方型散流器空调室内空气流动的数值模拟

 用N点风口动量模型和一个新零方程湍流模型对某办公室方型散 流器空调的室内温度场和速度场进行了模拟，并和实验数据进行对比. 结果表明，计算所得速度和温度分布与实测值吻合得很好，所用的风 口模型和湍流模型能快速地将方型散流器空调通风的温度和速度场合 理地模拟出来，可用于指导和优化同类空调通风气流组织设计.     

孔板空调风口送风射流的数值模拟

介绍Ｎ点风口模型用于数值模拟室内空气流动时描述孔板类送风口的入流边界条件．然后采用该风口模型对不同的孔板风口出流条件算例进行数值计算，并就轴心速度衰减、射流扩展角以及断面流速分布等射流特性与实验数据进行了对比．比较结果表明，Ｎ点风口模型用于描述数值模拟室内空气流动的孔板类风口入流边界条件，可以获得工程上足够满意的结果．     

大速差射流预燃室内三维回流两相湍流的数值模拟

本文由多流体两相流模型、气相湍流κ-ε模型和颗粒湍流代数模型出发,成功地模拟了真实形状大速差射流预燃室中三维湍流回流两相流动,得到了这类复杂的气固两相流中不同纵横截面上气相速度场、颗粒速度场及浓度场和两相湍流度场的分布,并且获得了与实验定性一致的合理结果,揭示了预燃室中气固两相流动与混合的主要物理特征,探讨了大速差射流技术稳焰和强化燃烧的两相流动机理。     

半封闭狭缝湍流冲击射流的数值模拟

将Yakhot和Orszag提出的RNGk-ε模型推广应用于半封闭狭缝冲击射流场的数值模拟，以评价该模型对这种复杂湍流的预测能力。将计算得到的流场平均速度分布、湍流强度分布和流函数分布与标准k—ε模型的预测结果以及相应的实验数据进行了比较，结果表明：RNGk—ε模型的预测结果总体上要好于标准k—ε模型，但与实验值相比，所有预测结果都还存在不同程度的误差，尤其是近壁区和滞止点较远下游处的湍流强度分布。说明RNG模型虽然已在某些湍流的预测中取得了一定的成功，但要定量准确地预测冲击射流场，还必须针对其流动特征对模型加以改进。     

风口区空气流动的有限元模拟与实验研究

通风和空调出风口的射流特性主要取决于出风口截面之前的一段管道内的流动状况,研究送风口的射流偏转特性有重要实用价值.应用湍流大涡模拟技术结合Taylor-Galerkin有限单元法对工程中常见工况下的风口区管道内的三维流场进行了数值模拟和实验研究,数值计算结果与实验结果符合较好.表明湍流大涡模拟方法适合于边界形状复杂,存在各向异性的大尺度涡的内流情况,能可靠地预报风口区空气流动的射流偏转特性.     

交通工具上的小空间睡眠区不同气流组织的数值分析

长途旅行中的睡眠区气流组织设计对于人体热舒适和空气质量控制是极其重要的。为了给小空间睡眠区提供更加舒适和空气质量更佳的气流组织,本文首次针对置换通风、个性通风、混合通风三种通风方式,利用CFD(计算流体力学)对睡眠区速度场、温度场、污染物CO2的浓度分布进行了数值模拟分析。对利用CFD计算出的面部舒适速度比例(FSR)、吹风感(DR)、空气龄(MA)进行比较,得出:在睡眠区采用个性送风可以在最节能的情况下得到更好的面部舒适速度比例和空气质量,优于置换通风和混合通风;1.5m3/min为个性通风的最佳通风量;为了避免在睡眠区使用个性通风时产生吹风感,应该保证送风温度不能过低;增大个性送风口送风面积可以有效降低吹风感。     

利用格子Boltzmann方法数值模拟Rayleigh-Benard对流

采用格子Boltzmann方法对较大Rayleigh数范围下的二维Rayleigh-Benard对流进行了模拟研究.引入能量分布函数,利用该能量分布函数与粒子速度分布函数耦合来求解一个热流场,能量分布函数与粒子速度分布函数和Boltzmann方程构成了一个新的双分布格子Boltzmann模型.在考虑密度随温度变化的情况下,进行数值模拟,得到了Rayleigh-Benard对流速度、温度随时间的变化规律、系统的流线和等温线分布及平均Nusselt数与Rayleigh数的之间的关系,与相关文献数据进行了对比,模拟结果非常吻合,证明了改进的双分布格子Boltzmann模型的有效性.     

