Efficient Low Dissipative High Order Schemes for Multiscale MHD Flows, II: Minimization of ∇·B Numerical Error

An adaptive numerical dissipation control in a class of high order filter methods for compressible MHD equations is systematically discussed. The filter schemes consist of a divergence-free preserving high order spatial base scheme with a filter approach which can be divergence-free preserving depending on the type of filter operator being used, the method of applying the filter step, and the type of flow problem to be considered. Some of these filter variants provide a natural and efficient way for the minimization of the divergence of the magnetic field (∇·B) numerical error in the sense that commonly used divergence cleaning is not required. Numerical experiments presented emphasize the performance of the ∇·B numerical error. Many levels of grid refinement and detailed comparison of the filter methods with several commonly used compressible MHD shock-capturing schemes will be illustratedA condensed version appears in the Proceedings of the International Conference on High Performance Scientific Computing, March 10-14, 2003, Hanoi, Vietnam. This is a revised version of a longer internal report, Feb. 19, 2004. The longer internal report was published as a RIACS Technical Report TR03.10, July 2003, NASA Ames Research Center     

Influence of surface oxidation on electric potential measurements in MHD liquid metal flows

Experimental investigations for magnetohydrodynamic flows in rectangular ducts are performed using GaInSn as model fluid. Measurements of electric potential on channel walls and inside the flow show reproducible discrepancies compared to analytical results. These discrepancies can be ascribed to the formation of oxide layers causing a contact resistance between the electrically conducting duct walls and the liquid metal. An exact analytical solution for pressure drop, velocity and potential distributions has been derived taking into account the presence of a contact resistance. Analytical results for velocity and potential profiles and for pressure drop are discussed for different values of contact resistance and strength of the applied magnetic field. A comparison of measured potential with data from the analytical solution allows estimating the order of magnitude of the contact resistance in the present experiments.     

空气开关电弧的数学模型及其特性的研究综述

从空气开关电弧的平衡态化学组成、基本属性、建模与仿真、实验测试等角度,综述了国内外空气开关电弧的数学模型及其特性的研究进展,介绍了空气开关电弧物性参数的计算方法,列举了多个有代表性的电弧数学模型以及各种电弧特性的测试手段及其应用,最后指出了空气开关电弧研究所面临的几个问题。     

Characteristics of plasma produced by MHD technology and its application to propulsion systems

This paper analyzes plasma characteristics for the newly proposed concept of a closed-loop MHD power generation combined cycle system, which is used as a pulse-driven MHD accelerator to accelerate plasma to high velocity, with a nuclear plant. In this paper, since the final goal is for the space propulsion system applications, the performance of a MHD acceleration system is also analyzed by the Q1D analysis program. Results reveal that the radial velocity with the MHD effect is accelerated rapidly at the channel exit, with a calculated maximum velocity of about 4700 m/s. Consequently, specific impulse approximately 480 s and thrust of about 6550 N are estimated. The static gas temperature is evaluated at less than 600 K, while the value of about 1800 K is calculated for the stagnation gas temperature in the MHD channel.     

Anomalous surface morphology of iron generated after anodic dissolution under magnetic fields

The effects of applied magnetic fields on the anodic dissolution of iron in a sulfuric acid solution were studied by potentiodynamic polarization measurements and electrode morphology observations. Uneven anodic dissolution occurs in the presence of magnetic field and the extent of the electrode surface inhomogeneity increases with magnetic flux density. Severely local dissolution at two edge areas of the iron electrode in the presence of magnetic fields is caused by the inhomogeneous distribution of the magnetic flux density at the ferromagnetic iron electrode and the resultant enhancement of the mass transport rate of interfacial film at local areas.     

MHD free convective flow through a porous medium in a rotating fluid

In the paper, the velocity and temperature distributions of an electrically conducting liquid flowing past an infinite vertical porous plate through a porous medium in a rotating frame of reference are analysed for the case when a stron magnetic field is imposed in a direction perpendicular to the free stream and at an angle α to the vertical direction. The. influences of various parameters on the velocity field are discussed.     

