Reynolds数22 000的孤立方柱绕流的大涡模拟

方柱绕流是典型的钝体绕流问题,蕴含了丰富的流体力学现象,对这类流动的准确预测面临着诸多挑战.采用自主发展的大涡模拟程序,对来流Mach数M=0.3,Reynolds数Re_D=22 000的绕孤立方柱流动进行了细致模拟,亚格子模型使用动力涡黏模型.对计算结果的分析表明,大涡模拟所得的平均流场及Reynolds应力分布与已有实验数据和直接数值模拟结果均吻合较好,验证了预测结果的可靠性;在此基础上对瞬态流场进行了研究,展示了计算条件下方柱绕流分离转捩及尾迹区旋涡交替脱落形成Karman涡街的全过程,为更细致的流动机理探索奠定了基础.      

板状燃料组件流道部分堵塞的安全边界研究

为掌握板状燃料组件内多个流道堵塞下的流动换热特性,获得流动堵塞致传热恶化的触发边界,以提高板状燃料反应堆的运行安全性,以典型板状燃料堆JRR-3M的标准燃料组件为对象,基于定性分析将流道堵塞事故分为非相邻流道堵塞与相邻流道堵塞两类,采用计算流体动力学软件ANSYS Fluent对两类流道堵塞事故下的流动换热特性进行模拟。模拟结果表明:非相邻流道完全堵塞或相邻流道最大堵塞率低于35%,流道内不会发生局部沸腾且燃料最高温度低于许用温度。基于上述结果,可确定JRR-3M反应堆在堵流事故下的安全运行边界。     

方柱-弹性分隔板涡致振动数值研究

本文开发了基于有限体积法的流固强耦合大变形求解器,流体采用ALE动网格技术,固体采用修正拉格朗日模型进行求解。研究100≤Re≤1000范围内,方柱-弹性分隔板的涡致振动特性及其尾流脱涡特性。结果表明:弹性分隔板阻断尾流区剪切层的相互作用,使钝体阻力减小,旋涡脱落至下游;随着雷诺数的增加,方柱和分隔板的升力系数与振幅逐渐增大;弹性分隔板的斯特努哈尔数明显较小,能够更好地抑制尾流区剪切层间的相互作用.     

脉动流方柱绕流特性研究

本文数值模拟雷诺数Re=100的条件下,脉动流振幅和频率分别为0.2≤A≤0.8和0≤f_P≤20 Hz时方柱绕流特性.通过数值计算得到方柱绕流的升、阻力系数,涡脱频率及尾涡特性,且稳定流下计算结果与文献结果一致。研究结果表明脉动流是一种有效的主动流动控制方法;在脉动流频率f_P为1.2~2.6自然涡脱频率f_(sn)时,旋涡脱落频率存在"锁定"现象;在锁定范围内,尾涡形成区域变短,时均阻力系数显著增大,且在脉动流频率等于两倍频率时,时均阻力系数达到峰值;随着振幅的增大,频率"锁定"范围增大。     

关于旋涡局部稳定性的研究

以线性近似方法研究了不可压流中任意形状旋涡局部稳定问题,考虑了流线曲率及螺线流动对旋涡稳定性的影响.得出了各类型二维旋涡局部稳定准则,这些准则直观简练,在工程研究中应用方便.研究表明,旋涡稳定存在上、下二种界限,前人的研究尽属下限稳定范围.当上限稳定条件不满足时,在尾涡内部会出现低压气穴并引起旋涡局部脱落或散裂.应用上限稳定准则可以方便地解释Taylor涡及Karman涡街现象产生的机理.     

疏水表面减阻的格子Boltzmann方法数值模拟

采用格子Boltzmann方法的多松弛模型和Shan-Chen多相流模型对雷诺数为100的疏水表面方柱绕流进行了数值模拟, 分析了疏水表面接触角和来流含气率对方柱绕流流场的影响. 研究结果表明: 疏水表面接触角一定时, 来流含气率在一定范围内, 疏水表面具有减阻的能力, 超出这一范围时会出现阻力系数、升力系数升高的现象, 同时在方柱近壁面处伴随涡的形成产生了气团脱落; 当来流含气率处于适当水平时, 接触角越大, 绕流物体近壁面处含气率越稳定, 减阻效果越明显. 分析发现疏水表面减阻的关键在于保证近壁面处气层的稳定性, 此时接触角越大, 减阻效果越明显. 本文从含气率角度出发分析疏水表面的减阻现象, 为进一步探索疏水表面减阻机理提出了新的思路.     

