#### Sample records for ideal mhd flows

1. An Energy Principle for Ideal MHD Equilibria with Flows

SciTech Connect

Yao Zhou and Hong Qin

2013-03-11

In the standard ideal MHD energy principle for equilibria with no flows, the stability criterion, which is the defi niteness of the perturbed potential energy, is usually constructed from the linearized equation of motion. Equivalently while more straightforwardly, it can also be obtained from the second variation of the Hamiltonian calculated with proper constraints. For equilibria with flows, a stability criterion was proposed from the linearized equation of motion, but not explained as an energy principle1. In this paper, the second variation of the Hamiltonian is found to provide a stability criterion equivalent to, while more straightforward than, what was constructed from the linearized equation of motion. To calculate the variations of the Hamiltonian, a complete set of constraints on the dynamics of the perturbations is derived from the Euler-Poincare structure of the ideal MHD. In addition, a previous calculation of the second variation of the Hamiltonian was claimed to give a different stability criterion2, and in this paper we argue such a claim is incorrect.

2. Flow stabilization of the ideal MHD resistive wall mode^1

Smith, S. P.; Jardin, S. C.; Freidberg, J. P.; Guazzotto, L.

2009-05-01

We demonstrate for the first time in a numerical calculation that for a typical circular cylindrical equilibrium, the ideal MHD resistive wall mode (RWM) can be completely stabilized by bulk equilibrium plasma flow, V, for a window of wall locations without introducing additional dissipation into the system. The stabilization is due to a resonance between the RWM and the Doppler shifted ideal MHD sound continuum. Our numerical approach introduces^2 u=φξ+ iV .∇ξ and the perturbed wall current^3 as variables, such that the eigenvalue, φ, only appears linearly in the linearized stability equations, which allows for the use of standard eigenvalue solvers. The wall current is related to the plasma displacement at the boundary by a Green's function. With the introduction of the resistive wall, we find that it is essential that the finite element grid be highly localized around the resonance radius where the parallel displacement, ξ, becomes singular. We present numerical convergence studies demonstrating that this singular behavior can be approached in a limiting sense. We also report on progress toward extending this calculation to an axisymmetric toroidal geometry. ^1Work supported by a DOE FES fellowship through ORISE and ORAU. ^2L.Guazzotto, J.P Freidberg, and R. Betti, Phys.Plasmas 15, 072503 (2008). ^3S.P. Smith and S. C. Jardin, Phys. Plasmas 15, 080701 (2008).

3. Three-dimensional nonlinear ideal MHD equilibria with field-aligned incompressible and compressible flows

SciTech Connect

Moawad, S. M. Ibrahim, D. A.

2016-08-15

The equilibrium properties of three-dimensional ideal magnetohydrodynamics (MHD) are investigated. Incompressible and compressible flows are considered. The governing equations are taken in a steady state such that the magnetic field is parallel to the plasma flow. Equations of stationary equilibrium for both of incompressible and compressible MHD flows are derived and described in a mathematical mode. For incompressible MHD flows, Alfvénic and non-Alfvénic flows with constant and variable magnetofluid density are investigated. For Alfvénic incompressible flows, the general three-dimensional solutions are determined with the aid of two potential functions of the velocity field. For non-Alfvénic incompressible flows, the stationary equilibrium equations are reduced to two differential constraints on the potential functions, flow velocity, magnetofluid density, and the static pressure. Some examples which may be of some relevance to axisymmetric confinement systems are presented. For compressible MHD flows, equations of the stationary equilibrium are derived with the aid of a single potential function of the velocity field. The existence of three-dimensional solutions for these MHD flows is investigated. Several classes of three-dimensional exact solutions for several cases of nonlinear equilibrium equations are presented.

4. Smoothed MHD equations for numerical simulations of ideal quasi-neutral gas dynamic flows

Popov, Mikhail V.; Elizarova, Tatiana G.

2015-11-01

We introduce a mathematical model and related numerical method for numerical modeling of ideal magnetohydrodynamic (MHD) gas flows as an extension of previously known quasi-gasdynamic (QGD) equations. This approach is based on smoothing, or averaging of the original MHD equation system over a small time interval that leads to a new equation system, named quasi-MHD, or QMHD system. The QMHD equations are closely related to the original MHD system except for additional strongly non-linear dissipative τ-terms with a small parameter τ as a factor. The τ-terms depend on the solution itself and decrease in regions with the small space gradients of the solution. In this sense the QMHD system could be regarded as an approach with adaptive artificial dissipation. The QMHD is a generalization of regularized (or quasi-) gas dynamic equation system suggested in last three decades. In the QMHD numerical method the evolution of all physical variables is presented in a non-split divergence form. Divergence-free evolution of the magnetic field provides by using a constrained transport method based on Faraday's law of induction. Accuracy and convergence of the QMHD method is verified on a wide set of standard MHD tests including the 3D Orszag-Tang vortex flow.

5. Divergence Free High Order Filter Methods for Multiscale Non-ideal MHD Flows

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sjoegreen, Bjoern

2003-01-01

Low-dissipative high order filter finite difference methods for long time wave propagation of shock/turbulence/combustion compressible viscous MHD flows has been constructed. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field (Delta . B) numerical error in the sense that no standard divergence cleaning is required. For certain 2-D MHD test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved.

6. The Statistical Mechanics of Ideal MHD Turbulence

NASA Technical Reports Server (NTRS)

Shebalin, John V.

2003-01-01

Turbulence is a universal, nonlinear phenomenon found in all energetic fluid and plasma motion. In particular. understanding magneto hydrodynamic (MHD) turbulence and incorporating its effects in the computation and prediction of the flow of ionized gases in space, for example, are great challenges that must be met if such computations and predictions are to be meaningful. Although a general solution to the "problem of turbulence" does not exist in closed form, numerical integrations allow us to explore the phase space of solutions for both ideal and dissipative flows. For homogeneous, incompressible turbulence, Fourier methods are appropriate, and phase space is defined by the Fourier coefficients of the physical fields. In the case of ideal MHD flows, a fairly robust statistical mechanics has been developed, in which the symmetry and ergodic properties of phase space is understood. A discussion of these properties will illuminate our principal discovery: Coherent structure and randomness co-exist in ideal MHD turbulence. For dissipative flows, as opposed to ideal flows, progress beyond the dimensional analysis of Kolmogorov has been difficult. Here, some possible future directions that draw on the ideal results will also be discussed. Our conclusion will be that while ideal turbulence is now well understood, real turbulence still presents great challenges.

7. Quaternions and ideal flows

Eshraghi, H.; Gibbon, J. D.

2008-08-01

After a review of some of the recent works by Holm and Gibbon on quaternions and their application to Lagrangian flows, particularly the incompressible Euler equations and the equations of ideal MHD, this paper investigates the compressible and relativistic Euler equations using these methods.

8. MHD Flow Control

DTIC Science & Technology

2006-09-01

tested is a model to simulate the hypersonic intake configuration. The corresponding photo is presented in Fig. 49. 75 i I I I I I I Figure 49. The third... hypersonic air stream within the propulsion system inlet. The extra benefit of this proposed Project is the experimental facility to be used for experimental...plasma aerodynamics, and in particular, MHD control of external and internal flows. The MHD control of the external hypersonic flow over the simplest

9. Statistical Theory of the Ideal MHD Geodynamo

NASA Technical Reports Server (NTRS)

Shebalin, J. V.

2012-01-01

A statistical theory of geodynamo action is developed, using a mathematical model of the geodynamo as a rotating outer core containing an ideal (i.e., no dissipation), incompressible, turbulent, convecting magnetofluid. On the concentric inner and outer spherical bounding surfaces the normal components of the velocity, magnetic field, vorticity and electric current are zero, as is the temperature fluctuation. This allows the use of a set of Galerkin expansion functions that are common to both velocity and magnetic field, as well as vorticity, current and the temperature fluctuation. The resulting dynamical system, based on the Boussinesq form of the magnetohydrodynamic (MHD) equations, represents MHD turbulence in a spherical domain. These basic equations (minus the temperature equation) and boundary conditions have been used previously in numerical simulations of forced, decaying MHD turbulence inside a sphere [1,2]. Here, the ideal case is studied through statistical analysis and leads to a prediction that an ideal coherent structure will be found in the form of a large-scale quasistationary magnetic field that results from broken ergodicity, an effect that has been previously studied both analytically and numerically for homogeneous MHD turbulence [3,4]. The axial dipole component becomes prominent when there is a relatively large magnetic helicity (proportional to the global correlation of magnetic vector potential and magnetic field) and a stationary, nonzero cross helicity (proportional to the global correlation of velocity and magnetic field). The expected angle of the dipole moment vector with respect to the rotation axis is found to decrease to a minimum as the average cross helicity increases for a fixed value of magnetic helicity and then to increase again when average cross helicity approaches its maximum possible value. Only a relatively small value of cross helicity is needed to produce a dipole moment vector that is aligned at approx.10deg with the

10. Eigenanalysis of Ideal Hall MHD Turbulence

Fu, T.; Shebalin, J. V.

