海水淡化双级真空引射器的射流和混合特性研究

引射器是实现热法海水淡化系统高效节能的重要装置,该文通过三维数值模拟方法研究了双级引射器内部流动和传输特性,分析了引射和工作流体的混合与扩散过程,探讨了降低能耗的方法.研究结果表明,喷射器内速度最大值均在轴线处,流体在喷嘴与混合室内流线均匀,而在吸入室内产生一个或多个涡流.不同引射流体速度下,其混动迹线为不对称分布,随...     

超临界状态航空煤油裂解的传热特性仿真

为研究超临界压力下航空煤油裂解时传热特性,构建了一步裂解总体反应模型,并对5 MPa压力下RP-3航空煤油在水平圆管内存在裂解时的传热特性进行数值模拟,研究了裂解反应和质量流量对航空煤油流动传热的影响.结果 表明,裂解反应的发生很大程度上提升了煤油的换热能力,出口处煤油的平均油温和壁面温度分别降低了8.33％和7.92％;RP-3航空煤油发生裂解反应后流体热物性变化明显,导致流速显著增大,流动压力损失增加;人口质量流量降低使煤油发生裂解位置提前且裂解率升高,裂解反应吸收的热量更多,但同时也显著增加了流动压力损失.     

电子调速器性能测试模拟试验方法的研究

用系统仿真法(即采用计算机仿真柴油机,构成一模拟试验装置)考核、测试和分析电子调速器性能,经济、方便且安全.对电子调速器的研制开发、使用维护都有很大的促进作用.国外已有使用的报道,而国内在这一方面的研究却刚起步.本文对如何利用系统仿真法考核与测试船用柴油机电子调速器配机性能进行了有益的探索与研究,并采用数字计算机仿真技术,试制了一柴油机电子调速器配机模拟试验装置,初步实验验证结果比较理想.     

船用螺旋桨敞水性能数值分析

为预测某船用螺旋桨在不同螺距下的敞水性能,对标准螺旋桨DTMB 4119的敞水性能进行数值模拟,得到的推力因数和扭矩因数计算值与试验值的对比表明通过求解RANS方程模拟螺旋桨黏性流场是可行的.用该方法预测某船用螺旋桨的敞水性能:模拟得到不同螺距下螺旋桨推力因数、扭矩因数和表面压力因数的变化以及尾流情况.通过RANS方法...     

EAST真空实时监测系统的设计与实现

在EAST核聚变实验中,装置真空室内的真空度是一个非常重要的参数.建立真空实时监测系统,旨在为真空分控和总控系统提供真实、可靠的真空度信息,实现对真空度的实时显示、故障报警、数据管理和数据通讯等功能.本文将就该系统的各项功能做全面介绍,并重点提出一种基于OPC技术和Winsock网络编程技术的数据通讯新方案.本文涉及了Microsofi Access数据库、ODBC、OPC和Winsock网络编程等多种技术.     

CZ60/30型船用空压机缸内压差数值模拟

为了解压差式空压机二级缸内压力相互作用情况,提高工作效率,基于CZ60/30船用空压机气缸和活塞的结构以及该型空压机工作特点,建立高、低压级气缸内压力和压差关系的数学模型,通过MATLAB进行模拟.通过模拟结果分析气缸余隙高度对缸内压力和压差的影响情况,并得到高、低压级气缸压力随时间的变化曲线,为高效的空压机设计和故障分析提供参考.     

基于文丘里流量传感器的湿气两相流量模型研究

研究旨在通过计算流体动力学(CFD)仿真技术预测的湿气气、液两相流量.以双差压长喉颈文丘里流量传感器为测量手段.模拟压力范围0.4,0.6,0.8,1.0,1.2 MPa,气相体积流量范围为140～283 m3/h,温度范围23 ～30℃,含液率范围0.5％～1.5％.文丘里流量传感器口径为DN100,节流比为0.55.多相流模型采用离散相模型(DPM),利用欧拉壁面(EWF)模型以模拟管壁上的薄液膜.分析得出压力、气相流速和液相体积含率(LVF)对液膜厚度的影响规律.根据仿真结果建立基于双差压比值法的气、液两相流量预测模型.将仿真值与实验值进行比较,气相流量模型预测的均方根误差为1.8％,且液相流量模型预测的均方根误差为6.1％.     

溢流管结构对α型旋流器分离性能的影响

以α型旋流器的溢流管为研究对象,采用CFD软件Fluent6.2提供的雷诺应力模型(RSM)对溢流管结构进行数值模拟.研究圆柱型和渐扩型溢流管结构对旋流器分离效果的影响、分析不同截面切向速度、轴向速度、压力等参数分布规律、并以水-细砂为实验物系进行了对比实验.模拟和实验结果表明:渐扩型溢流管结构使溢流口处流场更加稳定,部分动能转化为静压能,降低了设备的能耗,提高了设备的分离效率,确定设备的最佳流速为4.5m/s左右.     

