离体射流对S809翼型气动性能的影响

在Re=5×10⁶的条件下,分别在S809翼型前缘点附近不同位置处设置离体射流装置,改变射流动量的大小和射流口宽度,探究其对S809翼型气动性能的影响。并通过流场分析,研究这种流动控制手段有效的物理机理。结果表明:在射流装置位置和射流口宽度固定时,射流动量的大小对控制效果影响显著;在S809翼型表面附近设置微小离体射流装置后,即使关闭射流(射流动量为零时),也具有一定的流动分离控制效果;当射流动量逐渐增大时,射流能明显的减小流动分离泡的大小,降低阻力系数,同时可以有效提升升力系数,使得翼型的气动性能得到进一步显著提升。值得指出的是,射流口宽度与射流装置的位置对流动控制效果也具有一定的影响。     

Role of pressure gradient on intrinsic toroidal rotation in tokamak plasmas

The toroidal plasma rotation generated by the external momentum input and by the plasma itself (intrinsic rotation) has been separated through a novel momentum transport analysis in the JT-60U tokamak device. The toroidal rotation, which is not determined by the momentum transport coefficients and the external momentum input, has been observed. It is found that this intrinsic rotation is locally determined by the local pressure gradient and increases with increasing pressure gradient. This trend is almost the same for various plasmas: low and high confinement mode, co and counterrotating plasmas.     

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对等离子体气动激励控制边界层进行了数值仿真。将等离子体气动激励对边界层的作用建模成动量和热量。通过由基于表面放电的二维流体体力模型得到的等离子体气动激励的体力分布函数,得到向边界层注入的动量和热量分布,将动量和热量以源项的形式引入N-S方程求解。研究了等离子体气动激励的强度、激励电极的数目、来流速度的大小以及热量项的大小对等离子体气动激励作用效果的影响,仿真结果与实验一致。     

Time-dependent plasma transport simulation for the study of edge impurity radiation dynamics with magnetic island in large helical device

The dynamics of impurity radiation distribution during detachment transition with edge magnetic island induced by the application of resonant magnetic perturbation (RMP) is studied numerically by solving time-dependent plasma fluid equations together with impurity and neutral transports in a 2D grid system. Computations provide the appearance of a macroscopic structure in the heat transfer along the island separatrix and outside the island. The resultant parallel temperature gradient generates the plasma flow and the density gradient according to the parallel momentum balance. The resulting plasma flow effectively transports impurity towards the X-point region. As a result, the impurity radiation is more intense near the X-point than in the vicinity of the O-point. This leads to the predominant cooling of the region around the X-point. These results are in agreement with experimental observation with RMP application in the large helical device (LHD). The time scale of the thermal condensation instability is found to be of the order of 10 ms.     

Flow control with plasma-based actuator in different velocity regimes: Momentum and heat transfer effects

In this study, control of the airflow by the direct current (DC) electrical discharge with bare electrodes has been investigated in different velocity regimes. The discharge characteristics of the plasma model are obtained numerically. An induced electrohydrodynamic (EHD) force on neutral flow was characterized based on momentum transfer from charged particles. The change in the incident flow parameters was studied by applying Navier–Stokes (N-S) equations, considering source terms arising from a weakly ionized plasma. The effect of the discharge on the low- and high-speed flow was simulated in this study. It was concluded that the changes of the velocity profile, airflow pressure, and oblique shock wave could be attributed to the EHD force from a nonthermal plasma to the incoming airflow. It was seen that the incident airflow is accelerated also by the induced EHD force. Our results show that the most important mechanism in the plasma-based flow control is the momentum transfer from the electrical discharge to the incident flow and that the gas heating has no significant role.     

托卡马克边缘湍流中带状流的负粘滞阻尼

基于Hasegawa-Wakatani湍流模型,数值模拟了托卡马克边缘等离子体中漂移波湍流和相关的反常粒子输运。从等离子体动量守恒方程出发导出了不采用常规的布辛涅斯克近似的带状流方程,论证了大振幅密度扰动和湍性粒子流对激发带状流的贡献可等效地对应于低阶负粘滞阻尼效果。数值模拟表明,大振幅密度扰动的非线性大大增强了带状流饱和振幅,从而有效抑制了湍性粒子输运。研究结果阐明了托卡马克边缘等离子体大振幅密度扰动的非线性对驱动等离子体旋转、动量输运和带状流的重要性。     

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基于Hasegawa-Wakatani湍流模型,数值模拟了托卡马克边缘等离子体中漂移波湍流和相关的反常粒子输运.从等离子体动量守恒方程出发导出了不采用常规的布辛涅斯克近似的带状流方程,论证了大振幅密度扰动和湍性粒子流对激发带状流的贡献可等效地对应于低阶负粘滞阻尼效果.数值模拟表明,大振幅密度扰动的非线性大大增强了带状流饱和振幅,从而有效抑制了湍性粒子输运.研究结果阐明了托卡马克边缘等离子体大振幅密度扰动的非线性对驱动等离子体旋转、动量输运和带状流的重要性.     