巧求三角形板状物体的转动惯量

本文用填补的方法,将三角形填补为平行四边形,通过矩形板状物体的转动惯量和平行轴定理,间接地计算出三角形板状物体的转动惯量.     

吸力面小翼对扩压叶栅旋涡结构的影响

本文采用经过实验校核的数值模拟方法对某压气机动叶原始叶型和吸力面叶尖小翼叶型流道旋涡结构进行了详细分析.结果表明,原始叶栅流道中存在四个旋涡,即上通道涡、下通道涡、下集中脱落涡和叶顶泄漏涡。吸力面叶尖小翼的应用使得叶栅流道内的旋涡结构发生了变化,叶尖小翼抑制了叶顶泄漏涡的强度,从而使得上集中脱落涡得以出现,同时还使得叶顶泄漏涡的衍生涡被撕裂成两个衍生涡.正是由于叶尖小翼改变了叶栅流道内的旋涡结构,使叶栅流场的气动性能得到了改善.     

中国实验快堆燃料组件精细功率分布计算

在热工中,需要中子学计算给出燃料组件内各元件棒功率的相对分布。利用蒙特卡罗程序对中国实验快堆（CEFR）燃料组件内元件棒功率分布进行了理论计算分析,并保证计算结果相对统计误差小于0.8%。使用另一个基于六角形节块扩散理论的钠冷快堆中子学设计软件NAS计算得到的结果对蒙特卡罗程序计算结果进行了对比计算。结果表明,蒙特卡罗程序与NAS计算得到的元件棒相对功率分布结果的最大相对偏差小于3%。使用蒙特卡罗程序对CEFR燃料组件内精细功率分布的计算是可靠的,可用于设计计算当中。     

双波段芯片集成封装组件的低温光谱定量化

在同一组件中多芯片多波段的应用中,由于芯片的中心距越来越小,导致某些相邻波段通常被集成制备到一个芯片上。为减小波段串扰,本文针对一体化双波段芯片集成封装组件的低温光谱定量化展开研究,通过制备一体化双波段芯片集成封装组件,并通过波段间物理隔离、金属区物理遮盖等措施将两波段的光束隔离。测试结果表明隔离前后,芯片间光谱串光现象有了明显改善,波段间串扰从8%降到了4%以内,光谱带外响应从6.5%降低至0.78%。为了避免低温工况下物理隔离条与芯片的热失配问题,隔离条采用与芯片衬底完全一致材料。双波段芯片集成封装组件的高低温冲击试验表明,其在有效抑制组件内串扰的同时,也解决了组件内关键部件的热失配问题。     

铅基反应堆燃料组件间隙横流周期性研究

燃料组件内冷却剂的横流对反应堆堆芯的换热有很大影响,为研究铅基反应堆燃料组件内冷却剂的横向速度分布,对CiADS反应堆燃料组件组件局部的7,19棒束的单螺距及多螺距多种几何进行建模和CFD（Computational Fluid Dynamics）模拟,并对其间隙内横向速度进行分析。研究表明: 19棒束组件内通道、角通道的相邻间隙内横向速度的分布在组件轴向和横向上有明显周期性,横向上根据两个内通道间隙平移旋转的位置关系由一个间隙的结果经过平移一定相位角度可以得到另一个间隙分布结果,沿轴向多螺距模型每个螺距长度内横向速度分布一致。7棒束组件在相同类型通道内横向速度分布大小及趋势与19棒束一致。少棒束单螺距组件结果进行横向及轴向的周期性延拓可以得到多棒束多螺距模型间隙内的横流分布。Cross flow of a coolant in fuel assembly had a great impact on the heat transfer of a reactor core. In order to study the characteristics of the cross flow in lead-based fast reactor assemblies, the CiADS fuel assemblies were used as research object. Fine geometric models and CFD simulation of 7 and 19 pin bundle and multi-pitch length assemblies based on CiADS fuel assemblies were carried out. The distribution of the cross flow velocity in several geometric models was compared and analyzed. The results show that the distribution of the cross flow velocity in gaps of interior and corner channel in 19 pin bundle has obvious periodicity in both axial and horizontal direction. In the horizontal direction, the results of one gap can be translated by a certain phase angle to obtain another gap distribution result according to the positional relationship of the translational rotations of the two internal channel gaps. The distribution of cross flow velocity is uniform in each pitch length of multi-pitch model in the axial direction. And the distribution of transverse flow in gaps of 7 pin bundle is similar to the distribution in the same kind of gaps in 19 pin bundle. The results of fewer pin bundle with single pitch length can be periodically extended in axial and transverse direction to obtain the characteristics of cross flow in geometric models with multi-pitch length and more rods.     

