绝热毛细管长度数值计算

根据均相流假设,运用两相流动基本方程建立了绝热毛细管分布参数的稳态数学模型,结合制冷工质HFC-134a基于MH状态方程的热力学性质计算模型,采用新的基团贡献法计算粘度,用熵增判据考虑壅塞流动的影响,进行数值模拟计算确定毛细管长度。对理论计算结果与相关文献的实验数据进行比较,结果吻合得很好,计算精度有所提高。     

Experimental investigation of the reverse heat transfer of R134a flow through non-adiabatic coiled capillary tubes

This research represents an experimental investigation of the metastable flow and re-condensation phenomenon through non-adiabatic lateral helical capillary tubes and suction tube heat exchanger. The results show that mass flux ratio has a vital role: It affects metastable flow and also reverse heat transfer phenomenon through non-adiabatic helical capillary tube. Therefore, by increasing of the mass flux ratio, the rate of heat transfer between them decreases. In contrast to the strong rate condition of heat transfer between them, reverse heat transfer or re-condensation maybe happen. Moreover, experimental results show that for R134 flow with mass flux ratio more than 57.84, metastable flow exists in non-adiabatic capillary tube with 0.9144 mm inner diameter, 30 mm coil diameter, 6.18 m length, 4 mm inner diameter of compressor suction tube.

     

基于双流体模型的简易化两相揣拌流场数值模拟

基于双流体模型对混凝土搅拌运输车搅拌筒内搅拌介质进行了简易化的数值模拟,为搅拌筒参数优劣评定提供了有效的参照模型.即将混凝土搅拌运输车搅拌筒中搅拌介质(石子与泥浆)的流固多相处理成密度不同且互相贯穿的介质,以搅拌筒和搅拌叶片为动态边界条件,在流体有限元理论下,实现了基于搅拌筒设计参数变化的简易化多相流场数值模拟.从而在混凝土搅拌运输车搅拌筒数字化设计过程中,在对参数的优劣(减小搅拌介质的离析度和提高搅拌筒的出料速度等)评定时,提供了定量化、可视化的参照模型.     

基于双流体模型的简易化两相搅拌流场数值模拟

基于双流体模型对混凝土搅拌运输车搅拌筒内搅拌介质进行了简易化的数值模拟,为搅拌筒参数优劣评定提供了有效的参照模型。即将混凝土搅拌运输车搅拌筒中搅拌介质(石子与泥浆)的流固多相处理成密度不同且互相贯穿的介质,以搅拌筒和搅拌叶片为动态边界条件,在流体有限元理论下,实现了基于搅拌筒设计参数变化的简易化多相流场数值模拟。从而在混凝土搅拌运输车搅拌筒数字化设计过程中,在对参数的优劣(减小搅拌介质的离析度和提高搅拌筒的出料速度等)评定时,提供了定量化、可视化的参照模型。     

波纹管内流动与换热的数值模拟研究

利用计算流体力学软件Fluent,采用数值模拟方法究了幅值不同的两种波纹管传热状况,发现幅值为4mm的波纹管的传热状况优于幅值3mm波纹管的传热状况,这是由前者管内湍流强度高于后者所致.同时,回归了两波纹管的换热准则方程,为波纹管的校核计算及工程应用提供依据.     

火星熄灭器两相流数值模拟

针对某型号火星熄灭器,采用非定常雷诺时均（RANS）和离散型模型（DPM）对其内部流场和颗粒分离行为进行了数值模拟.计算了初始模型设计流速下的捕集效率和阻力损失;分析了内部速度场、压力场和颗粒运动轨迹特性.针对计算结果,对原火星熄灭器的结构进行了改进.采用相同的计算方法,对改进后的设计方案进行了仿真计算,结果表明提高了火星熄灭器的综合性能.该仿真计算方法能较好地预测火星熄灭器内部两相流的流动特性,对火星熄灭器性能预测和结构改进提供可靠依据.     

Performance investigation of capillary tubes for machine tool coolers retrofitted with HFC-407C refrigerant

The machine tool coolers are the best managers of coolant temperature in avoiding the deviation of spindle centerline for machine tools. However, the machine coolers are facing the compressed schedule to phase out the HCFC (hydro-chloro-floro-carbon) refrigerant and little attention has been paid to comparative study on sizing capillary tube for retrofitted HFC (hydro-floro-carbon) refrigerant. In this paper, the adiabatic flow in capillary tube is analyzed and modeled for retrofitting of HFC-407C refrigerant in a machine tool cooler system. A computer code including determining the length of sub-cooled flow region and the two phase region of capillary tube is developed. Comparative study of HCFC-22 and HFC-407C in a capillary tube is derived and conducted to simplify the traditional trial-and-error method of predicting the length of capillary tubes. Besides, experimental investigation is carried out by field tests to verify the simulation model and cooling performance of the machine tool cooler system. The results from the experiments reveal that the numerical model provides an effective approach to determine the performance data of capillary tube specific for retrofitting a HFC-407C machine tool cooler. The developed machine tool cooler system is not only directly compatible with new HFC-407C refrigerant, but can also perform a cost-effective temperature control specific for industrial machines.     

