三维PIV原理及其实现方法

粒子图像测量技术(PIV)在现代流场测量中发挥了重要作用,是流场测速研究的发展方向之一。随着二维PIV日益完善,新课题对流场测速技术提出更高的要求,推动了三维PIV的深入研究,但该技术的复杂性使得流场的三维速度测量更为困难。笔者以PIV技术为对象,重点阐述基于针孔相机模型的三维PIV原理和实现方法,并探讨了三维PIV研究工作的若干进展。

TVD SCHEME WITH CHEMICAL REACTION FLOW AND ITS APPLICATION IN COMBUSTION GAS JETTING FLOW

By conjugating features of combustion gas jetting flows of the solid-rocket and using mathematical methods, a numerical scheme is systematically derived based on Harten′s standard TVD scheme, which fits for the flow with high temperature, pressure and velocity. The rational calculation formula of pressure partial derivation is also given out. By using the chemical kinetics knowledge, problems of multi-component and finite rate chemical reaction contained in combustion gas of the rocket flow field are discussed. The method for solving the mass source term of chemical reaction is clarified. Taking 9 reaction equations with 12 components as an example and utilizing the established calculation program, the free jetting flow field of the rocket is simulated. Numerical results show the correctness of the numerical scheme.

Flow and natural convection heat transfer characteristics of non-Newtonian nanofluid flow bounded by two infinite vertical flat plates in presence of magnetic field and thermal radiation using Galerkin method

The main goal of this paper is to investigate natural convective heat transfer and flow characteristics of non-Newtonian nanofluid streaming between two infinite vertical flat plates in the presence of magnetic field and thermal radiation.Initially,a similarity transformation is used to convert momentum and energy conservation equations in partial differential forms into non-linear ordinary differential equations (ODE) applying meaningful boundary conditions.In order to obtain the non-linear ODEs analytically,Galerkin method (GM) is employed.Subsequently,the ODEs are also solved by a reliable numerical solution.In order to test the accuracy,precision and reliability of the analytical method,results of the analytical analysis are compared with the numerical results.With respect to the comparisons,fairly good compatibilities with insignificant errors are observed.Eventually,the impacts of effective parameters including magnetic and radiation parameters and nanofluid volume fraction on the velocity,skin friction coefficient and Nusselt number distributions are comprehensively described.Based on the results,it is revealed that with increasing the role of magnetic force,velocity profile,skin friction coefficient and thermal performance descend.Radiation parameter has insignificant influence on velocity profile while it obviously has augmentative and decreasing effects on skin friction and Nusselt number,respectively.

Diffusion of chemically reactive species in third grade fluid flow over an exponentially stretching sheet considering magnetic field effects

This article addresses the magnetohydrodynamics(MHD) flow of a third grade fluid over an exponentially stretching sheet. Analysis is carried out in the presence of first order chemical reaction. Both cases of constructive and destructive chemical reactions are reported. Convergent solutions of the resulting differential systems are presented in series forms. Characteristics of various sundry parameters on the velocity, concentration, skin friction and local Sherwood number are analyzed and discussed.

Simulation and Analysis on the Two-Phase Flow Fields in a Rotating-Stream-Tray Absorber by Using Computational Fluid Dynamics

The flow field of gas and liquid in a φ150mm rotating-stream-tray (RST) scrubber is simulated by using computational fluid dynamic (CFD) method. The sismulation is based on the two-equation RNG κ-ε turbulence model, Eulerian multiphase model, and a real-shape 3D model with a huge number of meshes. The simulation results include detailed information about velocity, pressure, volume fraction and so on. Some features of the flow field are obtained: liquid is atomized in a thin annular zone; a high velocity air zone prevents water drops at the bottom from flying towards the wall; the pressure varies sharply at the end of blades and so on. The results will be helpful for structure optimization and engineering design.

Numerical Analysis of the Flow Field in a Sloshing Tank with a Horizontal Perforated Plate

Liquid sloshing is a type of free surface flow inside a partially filled water tank.Sloshing exerts a significant effect on the safety of liquid transport systems;in particular,it may cause large hydrodynamic loads when the frequency of the tank motion is close to the natural frequency of the tank.Perforated plates have recently been used to suppress the violent movement of liquids in a sloshing tank at resonant conditions.In this study,a numerical model based on OpenF OAM(Open Source Field Operation and Manipulation),an open source computed fluid dynamic code,is used to investigate resonant sloshing in a swaying tank with a submerged horizontal perforated plate.The numerical results of the free surface elevations are first verified using experimental data,and then the flow characteristics around the perforated plate and the fluid velocity distribution in the entire tank are examined using numerical examples.The results clearly show differences in sloshing motions under first-order and third-order resonant frequencies.This study provides a better understanding of the energy dissipation mechanism of a horizontal perforated plate in a swaying tank.