压力管嵌入式燃料部件入口堵流事故多尺度热工模拟

压力管嵌入式燃料部件内冷却剂管道间不存在横向交混,若燃料辐照肿胀或碎片进入冷却管道内,容易引发堵流事故,造成局部冷却条件恶化,使燃料烧毁。考虑到次临界能源包层流动路径长、方向弯曲等特点,针对入口堵流事故提出一种多尺度热工模拟方法,通过RELAP5程序给计算流体力学(CFD)软件提供边界条件,对核功率密度最高的燃料部件入口处第一排单根流道部分堵塞和全部堵塞工况进行数值模拟,分析事故条件下燃料热工安全特性。结果表明:第一排单根流道部分堵塞时燃料温度仍满足安全限值,而全部堵塞时峰值温度将超过燃料相变温度限值。     

Monitoring neutrons from spent reactor fuel by bubble detectors

In order to eliminate the strong temperature-dependence of bubble detectors used for spent fuel assay, a simple way could be to keep them in the water pond but far from fuel assemblies before exposure for about 20 min, until the detectors warm up. Fast neutrons from fuel assemblies in the Paks Nuclear Power Plant, Hungary, were detected by BD-100R type detectors at 28°C (in winter) and at 35°C in summer). Calibration was performed by a standard ²⁵²Cf source in borated water. Burnup monitoring inside fuel assemblies can be provided by smaller diameter detectors prepared from BD-100R type ones.     

Vortex shedding noise of low tip speed,axial flow fans

Noise and performance tests were conducted on three low tip speed, half-stage, axial flow fans to determine the nature of the vortex shedding noise mechanism. Each fan was 356 mm in diameter and had eight equally spaced, variable pitch blades. The noise measurements were made in a free field environment and the fan back pressure and speed were varied during the tests. An acenaphthene coating on the blades was used to determine the regions of laminar and turbulent flow.Vortex shedding can be a significant source of noise when the fan is operated in a lightly loaded condition. Essentially it is due to instabilities in the laminar boundary layer on the suction side of the blade where these instabilities are in the form of Tollmien-Schlichting (T-S) waves. These instabilities interact with the trailing edge of the blade and generate acoustic waves which radiate from the trailing edge and form a feedback loop with the source of the instabilities. Vortex shedding noise can contribute as much as 5 dB in overall noise level and up to 22 dB at higher frequencies (8–14 kHz).Serrations located at the leading edge, at the mid-chord, or near the trailing edge on the suction side were found to reduce the vortex shedding noise significantly. The mid-chord location was found to be the most satisfactory because, as well as eliminating the noise, the serrations provided a 3% improvement in peak efficiency. This improvement occurred because separation of the laminar boundary layer was prevented on the suction side. On the other hand, serrations placed at the other two locations tended to degrade fan performance.     

177堆芯24个月换料可行性研究

与18个月换料相比,压水堆核电站24个月换料能减少大修次数,提高机组负荷因子,增加发电量。基于装载177组件的堆芯,通过提高新燃料组件富集度和增加批换料组件数使堆芯循环长度达到24个月换料周期要求,考虑实际24个月换料和名义24个月换料高低两种电厂可利用因子。考虑燃料组件费用、大修费用、乏燃料处理费用和发电收益等进行换料方案经济性分析评估,并和典型18个月换料经济性作比较。177堆芯平衡循环装载88组富集度为4.95%的燃料组件,能满足名义24个月换料循环长度的需要,组件平均卸料燃耗约48 GWd/tU;装载104个燃料组件的堆芯能满足实际24个换料循环长度的要求,堆芯参数满足相关安全限值要求。结果表明,177堆芯24个月换料具有可行性,其高负荷因子下的经济性与18个月换料相当。     

