分类: 核科学技术 >> 辐射防护技术 分类: 物理学 >> 核物理学 提交时间: 2024-06-23
摘要: The impact of the radiation dose produced by 222Rn/220Rn and its progeny on human health has garneredincreasing interest in the nuclear research field. The establishment of robust, regulatory, and competent 220Rnchambers is crucial for accurately measuring radioactivity levels. However, studying the uniformity of the 220Rnprogeny through experimental methods is challenging, because measuring the concentration of 220Rn and itsprogeny in multiple spatial locations simultaneously and in real time using experimental methods is difficult.Therefore, achieving precise control of the concentration of 220Rn and its progeny as well as the reliable samplingof the progeny pose significant challenges. To solve this problem, this study uses computational fluid dynamicsto obtain the flow-field data of the 220Rn chamber under different wind speeds and progeny-replenishment rates.Qualitative analysis of the concentration distribution of the progeny and quantitative analysis of the progenyconcentration and uniformity of the progeny concentration are conducted. The research findings indicatedthat the progeny-concentration level is primarily influenced by wind speed and the progeny-complement rate.Wind speed also plays a crucial role in determining progeny-concentration uniformity, whereas the progeny-complement rate has minimal impact on uniformity. To ensure the accuracy of 220Rn progeny-concentrationsampling, we propose a methodology for selecting an appropriate sampling area based on varying progenyconcentrations. This study holds immense importance for enhancing the regulation and measurement standardsof 220Rn and its progeny.
分类: 核科学技术 >> 核科学与技术 提交时间: 2024-07-30
摘要: To improve the heat transfer efficiency of the coolant in lead-based fast reactors, this study optimized the configuration and rotational direction of the spacer wires in fuel assemblies to design a new-pattern fuel assembly. This study conducted detailed comparisons between traditional and new pattern fuel assembly rod bundles utilizing the open-source computational fluid dynamics platform, OpenFOAM. The results indicated that the new design may significantly reduce the pressure drop along the rod bundle, which is beneficial for lowering the pressure drop. Furthermore, this new design improved coolant mixing in the subchannels, which facilitated a more uniform temperature distribution and lower thermal gradients at the assembly outlet. These factors collectively reduced the thermal fatigue and creep in nearby internal components. Overall, the new-pattern fuel assembly proposed in this study may have better heat transfer performance, thereby enhancing the Integrated Thermal-Hydraulic Factor by 48.2% compared to the traditional pattern.
分类: 核科学技术 >> 核科学与技术 提交时间: 2024-07-17
摘要: 搅混翼对降低堆芯热点因子发挥着重要作用,目前对于搅混翼精细结构对流场的影响研究较少。为了更加深入了解搅混翼结构特征对堆芯热工水力性能影响,开展搅混翼结构与流场的相关性研究。首先通过几何自动化构型与计算技术,实现参数化、自动化构建撕裂式搅混翼结构及CFD计算。其次,通过对搅混翼结构参数的正交设计及模拟结果分析,明确了搅混翼结构对流场压降及横流速度等热工参数影响。文章几何结构下,不同搅混翼出口压力最大相差1.1kPa,为整个计算流体域平均压降的41%,不同结构的搅混翼下的横流速度最大相差1.1m/s,最大横流速度为平均横流速度的173%,搅混翼角度与流场相关性强,其次是搅混翼形状和长度,并设计了较优的搅混翼。对后续搅混翼结构研究及工程应用提供设计依据。
分类: 核科学技术 >> 核科学与技术 提交时间: 2025-03-28
摘要: 我国将钠冷快堆技术作为未来核能技术的重要发展方向,蒸汽发生器作为我国示范快堆(CFR600)的核心部件,其热工水力性能对反应堆的整体效率和安全性至关重要。然而,钠冷却剂流量分配不均的问题主要由均流栅格设计、进口窗结构、环形通道宽度、入口接管高度和钠冷却剂入口流量等因素引起,这不仅影响热交换效率,还会导致系统不稳定。因此,研究基于计算流体力学(Computational Fluid Dynamics,CFD)数值仿真方法,对钠侧入口流量分配的影响因素进行了参数敏感性分析,揭示了均流栅格和进口窗设计对流量分配的影响规律,并提出了优化方案和流量分配非均匀度的评价指标非均匀度常数。研究结果显示,在优化设计后,均流格栅高度确定为1200毫米,进口窗结构采用1-4排开孔数量40,5-8排开孔数量30,9-11排开孔数量24。虽然流量分配装置会在一定程度上增加了流动过程中的压力损失,但整体上改善了蒸汽发生器的流动特性,使最大相对径向速度范围控制在120-150%区间内,最大非均匀性指数降至0.35以下。此研究成果为CFR600蒸汽发生器的设计优化提供了理论依据。