Elliptic flow of thermal photons in relativistic nuclear collisions

We predict the transverse momentum (p(T)) dependence of elliptic flow of thermal photons for Au + Au collisions at the BNL Relativistic Heavy Ion Collider. We model the system hydrodynamically, with a thermalized quark-gluon plasma at early times followed by hadronization and decoupling. Photons are emitted throughout the expansion history. Contrary to hadron elliptic flow, which increases monotonically with p(T), the elliptic flow nu2(p(T)) of thermal photons is predicted to first rise and then fall again. Photon elliptic flow at high p(T) reflects the quark momentum anisotropy at early times when it is small, while at low p(T) it mirrors the large pion momentum anisotropy during the late hadronic emission stage. An interesting structure is predicted at intermediate p(T) approximately 0.4 GeV/c, where photon elliptic flow reflects the momenta and the (compared to pions) reduced nu2 of heavy vector mesons in the late hadronic phase.     

Jets in tokamaks: A theoretical study

A new class of bifurcation of the momentum balance equations for a tokamak plasma is presented. The solution exhibits a monopolar localized jet of ExB flow. The jet is generated by the reduction of turbulent viscosity due to ExB velocity shear. Strong jets of localized plasma flow have been observed in tokamaks as a precursor to the development of a transport barrier region with reduced turbulent transport. The jet solution is shown to fit well with the experimental observations.     

Fuel consumption for interplanetary missions of solar sailing

The orbits of solar sails can be changed by adjusting the sail’s attitude through external control torques.The resulting momentum will be changed,either provided by a typical attitude control subsystem or by a propellantless device.This paper investigates the extra momentum input and fuel consumption for a typical attitude control subsystem.The minimum-time transfer trajectories are designed for two rendezvous missions using both indirect and direct methods,generating continuous and discrete attitude histories,respectively.The results show that the momentum variation is almost wholly due to the solar radiation pressure.The feasibility of using tip-mounted microthrusters for attitude control is evaluated.The results show that less than0.1 kg of propellant are required for an interplanetary transfer mission when pulsed plasma thrusters with a specific impulse of700 s and a thrust of 150 mN are mounted at the tip of a 20 m square solar sail.The fuel consumptions of two transfer missions indicate that a tip-mounted pulsed plasma thruster is a viable technique for the attitude control of a solar sail.     

Neoclassical toroidal plasma viscosity torque in collisionless regimes in tokamaks

Bumpiness in a magnetic field enhances the magnitude of the plasma viscosity and increases the rate of the plasma flow damping. A general solution of the neoclassical toroidal plasma viscosity (NTV) torque induced by nonaxisymmetric magnetic perturbation (NAMP) in the collisionless regimes in tokamaks is obtained in this Letter. The plasma angular momentum can be strongly changed, when there is a small deviation of the toroidal symmetry caused by a NAMP of the order of 0.1% of the toroidal field strength.     

Self-regulation of E x B flow shear via plasma turbulence

The momentum balance has been applied to the ExB flow in the edge region of a reversed field pinch (RFP) configuration. All terms, including those involving fluctuations, have been measured in stationary condition in the edge region of the Extrap-T2R RFP experiment. It is found that the component of the Reynolds stress driven by electrostatic fluctuations is the term playing the major role in driving the shear of the ExB flow to a value marginal for turbulent suppression, so that the results are in favor of a turbulence self-regulating mechanism underlying the momentum balance at the edge. Balancing the sheared flow driving and damping terms, the plasma viscosity is found anomalous and consistent with the diffusivity due to electrostatic turbulence.     

垂直冷弹发射装置装药燃烧数值分析

针对燃气活塞弹射装置,采用加质源项法,通过UDF(用户自定义函数)编译,向高压室注入火药燃气的质量、动量、能量,实现了复杂燃烧化学反应的数值模拟,得到了高压室压力和速度分布及变化规律,分析了压力和速度对弹射装置的影响。计算结果表明,装药燃烧数值模拟与理论计算基本吻合,能够较好地仿真弹射装置高压室燃气流场的特性,为弹射装置进一步优化设计和装药设计提供理论参考。     

Interaction of a Plasma Beam with a Transverse Magnetic Barrier

The interaction of an energetic He plasma beam with a quasi step-like transverse magnetic barrier is reported. When the rate of flow of momentum in the incident beam is less than the pressure of the magnetic field, a collisionless electrostatic shock is observed to form in front of the barrier as a result of the drastic compression of the plasma. The initially cold plasma is substantially thermalized by the shock and the electron density is increased by a factor of four. In the opposite limit the plasma penetrates the barrier in a flute-like manner.     