2011-12-01

Ideal, incompressible, homogeneous, Hall magnetohydrodynamic (HMHD) turbulence may be investigated through a Fourier spectral method. In three-dimensional periodic geometry, the independent Fourier coefficients represent a canonical ensemble described by a Gaussian probability density. The canonical ensemble is based on the conservation of three invariants: total energy, generalized helicity, and magnetic helicity. Generalized helicity in HMHD takes the place of cross helicity in MHD. The invariants determine the modal probability density giving the spectral structure and equilibrium statistics of ideal HMHD, which are compared to known MHD results. New results in absolute equilibrium ensemble theory are derived using a novel approach that involves finding the eigenvalues of a Hermitian covariance matrix for each modal probability density. The associated eigenvectors transform the original phase space variables into eigenvariables through a special unitary transformation. These are the normal modes which facilitate the analysis of ideal HMHD non-linear dynamics. The eigenanalysis predicts that the low wavenumber modes with very small eigenvalues may have mean values that are large compared to their standard deviations, contrary to the ideal ensemble prediction of zero mean values. (Expectation values may also be relatively large at the highest wave numbers, but the addition of even small levels of dissipation removes any relevance this may have for real-world turbulence.) This behavior is non-ergodic over very long times for a numerical simulation and is termed 'broken ergodicity'. For fixed values of the ideal invariants, the effect is seen to be enhanced with increased numerical grid size. Broken ergodicity at low wave number modes gives rise to large-scale, quasi-stationary, coherent structure. Physically, this corresponds to plasma relaxation to force-free states. For real HMHD turbulence with dissipation, broken ergodicity and coherent structure are still

11. On controlling nonlinear dissipation in high order filter methods for ideal and non-ideal MHD

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sjogreen, B.

2004-01-01

The newly developed adaptive numerical dissipation control in spatially high order filter schemes for the compressible Euler and Navier-Stokes equations has been recently extended to the ideal and non-ideal magnetohydrodynamics (MHD) equations. These filter schemes are applicable to complex unsteady MHD high-speed shock/shear/turbulence problems. They also provide a natural and efficient way for the minimization of Div(B) numerical error. The adaptive numerical dissipation mechanism consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and leave the rest of the region free from numerical dissipation contamination. The numerical dissipation considered consists of high order linear dissipation for the suppression of high frequency oscillation and the nonlinear dissipative portion of high-resolution shock-capturing methods for discontinuity capturing. The applicable nonlinear dissipative portion of high-resolution shock-capturing methods is very general. The objective of this paper is to investigate the performance of three commonly used types of nonlinear numerical dissipation for both the ideal and non-ideal MHD.

12. Activation of MHD reconnection on ideal timescales

Landi, S.; Papini, E.; Del Zanna, L.; Tenerani, A.; Pucci, F.

2017-01-01

Magnetic reconnection in laboratory, space and astrophysical plasmas is often invoked to explain explosive energy release and particle acceleration. However, the timescales involved in classical models within the macroscopic MHD regime are far too slow to match the observations. Here we revisit the tearing instability by performing visco-resistive two-dimensional numerical simulations of the evolution of thin current sheets, for a variety of initial configurations and of values of the Lunquist number S, up to 107. Results confirm that when the critical aspect ratio of S 1/3 is reached in the reconnecting current sheets, the instability proceeds on ideal (Alfvénic) macroscopic timescales, as required to explain observations. Moreover, the same scaling is seen to apply also to the local, secondary reconnection events triggered during the nonlinear phase of the tearing instability, thus accelerating the cascading process to increasingly smaller spatial and temporal scales. The process appears to be robust, as the predicted scaling is measured both in inviscid simulations and when using a Prandtl number P  =  1 in the viscous regime.

13. Nonlinear filtering and limiting in high order methods for ideal and non-ideal MHD

NASA Technical Reports Server (NTRS)

Yee,H. C.; Sjogreen, B.

2004-01-01

The various filtering mechanisms and base scheme options of the newly developed adaptive numerical dissipation control in spatially high order filter schemes for the ideal and non-ideal magnetohydrodynamics (MHD) equations are investigated. These filter schemes are applicable to complex unsteady MHD high-speed shock/shear/turbulence problems. They also provide a natural and efficient way for the minimization of Div(B) numerical error. The type of spatial base scheme to be used in conjunction with our filter idea is very general. For example, spectral, compact and non-compact spatially central finite difference schemes are possible candidates. The adaptive numerical dissipation mechanism consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and to leave the rest of the region free from numerical dissipation contamination. The numerical dissipation considered consists of high order linear dissipation for the suppression of high frequency oscillation and the nonlinear dissipative portion of high-resolution shock-capturing methods for discontinuity capturing. The applicable nonlinear dissipative portion of high-resolution shock-capturing methods is also very general. The objective of this paper is to investigate the performance of using compact and non-compact central base schemes in conjunction with three commonly used types of nonlinear numerical dissipation for both the ideal and non-ideal MHD. This extended abstract shows the performance of three nonlinear filters in conjunction with a sixth-order non-compact spatial central base scheme. In the final paper, the high order compact spatial central base scheme will be illustrated and compared with the non-compact base scheme. The reason for the investigation of the high order compact spatial central base scheme over the non-compact base scheme is to evaluate if additional accuracy can be gained in regions of

14. Nonlinear filtering and limiting in high order methods for ideal and non-ideal MHD

NASA Technical Reports Server (NTRS)

Yee,H. C.; Sjogreen, B.

2004-01-01

The various filtering mechanisms and base scheme options of the newly developed adaptive numerical dissipation control in spatially high order filter schemes for the ideal and non-ideal magnetohydrodynamics (MHD) equations are investigated. These filter schemes are applicable to complex unsteady MHD high-speed shock/shear/turbulence problems. They also provide a natural and efficient way for the minimization of Div(B) numerical error. The type of spatial base scheme to be used in conjunction with our filter idea is very general. For example, spectral, compact and non-compact spatially central finite difference schemes are possible candidates. The adaptive numerical dissipation mechanism consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and to leave the rest of the region free from numerical dissipation contamination. The numerical dissipation considered consists of high order linear dissipation for the suppression of high frequency oscillation and the nonlinear dissipative portion of high-resolution shock-capturing methods for discontinuity capturing. The applicable nonlinear dissipative portion of high-resolution shock-capturing methods is also very general. The objective of this paper is to investigate the performance of using compact and non-compact central base schemes in conjunction with three commonly used types of nonlinear numerical dissipation for both the ideal and non-ideal MHD. This extended abstract shows the performance of three nonlinear filters in conjunction with a sixth-order non-compact spatial central base scheme. In the final paper, the high order compact spatial central base scheme will be illustrated and compared with the non-compact base scheme. The reason for the investigation of the high order compact spatial central base scheme over the non-compact base scheme is to evaluate if additional accuracy can be gained in regions of

15. Perturbed Stability Analysis of External Ideal MHD Modes

Comer, K. J.; Callen, J. D.; Hegna, C. C.; Garstka, G. D.; Turnbull, A. D.; Garofalo, A. M.; Cowley, S. C.

2002-11-01

Traditionally, numerical parameter scans are performed to study the effects of equilibrium shaping and profiles on long wavelength ideal MHD instabilities. Previously, we introduced a new perturbative technique to more efficiently explore these dependencies: changes in delta-W due to small equilibrium variations are found using a perturbation of the energy principle rather than with an eigenvalue-solver instability code. With this approach, the stability properties of similar equilibria can be efficiently explored without generating complete numerical results for every set of parameters (which is time-intensive for accurate representations of several configurations). Here, we apply this approach to toroidal geometry using GATO (an ideal MHD stability code) and experimental equilibria. In particular, we explore ideal MHD stability of external kink modes in the spherical tokamak Pegasus and resistive wall modes in DIII-D.

16. Laboratory astrophysics and non-ideal equations of state: the next challenges for astrophysical MHD simulations

Carver, Robert L.; Cunningham, Andrew J.; Frank, Adam; Hartigan, Patrick; Coker, Robert; Wilde, B. H.; Foster, John; Rosen, Paula

2010-12-01

Laboratory astrophysics holds great promise not only as a highly effective validation tool for astrophysical magneto-hydrodynamics (MHD) codes but it also presents a unique challenge for these codes. The high-density plasmas found in these experiments are not well modeled by the ideal equations of state (EOS) found in most astrophysical simulation codes. To solve this problem, we replaced the ideal EOS scheme in an existing MHD code, AstroBEAR, with a non-ideal EOS method and validated our implementation with van der Waals shock tube tests. The improved code is also able to model flows that contain more than one material, as required in laboratory experiments. Simulations of jet experiments performed at the OMEGA Laser reproduce the morphology of the jet much better than when the code used a single material and an ideal EOS.