CFD simulation of high-temperature effect on EHD characteristics in a wire-plate electrostatic precipitator

A computational fluid dynamics （CFD） model is carried out to describe the wire-plate electrostatic precipitator （ESP） in high temperature conditions, aiming to study the effects of high temperature on the electro- hydrodynamic （EHD） characteristics. In the model, the complex interactions at high temperatures between the electric field, fluid dynamics and the particulate flow are taken into account. We apply different numerical methods for different fields, including an electric field model, Euler-Lagrange particle-laden flows model, and particle charging model. The effects of high temperature on ionic wind, EHD characteristics and collection effi- ciency are investigated. The numerical results show high temperature causes more significant effects of the ionic wind on the gas secondary flow. High viscosity of gas at high temperature makes particles follow the gas flow pattern more closely. High temperature reduces the surface electric strength, so that the mean electric strength weakens the space charging. On the contrary, there is an increase in the diffusion charging at high tem- perature compared with at low temperature. High temperature increases the ratio of mean drag force over mean electrostatic force actin~ on the ~atticles which mav contribute to a decline of collection efficiencv.

Analysis of a Propeller Wake Flow Field Using Viscous Fluid Mechanics

The computational fluid dynamics （CFD） method is used to numerically simulate a propeller wake flow field in open water. A sub-domain hybrid mesh method was adopted in this paper. The computation domain was separated into two sub-domains, in which tetrahedral elements were used in the inner domain to match the complicated geometry of the propeller, while hexahedral elements were used in the outer domain. The mesh was locally refined on the propeller surface and near the wake flow field, and a size function was used to control the growth rate of the grid. Sections at different axial location were used to study the spatial evolution of the propeller wake in the region ranging from the disc to one propeller diameter （D） downstream. The numerical results show that the axial velocity fluctuates along the wake flow; radial velocity, which is closely related to vortices, attenuates strongly. The trailing vortices interact with the tip vortex at the blades＇ trailing edge and then separate. The strength of the vortex shrinks rapidly, and the radius decreases 20% at one diameter downstream.

Characterizing and Analyzing the Airflow Field inside the Nozzle Block of Murata Vortex Spinning

A three-dimensional computational fluid dynamics model is developed by software Fluent 6.2, to simulate the flow field inside the nozzle block of the Murata vortex spinning. The flowing state and the distribution law of static pressure and velocity are characterized and analyzed. The relationship between the flowing state and the structure of the vortex spun yarn is also discussed. The research results can enhance the understanding of the yarn formation principle from viewpoint of the airflow field law inside the nozzle block of Murata vortex spinning.

Hydrodynamic Performance of Flapping-foil Propulsion in the Influence of Vortices

Fish are able to make good use of vortices.In a complex flow field,many fish continue to maintain both efficient cruising and maneuverability.Traditional man-made propulsion systems perform poorly in complex flow fields.With fish-like propulsion systems,it is important to pay more attention to complex flow fields.In this paper,the influence of vortices on the hydrodynamic performance of 2-D flapping-foils was investigated.The flapping-foil heaved and pitched under the influence of inflow vortices generated by an oscillating D-section cylinder.A numerical simulation was run based the finite volume method,using the computational fluid dynamics(CFD) software FLUENT with Reynolds-averaged Navier-Stokes(RANS) equations applied.In addition,dynamic mesh technology and post processing systems were also fully used.The calculations showed four modes of interaction.The hydrodynamic performance of flapping-foils was analyzed and the results compared with experimental data.This validated the numerical simulation,confirming that flapping-foils can increase efficiency by absorbing energy from inflow vortices.

Numerical simulation of the pulsing air separation field based on CFD

The flow field of pulsing air separation is normally in an unsteady turbulence state.With the application of the basic principles of multiphase turbulent flows,we established the dynamical computational model,which shows a remarkable variation of the unstable pulsing air flow field.CFD(computational fluid dynamics) was used to conduct the numerical simulation of the actual geometric model of the classifier.The inside velocity of the flowing fields was analyzed later.The simulation results indicate that the designed structure of the active pulsing air classifier provided a favorable environment for the separation of the particles with different physical characters by density.We shot the movement behaviors of the typical tracer grains in the active pulsing flow field using a high speed dynamic camera.The displacement and velocity curves of the particles in the continuous impulse periods were then analyzed.The experimental results indicate that the effective separation by density of the particles with the same settling velocity and different ranges of the density and particle size can be achieved in the active pulsing airflow field.The experimental results provide an agreement with the simulation results.

