Comparison between numerical computations and measurements by LDV for fluid flow in rectangular duct systems

Fluid flows in rectangular duct systems are measured by using the laser-Doppler velocity meter and computed by commercial software of Star-CD for comparisons between flows. Three rectangular systems are investigated in this study: a rectangular duct with a 90 degree bent elbow, a rectangular duct with two branches, and a rectangular duct in the middle of which a circular cylinder is located. These investigations show that the numerical solutions satisfactorily predict design factors: for example, the K -factor for an elbowed duct, the distribution ratio of flow rates into each branch from a main duct, and the Nusselt number around the circular duct. However, there are some disagreements in the velocity profile and turbulent kinetic energy at each cross section of the duct systems.     

Three-dimensional features of MHD flows turning in a right-angle duct

This study presents a numerical simulation of three-dimensional (3D) Liquid metal (LM) Magnetohydrodynamic (MHD) flows turning in a right-angle duct with a square cross section under a uniform magnetic field applied perpendicular to the plane of the main flow. The 3D features of the flow in a fluid region adjacent to the duct walls of the turning segment are investigated. Cases with different Hartmann numbers and conductance parameters are analyzed using the CFX code. The MHD features of the LM flow are examined in terms of fluid velocity, current density, electric potential, and pressure gradient. The formation of a velocity recirculation is observed in the inner region of the right-angle segment immediately after the turning of the flow because of the inertial force therein, thereby yielding a region of low electric potential with a complicated current distribution. In particular, in the right-angle segment, the axial velocity in the side layer near the outer wall (that is, in the outer side layer) is relatively lower than that in the inflow and outflow channels. In addition, the velocity recirculation region in the right-angle segment decreases and the pressure gradient increases with an increase in conductance parameter.     

基于格子Boltzmann方法的分叉微通道内非牛顿流体流动特性研究

为探究分叉微通道内非牛顿流体的流动特性,将非牛顿流体幂律模型引入牛顿流体格子Boltzmann模型,在不同分叉角度矩形截面微通道内数值模拟不同质量分数剪切稀化流体的流动行为;通过分析流动过程中密度随时间的变化趋势以及稳态流动下的密度,得到微通道内压力的分布以及流动区间的压力降;分析溶液质量分数、入口速度与分叉角度对非牛...     

Approximate method of determining the optimum cross section of microhannel heat sink

Microchannels are at the forefront of today’s cooling technologies. They are widely being considered for cooling of electronic devices and in micro heat exchanger systems due to their ease of manufacture. One issue which arises in the use of microchannels is related to the small length scale of the channel or channel cross-section. In this work, the maximum heat transfer and the optimum geometry for a given pressure loss have been calculated for forced convective heat transfer in microchannels of various cross-section having finite volume for laminar flow conditions. Solutions are presented for 10 different channel cross sections: parallel plate channel, circular duct, rectangular channel, elliptical duct, polygonal duct, equilateral triangular duct, isosceles triangular duct, right triangular duct, rhombic duct and trapezoidal duct. The model is only a function of the Prandtl number and the geometrical parameters of the cross-section, i.e., area and perimeter. This solution is performed with two exact and approximate methods. Finally, in addition to comparison and discussion of these two methods, validation of the relationship is provided using results from the open literature.     

Algebraic model of turbulent flow in ducts of rectangular cross-section with rounded corners

Of increasing importance are nowadays ducts of rectangular cross-section with large-radius rounded corners. They are used for large air flow rates at low pressure levels — typically for air flow distribution in buildings ventilation and heating systems. Paper develops an analytic model of turbulent flows in these ducts. It makes possible in particular evaluation of velocity profiles – and volume flow rates as a function of duct cross-section shapes. The model was validated by comparing the solutions with full-scale duct laboratory measurements.     