Attenuation of combustion instability in a fuel-staged dual-nozzle gas turbine combustor with asymmetric hydrogen composition

The instability attenuation mechanism of fuel staging was investigated in a CH₄/H₂ fueled dual-nozzle gas turbine combustor. Fuel staging was implemented using an asymmetry in fuel composition between the two nozzles. The fuel composition of the upper nozzle was varied while keeping that of the lower nozzle constant. Under these conditions, the self-excited and forced responses of fuel-staged flames were analyzed using OH* chemiluminescence imaging, OH planar laser-induced fluorescence, and particle image velocimetry. In the self-excited measurements, although strong combustion instability was exhibited in the symmetric condition, it weakened gradually with increasing asymmetry in fuel composition. The symmetric flame exhibited significant fluctuations in the heat release rate around the flame tip, which acted as the primary cause of driving combustion instability. However, in asymmetric flames, the H₂ addition induced phase leads in heat release rate fluctuations at the upper region, which damped combustion instability. Thus, our observations revealed a high correlation between the phase leads and the attenuation of combustion instability. Analyses of the forced responses showed that the heat release rate fluctuations were induced by interactions between the flame and the shedding vortex released from the nozzle tip into the downstream. Although these characteristics of shedding vortices did not depend on the H₂ addition, the change in the axial position of the flame caused by the H₂ addition induced the relocation of the site, at which the flame interacted with the vortex. Subsequently, it induced phase leads in the heat release rate fluctuations. The phase difference of heat release rate fluctuations between the two flames due to this phase leads enlarged progressively with increasing asymmetry in fuel composition, leading to the attenuation of combustion instability in asymmetric conditions.     

An investigation of some models and approximations used in calculating fuel assemblies of a high-temperature gas-cooled reactor of the GT-MHR type

The paper describes basic neutron-physics models developed in the Division of Advanced Nuclear Power Systems of the Institute of Nuclear Reactors, Russian Research Center Kurchatov Institute, as design models intended for calculating the characteristics of block fuel assemblies of a high-temperature gas-cooled reactor GT-MHR, namely, models for calculating burnup of fuel and isotopes of burnable neutron absorbers and calculating fuel assemblies at fixed points with respect to burnup with preparation of the neutron constants in a preassigned number of energy groups for full-scale design of a reactor. A model problem for investigation of calculated approximations is proposed. The outcome of this investigation is a developed stage-by-stage procedure of preparing group homogeneous cross sections of a fuel assembly and its parts that has been introduced into the practice of design calculations of a GT-MHR reactor.     

Burnup calculation by the method of first-flight collision probabilities using average chords prior to the first collision

A technique to calculate the burnup of materials of cells and fuel assemblies using the matrices of first-flight neutron collision probabilities rebuilt at a given burnup step is presented. A method to rebuild and correct first collision probability matrices using average chords prior to the first neutron collision, which are calculated with the help of geometric modules of constructed stochastic neutron trajectories, is described. Results of calculation of the infinite multiplication factor for elementary cells with a modified material composition compared to the reference one as well as calculation of material burnup in the cells and fuel assemblies of a VVER-1000 are presented.     

压力管式超临界水堆堆芯核热耦合

针对压力管式超临界水堆(PT-SCWR)新型62棒设计,其功率密度与燃料温度、冷却剂密度/温度紧密耦合,利用中子物理分析程序(WIMS-AECL)和子通道分析程序(ATHAS),对该设计堆芯进行核热耦合分析,并进行优化,结果表明该耦合方法是有效的。分析结果指出新型62棒燃料组件设计包壳最高温度和冷却剂出口温度都低于设计限值,满足设计目标;并且可以通过调整内外圈燃料富集度至5.5%和4.6%、调整燃料组件内圈棒束节圆由5.30cm到5.175cm,进行优化来获取一个均匀的温度分布;通过对比不同栅距下的慢化剂温度系数和空泡系数,得到一个最佳栅距为21cm。