17. High Order Filter Methods for the Non-ideal Compressible MHD Equations

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sjoegreen, Bjoern

2003-01-01

The generalization of a class of low-dissipative high order filter finite difference methods for long time wave propagation of shock/turbulence/combustion compressible viscous gas dynamic flows to compressible MHD equations for structured curvilinear grids has been achieved. The new scheme is shown to provide a natural and efficient way for the minimization of the divergence of the magnetic field numerical error. Standard divergence cleaning is not required by the present filter approach. For certain non-ideal MHD test cases, divergence free preservation of the magnetic fields has been achieved.

18. Splitting based finite volume schemes for ideal MHD equations

Fuchs, F. G.; Mishra, S.; Risebro, N. H.

2009-02-01

We design finite volume schemes for the equations of ideal magnetohydrodynamics (MHD) and based on splitting these equations into a fluid part and a magnetic induction part. The fluid part leads to an extended Euler system with magnetic forces as source terms. This set of equations are approximated by suitable two- and three-wave HLL solvers. The magnetic part is modeled by the magnetic induction equations which are approximated using stable upwind schemes devised in a recent paper [F. Fuchs, K.H. Karlsen, S. Mishra, N.H. Risebro, Stable upwind schemes for the Magnetic Induction equation. Math. Model. Num. Anal., Available on conservation laws preprint server, submitted for publication, URL: ]. These two sets of schemes can be combined either component by component, or by using an operator splitting procedure to obtain a finite volume scheme for the MHD equations. The resulting schemes are simple to design and implement. These schemes are compared with existing HLL type and Roe type schemes for MHD equations in a series of numerical experiments. These tests reveal that the proposed schemes are robust and have a greater numerical resolution than HLL type solvers, particularly in several space dimensions. In fact, the numerical resolution is comparable to that of the Roe scheme on most test problems with the computational cost being at the level of a HLL type solver. Furthermore, the schemes are remarkably stable even at very fine mesh resolutions and handle the divergence constraint efficiently with low divergence errors.

19. Adaptive Numerical Dissipation Control in High Order Schemes for Multi-D Non-Ideal MHD

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sjoegreen, B.

2005-01-01

The required type and amount of numerical dissipation/filter to accurately resolve all relevant multiscales of complex MHD unsteady high-speed shock/shear/turbulence/combustion problems are not only physical problem dependent, but also vary from one flow region to another. In addition, proper and efficient control of the divergence of the magnetic field (Div(B)) numerical error for high order shock-capturing methods poses extra requirements for the considered type of CPU intensive computations. The goal is to extend our adaptive numerical dissipation control in high order filter schemes and our new divergence-free methods for ideal MHD to non-ideal MHD that include viscosity and resistivity. The key idea consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and leave the rest of the region free from numerical dissipation contamination. These scheme-independent detectors are capable of distinguishing shocks/shears, flame sheets, turbulent fluctuations and spurious high-frequency oscillations. The detection algorithm is based on an artificial compression method (ACM) (for shocks/shears), and redundant multiresolution wavelets (WAV) (for the above types of flow feature). These filters also provide a natural and efficient way for the minimization of Div(B) numerical error.

20. An Unsplit, Cell-Centered Godunov Method for Ideal MHD

SciTech Connect

Fisher, R; Crockett, R; Colella, P; Klein, R; McKee, C

2003-10-16

We present a second-order Godunov algorithm for multidimensional, ideal MHD. Our algorithm is based on the unsplit formulation of Colella, with all of the primary dependent variables centered at the same location. To properly represent the divergence-free condition of the magnetic fields, we apply a discrete projection to the intermediate values of the field at cell faces, and apply a filter to the primary dependent variables at the end of each time step. We apply the method to a suite of linear and nonlinear tests to ascertain accuracy and stability of the scheme under a variety of conditions. The test suite includes rotated planar linear waves, MHD shock tube problems, and low-beta flux tubes. For all of these cases, we observe that the algorithm is second-order accurate for smooth solutions, converges to the correct weak solution for problems involving shocks, and exhibits no evidence of instability or loss of accuracy due to the possible presence of non-solenoidal fields.

1. An unsplit, cell-centered Godunov method for ideal MHD

SciTech Connect

Crockett, Robert K.; Colella, Phillip; Fisher, Robert T.; Klein, Richard I.; McKee, Christopher F.

2003-08-29

We present a second-order Godunov algorithm for multidimensional, ideal MHD. Our algorithm is based on the unsplit formulation of Colella (J. Comput. Phys. vol. 87, 1990), with all of the primary dependent variables centered at the same location. To properly represent the divergence-free condition of the magnetic fields, we apply a discrete projection to the intermediate values of the field at cell faces, and apply a filter to the primary dependent variables at the end of each time step. We test the method against a suite of linear and nonlinear tests to ascertain accuracy and stability of the scheme under a variety of conditions. The test suite includes rotated planar linear waves, MHD shock tube problems, low-beta flux tubes, and a magnetized rotor problem. For all of these cases, we observe that the algorithm is second-order accurate for smooth solutions, converges to the correct weak solution for problems involving shocks, and exhibits no evidence of instability or loss of accuracy due to the possible presence of non-solenoidal fields.

2. Stability of internal transport barriers to ideal MHD ballooning modes.

PubMed

Connor, J W; Hastie, R J

2004-02-20

Internal transport barriers (ITB) in tokamaks can form near a minimum in the q profile, q(min), where magnetic shear is weak. We have analyzed their stability to short wavelength (n>1, where n is the toroidal mode number) ideal MHD ballooning modes, by considering the s-alpha model equilibrium. We show that the ballooning transformation fails in regions of low shear but that one can then adopt a complementary approach based on the recurrence relation describing the toroidal coupling of radially localized modes on adjacent rational surfaces. Inclusion of the stabilizing effects of favorable average curvature or finite-n using this technique leads to stable high-pressure ITB configurations. The theory also shows the advantages of operating with low-order rational values of q(min).

3. Stability of ideal MHD configurations. I. Realizing the generality of the G operator

Keppens, R.; Demaerel, T.

2016-12-01

A field theoretical approach, applied to the time-reversible system described by the ideal magnetohydrodynamic (MHD) equations, exposes the full generality of MHD spectral theory. MHD spectral theory, which classified waves and instabilities of static or stationary, usually axisymmetric or translationally symmetric configurations, actually governs the stability of flowing, (self-)gravitating, single fluid descriptions of nonlinear, time-dependent idealized plasmas, and this at any time during their nonlinear evolution. At the core of this theory is a self-adjoint operator G , discovered by Frieman and Rotenberg [Rev. Mod. Phys. 32, 898 (1960)] in its application to stationary (i.e., time-independent) plasma states. This Frieman-Rotenberg operator dictates the acceleration identified by a Lagrangian displacement field ξ , which connects two ideal MHD states in four-dimensional space-time that share initial conditions for density, entropy, and magnetic field. The governing equation reads /d 2 ξ d t 2 = G [ ξ ] , as first noted by Cotsaftis and Newcomb [Nucl. Fusion, Suppl. Part 2, 447 and 451 (1962)]. The time derivatives at left are to be taken in the Lagrangian way, i.e., moving with the flow v. Physically realizable displacements must have finite energy, corresponding to being square integrable in the Hilbert space of displacements equipped with an inner product rule, for which the G operator is self-adjoint. The acceleration in the left-hand side features the Doppler-Coriolis operator v . ∇ , which is known to become an antisymmetric operator when restricting attention to stationary equilibria. Here, we present all derivations needed to get to these insights and connect results throughout the literature. A first illustration elucidates what can happen when self-gravity is incorporated and presents aspects that have been overlooked even in simple uniform media. Ideal MHD flows, as well as Euler flows, have essentially 6 + 1 wave types, where the 6 wave modes

4. Evolution of generalized two-dimensional magnetotail equilibria in ideal and resistive MHD

Merkin, V. G.; Sitnov, M. I.; Lyon, J. G.

2015-03-01

We present results of two-dimensional (2-D) magnetohydrodynamic (MHD) simulations of the terrestrial magnetotail. A regional adaptation of the Lyon-Fedder-Mobarry global MHD model is used. As initial conditions, we employ a class of asymptotic magnetotail equilibria with and without an accumulation of magnetic flux at the tailward end (a Bz hump). The former have been recently shown by full particle simulations to be unstable to a kinetic mode with formal properties of ion tearing. Thus, our goal here is to investigate the evolution of the same equilibria in the MHD approximation and assist in the physical interpretation of the kinetic simulations. This is additionally motivated by the energy principle considerations which suggest that if the system is unstable kinetically, it may also be unstable ideally. To seek dynamical MHD regimes similar to those observed in kinetic simulations, we implement two sets of boundary conditions (velocity balanced, VB, and momentum balanced, MB), one allowing plasma flows through the boundaries and the other inhibiting such flows. The use of more reflecting MB boundary conditions results in suppression of any significant dynamics, and we see no substantial changes beyond initial equilibrium relaxation. On the other hand, VB boundary conditions allow a more efficient relaxation of initial equilibrium and absorb subsequently generated plasma flows. With these boundary conditions we find the equilibrium without a flux accumulation (i.e., with constant magnetic field component normal to the current sheet) to develop an apparently resistive mode accompanied by tailward plasma flows. At the same time, the equilibria with a Bz hump of sufficiently large amplitude develop a different, ideal, mode characterized by spontaneous generation of earthward plasma flows and an exponential growth of the corresponding electric field. This growth is qualitatively similar to the corresponding fully kinetic simulations although no explosive growth of

5. Adaptive Numerical Dissipative Control in High Order Schemes for Multi-D Non-Ideal MHD

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sjoegreen, B.