基于Fluent平衡大气边界层流场模拟及应用

采用Fluent进行平衡大气边界层流场模拟,在地面边界引入气动粗糙壁面函数,上边界分别采用剪力驱动和速度驱动。首先对平坦区域进行流场模拟,然后基于模拟的流场对立方体建筑物表面风压分布进行了计算。结果表明:基于本文的边界条件设置方法,三种k-ε湍流模型均能获得良好的自保持性平衡大气边界层流场;在地面边界引入气动粗糙壁面函数,可实现任意类型的平衡大气边界层流场模拟,且对近地单元的高度无限制,有利于精细化网格计算;在上边界采用剪力驱动和速度驱动是等效的,采用速度驱动边界条件有利于提高计算效率;三种k-ε湍流模型计算的立方体中心面表面压力分布基本在测量值变化范围内,说明基于本文的平衡大气边界层流场可应用于结构风荷载数值模拟研究中。     

气固两相流场的湍流颗粒浓度理论模型

本文进行了气固两相流动颗粒湍流扩散现象的理论分析，提出了颗粒湍流扩散系数和气流弥散效应二个颗粒湍流模化新概念，在此基础上建立了气固两相流场湍流颗粒浓度模型。理论模型包括离心力和其它外加力场作用下颗粒运动和浓度分布的计算方法。运用湍流颗粒浓度模型，对直管气固两相流动、受限射流气固两相流动和９０°弯管气固两相流动等三种流动做了数值模拟，计算获得颗粒速度、颗粒浓度等主要流动参数。讨论了湍流颗粒浓度模型的适用性。     

统一二阶矩模型用于模拟旋流湍流两相流动

用统一二阶矩模型（ＵＳＭ）模拟了旋流数为０４７和１５的气粒两相流动，并和实验结果以及ｋ ε ｋｐ模型的模拟结果进行了对比．研究结果表明，提高旋流数减小了轴向速度反流区，增大了切向速度似固核区．ＵＳＭ和ｋ ε ｋｐ模型预报旋流数为０４７时的两相速度场差别不大，并都和实验结果接近，但前者预报的旋流数为１５的两相速度场比后者有改进，在两种情况下，前者都能揭示出后者无法预报的两相湍流各向异性规律．     

Effects of supply air temperature and inlet location on particle dispersion in displacement ventilation rooms

The effects of supply temperature and vertical location of inlet air on particle dispersion in a displacement ventilated (DV) room were numerically modeled with validation by experimental data from the literature. The results indicate that the temperature and vertical location of inlet supply air did not greatly affect the air distribution in the upper parts of a DV room, but could significantly influence the airflow pattern in the lower parts of the room, thus affecting the indoor air quality with contaminant sources located at the lower level, such as particles from working activities in an office. The numerical results also show that the inlet location would slightly influence the relative ventilation efficiency for the same air supply volume, but particle concentration in the breathing zone would be slightly lower with a low horizontal wall slot than a rectangular diffuser. Comparison of the results for two different supply temperatures in a DV room shows that, although lower supply temperature means less incoming air volume, since the indoor flow is mainly driven by buoyancy, lower supply temperature air could more efficiently remove passive sources (such as particles released from work activities in an office). However, in the breathing zone it gives higher concentration as compared to higher supply air temperature. To obtain good indoor air quality, low supply air temperature should be avoided because concentration in the breathing zone has a stronger and more direct impact on human health.     

Investigation of three dimensional air flow characteristic and effect of heated obstruction within room

This study reports the results of a numerical investigation of three-dimensional turbulent buoyant recirculating flow within rooms with heated obstruction. The study involves the solution of partial differential equations for the conservation of mass, momentum, energy, concentration, turbulent energy and its dissipation rate. These equations were solved together with algebraic expressions for the turbulent viscosity and heat diffusivity using k-ε turbulence model by performing simulations on FLUENT 6.3. The CFD method was validated via comparing with the available experimental data. A comparison with experimental results shows good agreement. This means that the present computer code has a good capability to simulate 3D airflow and effect of obstruction within room. The present study demonstrates the flow behavior, thermal distribution and CO₂ concentration inside the room in the presence of heat flux obstruction. Two different configurations of ventilation system have been studied. Mixing and Displacement ventilation system have been used in two geometries depending on location of opening inlet. The ventilation effectiveness for heat removal (E_T) is used to evaluate the indoor climate and average temperature is an important parameter in designs the ventilation systems. Two notable points are presented; first, mixing ventilation is depending on throw of jet. CO₂ concentration and temperature distribution have been effected in upper zone more than occupied zone with presence the obstruction. Second notable points are presented; in displacement ventilation buoyancy effect is considerable. Vertical temperature gradient above the obstruction implies that both fresh air and CO₂ concentration.     

