Numerical investigation on properties of attack angle for an opposing jet thermal protection system

The three-dimensional Navier-Stokes equation and the k-ε viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow conditions.The numerical method is validated by the relevant experiment.The flow field parameters,aerodynamic forces,and surface heat flux distributions for attack angles of 0°,2°,5°,7°,and 10° are obtained.The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters,aerodynamic force,and surface heat flux distribution of the supersonic vehicle nose-tip with an opposing jet thermal protection system.When the attack angle reaches 10°,the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system,thus the thermal protection has failed.     

Numerical simulation of the flow within and over an intersection model with Reynolds-averaged Navier--Stokes method

In this study, the Reynolds-averaged Navier--Stokes (RANS) method is employed to simulate the flow within and over an intersection model with three kinds of $k$--$\varepsilon$ turbulence closure schemes, namely, standard model, renormalization group (RNG) model and realizable $k$--$\varepsilon$model. The comparison between the simulated and observed flow fields shows that the RANS simulation with all the three turbulence models cannot completely and accurately reproduce the observed flow field in all details. A detailed comparison between the predicted profiles of wind velocities and the measured data shows that the realizable $k$--$\varepsilon$ model is the best one among the three turbulence closure models in general. However, the extent to which the improvement is achieved by the realizable $k$--$\varepsilon$ model is still not enough to completely and accurately describe the turbulent flow in a relatively complex environment.     

A Three-Component Model Suitable for Natural and Ventilated Cavitation

A three-component model based on mass transfer equation is proposed to simulate both the natural and ventilated cavitations. In the present cavitation model, the content of nuclei in the local flow field is updated synchronously, and is coupled with the Rayleigh-Plesset equation so as to capture the cavity development. The proposed model is applied for simulating the cavitating flow around a super-cavitating vehicle in different cavitation conditions. In the ease of the natural cavitation simulation, the predicted cavitation characteristics including the cavity length and cavity diameter agrees fairly well with the analytical results. In the case of the mixed cavitation simulation, the gas ventilation obviously influences the development of cavity. With the increase of the gas ventilated rate, the natural cavitation is suppressed remarkably, and a super cavitation is formed even at a relatively larger natural cavitation number.     

The effect of surface roughness on rarefied gas flows by lattice Boltzmann method

This paper studies the roughness effect combining with effects of rarefaction and compressibility by a lattice Boltzmann model for rarefied gas flows at high Knudsen numbers. By discussing the effect of the tangential momentum accommodation coefficient on the rough boundary condition, the lattice Boltzmann simulations of nitrogen and helium flows are performed in a two-dimensional microchannel with rough boundaries. The surface roughness effects in the microchannel on the velocity field, the mass flow rate and the friction coefficient are studied and analysed. Numerical results for the two gases in micro scale show different characteristics from macroscopic flows and demonstrate the feasibility of the lattice Boltzmann model in rarefied gas dynamics.     

Multi-bubble motion behavior of uniform magnetic field based on phase field model

Aiming at the interaction and coalescence of bubbles in gas–liquid two-phase flow, a multi-field coupling model was established to simulate deformation and dynamics of multi-bubble in gas–liquid two-phase flow by coupling magnetic field, phase field, continuity equation, and momentum equation. Using the phase field method to capture the interface of two phases, the geometric deformation and dynamics of a pair of coaxial vertical rising bubbles under the applied uniform magnetic field in the vertical direction were investigated. The correctness of results is verified by mass conservation method and the comparison of the existing results. The results show that the applied uniform magnetic field can effectively shorten the distance between the leading bubble and the trailing bubble, the time of bubbles coalescence, and increase the velocity of bubbles coalescence. Within a certain range, as the intensity of the applied uniform magnetic field increases, the velocity of bubbles coalescence is proportional to the intensity of the magnetic field, and the time of bubbles coalescence is inversely proportional to the intensity of the magnetic field.     