Theory for toroidal momentum pinch and flow reversal in tokamaks

It is demonstrated that besides the well-known toroidal momentum diffusion flux there is a pinchlike flux in the fluctuation-induced toroidal stress. A toroidal flow profile is determined up to a constant, e.g., the value of the flow at the magnetic axis, by balancing these two fluxes. The remaining residual toroidal stress determines the value of the flow at the axis. It is illustrated that the direction of the flow at the axis can change after plasma confinement is improved. The theory is applied to explain the toroidal flow reversal in tokamak experiments.     

Turbulent equipartition and homogenization of plasma angular momentum

A physical model of turbulent equipartition (TEP) of plasma angular momentum is developed. We show that using a simple, model insensitive ansatz of conservation of total angular momentum, a TEP pinch of angular momentum can be obtained. We note that this term corresponds to a part of the pinch velocity previously calculated using quasilinear gyrokinetic theory. We observe that the nondiffusive TEP flux is inward, and therefore may explain the peakedness of the rotation profiles observed in certain experiments. Similar expressions for linear toroidal momentum and flow are computed and it is noted that there is an additional effect due the radial profile of moment of inertia density.     

Heat and momentum transport to particulates injected intolow-pressure (~80 mbar) nonequilibrium plasmas

An analytical model for plasma flow around a spherical particle has been developed using a two-temperature chemical nonequilibrium approach that includes rarefaction and particle-charging effects. The contribution of each component of the plasma to the heat and momentum transfer to injected particulates is studied by simulating the plasma flow around a sphere for conditions typical of thermal spray processes at pressures from 80 mbar to 1 bar. A parametric study of the 80-mbar case is also presented for free-stream velocities in the 0-3000 m/s range and free-stream temperatures in the 8000-12000 K range for both ionization equilibrium and nonequilibrium. The results demonstrate that there are departures from kinetic and ionization equilibrium in the plasma around a particle, and that heat transfer to a particle can be enhanced by the increased ion flux to the particle surface when the surrounding plasma is in ionization nonequilibrium     

等离子体激励器的静特性与高速特性仿真研究

A parametric study of high-frequency plasma jet actuator was carried out, using the experiment- tally measured energy distribution law of arc discharge as an ideal heat source. The influence of the exit angle of the actuator on the flow field was explored. The jet flow field characteristics of the spark discharge actuator under supersonic flow (Ma0=2.0) were investigated. The results show that the energy density of heat flux increases and the jet front and forward shock wave moves faster with the decrease of discharge region, and the smaller the exit angle of the jet is, the stronger the momentum injection ability of the actuator along the flow direction is. The rule still applies under high-speed air flow conditions. Compared to the static condition, the momentum injection capability of the jet is stronger and the influence domain is larger under supersonic flow conditions.     

Penalization modeling of a limiter in the Tokamak edge plasma

An original penalization method is applied to model the interaction of magnetically confined plasma with limiter in the frame of a minimal transport model for ionic density and parallel momentum. The limiter is considered as a pure particle sink for the plasma and consequently the density and the momentum are enforced to be zero inside. Comparisons of the numerical results with one-dimensional analytical solutions show a very good agreement. In particular, the penalization scheme followed in this paper tends to ensure an almost sonic plasma condition at the plasma-obstacle interface, Bohm-like criterion, with relatively weak dependence on the target Mach number profile within the obstacle. The new system being solved in a periodic obstacle free domain, an efficient pseudo-spectral algorithm based on a Fast Fourier transform is also proposed, and associated with an exponential filtering of the unphysical oscillations due to Gibbs phenomenon. Finally, the efficiency of the method is illustrated by investigating the flow spreading from the plasma core to the Scrape-Off Layer at the wall in a two-dimensional system with one, then two neighboring limiters.     

Stirring unmagnetized plasma

A new concept for spinning unmagnetized plasma is demonstrated experimentally. Plasma is confined by an axisymmetric multicusp magnetic field and biased cathodes are used to drive currents and impart a torque in the magnetized edge. Measurements show that flow viscously couples momentum from the magnetized edge (where the plasma viscosity is small) into the unmagnetized core (where the viscosity is large) and that the core rotates as a solid body. To be effective, collisional viscosity must overcome the ion-neutral drag due to charge-exchange collisions.