Comparison between grooved and plane aerostatic thrust bearings: static performance

The demand of air bearings is increasing for those applications that require precision linear movements or high-speed rotations. In particular in this paper air pads for air motion technology are studied. The paper analyses the effect of a circumferential groove machined on the pad surface on pressure distribution, air flow consumption and stiffness. Two geometries are investigated and compared: one with three supply orifices and the other with a circumferential groove as well. The static characteristics of the pads are experimentally determined with also the pressure distributions under the pads along the radial and circumferential directions. The experimental pressure distributions are compared with the simulated ones, obtained with a numerical program at the purpose developed. The numerical model considers a general formulation of the supply holes discharge coefficient that can be used also in presence of a circumferential groove.     

封闭和半封闭通风空间的环境流体问题

半封闭与全封闭空间的环境流体力学包括系统内的空气流动、 温度和湿度分布以及污染物的凝积等问题, 其中涉及控制空间的空气质量、 通风设计以及预防水汽凝结等多个方面的研究. 本文着重介绍国内外近年来相关的工作, 研究如何从理论分析、实验研究以及数值模拟等方面入手, 解决通风问题, 以达到获得高通风效率、低能耗和提高空气舒适度的目的. 研究的对象包括房间, 建筑物, 城市等半封闭空间, 以及汽车、 地铁、 飞机、潜艇、载人航天飞行器等不同程度的全封闭空间. 现有的理论研究已经从解释单点源纯浮力对流的基础模型发展到能够描述具有体积流量和动量流量的扩散流的湍流喷泉模型. 然而, 理论研究上的进步还不足以使它能够处理实际问题中多样的通风情况和复杂的空间结构, 工程应用中还需更多依靠实验研究和数值模拟的结论. 对载人航天飞行器中的环境流体问题的研究虽然刚刚起步, 但其研究手段和经验可以从相对成熟的半封闭与全封闭空间的相关研究中获得借 鉴.     

Effect of source location on particle dispersion in displacement ventilation rooms

A proposed computer model for predicting aerosol particle dispersion in indoor spaces was validated with experimental data found in the literature,and is then used to study the effect of the area and point source locations on particle dispersion in displacement ventilation (DV) rooms.The results show that aerosol source location has a strong impact on the spatial distribution and removal rate of indoor particles.Particle removal performance depends strongly on ventilation efficiency and particle deposition rate on indoor surfaces.Important consideration for both relative ventilation efficiency and deposition rate consists of the position of the aerosol source relative to the main airflow pattern and the occupied zone.     

Effect of source location on particle dispersion in displacement ventilation rooms

A proposed computer model for predicting aerosol particle dispersion in indoor spaces was validated with experimental data found in the literature, and is then used to study the effect of the area and point source locations on particle dispersion in displacement ventilation （DV） rooms. The results show that aerosol source location has a strong impact on the spatial distribution and removal rate of indoor particles. Particle removal performance depends strongly on ventilation efficiency and particle deposition rate on indoor surfaces. Important consideration for both relative ventilation efficiency and deposition rate consists of the position of the aerosol source relative to the main airflow pattern and the occupied zone.     

Stress Analysis And Geometrical Configuration Selection for Multilayer Piezoelectric Displacement Actuator

Multilayer piezoelectric ceramic displacement actuators are susceptible to cracking in the region near the edge of the internal electrode, which may cause system damage or failure. In this paper, the stress distribution of a multilayer piezoelectric composite is investigated in a working environment and the optimized geometrical con?guration of the piezoelectric layer is obtained. The stress distribution in the structure and the stress concentration near the edge of th…     

A cohesive model based fragmentation analysis: effects of strain rate and initial defects distribution

A one-dimensional fragmentation analysis that incorporates elastic wave propagation and a cohesive failure process is presented. An irreversible cohesive law models the internal crack nucleation and opening process, and the elastodynamic states of the intact material are calculated using the method of characteristics. Both the average fragment size and the fragment size distribution are obtained. The fragmentation of a model ceramic system is simulated over a wide range of strain rates, and the calculated results are compared to existing theoretical, numerical and experimental results. In the high strain-rate regime, the calculated average fragment size is smaller than that predicted by energy models, but at quasistatic rates the calculated average size is larger than that estimated by such models. The intrinsic mechanisms leading to these deviations are discussed. The fragment size distributions exhibit similarity under all strain-rate range. The effect of the distribution of internal defects on the fragmentation and fragment size distribution is also investigated using this methodology.