分类: 物理学 >> 核物理学 提交时间: 2023-09-04
摘要: Steam generator tube rupture (SGTR) accident is an important scenario needed to be considered in the safety analysis of lead-based fast reactors. When the steam generator tube breaks close to the main pump, water vapor will enter the reactor core, resulting in a two-phase flow of heavy liquid metal and water vapor in fuel assemblies. The thermal-hydraulic problems caused by the SGTR accident may seriously threaten reactor cores safety performance. In this paper, the open source CFD calculation software OpenFOAM was used to encapsulate the improved Euler method into the self-developed solver LBEsteamEulerFoam. By changing different heating boundary conditions and inlet coolant types, the two-phase flow in the fuel assembly with different inlet gas content was simulated under various accident conditions. The calculation results show that the water vapor may accumulate in edge and corner channels. With the increase of inlet water vapor content, outlet coolant velocity increases gradually. When the inlet water vapor content is more than 15%, the outlet coolant temperature rises sharply with strong temperature fluctuation. When the inlet water vapor content is in the range of 5% to 20%, the upper part of the fuel assembly will gradually accumulate to form large bubbles. Compared with the VOF method, Euler method has higher computational efficiency. However, Euler method may cause an underestimation of the void fraction, so it still needs to be calibrated with future experimental data of the two-phase flow in fuel assembly.
分类: 动力与电气工程 >> 工程热物理学 提交时间: 2017-03-31 合作期刊: 《热科学学报》
摘要: For centrifugal compressors used in automotive turbochargers, the extension of the surge margin is demanded because of lower engine speed. In order to estimate the surge line exactly, it is required to acquire the compressor characteristics at small or negative flow rate. In this paper, measurement and numerical simulation of the charac- teristics at small or negative flow rate are carried out. In the measurement, an experimental facility with a valve immediately downstream of the compressor is used to suppress the surge. In the numerical work, a new boundary condition that specifies mass flow rate at the outlet boundary is used to simulate the characteristics around the zero flow rate region. Furthermore, flow field analyses at small or negative flow rate are performed with the nu- merical results. The separated and re-circulated flow fields are investigated by visualization to identify the origin of losses.
分类: 农、林、牧、渔 >> 农、林、牧、渔业科学其他学科 提交时间: 2023-02-17 合作期刊: 《智慧农业(中英文)》
摘要: 塔式果园风送喷雾机是目前普遍使用的果园喷雾机,塔式结构易产生旋转和不规则的垂直气流, 导致喷雾机出风口两侧风场分布不对称,且分布规律不易预测。为探究适用塔式果园风送喷雾机出风口风 场建模方法,本研究基于喷雾机出风口风场计算流体动力学(Computational Fluid Dynamics,CFD) 建模方 法,提出了用户定义函数(User-Defined Function,UDF) 分段式三维风速入口边界条件设置方法,并研究 了湍流模型和计算域尺寸对喷雾机CFD风场模拟结果的影响特性。采用Fluent软件,建立了三种CFD模型: 模型一以11个区域的平均风速作为边界条件; 模型二采用UDF分段式三维风速入口作为边界条件; 为进一 步研究计算域尺寸对风场模拟的影响,建立了小计算域尺寸的模型三。三种模型均采用基于雷诺时均控制 (Reynolds-Averaged Navier-Stokes,RANS) 方程的k - 湍流模型和k - 湍流模型进行风场计算。为了验证模 型的可靠性,设计了空间风场立体测量系统,实现了精确快速空间风速测量。验证结果表明,Standard k - 、 Realizable k - 、BSL k - 和SST k - 湍流模型较适合风场CFD建模,其中Standard k - 湍流模型运算结果最 优,模型决定系数R2为0.81。基于UDF分段式三维风速入口边界条件设置方法不仅提高了仿真结果的准确 性(提高了5%),而且降低了计算的复杂性。在其他参数设置相同的情况下,大尺寸计算域模型的性能略优 于小尺寸计算域。实际建模过程中建议根据计算机计算能力、仿真的实际要求设置合适的计算域尺寸。本 研究结果可为喷雾机出风口风场CFD建模方法提供参考。
分类: 力学 >> 应用力学 提交时间: 2022-11-01 合作期刊: 《应用力学学报》
摘要: 深入开展鱼类自主游动机理研究,对鱼类运动行为以及仿生技术研究都具有重要的意义。以某型仿生鱼为研究对象建立了鱼体的简化模型和鱼体摆动的计算模型,采用动网格技术开发了控制鱼体摆动的UDF程序,利用Fluent软件对仿生鱼的自主游动行为进行了仿真模拟,研究了鱼类自主游动的机理以及在逆流情况下不同来流方向时的受力情况。通过计算发现,逆流时水流方向对仿生鱼的自主游动有很大的影响,当水流方向和鱼游动方向成180,鱼向前游动的阻力最小,侧向分量的存在会减小鱼向前运动的驱动力。