2004-01-01

The goal is to extend our adaptive numerical dissipation control in high order filter schemes and our new divergence-free methods for ideal MHD to non-ideal MHD that include viscosity and resistivity. The key idea consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and leave the rest of the region free of numerical dissipation contamination. These scheme-independent detectors are capable of distinguishing shocks/shears, flame sheets, turbulent fluctuations and spurious high-frequency oscillations. The detection algorithm is based on an artificial compression method (ACM) (for shocks/shears), and redundant multi-resolution wavelets (WAV) (for the above types of flow feature). These filter approaches also provide a natural and efficient way for the minimization of Div(B) numerical error. The filter scheme consists of spatially sixth order or higher non-dissipative spatial difference operators as the base scheme for the inviscid flux derivatives. If necessary, a small amount of high order linear dissipation is used to remove spurious high frequency oscillations. For example, an eighth-order centered linear dissipation (AD8) might be included in conjunction with a spatially sixth-order base scheme. The inviscid difference operator is applied twice for the viscous flux derivatives. After the completion of a full time step of the base scheme step, the solution is adaptively filtered by the product of a 'flow detector' and the 'nonlinear dissipative portion' of a high-resolution shock-capturing scheme. In addition, the scheme independent wavelet flow detector can be used in conjunction with spatially compact, spectral or spectral element type of base schemes. The ACM and wavelet filter schemes using the dissipative portion of a second-order shock-capturing scheme with sixth-order spatial central base scheme for both the inviscid and viscous MHD flux

6. Transport in EHD flows distinct from HD and MHD flows

Kikuchi, H.

2003-04-01

EHD flows are typically composed of a charged (positively or negatively) fluid, though not all, that may be an electron fluid, an ion fluid or a dust fluid for a single fluid, or their mixtures for multi-component fluids in contrast to nonionized HD or plasma MHD flows. Electric or ponderomotive forces are newly exerted on EHD flows in addition to mechanical, viscous, and magnetic forces on HD and MHD flows. Accordingly, EHD flows hold electric pressure in addition to gas or plasma and magnetic pressure in HD and MHD flows. EHD flows hold space charge and displacement currents and are regarded as a dielectric or semiconducting fluid in contrast to nonionized HD flows or conducting plasma MHD flows. EHD flows are governed by a new equation of electric field transport in addition to fluid vortex transport (HD) and magnetic field transport (MHD), though their equations have to be supplemented by additional terms involving effects of space charge and electric fields, and are characterized by a new electric Reynolds number, R_E with spatial and temporal factors in addition to the fluid Reynolds number, R (spatial) and the magnetic Reynolds number, R_M (spatial) for HD and MHD flows. When R_E >> 1, however, the equation of electric field transport for EHD flows is reduced to the so-called Kelvin-Helmholtz equation just like equations of fluid vortex and magnetic field transport for R >> 1 for HD flows and R_M >> 1 for MHD flows. Accordingly, the EHD relation, H^* = H + v × .D ≈ 0 holds, analogous to the so-called MHD relation, E^* = E + v ×.B ≈ 0. In EHD flows, electric cusp or electrically neutral point can be formed as a bifurcation point of equipotential line or surface, analogous to a stagnation point in HD flows and magnetic cusp or separatrix in MHD flows. Accordingly, electric reconnection or space-charge related electric field line merging with particle acceleration or ionization due to critical velocity effects is possible in EHD flows, analogous to fluid

7. Free-boundary ideal MHD stability of W7-X divertor equilibria

Nührenberg, C.

2016-07-01

Plasma configurations describing the stellarator experiment Wendelstein 7-X (W7-X) are computationally established taking into account the geometry of the test-divertor unit and the high-heat-flux divertor which will be installed in the vacuum chamber of the device (Gasparotto et al 2014 Fusion Eng. Des. 89 2121). These plasma equilibria are computationally studied for their global ideal magnetohydrodynamic (MHD) stability properties. Results from the ideal MHD stability code cas3d (Nührenberg 1996 Phys. Plasmas 3 2401), stability limits, spatial structures and growth rates are presented for free-boundary perturbations. The work focusses on the exploration of MHD unstable regions of the W7-X configuration space, thereby providing information for future experiments in W7-X aiming at an assessment of the role of ideal MHD in stellarator confinement.

8. Instability of periodic MHD shear flows

SciTech Connect

Zaqarashvili, T.V.; Oliver, R.; Ballester, J.L.; Belvedere, G.

2004-11-12

The stability of periodic MHD shear flows generated by an external transversal periodic force in magnetized plasma is studied. It is shown that the temporal behaviour of magnetosonic wave spatial Fourier harmonics in such flows is governed by Mathieu equation. Consequently the harmonics with the half frequency of the shear flows grow exponentially in time. Therefore the periodic shear motions are unstable to the perturbations of compressible magnetosonic waves. The motions represent the kinetic part of the transversal oscillation in magnetized plasma. Therefore due to the instability of periodic shear motions, the transversal oscillations may quickly be damped, so transferring their energy to compressible magnetosonic perturbations.

9. Variational Integration for Ideal MHD with Built-in Advection Equations

SciTech Connect

Zhou, Yao; Qin, Hong; Burby, J. W.; Bhattacharjee, A.

2014-08-05

Newcomb's Lagrangian for ideal MHD in Lagrangian labeling is discretized using discrete exterior calculus. Variational integrators for ideal MHD are derived thereafter. Besides being symplectic and momentum preserving, the schemes inherit built-in advection equations from Newcomb's formulation, and therefore avoid solving them and the accompanying error and dissipation. We implement the method in 2D and show that numerical reconnection does not take place when singular current sheets are present. We then apply it to studying the dynamics of the ideal coalescence instability with multiple islands. The relaxed equilibrium state with embedded current sheets is obtained numerically.

10. Ideal MHD Stability Prediction and Required Power for EAST Advanced Scenario

Chen, Junjie; Li, Guoqiang; Qian, Jinping; Liu, Zixi

2012-11-01

The Experimental Advanced Superconducting Tokamak (EAST) is the first fully superconducting tokamak with a D-shaped cross-sectional plasma presently in operation. The ideal magnetohydrodynamic (MHD) stability and required power for the EAST advanced tokamak (AT) scenario with negative central shear and double transport barrier (DTB) are investigated. With the equilibrium code TOQ and stability code GATO, the ideal MHD stability is analyzed. It is shown that a moderate ratio of edge transport barriers' (ETB) height to internal transport barriers' (ITBs) height is beneficial to ideal MHD stability. The normalized beta βN limit is about 2.20 (without wall) and 3.70 (with ideal wall). With the scaling law of energy confinement time, the required heating power for EAST AT scenario is calculated. The total heating power Pt increases as the toroidal magnetic field BT or the normalized beta βN is increased.

11. Electric vortex in MHD flow

SciTech Connect

Garcia, M.

1995-05-01

An electric vortex is the circulation of electron space charge about a magnetic field line that is transported by ion momentum. In cold, or low {beta} flow the vortex diameter is the minimum length scale of charge neutrality. The distinctive feature of the vortex is its radial electric field which manifests the interplay of electrostatics, magnetism, and motion.

12. Linear stability of ideal MHD configurations. II. Results for stationary equilibrium configurations

Demaerel, T.; Keppens, R.