双向流水槽模拟潮汐的控制软件设计与实现

在双向流水槽中模拟潮汐是研究海岸灾害防护的重要手段之一,而潮汐模拟过程中,系统控制软件的性能决定仿真精度.利用双向流水槽结合尾门和双向水泵控制的模拟潮汐控制软件可实现对水位和流速精确控制.首先由下位机获取检测仪器采集的水位和流速数据,并进行非线性校正处理;然后上位机通过自适应水位水流控制算法求得控制量、发出控制指令调节现场尾门和双向水泵状态,从而生成模拟潮汐.实验通过对周期为48小时的不规则潮汐进行模拟,得到水位和流速的误差均小于5%.结果表明该控制软件具有高精度和稳定性,可满足科研需求.     

基于比例阀门的精密气压控制方法研究

对精密气压控制方法进行了研究,应用气动比例阀门作为压力产生的执行机构,采用模拟和数字PID双闭环反馈控制,采用硅压阻模拟传感器和数字石英谐振传感器的双传感器结构,对系统控制结构进行设计,实现了气体压力的精密控制,压力输出准确度为0.02％,控制稳定性达0．003％。系统压力产生速度快、没有压力过冲,控制精度高,稳定性好。该系统为压力参数的自动检定提供了精密压力基准源,可以实现压力表、压力变送器和压力传感器的自动检定校准。     

双螺杆挤出机流场数值模拟中流道进出口边界条件的探讨

在对双螺杆挤出机流场的数值模拟中,流道进出口边界条件的设置一直是一个颇具争议的问题。由于事先无法获得计算域进出口平面上的真实边界条件,研究人员在进行双螺杆挤出机的流场分析时,大都采用放松边界条件。为了考察放松边界条件对双螺杆挤出机流场数值模拟结果的影响,本文采用聚合物流动分析软件POLYFLOW,在流量恒定的前提下对双螺杆挤出机流道进出口给定三种不同分布形式的速度边界条件,对其流场进行了数值模拟。数值计算结果表明,在体积流量恒定的条件下,流道进出口不同分布形式的速度边界条件对流场的影响主要集中在进出口附近区域,但对离进出口边界较远的流场影响很小。一般而言,当计算域所对应的螺杆较长时,可以忽略流道进出口的放松边界条件所引起的误差;当计算域较短时,不宜直接采用放松边界条件,而应根据螺杆的实际构型．在计算域的进出口增加适当长度的发展段。     

反应堆流场分析的数值模拟

运用CFD分析工具对反应堆内的流场分布进行数值模拟,给出反应堆燃料组件入口处流场的速度和流量分配情况.通过对计算结果的比较分析,对核电厂反应堆内的流动特性有比较全面的了解,从而为反应堆堆内构件的设计和优化提供分析依据.结果表明反应堆内流场采用CFD技术进行模拟计算是可行的.     

基于Fluent的动态旋流器流场计算机模拟仿真

Fluent软件是一款集流场、热传质、燃烧以及化学反应于一体的商业CFD 软件. 针对动态旋流器流场的复杂多变性, 以Total型动态旋流分离器为例, 在Gambit软件中简化并建立了物理模型, 通过fluent软件对其速度场进行计算机模拟仿真, 得出了柱坐标系统下, 切向速度、轴向速度和径向速度三个速度分量云图, 通过研究发现, 基于Fluent的动态旋流器流场计算机模拟仿真可以有效地解决复杂流动问题, 为动态旋流器工艺设计和性能优化提供可靠的依据, 且节省开发费用, 缩短设计周期.     

扩散式旋风除尘器三维气相场的数值模拟

采用计算流体动力学(CFD)的数值方法,用RSM模型模拟计算扩散式旋风除尘器内气相流场的三维速度分布和压力分布。模拟结果显示:在反射屏以下部分,其速度和压力变化不明显;反射屏顶部以上速度呈"三峰"对称分布;压力损失最大的位置在排气管下端与进气口下端相平齐的位置。     

Design of a flow-controlled asymmetric droplet splitter using computational fluid dynamics

In this work the design of a segmented flow microfluidic device is presented that allows droplet splitting ratios from 1:1 up to 20:1. This ratio can be dynamically changed on chip by altering an additional oil flow. The design was fabricated in PDMS chips using the standard SU-8 mold technique and does not require any valves, membranes, optics or electronics. To avoid a trial and error approach, fabricating and testing several designs, a computational fluid dynamics model was developed and validated for droplet formation and splitting. The model was used to choose between several variations of the splitting T-junction with the extra oil inlet, as well to predict the additional flow rate needed to split the droplets in various ratios. Experimental and simulated results were in line, suggesting the model’s suitability to optimize future designs and concepts. The resulting asymmetric droplet splitter design opens possibilities for controlled sampling and improved magnetic separation in bio-assay applications.     