分类: 动力与电气工程 >> 工程热物理学 提交时间: 2017-06-22 合作期刊: 《热科学学报》
摘要: The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge (i.e., the leading-edge vortex (LEV)) in a centrifugal compressor were investigated by experiments and numerical analysis. The results of the experiments revealed that both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. For both, stall cells existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. According to the CFD results, the LEV is made up of multiple vortices. The LEV is a combination of a separated vortex near the leading-edge and a longitudinal vortex generated by the extended tip-leakage flow from the impeller. Therefore, the LEV is generated by the accumulation of vorticity caused by the velocity gradient of the impeller discharge flow. In partial-flow operation, the spanwise extent and the position of the LEV origin are temporarily transmuted. The LEV develops with a drop in the velocity in the diffuser passage and forms a significant blockage within the diffuser passage. Therefore, the LEV may be regarded as being one of the causes of a diffuser stall in a centrifugal compressor.
分类: 地球科学 >> 地理学 提交时间: 2023-02-02 合作期刊: 《干旱区地理》
摘要: 台特玛湖干涸湖盆区风蚀沙漠化快速发展,发育了以新月形沙丘和风蚀坑(主要为槽状坑和碟状坑)为主的风沙地貌。风蚀坑的发育不仅受来流风影响,还与坑内三维流场有关。基于风洞实验和计算机流体力学(Computational fluid dynamics, CFD)数值模拟,对风蚀坑三维流场进行了探究。结果表明:(1)从入风侧到出风侧,槽状风蚀坑和碟状风蚀坑底面的风速均呈减速加速减速加速的变化模式,上口所在水平面的风速变化呈加速减速加速变化模式,上口气流压强也相应地发生变化,槽状风蚀坑和碟状风蚀坑整体呈低压高压低压变化模式,其中槽状坑变化更为明显。(2)两种形状风蚀坑对气流均具有一定的吸附效应,使坑外一定范围的风沙流被吸入坑内,聚集能量和风沙流,加剧风蚀坑风蚀发育。(3)风蚀坑加剧了地表侵蚀,侵蚀程度与风蚀坑尺度有关,风蚀坑尺度越大,对地表侵蚀越强。本文直观展示了两种典型风蚀坑中的三维速度、压力、风沙流流向分布,揭示了风蚀坑的风沙流吸附机制,研究结果可加深对风蚀坑形态动力学的理解,也可为内陆干涸湖盆沙漠化防治提供理论指导。
分类: 动力与电气工程 >> 工程热物理学 提交时间: 2017-06-22 合作期刊: 《热科学学报》
摘要: Rotor blades in a radial turbine with nozzle guide vanes typically experience harmonic aerodynamic excitations due to the rotor stator interaction. Dynamic stresses induced by the harmonic excitations can result in high cycle fatigue (HCF) of the blades. A reliable prediction method for forced response issue is essential to avoid the HCF problem. In this work, the forced response mechanisms were investigated based on a fluid structure interaction (FSI) method. Aerodynamic excitations were obtained by three-dimensional unsteady computational fluid dynamics (CFD) simulation with phase shifted periodic boundary conditions. The first two harmonic pressures were determined as the primary components of the excitation and applied to finite element (FE) model to conduct the computational structural dynamics (CSD) simulation. The computed results from the harmonic forced response analysis show good agreement with the predictions of Singh's advanced frequency evaluation (SAFE) diagram. Moreover, the mode superposition method used in FE simulation offers an efficient way to provide quantitative assessments of mode response levels and resonant strength.
分类: 动力与电气工程 >> 工程热物理学 提交时间: 2017-06-26 合作期刊: 《热科学学报》
摘要: This paper presents a numerical analysis of the atmospheric air transonic flow through de Laval nozzles. By nature, atmospheric air always contains a certain amount of water vapor. The calculations were made using a Laval nozzle with a high expansion rate and a convergent-divergent (CD) "half-nozzle", referred to as a transonic diffuser, with a much slower expansion rate. The calculations were performed using an in-house CFD code. The computational model made it possible to simulate the formation of the liquid phase due to spontaneous condensation of water vapor contained in moist air. The transonic flow calculations also take account of the presence of a normal shock wave in the nozzle supersonic part to analyze the effect of the liquid phase evaporation.