2016-12-01

In this paper, we continue exploring the consequences of the general equation of motion (EOM) governing all Lagrangian perturbations ξ about a time-dependent, ideal magnetohydrodynamic (MHD) configuration, which includes self-gravity, external gravity, pressure gradients, compressibility, inertial effects, and anisotropic Lorentz force. We here address the specific case of MHD stability for 3D stationary equilibria, where the perturbed EOM features a symmetric operator F and an antisymmetric Doppler-Coriolis operator v . ∇ . For this case, we state and prove the general properties for the solutions ξ of the governing dynamical system. For axisymmetric perturbations about axisymmetric equilibria with purely toroidal, or purely poloidal magnetic fields, specific stability theorems can be formulated. We derive a useful integral expression for the quadratic quantity given by the inner product ⟨ ξ , F [ ξ ] ⟩ . For deriving stability statements on MHD states where self-gravity is involved as well, we provide an upper bound on the perturbed self-gravitational energy associated with the displacement ξ . The resulting expression elucidates the role of potentially stabilizing versus destabilizing contributions and shows the role of gravity, entropy gradients, velocity shear, currents, Lorentz forces, inertia, and pressure gradients in offering many routes to unstable behavior in flowing gases and plasmas. These have historically mostly been studied for static v = 0 configurations, looking at stability of exactly force-balanced states, or by assuming stationarity similar to our approach here (i.e., ∂ t ≡ 0 for the state we perturb), but typically in combination with some reduced dimensionality on the configuration of interest (translational or axisymmetry). We show that in these limits, we find and generalize expressions well-known from, e.g., the study of ideal MHD stability of tokamak plasmas or from Schwarzschild's criteria controlling convection in

13. The ideal tearing mode: theory and resistive MHD simulations

Del Zanna, L.; Landi, S.; Papini, E.; Pucci, F.; Velli, M.

2016-05-01

Classical MHD reconnection theories, both the stationary Sweet-Parker model and the tearing instability, are known to provide rates which are too slow to explain the observations. However, a recent analysis has shown that there exists a critical threshold on current sheet's thickness, namely a/L ∼ S -1/3, beyond which the tearing modes evolve on fast macroscopic Alfvénic timescales, provided the Lunquist number S is high enough, as invariably found in solar and astrophysical plasmas. Therefore, the classical Sweet-Parker scenario, for which the diffusive region scales as a/L ∼ S -1/2 and thus can be up to ∼ 100 times thinner than the critical value, is likely to be never realized in nature, as the current sheet itself disrupts in the elongation process. We present here two-dimensional, compressible, resistive MHD simulations, with S ranging from 105 to 107, that fully confirm the linear analysis. Moreover, we show that a secondary plasmoid instability always occurs when the same critical scaling is reached on the local, smaller scale, leading to a cascading explosive process, reminiscent of the flaring activity.

14. Magnetogasdynamic Phenomena in Pulsed MHD Flows.

DTIC Science & Technology

1979-10-01

r D-A079 919 STD RESEARCH CORP ARCADIA CALIF F/a 20/9 VA NETOGASDYNAMIC PHENODE’A IN PULSED MHD FLOWS.(U) OCT 79 D A OLIVER, T F SWEAN. D M MARKHAN...N00014-77-C-0574 UNCLASSIFIED STD -UP-002-77-1 NL ".’ rnunnnnunnnnSllflflflflflflf lllll /////IlEEEEE//!i *fl///////lfl l I/fflIEN I2) STD -UP-002-77-1...DEMETRIADES OCTOBER 1979 --A li JTlrSUMMARY REPORT FOR THE PERIOD 1 OCTOBER 1978 THROUGH 30 SEPTEMBER 1979 STD RESEARCH CORPORATION ARCADIA, CA S1006 PREPARED

15. Implicit Predictor-Corrector finite difference scheme for the ideal MHD simulations

Tsai, T.; Yu, H.; Lai, S.

2012-12-01

A innovative simulation code for ideal magnetohydrodynamics (MHD) is developed. We present a multiple-dimensional MHD code based on high-order implicit predictor-corrector finite difference scheme (high-order IPCFD scheme). High-order IPCFD scheme adopts high-order predictor-corrector scheme for the time integration and high-order central difference method as the spatial derivative solver. We use Elimination-of-the-Runoff-Errors (ERE) technology to avoid the numerical oscillations and numerical instability in the simulation results. In one-dimensional MHD problem, our simulation results show good agreement with the Brio & Wu MHD shock tube problem. The divergent B constraint remains fully satisfied, that is the divergent B equals to zero throughout the simulation. When solving the two-dimensional (2D) linear wave in MHD plasma, we clearly obtain the group-velocity Friedrichs diagrams of the MHD waves. Here we demonstrate 2D simulation results of rotor problem, Orszag-Tang vortex system, vortex type K-H instability, and kink type K-H instability by using our IPCFD MHD code and discuss the advantage of our simulation code.

16. Ideal MHD stability of double transport barrier plasmas in DIII-D

Li, G. Q.; Wang, S. J.; Lao, L. L.; Turnbull, A. D.; Chu, M. S.; Brennan, D. P.; Groebner, R. J.; Zhao, L.

2008-01-01

The ideal MHD stability for double transport barrier (DTB or DB) plasmas with varying edge and internal barrier width and height was investigated, using the ideal MHD stability code GATO. A moderate ratio of edge transport barriers (ETB) height to internal transport barriers (ITBs) height is found to be beneficial to MHD stability and the βN is limited by global low n instabilities. For moderate ITB width DB plasmas, if the ETB is weak, the stability is limited by n = 1 (n is the toroidal mode number) global mode; whereas if the ETB is strong it is limited by intermediate-n edge peeling-ballooning modes. Broadening the ITB can improve stability if the ITB half width wi lsim 0.3. For very broad ITB width plasmas the stability is limited by stability to a low n (n > 1) global mode.

17. An FCT finite element scheme for ideal MHD equations in 1D and 2D

Basting, Melanie; Kuzmin, Dmitri

2017-06-01

This paper presents an implicit finite element (FE) scheme for solving the equations of ideal magnetohydrodynamics in 1D and 2D. The continuous Galerkin approximation is constrained using a flux-corrected transport (FCT) algorithm. The underlying low-order scheme is constructed using a Rusanov-type artificial viscosity operator based on scalar dissipation proportional to the fast wave speed. The accuracy of the low-order solution can be improved using a shock detector which makes it possible to prelimit the added viscosity in a monotonicity-preserving iterative manner. At the FCT correction step, the changes of conserved quantities are limited in a way which guarantees positivity preservation for the density and thermal pressure. Divergence-free magnetic fields are extracted using projections of the FCT predictor into staggered finite element spaces forming exact sequences. In the 2D case, the magnetic field is projected into the space of Raviart-Thomas finite elements. Numerical studies for standard test problems are performed to verify the ability of the proposed algorithms to enforce relevant constraints in applications to ideal MHD flows.

18. Drag reduction in turbulent MHD pipe flows

NASA Technical Reports Server (NTRS)

Orlandi, P.

1996-01-01

This is a preliminary study devoted to verifying whether or not direct simulations of turbulent Magneto-Hydro-Dynamic (MHD) flows in liquid metals reproduce experimental observations of drag reduction. Two different cases have been simulated by a finite difference scheme which is second order accurate in space and time. In the first case, an external azimuthal magnetic field is imposed. In this case, the magnetic field acts on the mean axial velocity and complete laminarization of the flow at N(sub a) = 30 has been achieved. In the second case, an axial magnetic field is imposed which affects only fluctuating velocities, and thus the action is less efficient. This second case is more practical, but comparison between numerical and experimental results is only qualitative.

19. Physics of the Solar Chromosphere: Beyond the Ideal MHD Description

Leake, James

2015-08-01

The solar chromosphere is the dynamic, physically complex, layer that lies between the visible solar surface and the magnetically dominated corona. Despite being a moderator of the amount of mass, magnetic field, and energy, that is transferred into the solar corona and the heliosphere and beyond, there are still important open questions regarding the chromosphere. Recent advancements in both observation and theoretical descriptions of the chromosphere have created new ideas about how the chromosphere controls the transfer of the above quantities from the Sun's interior into the heliosphere. Open questions still remain, such as, how is the chromosphere heated, and how do chromospheric events such as spicules, jets, reconnection, and wave propagation and dissipation contribute to the mass and energy balance in the solar atmosphere. Central to these questions are extensions to the standard magneto-hydro-dynamic (MHD) model of the Sun, such as non-local-thermodynamic-equilibrium radiation, and multi-fluid physics. In this talk, we summarize the importance of these extensions and look for the necessary developments to answer open questions about the chromosphere.

20. An unsplit Godunov method for ideal MHD via constrained transport in three dimensions

Gardiner, Thomas A.; Stone, James M.

2008-04-01

We present a single step, second-order accurate Godunov scheme for ideal MHD which is an extension of the method described in [T.A. Gardiner, J.M. Stone, An unsplit godunov method for ideal MHD via constrained transport, J. Comput. Phys. 205 (2005) 509] to three dimensions. This algorithm combines the corner transport upwind (CTU) method of Colella for multidimensional integration, and the constrained transport (CT) algorithm for preserving the divergence-free constraint on the magnetic field. We describe the calculation of the PPM interface states for 3D ideal MHD which must include multidimensional “MHD source terms” and naturally respect the balance implicit in these terms by the ∇·B=0 condition. We compare two different forms for the CTU integration algorithm which require either 6- or 12-solutions of the Riemann problem per cell per time-step, and present a detailed description of the 6-solve algorithm. Finally, we present solutions for test problems to demonstrate the accuracy and robustness of the algorithm.