Magnetohydrodynamic flows in a dis-aligned duct system under a uniform magnetic field

In the present study, three-dimensional Magnetohydrodynamic (MHD) Liquid-metal (LM) flows in a dis-aligned duct system under a uniform magnetic field are investigated by numerical method. Computational fluid dynamics (CFD) simulations are carried out to analyzed the characteristics of the MHD flows and to examine the inter-relationship of the LM velocity, current density, electric potential and pressure, using CFX. The duct system consists of two dis-aligned parallel channels (One inflow channel and one outflow channel) and one channel connecting the above channels. In the present study, cases with different lengths of the connecting channel are considered. Because of the inertial force therein, a velocity recirculation is found in the region just after the first turning, resulting in a region of peak value in electric potential together with complex distribution of the current. Also, another velocity recirculation is seen in the region just after the second turning, creating another region of peak value in electric potential. In a situation where the magnetic field is applied in a direction perpendicular to the plane of the main flow in a dis-aligned duct system, until the fluid reaches an edge, the velocity component parallel to the magnetic field converges, with an increasing in the peak value of the side layer velocity, and then, after the fluid passes the edge, the velocity component parallel to the magnetic field diverges, with a decrease in the peak value of the side layer velocity. Oppositely, until the fluid reaches a corner, the velocity component parallel to the magnetic field diverges, with a decrease in the peak value of the side layer velocity, and then, after the fluid passes the corner, the velocity component parallel to the magnetic field converges, with an increase in the peak value of the side layer velocity. It is found that this type of velocity pattern is closely associated with the current distribution in the region of right-angle segments in the sense that the magnitude of the electromotive component of electric current is proportional to the fluid velocity.     

A Large-Scale Prototype of a Tritium Pellet Injector for the ITER International Tokamak

An injector of solid tritium pellets (as well as those of deuterium and protium) satisfying the basic requirements of the ITER tokamak is developed. The main elements of the injector are a screw extruder ensuring the continuous formation of pellets from a solid thermonuclear fuel and a fuel duct compatible with tritium handling and environmental safety requirements. The design, technological, and performance characteristics of the injector are presented. The results of experimental adjustment of the extrusion and protium-pellet pneumatic acceleration modes are described. A solid-protium rod with a rectangular cross section of 3 × 4 mm² was continuously extruded at a temperature of 10–11 K for 1500 s at a velocity of 20–25 mm/s. Pellets with a size of 3–3.5 mm formed from the rod were accelerated by helium at a pressure of 1 MPa up to a speed of 300–500 m/s in the periodic mode at a frequency of 1–6 Hz.     

A simple model for estimation of dimensionless isovel contours in open channels

A simple model is proposed for predicting the dimensionless isovel contours in straight ducts and open channels. It is assumed that each element of the boundary influences the velocity at an arbitrary point in the cross section. Then, the total effect of the boundary can be obtained using integration along the wetted perimeter. In this paper, power and logarithmic laws are used, while any velocity profile can be applied in the model. The model is applied to calculate the normalized isovel contours in rectangular channels. Then they are used, in combination with a single-point velocity measurement at a cross section of the uniform flow, to estimate the discharge. The kinetic energy and momentum correction factors, and the ratio of maximum to mean velocity, are also calculated from isovel patterns. Calibration and validation of the model are carried out by comparing the results obtained with measurements of the velocity in the main flow direction along the centerline of a rectangular flume as well as in the transverse direction. Each point of measurement can be used to estimate the discharge. Then, the estimated discharge is compared with the actual measured one. Depending on the position of the measurement, the deviation of the calculated and measured discharges will be altered. Model predictions are well correlated with experimental data for rectangular open channels.     

基于ANSYS的轴向柱塞液压电机泵电磁场数值计算与分析

提出了一种新型轴向柱塞液压电机泵,简要介绍了其结构组成和工作原理。应用ANSYS/Emag模块对带有不同冷却流道的三种电机泵的定子模型对应的空载电磁场进行了数值计算。通过对计算结果进一步的分析和计算得到了电机泵电磁场的分布及油隙磁感应强度,并进行了对比分析。研究表明,带有12个条形冷却流道的定子结构的磁感应强度最大,带有24个圆形冷却流道的定子磁感应强度最低,带有8个条形冷却流道的定子结构的磁感应强度介于上述两种之间。所作研究为新型轴向柱塞液压电机泵定子的结构设计和优化提供了依据。     