Numerical simulation of free flow through side orifice in a circular open-channel using response surface method

A side orifice is an important type of hydraulic structure which is used widely in irrigation and waste management systems to divert desired discharges from a main channel or to distribute the flow within the basins. Circular pipes flowing partially full are often used in these systems, but existing predictive relations developed for rectangular channels result in significant error. In the present study, the flow through a side orifice in a circular open-channel is numerically simulated and validated to test the effect of different parameters on the discharge coefficient and propose an appropriate predictive equation. To minimize the number of required simulations and validations, a Response Surface Method-Central Composite Design (RSM-CCD) is employed. Results showed that the discharge coefficient is inversely related to the Froude number (Fr) and the ratio of the side orifice length to the approaching flow water depth. However, any increase in either the ratio of the orifice length to the main channel diameter or the ratio of the lower crest level to the orifice length will increase the discharge coefficient. A new equation is presented to determine the discharge coefficient of side orifice in a circular open-channel using RSM-CCD. The sensitivity analysis showed that all linear terms must considered in the equation but that the interaction terms can be dropped. The maximum error of the equation to predict the training and validation data are 1% and 2% respectively.     

Numerical simulation of the flow around two fixed circular airfoils positioned in tandem using the LS-STAG method

In recent years the popularity of immersed boundary methods has been increasing in computational hydrodynamics. One of the most effective methods of this class is the LS-STAG method developed in 2010, which allows computations on sufficiently coarse grids. A software package was developed to solve a number of hydrodynamics and hydroelasticity problems by the LS-STAG method. We present the results of the testing the developed software package by simulating a flow around two fixed circular airfoils positioned in tandem at different distances between the airfoils. We simulate the flow modes for which two symmetric vortices, two asymmetrical vortices, and a vortex wake form behind the front airfoil. For each mode, the typical time dependences of the drag force and lift coefficients are presented. The results agree well with the experimental data in the literature and numerical results of other authors.     

Numerical simulation of the flow around two circular airfoils positioned across the stream using the LS-STAG method

The flow around two circular airfoils positioned side by side (across the stream) at different distances between the airfoils is considered. The LS-STAG method, which belongs to the class of immersed boundary method is used for numerical simulation that makes it possible to calculate using rather coarse meshes. Stationary and trigger flow regimes have been simulated, as well as the patterns of flow with synchronization of two vortex trails in-phase and in anti-phase. For each regime, the typical dependences of coefficients of drag force and lift force on the time are presented. The obtained results are in good agreement with the known experimental and computational data.     

一种新型湍流超细粉碎机流场的数值模拟

根据新型湍流超细粉碎机的实验设备,建立单曲率叶型的一般曲线方程,并借助先进的CFD技术,对用Pro/E建立的计算模型进行验证,模拟两种不同叶型时湍流超细粉碎机粉碎腔内的单相三维紊流定常流场,直观显示粉碎腔内中间面的速度和流线,并比较了两种叶片时中间面的速度和流线的区别,为认识粉碎腔内的粉碎机理和叶片的改进提供了直观的模拟结果。     

基于ANSYS CFX的航空管件清洗设备管流数值模拟与分析

针对航空企业的需求,以实现航空管件高清洁度的清洗设备设计与优化为目标,根据清洗设备的工作特点和工作要求,重点研究分析了清洗液在航空管件内部的流动情况.运用ANSYSWorkbench有限元分析软件中的ANSYS CFX模块,建立了航空管件的有限元模型并进行了模拟试验与数值计算,得到了清洗液在管内的流动特性,为以后清洗设备的设计与优化提供了参考.     