1. A Simple Ideal MHD Model of Vertical Disruption Events in Tokamaks

Fitzpatrick, Richard

2008-11-01

A simple model of axisymmetric vertical disruption events (VDEs) in tokamaks is presented in which the halo current force exerted on the vacuum vessel is calculated directly from linear, marginally stable, ideal-magnetohydrodynamical (MHD) stability analysis. The basic premise of the model is that the halo current force modifies pressure balance at the edge of the plasma, and therefore also modifies ideal-MHD plasma stability. In order to prevent the ideal vertical instability, responsible for the VDE, from growing on the very short Alfv'en time- scale, the halo current force must adjust itself such that the instability is rendered marginally stable. The model predicts halo currents which are similar in magnitude to those observed experimentally. An approximate non-axisymmetric version of the model is developed in order to calculate the toroidal peaking factor of the halo current force.

2. Newtonian CAFE: a new ideal MHD code to study the solar atmosphere

González, J. J.; Guzmán, F.

2015-12-01

In this work we present a new independent code designed to solve the equations of classical ideal magnetohydrodynamics (MHD) in three dimensions, submitted to a constant gravitational field. The purpose of the code centers on the analysis of solar phenomena within the photosphere-corona region. In special the code is capable to simulate the propagation of impulsively generated linear and non-linear MHD waves in the non-isothermal solar atmosphere. We present 1D and 2D standard tests to demonstrate the quality of the numerical results obtained with our code. As 3D tests we present the propagation of MHD-gravity waves and vortices in the solar atmosphere. The code is based on high-resolution shock-capturing methods, uses the HLLE flux formula combined with Minmod, MC and WENO5 reconstructors. The divergence free magnetic field constraint is controlled using the Flux Constrained Transport method.

3. NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION

SciTech Connect

Li Zhiyun; Krasnopolsky, Ruben; Shang Hsien

2011-09-10

Dense, star-forming cores of molecular clouds are observed to be significantly magnetized. A realistic magnetic field of moderate strength has been shown to suppress, through catastrophic magnetic braking, the formation of a rotationally supported disk (RSD) during the protostellar accretion phase of low-mass star formation in the ideal MHD limit. We address, through two-dimensional (axisymmetric) simulations, the question of whether realistic levels of non-ideal effects, computed with a simplified chemical network including dust grains, can weaken the magnetic braking enough to enable an RSD to form. We find that ambipolar diffusion (AD), the dominant non-ideal MHD effect over most of the density range relevant to disk formation, does not enable disk formation, at least in two dimensions. The reason is that AD allows the magnetic flux that would be dragged into the central stellar object in the ideal MHD limit to pile up instead in a small circumstellar region, where the magnetic field strength (and thus the braking efficiency) is greatly enhanced. We also find that, on the scale of tens of AU or more, a realistic level of Ohmic dissipation does not weaken the magnetic braking enough for an RSD to form, either by itself or in combination with AD. The Hall effect, the least explored of these three non-ideal MHD effects, can spin up the material close to the central object to a significant, supersonic rotation speed, even when the core is initially non-rotating, although the spun-up material remains too sub-Keplerian to form an RSD. The problem of catastrophic magnetic braking that prevents disk formation in dense cores magnetized to realistic levels remains unresolved. Possible resolutions of this problem are discussed.

4. On the Motion of Free Interface in Ideal Incompressible MHD

Hao, Chengchun

2017-05-01

For the free boundary problem of the plasma-vacuum interface to 3D ideal incompressible magnetohydrodynamics, the a priori estimates of smooth solutions are proved in Sobolev norms by adopting a geometrical point of view and some quantities such as the second fundamental form and the velocity of the free interface are estimated. In the vacuum region, the magnetic fields are described by the div-curl system of pre-Maxwell dynamics, while at the interface the total pressure is continuous and the magnetic fields are tangential to the interface, but we do not need any restrictions on the size of the magnetic fields on the free interface. We introduce the "fictitious particle" endowed with a fictitious velocity field in vacuum to reformulate the problem to a fixed boundary problem under the Lagrangian coordinates. The L 2-norms of any order covariant derivatives of the magnetic fields both in vacuum and on the boundaries are bounded in terms of initial data and the second fundamental forms of the free interface and the rigid wall. The estimates of the curl of the electric fields in vacuum are also obtained, which are also indispensable in elliptic estimates.

5. Magnetorotational Instability of Dissipative MHD Flows

SciTech Connect

HERRON, ISOM H

2010-07-10

Executive summary Two important general problems of interest in plasma physics that may be addressed successfully by Magnetohydrodynamics (MHD) are: (1) Find magnetic field configurations capable of confining a plasma in equilibrium. (2) Study the stability properties of each such an equilibrium. It is often found that the length scale of many instabilities and waves that are able to grow or propagate in a system, are comparable with plasma size, such as in magnetically confined thermonuclear plasmas or in astrophysical accretion disks. Thus MHD is able to provide a good description of such large-scale disturbances. The Magnetorotational instability (MRI) is one particular instance of a potential instability. The project involved theoretical work on fundamental aspects of plasma physics. Researchers at the Princeton Plasma Physics Laboratory (PPPL) began to perform a series of liquid metal Couette flow experiments between rotating cylinders. Their purpose was to produce MRI, which they had predicted theoretically 2002, but was only observed in the laboratory since this project began. The personnel on the project consisted of three persons: (1) The PI, who was partially supported on the budget during each of four summers 2005-2008. (2) Two graduate research assistants, who worked consecutively on the project throughout the years 2005-2009. As a result, the first student, Fritzner Soliman, obtained an M.S. degree in 2006; the second student, Pablo Suarez obtained the Ph.D. degree in 2009. The work was in collaboration with scientists in Princeton, periodic trips were made by the PI as part of the project. There were 4 peer-reviewed publications and one book produced.

6. Roe Matrices for Ideal MHD and Systematic Construction of Roe Matrices for Systems of Conservation Laws

Cargo, Patricia; Gallice, Gérard

1997-09-01

In this paper, the construction of a Roe's scheme for the conservative system of ideal magnetohydrodynamics (MHD) is presented. As this method relies on the computation of a Roe matrix, the problem is to find a matrixA(Ul,Ur) which satisfies the following properties. It is required to be consistent with the jacobian of the fluxF, to have real eigenvalues, a complete set of eigenvectors and to satisfy the relation: ΔF=A(Ul,Ur) ΔU, whereUlandUrare two admissible states and ΔUtheir difference. For the ideal MHD system, using eulerian coordinates, a Roe matrix is obtained without any hypothesis on the specific heat ratio. Especially, its construction relies on an original expression of the magnetic pressure jump. Moreover, a Roe matrix is computed for lagrangian ideal MHD, by extending the results of Munz who obtained such a matrix for the system of lagrangian gas dynamics. So this second matrix involves arithmetic averages unlike the eulerian one, which contains classical Roe averages like in eulerian gas dynamics. In this paper, a systematic construction of lagrangian Roe matrices in terms of eulerian Roe matrices for a general system of conservation laws is also presented. This result, applied to the above eulerian and lagrangian matrices for ideal MHD, gives two new matrices for this system. In the same way, by applying this construction to the gas dynamics equations new Roe matrices are also obtained. All these matrices allow the construction of Roe type schemes. Some numerical examples on the shock tube problem show the applicability of this method.

7. Nonlinear tearing mode study using the almost ideal magnetohydrodynamics (MHD) constraint

SciTech Connect

Ren, C.; Callen, J.D.; Jensen, T.H.

1998-12-31

The tearing mode is an important resistive magnetohydrodynamics (MHD) mode. It perturbs the initial equilibrium magnetic flux surfaces through magnetic field line reconnection to form new flux surfaces with magnetic islands. In the study of the tearing mode, usually the initial equilibria are one dimensional with two ignorable coordinates and the perturbed equilibria are two dimensional with one ignorable coordinate. The tearing mode can be linearly unstable and its growth saturates at a fine amplitude. The neoclassical tearing mode theory shows that the mode can be nonlinearly driven by the bootstrap current even when it is linearly stable to the classical tearing mode. It is important to study the nonlinear behavior of the tearing mode. As an intrinsically nonlinear approach, the use of the almost ideal MHD constraint is suited to study the nonlinear properties of the tearing mode. In this paper, as a validation of the method, the authors study two characteristics of the tearing mode using the almost ideal MHD constraint: (1) the linear stability condition for the initial one dimensional equilibrium; and (2) the final saturation level for the unstable case. In this work, they only consider the simplest case where no gradient of pressure or current density exists at the mode resonant surface.

8. Newtonian CAFE: a new ideal MHD code to study the solar atmosphere

González-Avilés, J. J.; Cruz-Osorio, A.; Lora-Clavijo, F. D.; Guzmán, F. S.