分类: 动力与电气工程 >> 工程热物理学 提交时间: 2017-06-22 合作期刊: 《热科学学报》
摘要: The aerodynamic performance of a high-load low-pressure turbine blade cascade has been analyzed for three different distributed surface roughness levels (Ra) for steady and unsteady inflows. Results from CFD simulations and experiments are presented for two different Reynolds numbers (300000 and 70000 representative of take-off and cruise conditions, respectively) in order to evaluate the roughness effects for two typical operating conditions. Computational fluid dynamics has been used to support and interpret experimental results, analyzing in detail the flow field on the blade surface and evaluating the non-dimensional local roughness parameters, further contributing to understand how and where roughness have some influence on the aerodynamic performance of the blade. The total pressure distributions in the wake region have been measured by means of a five-hole miniaturized pressure probe for the different flow conditions, allowing the evaluation of profile losses and of their dependence on the surface finish, as well as a direct comparison with the simulations. Results reported in the paper clearly highlight that only at the highest Reynolds number tested (Re=300000) surface roughness have some influence on the blade performance, both for steady and unsteady incoming flows. In this flow condition profile losses grow as the surface roughness increases, while no appreciable variations have been found at the lowest Reynolds number. The boundary layer evolution and the wake structure have shown that this trend is due to a thickening of the suction side boundary layer associated to an anticipation of transition process. On the other side, no effects have been observed on the pressure side boundary layer.
分类: 地球科学 >> 地理学 提交时间: 2023-08-15 合作期刊: 《干旱区科学》
摘要: In grassland ecosystems, the aerodynamic roughness (Z0) and frictional wind speed (u*) contribute to the aerodynamic impedance of the grassland canopy. Thus, they are often used in the studies of wind erosion and evapotranspiration. However, the effect of wind speed and grazing measures on the aerodynamic impedance of the grassland canopy has received less analysis. In this study, we monitored wind speeds at multiple heights in grazed and grazing-prohibited grasslands for 1 month in 2021, determined the transit wind speed at 2.0 m height by comparing wind speed differences at the same height in both grasslands, and divided these transit wind speeds at intervals of 2.0 m/s to analyze the effect of the transit wind speed on the relationship among Z0, u*, and wind speed within the grassland canopy. The results showed that dividing the transit wind speeds into intervals has a positive effect on the logarithmic fit of the wind speed profile. After dividing the transit wind speeds into intervals, the wind speed at 0.1 m height (V0.1) gradually decreased with the increase of Z0, exhibiting three distinct stages: a sharp change zone, a steady change zone, and a flat zone; while the overall trend of u* increased first and then decreased with the increase of V0.1. Dividing the transit wind speeds into intervals improved the fitting relationship between Z0 and V0.1 and changed their fitting functions in grazed and grazing-prohibited grasslands. According to the computational fluid dynamic results, we found that the number of tall-stature plants has a more significant effect on windproof capacity than their height. The results of this study contribute to a better understanding of the relationship between wind speed and the aerodynamic impedance of vegetation in grassland environments.