Numerical investigation on properties of attack angle for opposing jet thermal protection system

The three-dimensional Navier-Stokes equation and the k-ε viscous model are used to simulate the attack angle characteristics of a hemisphere nose-tip with an opposing jet thermal protection system in supersonic flow condition. The numerical method is validated by the relevant experiment. The flow field parameters, aerodynamic forces, and surface heat flux distributions for attack angles of 0°, 2°, 5°, 7°, and 10° are obtained. The detailed numerical results show that the cruise attack angle has a great influence on the flow field parameters, aerodynamic force, and surface heat flux distribution of the supersonic vehicle nose-tip with opposing jet thermal protection system. When the attack angle reaches 10°, the heat flux on the windward generatrix is close to the maximal heat flux on the wall surface of the nose-tip without thermal protection system, thus the thermal protection is failure.     

Simultaneous effects of magnetic field and space porosity on compressible Maxwell fluid transport induced by a surface acoustic wave in a microchannel

Peristaltic motion induced by a surface acoustic wave of a viscous, compressible and electrically conducting Maxwell fluid in a confined parallel-plane microchannel through a porous medium is investigated in the presence of a constant magnetic field. The slip velocity is considered and the problem is discussed only for the free pumping case. A perturbation technique is employed to analyze the problem in terms of a small amplitude ratio. The phenomenon of a “backward flow” is found to exist in the center and at the boundaries of the channel. In the second order approximation, the net axial velocity is calculated for various values of the fluid parameters. Finally, the effects of the parameters of interest on the mean axial velocity, the reversal flow, and the perturbation function are discussed and shown graphically. We find that in the non-Newtonian regime, there is a possibility of a fluid flow in the direction opposite to the propagation of the traveling wave. This work is the most general model of peristalsis created to date with wide-ranging applications in biological, geophysical and industrial fluid dynamics.     

Numerical investigation of the interaction of the turbulent dual-jet and acoustic propagation

In order to study the interaction between two independent jets, a three-dimensional(3D) transient mathematical model is developed to investigate the flow field and acoustic properties of the two-stream jets. The results are compared with those of the single-stream jet at Mach number 0.9 and Reynolds number 3600. The large eddy simulation(LES) with dynamic Smagorinsky sub-grid scale(SGS) approach is used to simulate the turbulent jet flow structure. The acoustic field is evaluated by the Ffowcs Williams–Hawkings(FW-H) integral equation. Considering the compressibility of high-speed gas jets, the density-based explicit formulation is adopted to solve the governing equations. Meanwhile, the viscosity is approximated by using the Sutherland kinetic theory. The predicted flow characteristics as well as the acoustic properties show that they are in good agreement with the existing experimental and numerical results under the same flow conditions available in the literature. The results indicate that the merging phenomenon of the dual-jet is triggered by the deflection mechanism of the Coanda effect, which sequentially introduces additional complexity and instability of flow structure. One of the main factors affecting the dual-jet merging is the aperture ratio, which has a direct influence on the potential core and surrounding flow fluctuation. The analysis on the noise pollution reveals that the potential core plays a fundamental role in noise emission while the additional mixing noise makes less contribution than the single jet noise. The overall sound pressure level(OASPL) profiles have a directive property, suggesting an approximate 25° deflection from the streamwise direction, however, shifting toward lateral direction of about 10° to 15° in the dual-jet. The conclusion obtained in this study can provide valuable data to guide the development of manufacturing-green technology in the multi-jet applications.     

Comparison of the PIC model and the Lie algebraic method in the simulation of intense continuous beam transport

Both the PIC (Particle-In-Cell) model and the Lie algebraic method can be used to simulate the transport of intense continuous beams. The PIC model is to calculate the space charge field, which is blended into the external field, and then simulate the trajectories of particles in the total field; the Lie algebraic method is to simulate the intense continuous beam transport with transport matrixes. Two simulation codes based on the two methods are developed respectively, and the simulated results of transport in a set of electrostatic lenses are compared. It is found that the results from the two codes are in agreement with each other, and both approaches have their own merits.     