A new approach to quantifying vehicle induced turbulence for complex traffic scenarios

Traffic-related pollutants adversely affect air quality, especially in regions near major roadways. The vehicleinduced turbulence(VIT) is a significant factor that controls the initial dilution, dispersion, and ultimately the chemical and physical fate of pollutants by altering the conditions in the microenvironment. This study used a computational fluid dynamics(CFD) software FLUENT to model the vehicle-induced turbulence(VIT) generated on roadways, with a focus on impact of vehicle-vehicle interactions, traffic density and vehicle composition on turbulent kinetic energy(TKE). We show, for the first time, that the overall TKE from multiple vehicles traveling in series can be estimated by superimposing the TKE of each vehicle, without considering the distance between them while the distance is greater than one vehicle length. This finding is particularly significant since it enables a new approach to VIT simulations where the overall TKE is calculated as a function of number of vehicles. We found that the interactions between vehicles traveling next to each other in adjacent lanes are insignificant,regardless the directions of the traffic flow. Consequently, simulations of different traffic scenarios can be substantially simplified by treating two-way traffic as one-way traffic, with less than 5% difference in the overall volume-averaged TKE. We also developed equations that allow the estimation of the overall volume-averaged TKE as a function of the number and the type of vehicles.

Numerical simulation on melt flow with bubble stirring and temperature field in aluminum holding furnace

The numerical model for predicting the flow and temperature fields of the melt in holding furnace with porous brick purging system were set up using Euler-Lagrange approach.In this model,bubbles coalescence and disintegration were ignored based on the dimensionless analysis,and the bubble size was assumed to be obedient to Rosin-Rammler distribution with a mean size of 0.6 mm.The results show that on reference operating condition,during the heating and agitation process,melt mixes well in the furnace,and the melt velocity increases with the increase of gas flux.Holding the melt for 30 min causes the max temperature in the bulk melt to increase to 60 K.After holding the heat,the agitation processing restarts,and it takes 10 min for the stratified melt to retrieve the homogeneous temperature field when the gas flux is 10 L/min,which shows deficient alloying and degassing in the melt.With the increase of gas flux from 10 to 20,30 and 40 L/min,the necessary recovery time decreases from 10 to 6,5 and 4 min gradually,which shows the improvement of the stirring efficiency.Depending on the processing purposes,for both good degassing performance and gas saving,proper operating strategy and parameters (gas flux,primarily) could be adjusted.

Research on hydrokinetics characteristics of rotating pipe fluid in the crossed electric and magnetic field

The rotating pipe fluid in the crossed electric and magnetic field not only suffered the forces in the steady condition, but also suffered Coriolis force, centrifugal force because of rotation and electromagnetic volume force. The motion equation of fluid and the hydrokinetics equations of rotating pipe were described in the Cartesians coordinates. The equations showed that the solutions to hydrokinetics equations of rotating pipe in the crossed electric and magnetic electromagnetic field were highly complicated and numerical calculations were also astronomical. The pressure distribution and temperature distribution of one dimension were solved using the electromagnetic equations set. The results showed that the fluid in rotating pipe was in the asymmetrical pressure field and temperature field because it was in the energy exchange and thermo-electrical coupling course. The primary characteristic of flow course could be expressed using the proposed hydrokinetics equations.

CFD Simulation of Reactor Internal Flow in the Scaled APR＋

A series of 1/5 scale reactor flow model tests have been conducted in order to determine the hydraulic characteristics of the APR＋ （advanced power reactor plus）. The objective of test was to determine the core inlet flow field of the model reactor in order to provide input information required by the open core thermal margin analysis code such as TORC. In this study, in order to examine the validity of the results of reactor flow model tests and the applicability of CFD （computational fluid dynamics） in the simulation of reactor internal flow, CFD simulation was conducted with the commercial multi-purpose CFD software, ANSYSCFX V. 14. It was found that the velocity field in the downcomer had the inhomogeneous feature. Relative high velocity region was located in the core region. This result was different from measurement and this difference may result from the fact that some internal structures were not modeled with the real geometry but treated as the porous domain.