2015-12-01

We present a new code designed to solve the equations of classical ideal magnetohydrodynamics (MHD) in three dimensions, submitted to a constant gravitational field. The purpose of the code centres on the analysis of solar phenomena within the photosphere-corona region. We present 1D and 2D standard tests to demonstrate the quality of the numerical results obtained with our code. As solar tests we present the transverse oscillations of Alfvénic pulses in coronal loops using a 2.5D model, and as 3D tests we present the propagation of impulsively generated MHD-gravity waves and vortices in the solar atmosphere. The code is based on high-resolution shock-capturing methods, uses the Harten-Lax-van Leer-Einfeldt (HLLE) flux formula combined with Minmod, MC, and WENO5 reconstructors. The divergence free magnetic field constraint is controlled using the Flux Constrained Transport method.

9. Ideal and resistive MHD stability of one-dimensional tokamak equilibria

SciTech Connect

Chance, M.S.; Furth, H.P.; Glasser, A.H.; Selberg, H.

1981-07-01

The MHD equilibrium and stability of a vertically elongated tokamak configuration are analyzed in the one-dimensional limit corresponding to infinite elongation. Stability against all ideal MHD modes can be obtained for beta-values arbitrarily close to unity. In the finite-resistivity stability analysis, axisymmetric (m = 0) tearing modes, centered on the null trace of the poloidal field, can be stabilized by a loosely fitting conducting shell. The presence of the toroidal field component, however, introduces the possibility of nonsymmetric tearing modes (m not equal to 0), centered away from the null trace. These modes can be stabilized only by a more tightly-fitting shell, plus reliance on finite-pressure effects on the small-major-radius side of the plasma profile. Under these conditions, stable configurations with peak beta values approaching unity are readily found.

10. Flux and Field Line Conservation in 3-D Non-Ideal MHD Flows: Remarks About Criteria for 3-D Reconnection Without Magnetic Neutral Points and Their Application to the Heliospheric Interface

Nickeler, D. H.; Fahr, H.-J.

2006-05-01

In this paper, we address the issue of finding velocity fields which conserve magnetic flux or at least magnetic fieldline connectivity. We start from the basic principles of flux and line conservation and present and discuss the criterion, given by Newcomb (1958), Stern (1966), and Vasyliunas (1972). In addition, we find a new formulation of the line-conserving velocity field by solving the system of partial differential equations which corresponds to Newcomb's criterion for line conservation. This velocity field is given by a correlation between the non-idealness, described by a generalized form of the Ohm's law and a general transporting velocity, which is fieldline conserving. Our considerations give additional insights into the discussion on violations of the frozen-in field concept which started recently with the papers by Baranov and Fahr (2003a,b). These authors analyzed a generalized form of Ohm's law, which is valid for the heliosphere and claimed that the transport velocity for the magnetic flux may be different from the plasma velocity. We can show that the non-idealness given in the paper by Baranov and Fahr could not change the magnetic topology and can therefore not be responsible for magnetic reconnection. But we found that it is in general not clear if the flux-conserving velocity field is identical to the plasma flow or to any species velocity field.

11. Remarks on Singularities, Dimension and Energy Dissipation for Ideal Hydrodynamics and MHD

Caflisch, Russel E.; Klapper, Isaac; Steele, Gregory

For weak solutions of the incompressible Euler equations, there is energy conservation if the velocity is in the Besov space B3s with s greater than 1/3. B3s consists of functions that are Lip(s) (i.e., Hölder continuous with exponent s) measured in the Lp norm. Here this result is applied to a velocity field that is Lip(α0) except on a set of co-dimension on which it is Lip($agr;1), with uniformity that will be made precise below. We show that the Frisch-Parisi multifractal formalism is valid (at least in one direction) for such a function, and that there is energy conservation if . Analogous conservation results are derived for the equations of incompressible ideal MHD (i.e., zero viscosity and resistivity) for both energy and helicity . In addition, a necessary condition is derived for singularity development in ideal MHD generalizing the Beale-Kato-Majda condition for ideal hydrodynamics. 12. New method for computing ideal MHD normal modes in axisymmetric toroidal geometry SciTech Connect Wysocki, F.; Grimm, R.C. 1984-11-01 Analytic elimination of the two magnetic surface components of the displacement vector permits the normal mode ideal MHD equations to be reduced to a scalar form. A Galerkin procedure, similar to that used in the PEST codes, is implemented to determine the normal modes computationally. The method retains the efficient stability capabilities of the PEST 2 energy principle code, while allowing computation of the normal mode frequencies and eigenfunctions, if desired. The procedure is illustrated by comparison with earlier various of PEST and by application to tilting modes in spheromaks, and to stable discrete Alfven waves in tokamak geometry. 13. A Complete 2D Stability Analysis of Fast MHD Shocks in an Ideal Gas NASA Astrophysics Data System (ADS) Trakhinin, Yuri An algorithm of numerical testing of the uniform Lopatinski condition for linearized stability problems for 1-shocks is suggested. The algorithm is used for finding the domains of uniform stability, neutral stability, and instability of planar fast MHD shocks. A complete stability analysis of fast MHD shock waves is first carried out in two space dimensions for the case of an ideal gas. Main results are given for the adiabatic constant γ=5/3 (mono-atomic gas), that is most natural for the MHD model. The cases γ=7/5 (two-atomic gas) and γ>5/3 are briefly discussed. Not only the domains of instability and linear (in the usual sense) stability, but also the domains of uniform stability, for which a corresponding linearized stability problem satisfies the uniform Lopatinski condition, are numerically found for different given angles of inclination of the magnetic field behind the shock to the planar shock front. As is known, uniform linearized stability implies the nonlinear stability, that is local existence of discontinuous shock front solutions of a quasilinear system of hyperbolic conservation laws. 14. A novel averaging technique for discrete entropy-stable dissipation operators for ideal MHD NASA Astrophysics Data System (ADS) Derigs, Dominik; Winters, Andrew R.; Gassner, Gregor J.; Walch, Stefanie 2017-02-01 Entropy stable schemes can be constructed with a specific choice of the numerical flux function. First, an entropy conserving flux is constructed. Secondly, an entropy stable dissipation term is added to this flux to guarantee dissipation of the discrete entropy. Present works in the field of entropy stable numerical schemes are concerned with thorough derivations of entropy conservative fluxes for ideal MHD. However, as we show in this work, if the dissipation operator is not constructed in a very specific way, it cannot lead to a generally stable numerical scheme. The two main findings presented in this paper are that the entropy conserving flux of Ismail & Roe can easily break down for certain initial conditions commonly found in astrophysical simulations, and that special care must be taken in the derivation of a discrete dissipation matrix for an entropy stable numerical scheme to be robust. We present a convenient novel averaging procedure to evaluate the entropy Jacobians of the ideal MHD and the compressible Euler equations that yields a discretization with favorable robustness properties. 15. A uniquely defined entropy stable matrix dissipation operator for high Mach number ideal MHD and compressible Euler simulations NASA Astrophysics Data System (ADS) Winters, Andrew R.; Derigs, Dominik; Gassner, Gregor J.; Walch, Stefanie 2017-03-01 We describe a unique averaging procedure to design an entropy stable dissipation operator for the ideal magnetohydrodynamic (MHD) and compressible Euler equations. Often in the derivation of an entropy conservative numerical flux function much care is taken in the design and averaging of the entropy conservative numerical flux. We demonstrate in this work that if the discrete dissipation operator is not carefully chosen as well it can have deleterious effects on the numerical approximation. This is particularly true for very strong shocks or high Mach number flows present, for example, in astrophysical simulations. We present the underlying technique of how to construct a unique averaging technique for the discrete dissipation operator. We also demonstrate numerically the increased robustness of the approximation. 16. Numerical MHD codes for modeling astrophysical flows NASA Astrophysics Data System (ADS) Koldoba, A. V.; Ustyugova, G. V.; Lii, P. S.; Comins, M. L.; Dyda, S.; Romanova, M. M.; Lovelace, R. V. E. 2016-05-01 We describe a Godunov-type magnetohydrodynamic (MHD) code based on the Miyoshi and Kusano (2005) solver which can be used to solve various astrophysical hydrodynamic and MHD problems. The energy equation is in the form of entropy conservation. The code has been implemented on several different coordinate systems: 2.5D axisymmetric cylindrical coordinates, 2D Cartesian coordinates, 2D plane polar coordinates, and fully 3D cylindrical coordinates. Viscosity and diffusivity are implemented in the code to control the accretion rate in the disk and the rate of penetration of the disk matter through the magnetic field lines. The code has been utilized for the numerical investigations of a number of different astrophysical problems, several examples of which are shown. 17. Polydispersed MHD flow in a cylindrical vessel SciTech Connect Gorislavets, Yu.M. 1986-07-01 A large number of works on MHD separation of nonelectrically conducting particles assume that particle growth does not occur. The authors adopt the well-known model of coagulation according to which the collision of particles is determined only by their mutual displacement in the carrying liquid. Figures show relative density of coagulating particles, and particle-size distribution. It was shown that the process of coagulation in the situation under study develops in an avalanchelike fashion. 18. High Order Filter Methods for Shock/Turbulence MHD Flows NASA Technical Reports Server (NTRS) Yee, H. C.; Sjoegreen, Bjoern 2003-01-01 Low-dissipative high order filter finite difference methods for shock/turbulence/combustion compressible viscous MHD flows has been constructed. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field (del (raided dot) B) numerical error in the sense that no standard divergence cleaning is required. For certain 2-D MHD test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved. 19. Performance and flow characteristics of MHD seawater thruster SciTech Connect Doss, E.D. 1990-01-01 The main goal of the research is to investigate the effects of strong magnetic fields on the electrical and flow fields inside MHD thrusters. The results of this study is important in the assessment of the feasibility of MHD seawater propulsion for the Navy. To accomplish this goal a three-dimensional fluid flow computer model has been developed and applied to study the concept of MHD seawater propulsion. The effects of strong magnetic fields on the current and electric fields inside the MHD thruster and their interaction with the flow fields, particularly those in the boundary layers, have been investigated. The results of the three-dimensional computations indicate that the velocity profiles are flatter over the sidewalls of the thruster walls in comparison to the velocity profiles over the electrode walls. These nonuniformities in the flow fields give rise to nonuniform distribution of the skin friction along the walls of the thrusters, where higher values are predicted over the sidewalls relative to those over the electrode walls. Also, a parametric study has been performed using the three-dimensional MHD flow model to analyze the performance of continuous electrode seawater thrusters under different operating parameters. The effects of these parameters on the fluid flow characteristics, and on the thruster efficiency have been investigated. Those parameters include the magnetic field (10--20 T), thruster diameter, surface roughness, flow velocity, and the electric load factor. The results show also that the thruster performance improves with the strength of the magnetic field and thruster diameter, and the efficiency decreases with the flow velocity and surface roughness. 20. Impact of ideal MHD stability limits on high-beta hybrid operation SciTech Connect Piovesan, Paolo; Igochine, V.; Turco, F.; Ryan, D. A.; Cianciosa, M. R.; Liu, Y. Q.; Marrelli, L.; Terranova, D.; Wilcox, R. S.; Wingen, A.; Angioni, C.; Bock, A.; Chrystal, C.; Classen, I.; Dunne, M.; Ferraro, N. M.; Fischer, R.; Gude, A.; Holcomb, C. T.; Lebschy, A.; Luce, T. C.; Maraschek, M.; McDermott, R.; Odstrcil, T.; Paz-Soldan, C.; Reich, M.; Sertoli, M.; Suttrop, W.; Taylor, N. Z.; Weiland, M.; Willensdorfer, M. 2016-10-27 Here, the hybrid scenario is a candidate for stationary high-fusion gain tokamak operation in ITER and DEMO. To obtain such performance, the energy confinement and the normalized pressure${{\\beta}_{N}}$must be maximized, which requires operating near or above ideal MHD no-wall limits. New experimental findings show how these limits can affect hybrid operation. Even if hybrids are mainly limited by tearing modes, proximity to the no-wall limit leads to 3D field amplification that affects plasma profiles, e.g. rotation braking is observed in ASDEX Upgrade throughout the plasma and peaks in the core. As a result, even the small ASDEX Upgrade error fields are amplified and their effects become visible. To quantify such effects, ASDEX Upgrade measured the response to 3D fields applied by$8\\times 2$non-axisymmetric coils as${{\\beta}_{N}}$approaches the no-wall limit. The full n = 1 response profile and poloidal structure were measured by a suite of diagnostics and compared with linear MHD simulations, revealing a characteristic feature of hybrids: the n = 1 response is due to a global, marginally-stable n = 1 kink characterized by a large m = 1, n = 1 core harmonic due to qmin being just above 1. A helical core distortion of a few cm forms and affects various core quantities, including plasma rotation, electron and ion temperature, and intrinsic W density. In similar experiments, DIII-D also measured the effect of this helical core on the internal current profile, providing information useful to understanding of the physics of magnetic flux pumping, i.e. anomalous current redistribution by MHD modes that keeps${{q}_{\\text{min}}}>1$. Thanks to flux pumping, a broad current profile is maintained in DIII-D even with large on-axis current drive, enabling fully non-inductive operation at high${{\\beta}_{N}}\$ up to 3.5–4.