汽车并列行驶湍流数值模拟

采用通用计算流体力学软件FLUENT对并列行驶的汽车进行了湍流数值模拟,并对结果进行了处理与分析。以0.5倍车宽侧向间距的两辆汽车为典型算例,给出了汽车车身表面的速度和压力分布。重点对比了0.1、0.5、2倍车宽间距两车对称面上的压力分布情况。对比汽车侧向力系数分析说明过小的汽车侧向间距会使两车间产生大的侧向力,出现中心挤压趋势。为保证安全性和操控性,应保证两车侧向间距在0.5倍车宽以上。     

Numerical simulation of HVAB rotor in hover using a mixed-mesh flow solver

Numerical simulations of the HVAB were carried out by using a Reynolds-averaged Navier-Stokes computational fluid dynamics flow solver. For the computation, mixed meshes of unstructured/Cartesian grids were used. An improved laminar-turbulent crossflow transition model γ − Re_θt − CF⁺ was used to predict laminar-turbulent transition phenomena. In addition, to achieve high resolute flow solutions, an improved scheme ESWENO-P was employed when calculating inviscid fluxes. To find the turbulence intensity for the simulations, a parametric study was first conducted with the PSP rotor configuration. The influence of the facility walls of the National Full-Scale Aerodynamics Complex was also investigated. Then, the HVAB rotor performance was predicted under conditions obtained by simulations of the PSP rotor. The HVAB rotor performance of the rotor, including thrust/torque coefficients and figure of merit, were analyzed. In addition, flow characteristics, such as laminar-turbulent locations and tip vortex trajectories, were also investigated.

     

Noise reduction of refrigerant two-phase flow using flow conditioners near the electric expansion valve

Journal of Mechanical Science and Technology - Two-phase flow, particularly generated in an expansion device, is a primary cause of refrigerant-induced noise in an air-conditioning system. The...     

固液两相流离心泵内颗粒运动规律的数值研究

针对分析固相参数对颗粒在流道内运动规律影响的问题,对不同固相参数工况下流道内颗粒运动轨迹、固相速度分布和颗粒雷诺数分布规律进行了研究,对颗粒直径以及颗粒浓度对颗粒运动规律影响进行了归纳。应用RNG k-ε湍流模型以及离散相模型进行了离心泵内部固液两相流场数值模拟。研究结果表明,颗粒与蜗壳碰撞的次数随着直径和颗粒浓度的增大而减少;叶轮流道内,颗粒与叶片发生碰撞的位置在叶片工作面;流道内的固相速度随着直径的增大整体会有减小的趋势;蜗壳和叶轮流道内两相分离严重,两相滑移速度较大。     

Numerical study on characteristics of turbulent two-phase gas-particle flow using multi-fluid model

The purpose of this research is to study numerically the turbulent gas-particle two-phase flow characteristics using the Eulerian-Eulerian method. A computer code is developed for the numerical study by using the k-ɛ-k _p two-phase turbulent model. The developed code is applied for particle-laden flows in which the particle volume fraction is between 10⁻⁵ and 10⁻² for the Stokes numbers smaller than unity. The gas and particle velocities and the particle volume fraction obtained by using this code are in good agreement with those obtained by a commercial code for the gas-particle jet flows within a rectangular enclosure. The gas-particle jet injected into a vertical rectangular 3D enclosure is numerically modeled to study the effect of the Stokes number, the particle volume fraction and the particle Reynolds numbers. The numerical results show that the Stokes number and the particle volume fraction are important parameters in turbulent gas-particle flows. A small Stokes number (St ≤ 0.07) implies that the particles are nearly at the velocity equilibrium with the gas phase, while a large Stokes number (St ≥ 0.07) implies that the slip velocity between the gas and particle phase increases and the particle velocity is less affected by the gas phase. A large particle volume fraction (α _p ≥ 0.0001) implies that the effect of the particles on the gas phase momentum increases, while a small particle volume fraction (α _p ≤ 0.0001) implies that the particles would have no or small effect on the gas flow field. For fixed Stokes number and particle volume fraction, an increase of the particle Reynolds number results in a decrease of the slip velocity between the gas and particle velocities.     

Numerical simulation of resistance welding of solar cell using a thermal-electrical-mechanical coupled model

Journal of Mechanical Science and Technology - A thermal-electrical-mechanical coupled model was established to simulate the Parallel-gap resistance welding (PGRW) process between the...     

细粉加料装置料腔内气相流场的数值模拟

为解决活性炭等细微粉料加料过程中出现的布料不均匀、物料损失等问题,采用Fluent 软件对加料装置料腔内气相流场进行数值模拟,重点讨论挡板角度对料腔内气相流场的影响规律.模拟结果直观显示了料腔内气流的运动过程,为分析加料腔内颗粒的运动提供了一定的理论依据,并表明:挡板角度设置合理时,丝束布料均匀性较好,物料损失较少.