间隙对薄壁矩形管绕弯成形截面畸变影响的研究

基于ABAQUS/Explicit,建立了铝合金薄壁矩形管绕弯成形过程三维有限元模型,并对其可靠性进行了验证.模拟分析了芯棒与管坯间隙、压块与管坯间隙、防皱块与管坯间隙及弯曲模与管坯间隙对管坯截面畸变的影响规律.研究结果表明:减小芯棒与管坯间的间隙及弯曲模与管坯间的间隙都可减小管坯截面畸变的程度;而压块与管坯间隙及防皱块与管坯间隙的改变对管坯截面畸变率影响不大.     

基于Fluent的电动客车空调风道流场模拟

运用Fluent软件,对某电动客车整车开发设计阶段的空调系统主风道的变截面和直通型截面2种设计方案进行CFD流场数值模拟对比,评估出风口风速大小及均匀性、是否满足设计要求。模拟结果表明,主风道截面变化过大,影响出风口风速大小及均匀性,主风道应以直通型截面设计为主。     

气体对磁流体动力学传感器影响机理的探讨

由于气体和导电流体性质上的差异,导电流体中气体的存在将对磁流体动力学(MHD)传感器的输出特性产生影响。基于电磁感应理论和两相流理论,文章推导并建立了导电流体中含气体的MHD传感器VOF模型。通过ANSYS Fluent对含气体的MHD传感器输出特性进行仿真分析,同时搭建试验平台对不同气体含量MHD传感器进行试验验证。结果表明,导电流体中的气泡在低频时容易被拉伸撕裂成小气泡并随着角振动分散,同时使得流体环流场和电场产生偏移和畸变,角振动频率越低,此现象越明显;当导电流体中不含气体时角振动频率和幅值、重力加速度及偏心等外部因素对MHD传感器的输出特性无影响;当导电流体中含有气体时,MHD传感器的输出特性畸变等随气体含量、重力加速度和偏心的增大而增大,随角振动频率和幅值的增大而减小。文章研究成果能够为MHD传感器导电流体灌装工艺控制提供指导,有助于MHD传感器精度和稳定性的提升。     

Numerical Simulations of Lubricating Grease Flow in a Rectangular Channel with and without Restrictions

This article presents numerical simulations of the laminar flow of lubricating greases in a channel with rectangular cross section. Three greases with different consistencies (NLGI grades 00, 1, and 2) have been considered in three different configurations composed of a rectangular channel without restrictions, one rectangular step restriction, and one double-lip restriction. The driving pressure drop over the channel spans from 30 to 250 kPa. The grease rheology is described by the Herschel-Bulkley rheology model, and both the numerical code and rheology model have been validated with analytical solutions and flow measurements using micro-particle image velocimetry.     

陶瓷浆料微流挤压成形关键问题研究

利用流体力学理论,针对基于微流挤压成形的陶瓷浆料挤出过程的关键部件挤压凹模的流道形状进行了设计,使用ANSYS软件对挤压凹模出口横截面的流速和流道内部压力场的分布情况进行模拟,分析了四种不同流道形状挤压凹模内部压力场和出口流速的分布规律。研究结果为解决陶瓷浆料挤压成形工艺的难点问题提供了理论依据,具有重要的参考价值。     

药芯焊带轧制成型过程的实验研究

以典型的矩形断面形状药芯焊带成型过程为研究对象 ,通过实验测试 ,得出了成型时单位轧制压力、宽展、前滑值与压下率之间的变化规律 ,为药芯焊带轧制成型工艺设计提供了理论指导     

Optimization of a subsonic wind tunnel nozzle with low contraction ratio via ball-spine inverse design method