The Research on Optimization of the Multiphase Flow Field of Biogas Plant by Using CFD Software

The inner flow field of a biogas plant can be optimized by agitating the feedstock to be evenly distributed for a rising biogas production rate. A hydraulic agitator can be installed in the digester with outlets far above the bottom. Hydraulic mixing is essential in a solid-liquid two-phase flow process, in which large solid particles can be found at the initial stage and turn to being high-concentration viscous liquid （non-Newtonian fluid）. A 0.75 m3 digester was taken as a case study with CFD （computational fluid dynamics） software. The basic pattern was simulated by using water as the medium and the pattern of pseudo plastic fluid state was simulated by the Euler-Euler Model, then the effect of optimized design with bottom inflow and high dispersed outlets could be verified. Viewed from the mixing effects, the velocity of 0.6 m/s is better than l m/s for water medium, while 1 m/s better than 0.6 m/s for pseudo plastic fluid medium.

Numerical Hydrodynamics Study Around Turbine Array of Tidal Stream Farm in Zhoushan, China

In recent decades,great efforts have been made to efficiently explore tidal stream energy due to its unique advantages of easy prediction and great potential.China recently launched a national tidal stream farm demonstration project in the waterway between Putuoshan and Hulu Islands in the Zhoushan area.Before deployment of the turbine array,it is necessary to understand the hydrodynamic changes associated with the construction of a turbine array.In this study,we developed a depth-averaged hydrodynamics model that solves the shallow water governing equations to simulate the tidal hydrodynamics around the Zhoushan Archipelago.The simulation results agree with field data in terms of the water elevation and stream velocity.We considered two types of turbine arrays in this study and investigated their impacts on the local hydrodynamics.In general,the stream velocity in the northern and southern areas is reduced due to the power take-off of the turbine array,whereas stream velocity in the western and eastern areas is slightly increased due to the blockage impact of the turbine array.

Developing Spline Based Overset Grid Assembling Approach and Application to Unsteady Flow Around a Moving Body

Overset or Chimera grid approach is one of methods to cope with complex geometries. A spline based overset grid assembling system has been developed. The system is based on structured grid approach and covers comprehensive features for overset assembling, i.e., grid generation, grid modification, and computing Domain Connectivity Information （DCI） for overset interpolation. Ferguson spline curve is used to compute curves through grid points and cell centers for trimming grids and computing DCI robustly and accurately. Flow simulation around Kriso Container Ship （KCS） with jointed grids shows good continuity of flow field between the grids. The overset grid assembling is enhanced to unsteady problem as dynamic overset approach coupled with a solver which also has been developed in National Maritime Research Institute, Japan. Computed results for pitchup spheroid are compared with measured data and show good agreement in unsteady force acting on the spheroid. It is confirmed that the system has capability to simulate flow field around jointed grids and unsteady flow with dynamic overset assembling approach practically.

How Does the Diffusion Dynamics Reconnect the Magnetic Field？

We clarify how magnetic reconnection can be derived from magnetohydrodynamics （MHD） equations in a way that is easily understandable to university students. The essential mechanism governing the time evolution of the magnetic field is diffusion dynamics. The magnetic field is represented by two components. It is clarified that the diffusion of a component causes agene ration of another component that is initially zero and, accordingly, that the magnetic force lines are reconnected. For this reconnection to occur correctly, the initial magnetic field must be directed oppositely in the two regions, e.g., y 〉 0 and y 〈 O; must be concave （convex） for y 〉 0 （y 〈 0）; and must be saturated foryfar from the x axis, which would indicate the existence of the current sheet. It will be clear that our comprehension based on diffusion runs parallel to the common qualitative explanation about the magnetic reconnection.

Numerical Analysis of the Thermal Behavior of a Hermetic Reciprocating Compressor

A numerical model to predict the temperature field in a hermetic reciprocating compressor for household refrigeration appliances is presented in this work. The model combines a high resolution three-dimensional heat conduction formulation of the compressor＇s solid parts, a three-dimensional CFD （computational fluid dynamics） approach for the gas line domain and lumped formulations of the shell gas and the lubrication oil. Heat transfer coefficients are determined by applying CFD to the gas line side and correlations from the literature on the shell gas and oil side, respectively. The valve in the gas line simulation is modelled as a parallel moving fiat plate. By means of an iterative loop the temperature field of the solid parts acts as boundary condition for the CFD calculation of the gas line which returns a cycle averaged quantity of heat to the solid parts. Using an iteration method which is based on the temperature deviation between two iteration steps, the total number of iterations and consequently the computational time can be reduced. The loop is continued until a steady-state temperature field is obtained. Calculated temperatures of the solid parts are verified by temperature measurements of a calorimeter test bench.