Pion and σ-meson Properties in a Strong Magnetic Field

With the Nambu–Jona-Lasinio(NJL) model we calculate the properties of pion and σ-meson at finite temperature and finite magnetic field. The obtained temperature and magnetic field strength dependence of the constituent quark mass M, the pion and σ-meson masses and the neutral pion decay constant indicates that, in the simple four fermion interaction model, there exists the magnetic catalysis effect. It also shows that the Gell-Mann–Oakes–Renner relation is violated obviously with the increasing of the temperature, and the effect of the magnetic field becomes pronounced only around the critical temperature. The deviation of the critical temperatures obtained with different criteria indicates that the chiral phase transition driven by the temperature in the magnetic field strength region we have considered is in fact a crossover.     

Lattice—BGK simulation of a two—dimensional channel flow around a square cylinder

The confined flow around a square cylinder mounted inside a two-dimensional channel (blockage ratio $\be=1/8$) was investigated in detail by a newly developed incompressible nonuniform lattice-BGK model. It is found that the vortex shedding behind the cylinder induces periodicity in the flow field, and the periodicity of the flow will lose for $Re>$300. A detailed analysis for a range of Reynolds numbers between 1 and 500 was presented. Quantitative comparisons with other methods show that the model gives accurate results for complex flows.     

Numerical Simulation of the 12 May 1997 CME Event

Our newly developed CESE MHD model is used to simulate sun-earth connection event with the well-studied 12 May 1997 CME event as an example. The main features and approximations of our numerical model are as follows： （1） The modifed conservation element and solution element （CESE） numerical scheme in spherical geometry is implemented in our code. （2） The background solar wind is derived from a 3D time-dependent numerical MHD model by input measured photospheric magnetic fields. （3） Transient disturbances are derived from solar surface by introducing a mass flow of hot plasma. The numerical simulation has enabled us to predict the arrival of the interplanetary shock and provided us with a relatively satisfactory comparison with the WIND spacecraft observations.     

Modelling the unsteady melt flow under a pulsed magnetic field

A numerical model for the unsteady flow under a pulsed magnetic field of a solenoid is developed, in which magnetohydrodynamic flow equations decouple into a transient magnetic diffusion equation and unsteady Navier–Stokes equations in conjunction with two equations of the k–ε turbulent model. A Fourier series method is used to implement the boundary condition of magnetic flux density under multiple periods of a pulsed magnetic field （PMF）. The numerical results are compared with the theoretical or experimental results to validate the model under a time-harmonic magnetic field; it is found that the toroidal vortex pair is the dominating structure within the melt flow under a PMF. The velocity field of a molten melt is in a quasi-steady state after several periods; changing the direction of the electromagnetic force causes the vibration of the melt surface under a PMF.     

A Thermodynamic Cavitation Model for Cavitating Flow Simulation in a Wide Range of Water Temperatures

A thermodynamic cavitation model is developed to simulate the cavitating water flow in a wide temperature range. The thermal effect on bubble growth during cavitation is introduced in the developed model by considering both pressure difference and heat transfer between the vapor and liquid phase. The cavitating turbulent flow over a NACA0015 hydrofoil has been simulated at various temperatures from room temperature to 150°C by using the present cavitation model, which has been validated by the experimental data. It is seen that the thermodynamic effects of cavitation, vapor depression and temperature depression are much more predominant in high temperature water compared with those in room temperature water. These results indicate that the proposed thermodynamic cavitation model is reasonably applicable to the cavitating water flow in a wide temperature range.     

Experimental verification of Foreman dislocation model

We present a strain analysis of an edge dislocation core, and a detailed discussion of the Foreman dislocation model. In order to examine the model, the quantitative measurement of strain field around an edge dislocation in aluminum is performed, and high-resolution transmission electron microscopy and geometric phase analysis are employed to map the strain field of the edge dislocation core in aluminum. The strain measurements are compared with the Foreman dislocation model, showing that they are in good agreement with each other when 0.7 ≤ a ≤ 1.5.     