Progress in lattice Boltzmann methods for magnetohydrodynamic flows relevant to fusion applications

In this paper, an approach to simulating magnetohydrodynamic (MHD) flows based on the lattice Boltzmann method (LBM) is presented. The dynamics of the flow are simulated using a so-called multiple relaxation time (MRT) lattice Boltzmann equation (LBE), in which a source term is included for the Lorentz force. The evolution of the magnetic induction is represented by introducing a vector distribution function and then solving an appropriate lattice kinetic equation for this function. The solution of both distribution functions are obtained through a simple, explicit, and computationally efficient stream-and-collide procedure. The use of the MRT collision term enhances the numerical stability over that of a single relaxation time approach. To apply the methodology to solving practical problems, a new extrapolation-based method for imposing magnetic boundary conditions is introduced and a technique for simulating steady-state flows with low magnetic Prandtl number is developed. In order to resolve thin layers near the walls arising in the presence of high magnetic fields, a non-uniform gridding strategy is introduced through an interpolated-streaming step applied to both distribution functions. These advances are particularly important for applications in fusion engineering where liquid metal flows with low magnetic Prandtl numbers and high Hartmann numbers are introduced. A number of MHD benchmark problems, under various physical and geometrical conditions are presented, including 3-D MHD lid driven cavity flow, high Hartmann number flows and turbulent MHD flows, with good agreement with prior data. Due to the local nature of the method, the LBM also demonstrated excellent performance on parallel machines, with almost linear scaling up to 128 processors for a MHD flow problem.     

An electrical network for the numerical solution of transient mhd couette flow of a dusty fluid: Effects of variable properties and hall current

The Network Simulation Method (NSM) has been used to study the variations with velocity of suction, hall effect, Reynolds and Hartmann number, particle concentration and Eckert number on the unsteady MHD Couette Flow and heat transfer of a dusty and electrically conducting fluid between parallel plates in the presence of an external uniform magnetic field and uniform suction and injection. The solutions are obtained with the network model proposed and the electric circuit simulation program PSpice. The fluid is acted upon by a constant pressure gradient and an external uniform magnetic field is applied perpendicular to the plates. Due to the presence of uniform suction and injection, the Hall Effect is not dismissed. The NSM is applied to solve the steady-state and transient problems of flow and heat transfer for both the fluid and dust particles. This method requires only discretization of the spatial co-ordinates, while time remains a real continuous variable. Velocity and temperature are studied for different values of the viscosity and magnetic field parameters and for different particle concentrations and upper wall velocities.     

Experimental and numerical studies of pressure drop in PbLi flows in a circular duct under non-uniform transverse magnetic field

Experiments and three-dimensional (3D) numerical simulations are performed to investigate the magnetohydrodynamic (MHD) characteristics of liquid metal (LM) flows of molten lead-lithium (PbLi) eutectic alloy in an electrically conducting circular duct subjected to a transverse non-uniform (fringing) magnetic field. An indirect measurement approach for differential pressure in high temperature LM PbLi is first developed, and then detailed data on pressure drop in this PbLi MHD flow are measured. The obtained experimental results for the pressure distribution are in good agreement with numerical simulations. Using the numerical simulation results, the 3D effects caused by fringing magnetic field on the LM flow are illustrated via distributions for the axial pressure gradients and transverse pressure differences. It has been verified that a simple approach for estimation of pressure drop in LM MHD flow in a fringing magnetic field proposed by Miyazaki et al. [22] i.e., a simple integral of pressure gradient along the fringing field zone using a quasi-fully-developed flow assumption, is also applicable to the conditions of the present experiment providing the magnetic interaction parameter is large enough. Furthermore, for two different sections of the LM flow at the entry to and at the exit from the magnet, it is found that the pressure distributions in the duct cross sections in these two regions are different.