Effect of inlet and outlet boundary conditions on swirling flows

Numerical simulations are conducted for both three-dimensional, turbulent flow in a multi-channel swirler and axisymmetric, isothermal, turbulent flow in combustion chambers using the standard κ−ε turbulence model. Calculations are first carried out for three-dimensional, isothermal and turbulent flow inside the swirler channels in order to derive the velocity profiles of both air and gas at the swirler outlets, which are used as inlet boundary conditions of the model combustor and can also be used in future studies for different combustors with the same type of swirler. In order to study the sensitivity of swirling flow inside the chamber to the inlet and outlet boundary conditions, different inlet velocity profiles and outlet boundary conditions are also employed. The results show that in the cases considered, the flow behaviour in the chamber is not very sensitive to the actual shape of the inlet velocity profiles provided the averages of the inlet axial, radial and azimuthal velocity components are separately preserved. Other conditions being equal, we find that the swirling flow performance in the combustor depends not only on the inlet swirl number, but also strongly on the relative magnitude of the radial velocity component at inlet and introduce a new dimensionless number N_r, analogous to the swirl number, to measure the relative importance of this quantity. Outlet boundary conditions have some influence near the outlet, but nearly no effect further upstream for the cases investigated.     

前输出轴涡轴发动机高空台进气装置设计及验证

对某前输出轴涡轴发动机高空模拟试验进气装置进行了设计,通过三维数值仿真的方法对比分析了典型工况进气涡壳内有无整流装置情况下发动机进口的流场品质,确定在增加整流装置的情况下,发动机进口压力不均匀度小于1%,温度不均匀度小于1%。为降低进气装置压力损失,对进气装置进行了优化设计,仿真结果表明,在最大流量下,压损降低了30%。最后通过吹风试验验证了流场品质满足设计要求,解决了涡壳进气方式产生的流场畸变问题。同时将导管流量数据与导流盆流量数据进行对比,证明了导流盆测流量方案的合理性。该设计可在此类涡轴发动机高空模拟试验中推广运用。     

On the application of boundary conditions to time dependent computations for quasi one-dimensional fluid flows

A study is made of the influence of boundary and initial conditions on time-dependent finite-difference solutions of quasi-one-dimensional duct flows. Several questions are addressed: (1) Under what conditions will a time-dependent solution converge to a steady-state supersonic flow, (2) Under what conditions will it converge to subsonic flow and (3) What conditions are necessary to insure a particular unique solution for subsonic flows. The results provide an orientation, or way of thinking, about the role of such conditions in time-dependent solutions of steady-state flows. The results also show that supersonic solutions are readily obtained by holding only pressure and temperature fixed at the duct inlet, and allowing velocity to float. However, subsonic solutions require pressure, temperature and velocity to be fixed at both the duct inlet and exit. If no conditions are held fixed at the exit, the results always converge to the supersonic solution, even if the fixed inlet mass flow is less than critical. In such a case, the program appears to generate additional mass flow between the inlet and throat, sufficient to choke the flow. These results also have some impact on two- and three-dimensional time-dependent solutions where subsonic flow is present on some or all portions of the flow boundaries.     

Evaluation of flow maldistribution in air-cooled heat exchangers

Investigation of the evaluation of flow maldistribution in air-cooled heat exchangers is presented. The flow field in the inlet and return headers was obtained through the numerical solution of the governing partial differential equations including the conservation equations of mass and momentum in addition to the equations of the turbulence model. The effects of the number of nozzles, nozzle location, nozzle geometry, nozzle diameter, inlet flow velocity and the incorporation of a second header on the flow maldistribution inside the tubes of an air-cooled heat exchanger were investigated using a 3-D computational method. The results are presented in terms of the standard deviations of the mass flow rate and static pressure in addition to the distributions in the static pressure inside the inlet header of the air-cooled heat exchanger. The results indicate that reducing the nozzle diameter results in an increase in the flow maldistribution. 25% increase is obtained in the standard deviation as a result of decreasing the diameter by 25%. Increasing the number of nozzles has a significant influence on the flow maldistribution. A reduction of 62.5% in the standard deviation of the mass flow rate inside the tubes is achieved by increasing the number of nozzles from 2 to 4. The results indicate that incorporating a second header results in a significant reduction in the flow maldistribution. Fifty percent decrease in the standard deviation is achieved as a result of incorporation of a second header of 7 holes. The results indicate that the mass flow rate and the static pressure distributions become uniform at the inlet of the second pass.