Self-organized phenomena of pedestrian counter flow in a channel under periodic boundary conditions

In this paper we investigate self-organized phenomena such as lane formation generated by pedestrian counter flow in a channel.The lattice gas model is extended to take the effect of walkers in the opposite direction into account simultaneously when they are in the view field of a walker,i.e.,walkers tend to follow the leaders in the same direction and avoid conflicts with those walking towards them.The improved model is then used to mimic pedestrian counter flow in a channel under periodic boundary conditions.Numerical simulations show that lane formation is well reproduced,and this process is rather rapid which coincides with real pedestrian traffic.The average velocity and critical density are found to increase to some degree with the consideration of view field.     

Study on the mixing of fluid in curved microchannelswith heterogeneous surface potentials

In this paper the mixing of a sample in the curved microchannel with heterogeneous surface potentials is analysed numerically by using the control-volume-based finite difference method. The rigorous models for describing the wall potential and external potential are solved to get the distribution of wall potential and external potential, then momentum equation is solved to get the fully developed flow field. Finally the mass transport equation is solved to get the concentration field. The results show that the curved microchannel has an optimized capability of sample mixing and transport when the heterogeneous surface is located at the left conjunction between the curved part and straight part. The variation of heterogeneous surface potential $\psi_{\rm n}$has more influence on the capability of sample mixing than on that of sample transport. The ratio of the curved microchannel's radius to width has a comparable effect on the capability of sample mixing and transport. The conclusions above are helpful to the optimization of the design of microfluidic devices for the improvement of the efficiency of sample mixing.     

Lattice Boltzmann method for three-dimensional moving particles in a Newtonian fluid

A lattice Boltzmann method is developed to simulate three-dimensional solid particle motions in fluids. In the present model, a uniform grid is used and the exact spatial location of the physical boundary of the suspended particles is determined using an interpolation scheme. The numerical accuracy and efficiency of the proposed lattice Boltzmann method is demonstrated by simulating the sedimentation of a single sphere in a square cylinder. Highly accurate simulation results can be achieved with few meshes, compared with the previous lattice Boltzmann methods. The present method is expected to find applications on the flow systems with moving boundaries, such as the blood flow in distensible vessels, the particle－flow interaction and the solidification of alloys.     

In Vivo Magnetic Particle Targeting by Local Gradient Field of Interstitial Seeds Magnetized in an Ex Vivo Uniform Field

The possibility of in vivo magnetic particle targeting by the locally induced gradient field of interstitial ferro- magnetic implants, magnetized in an ex vivo uniform field, is evaluated by a modelling analysis. A simplified 3D model analogous to a torso size, with a continuous laminar flow through the volume with the typical velocity and viscosity values of in vivo blood flow and a ferromagnetic seed inserted in the volume center vertical to the flow, is used to evaluate the magnetic particle capturing efficiency by the seed, which is magnetized in a uniform field. The initial modelling results indicate that for 1-10μm iron oxide particles transporting with a blood flow of 0.5-5 mm/s, the seeds of tungsten steel, magnet steel and cast cobalt all present an effective particle capturing efficiency, which shows a fast initial increase and a slow saturation with the increasing magnetic field, a quasilinear increase with the increasing particle size, and a nonlinear decrease with the increasing blood velocity.     

Built-in electric field effect on cyclotron mass of magnetopolarons in a wurtzite In_xGa_（1-x）N/GaN quantum well

The cyclotron mass of magnetopolarons in wurtzite In x Ga 1 x N/GaN quantum well is studied in the presence of an external magnetic field by using the Larsen perturbation method.The effects of the built-in electric field and different phonon modes including interface,confined and half-space phonon modes are considered in our calculation.The results for a zinc-blende quantum well are also given for comparison.It is found that the main contribution to the transition energy comes from half-space and interface phonon modes when the well width is very small while the confined modes play a more important role in a wider well due to the location of the electron wave function.As the well width increases,the cyclotron mass of magnetopolarons first increases to a maximum and then decreases either with or without the built-in electric field in the wurtzite structure and the built-in electric field slightly reduces the cyclotron mass.The variation of cyclotron mass in a zinc-blende structure is similar to that in a wurtzite structure.With the increase of external magnetic field,the cyclotron mass of polarons almost linearly increases.The cyclotron frequency of magnetopolarons is also discussed.