The goal of wind tunnel design is to generate a uniform air flow with minimum turbulence intensity and low flow angle. The nozzle is the main component of wind tunnels to create a uniform flow with minimal turbulence. Pressure distribution along nozzle walls directly affects the boundary layer thickness, pressure losses and non-uniformity of flow velocity through the test section. Although reduction of flow turbulences and non-uniformity through the test section can be carried out by nozzles with high contraction ratio, it increases the construction cost of the wind tunnel. For decreasing the construction cost of nozzle with constant test section size and mass flow rate, the contraction ratio and length of nozzle should be decreased; that causes the non-uniformity of outlet velocity to increase. In this study, first, three types of nozzle are numerically investigated to compare their performance. Then, Sargison nozzle with contraction ratio of 12.25 and length of 7 m is scaled down to decrease its weight and construction cost. Having scaled and changed to a nozzle with contraction ratio of 9 and length of 5 m, its numerical solution reveals that the non-uniformity of outlet velocity increases by 21%. By using the Ballspine inverse design method, the pressure distribution of the original Sargison nozzle is first scaled and set as the target pressure of the scaled down nozzle and geometry correction is done. Having reached the target nozzle, numerical solution of flow inside the optimized nozzle shows that the non-uniformity just increases by 5% in comparison with the original Sargison nozzle.     

基于全局模型的直流内磁式磁流体推进系统研究

阐述了磁流体推进系统的不同分类和面临的问题,着重研究了直流内磁式磁流体推进系统的结构设计和优化.为进一步提高推进效率,从动量和能量守恒出发提出一种全局计算方法,研究船舶磁流体推进器的几何形状、尺寸和位置等参数,并通过对其不同组件和产生损失的综合分析得出一种优化模型.     

The Analysis of the Lubrication Condition and Friction Losses of a Single Acting Cross Head Guide Shoe of a Low Speed Cross Head Diesel Engine: Part I—An Alogrithm For The Prediction of Oil Film Thickness

The lubrication condition pertaining to the cross head guide shoe of a low speed cross head diesel engine is evaluated in this paper under the principles of hydrodynamic lubrication. The Reynolds differential equation which describes the pressure and oil film thickness distribution of the cross head guide shoe system operating under unsteady load will be solved using a finite difference method. The influence of the width to length ratio of the rectangular cross head guide shoe plate will be considered in terms of variation of the pressure distribution within the bearing and its load carrying capacity.     

Upper bound analysis for extrusion at various die land lengths and shaped profiles

The effects of die land lengths, a rarely investigated die extrusion parameter on the die-shaped profiles, on the extrusion pressures are investigated and presented. The analyses of the extrusion pressures by the upper bound method have been extended for the evaluations of the extrusion pressures to complex extruded sections such as square, rectangular, I,- and T-shaped sections with power of deformation due to ironing effect at the die land taken into account. The extrusion pressure contributions due to the die land evaluated theoretically for shaped sections considered are found to increase with die land lengths for any given percentage reduction and also increase with increasing percentage die reductions at any given die land length. The effect of die land lengths on the extrusion pressure increases with increasing complexity of die openings geometry with I-shaped section giving the highest extrusion pressure followed by T-shaped section, rectangular, circular-shaped die openings with square section die opening, giving the least extrusion pressure for any given die reduction at any given die land lengths.     

Calibration of tapping AFM cantilevers and uncertainty estimation: Comparison between different methods

We present a comparative study between three different methods for the spring constant calibration of silicon beam-shaped Atomic Force Microscope (AFM) cantilevers, used in tapping AFM mode in air. The geometries of these levers can be quite different from the standard rectangular cross section. We examine a method that combines the knowledge of cantilever dimensions and eigenfrequencies (Cleveland formula), the Sader method and we build cantilever models based on Finite Element Analysis (FEA). We demonstrate that with accurate measurement of dimensions, resonance frequency and quality factor, the Cleveland formula yields a combined cantilever stiffness uncertainty of approximately ±7% and the Sader method an uncertainty of ±5%. We also use FEA to show that when trying to approximate a realistic trapezoidal 3D tipped geometry, there exists a systematic overestimation in cantilever stiffness of ±2%, compared to when considering a simple rectangular cross section. Our constructed FE models are able to account for inhomogeneities in material properties as well as the influence of the added reflective coating in the cantilever stiffness estimation.