice with a smooth wall. The flow and temperature fields are redistributed for the introduction of roughness elements. The friction factor gradually decreases with the increase of p/e; however, minimal value of heat transfer is obtained in the lattice with p/e = 8. The friction factor and heat transfer in the new lattices are 2.64–3.59 and 3.14–3.30 times larger than those in the lattices with smooth walls, respectively. Considering the effects of both flow resistance and heat transfer coefficient, a new lattice with p/e = 15 is recommended. 相似文献
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通过开展先进安注箱阻尼器压降特性实验,获得了阻尼器两种不同形式的压降特性,研究了不同几何参数对压降系数的影响规律,并且拟合了压降系数关系式。结果表明:在实验参数范围内,漩涡压降系数随雷诺数增加而逐渐增大,交混压降系数随大/小管流量比的增加,先快速减小而后缓慢增加。小管宽度和阻尼器直径对漩涡压降系数有一定程度影响,大小管夹角、阻尼器直径和大管宽度对交混压降系数有影响,小管宽度对交混压降系数影响不明显。漩涡压降系数关系式预测值与实验值偏差在±10%以内,交混压降系数关系式预测值与实验值偏差较大。 相似文献
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Zhi SU 《等离子体科学和技术》2022,24(6):65501
An array of 30 plasma synthetic jet actuators (PSJAs) is deployed using a modified multichannel discharge circuit to suppress the flow separation over a straight-wing model. The lift and drag of the wing model are measured by a force balance, and the velocity fields over the suction surface are captured by a particle imaging velocimetry system. Results show that the flow separation of the straight wing originates from the middle of the model and expands towards the wingtips as the angle of attack increases. The flow separation can be suppressed effectively by the PSJAs array. The best flow control effect is achieved at a dimensionless discharge frequency of F+ = 1, with the peak lift coefficient increased by 10.5% and the stall angle postponed by 2°. To further optimize the power consumption of the PSJAs, the influence of the density of PSJAs on the flow control effect is investigated. A threshold of the density exits (with the spanwise spacing of PSJAs being 0.2 times of the chord length in the current research), below which the flow control effect starts to deteriorate remarkably. In addition, for comparison purposes, a dielectric barrier discharge (DBD) plasma actuator is installed at the same location of the PSJAs. At the same power consumption, 4.9% increase of the peak lift coefficient is achieved by DBD, while that achieved by PSJAs reaches 5.6%. 相似文献
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The local loss coefficient for a 90° bend in rolling motion is investigated with CFD code FLUENT. The calculation results are validated with experimental and theoretical results in steady state. The effect of spanwise and transverse additional forces on the bend loss is significant. The effects of additional forces on the bend loss are mainly embodied in the downstream section. The oscillation of bend loss caused by the spanwise and transverse additional forces is very regular while that caused by velocity oscillation is very irregular. The effect of velocity oscillation on the bend loss is significant in rolling motion with low Reynolds number. But the variation of bend loss coefficient with velocity oscillating period is very limited. 相似文献
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Sang-Gyu Lim 《Nuclear Engineering and Design》2010,240(5):1139-1150
A passive flow controller or a fluidic device (FD) is used for a safety injection system (SIS) for efficient use of nuclear reactor emergency cooling water since it can control the injection flow rate in a passive and optimal way. The performance of the FD is represented by pressure loss coefficient (K-factor) which is further affected by the configuration of the components such as a control port direction and a nozzle angle. The flow control mechanism that is varied according to the water level inside a vortex chamber determines the duration of the safety injection.This paper deals with a computational fluid dynamics (CFD) analysis for simulating the flow characteristics of the FD using the ANSYS CFX 11.0. The CFD analysis is benchmarked against existing experimental data to obtain applicability to the prediction of the FD performance in terms of K-factor. The CFD calculation is implemented with Shear Stress Transport (SST) model for a swirling flow and a strong streamline curvature in the vortex chamber of the FD, considering a numerical efficiency.Based on the benchmark results, parametric analyses are performed for an optimal design of the FD by varying the control port direction and the nozzle angle. Consequently, the FD performance is enhanced according to the angle of the control port nozzle. 相似文献
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B.H. Yan 《Nuclear Engineering and Design》2011,241(8):2948-2955
The periodic large scale vortex structure is highly accounted for the local flow and heat transfer and turbulent mixing in rod bundles. In this paper, the mechanism of the periodic large scale structures is studied in terms of the vortex dynamics. The vortex structure in rectangular channels with different inlet velocities is also analyzed. It is found that the periodic large scale vortex structure exists in the rectangular channels with transverse vorticity gradient. The distribution of vorticity is strictly related with that of vortex structure. 相似文献
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《等离子体科学和技术》2015,17(6):502-509
Experimental investigation of active flow control on the aerodynamic performance of a flying wing is conducted.Subsonic wind tunnel tests are performed using a model of a 35°swept flying wing with an nanosecond dielectric barrier discharge(NS-DBD) plasma actuator,which is installed symmetrically on the wing leading edge.The lift and drag coefficient,lift-todrag ratio and pitching moment coefficient are tested by a six-component force balance for a range of angles of attack.The results indicate that a 44.5%increase in the lift coefficient,a 34.2%decrease in the drag coefficient and a 22.4%increase in the maximum lift-to-drag ratio can be achieved as compared with the baseline case.The effects of several actuation parameters are also investigated,and the results show that control efficiency demonstrates a strong dependence on actuation location and frequency.Furthermore,we highlight the use of distributed plasma actuators at the leading edge to enhance the aerodynamic performance,giving insight into the different mechanism of separation control and vortex control,which shows tremendous potential in practical flow control for a broad range of angles of attack. 相似文献