分类: 核科学技术 >> 核科学与技术 提交时间: 2024-05-12
摘要: 为更好的理解和掌握熔盐换热器的运行特征,并给熔盐堆中换热器的设计和运行累积经验,本文以美国橡树岭国家实验室10MWt熔盐实验堆(MSRE)用的主换热器为研究对象,基于该换热器的设计参数,应用管壳式换热器的理论计算方法(包括Kern方法和Bell-Delaware方法)、换热器设计软件HTRI Xchanger Suite和计算流体力学方法(Computational Fluid Dynamics, CFD)对换热器的关键性能指标(如换热系数、压降和换热功率)分别进行了计算分析,并与MSRE主换热器的实验数据进行比较分析。结果表明:两种理论计算方法(Kern方法、Bell-Delaware方法)、HTRI软件及CFD仿真模拟的结果与实验结果的差异均在可接受范围内,其中Kern方法与MSRE实验所得的换热量相差最大、约为15%,HTRI软件模拟与MSRE实验所得的总换热系数相差最小、为0.16%;理论计算方法、换热器设计软件及CFD仿真均不同程度适用于熔盐-熔盐换热器设计,且CFD仿真还可对换热器内部传热和流动细节进行直观描述。
分类: 力学 >> 应用力学 提交时间: 2023-03-20 合作期刊: 《应用力学学报》
摘要: 采用计算流体力学(CFD)方法,研究了在不同开合情况下,受单体干扰建筑影响时大跨度开合屋盖结构的风压分布规律及风致干扰效应。首先采用TTU试验数据和风洞试验数据验证了CFD方法的准确性;然后研究了施扰建筑在不同条件下,目标大跨度开合屋盖表面的风压分布规律。研究结果表明:随着干扰建筑物与大跨度开合屋盖间距增大,结构表面的风压系数逐渐增大,遮挡效应减小;大跨度开合结构屋盖的开合情况对屋盖表面的风压系数的分布起着较为明显的影响作用;当周围存在干扰建筑时,大跨度开合屋盖的表面风压分布发生明显变化,风致干扰效应不容忽略。
分类: 天文学 >> 天文学 提交时间: 2017-09-26 合作期刊: 《天文研究与技术》
摘要: 遮光筒会影响主镜上方的空气流动,不利于主镜表面与周围空气的热交换。以兴隆基地50 cm望远镜为例,应用CFD软件分析了两种消杂散光装置(遮光筒和独立档光环结构)对主镜区域气流运动和温度的影响。同时根据温度数据计算主镜视宁度。分析结果表明,遮光筒会造成温度分布不均匀、湍流影响范围大、非对称的漩涡绕流等影响。独立档光环结构的情况下,主镜视宁度减小74 %。由此说明,在主镜散热和空气流通方面,主镜遮光筒有较大弊端。将该分析方法与杂散光分析结合,可合理选择杂散光抑制方案,对望远镜设计及改造具有一定参考和应用价值。
分类: 力学 >> 应用力学 提交时间: 2023-03-20 合作期刊: 《应用力学学报》
摘要: 为了验证某型大展弦比电动飞机气动设计的合理性以及为飞行性能及品质计算提供数据,采用有限体积法离散求解三维可压雷诺平均Navier-Stokes方程,并选用Spalart-Allmaras湍流模型对该电动飞机流场进行CFD数值模拟。结果表明,该型电动飞机气动设计合理,巡航速度升阻比最高可达23,具有较高气动效率;通过CFD数值模拟得到了全机升力系数,阻力系数和升阻比。为了验证CFD计算结果,对该型电动飞机进行了缩比模型风洞实验,结果显示,CFD数值模拟法计算结果与风洞实验结果高度吻合,说明CFD计算结果准确。该方法可为大展弦比电动飞机气动设计提供指导。
分类: 土木建筑工程 >> 土木建筑工程设计 提交时间: 2017-12-21 合作期刊: 《土木建筑工程信息技术》
摘要: 以厦门地区主导风向、风速为初始条件,结合CFD软件建立理想模型,模拟垃圾中转站恶臭污染物扩散范围。结果表明在以垃圾中转站为起点,沿主导风向60m的区域范围内,恶臭污染物浓度大于允许值,并以此为原则进行总图设计。纳入垃圾中转站周边敏感建筑建立实际模型进行模拟计算验证,模拟结果表明:本项目在夏季、冬季主导风向下垃圾中转站周围邵分敏感建筑受到恶臭污染物影响,但污染物浓度很小,符合要求;在对夏季静风模拟中西北、西南方向住宅室外环境恶臭污染物浓度超过规范标准,应采取技术措施降低其恶臭污染物的生成量;采取除臭措施后,西北、西南方向住宅室外环境恶臭污染物显著降低,符合要求。
分类: 核科学技术 >> 核科学与技术 提交时间: 2025-05-04
摘要: 当前反应堆热工水力多尺度耦合研究主要聚焦于多尺度耦合程序开发与验证,针对耦合程序不确定性的系统性研究仍较为匮乏。本研究基于preCICE开源框架,集成CFD程序FLUENT、子通道程序SUBCHANFLOW以及DAKOTA不确定性量化模块,构建多尺度耦合不确定性分析程序。通过建立3×3棒束模型,开展稳态与瞬态条件下的数值验证,并实施不确定性量化与灵敏度分析。实验数据显示:(1)稳态工况下耦合系统轴向温度分布与单体程序计算结果高度吻合;(2)瞬态验证中,入口流量正弦扰动工况下,出口流量波动在周期和相位上完全同步;(3)不确定性量化表明冷却剂温度、包壳峰值温度等参数均呈现正态分布特征;(4)灵敏度分析揭示入口质量流量、出口压力、入口温度和燃料棒热流密度为系统响应的主导因素,研究结果验证了多尺度耦合系统在动态工况下的响应可靠性。