1. Impact of ideal MHD stability limits on high-beta hybrid operation

DOE PAGES

Piovesan, Paolo; Igochine, V.; Turco, F.; ...

2016-10-27

Here, the hybrid scenario is a candidate for stationary high-fusion gain tokamak operation in ITER and DEMO. To obtain such performance, the energy confinement and the normalized pressuremore » $${{\\beta}_{N}}$$ must be maximized, which requires operating near or above ideal MHD no-wall limits. New experimental findings show how these limits can affect hybrid operation. Even if hybrids are mainly limited by tearing modes, proximity to the no-wall limit leads to 3D field amplification that affects plasma profiles, e.g. rotation braking is observed in ASDEX Upgrade throughout the plasma and peaks in the core. As a result, even the small ASDEX Upgrade error fields are amplified and their effects become visible. To quantify such effects, ASDEX Upgrade measured the response to 3D fields applied by $$8\\times 2$$ non-axisymmetric coils as $${{\\beta}_{N}}$$ approaches the no-wall limit. The full n = 1 response profile and poloidal structure were measured by a suite of diagnostics and compared with linear MHD simulations, revealing a characteristic feature of hybrids: the n = 1 response is due to a global, marginally-stable n = 1 kink characterized by a large m = 1, n = 1 core harmonic due to qmin being just above 1. A helical core distortion of a few cm forms and affects various core quantities, including plasma rotation, electron and ion temperature, and intrinsic W density. In similar experiments, DIII-D also measured the effect of this helical core on the internal current profile, providing information useful to understanding of the physics of magnetic flux pumping, i.e. anomalous current redistribution by MHD modes that keeps $${{q}_{\\text{min}}}>1$$ . Thanks to flux pumping, a broad current profile is maintained in DIII-D even with large on-axis current drive, enabling fully non-inductive operation at high $${{\\beta}_{N}}$$ up to 3.5–4.« less

2. Robustness and flexibility in compact quasiaxial stellarators: Global ideal MHD stability and energetic particle transport

SciTech Connect

Redi, M.H.; Diallo, A.; Cooper, W.A.; Fu, G.Y.

2000-01-27

Concerns about the flexibility and robustness of a compact quasiaxial stellarator design are addressed by studying the effects of varied pressure and rotational transform profiles on expected performance. For thirty, related, fully three-dimensional configurations the global, ideal magnetohydrodynamic stability is evaluated as well as energetic particle transport. It is found that tokamak intuition is relevant to understanding the magnetohydrodynamic stability, with pressure gradient driving terms and shear stabilization controlling both the periodicity preserving, N=0, and the non-periodicity preserving, N=1, unstable kink modes. Global kink modes are generated by steeply peaked pressure profiles near the half radius and edge localized kink modes are found for plasmas with steep pressure profiles at the edge as well as with edge rotational transform above 0.5. Energetic particle transport is not strongly dependent on these changes of pressure and current (or rotational transform) profiles, although a weak inverse dependence on pressure peaking through the corresponding Shafranov shift is found. While good transport and MHD stability are not anticorrelated in these equilibria, stability only results from a delicate balance of the pressure and shear stabilization forces. A range of interesting MHD behaviors is found for this large set of equilibria, exhibiting similar particle transport properties.

3. Ideal MHD stability properties of pressure-driven modes in low shear tokamaks

SciTech Connect

Manickam, J.; Pomphrey, N.; Todd, A.M.M.

1987-03-01

The role of shear in determining the ideal MHD stability properties of tokamaks is discussed. In particular, we assess the effects of low shear within the plasma upon pressure-driven modes. The standard ballooning theory is shown to break down, as the shear is reduced and the growth rate is shown to be an oscillatory function of n, the toroidal mode number, treated as a continuous parameter. The oscillations are shown to depend on both the pressure and safety-factor profiles. When the shear is sufficiently weak, the oscillations can result in bands of unstable n values which are present even when the standard ballooning theory predicts complete stability. These instabilities are named ''infernal modes.'' The occurrence of these instabilities at integer n is shown to be a sensitive function of q-axis, raising the possibility of a sharp onset as plasma parameters evolve. 20 refs., 31 figs.

4. Efficient Low Dissipative High Order Schemes for Multiscale MHD Flows

NASA Technical Reports Server (NTRS)

Sjoegreen, Bjoern; Yee, Helen C.; Mansour, Nagi (Technical Monitor)

2002-01-01

Accurate numerical simulations of complex multiscale compressible viscous flows, especially high speed turbulence combustion and acoustics, demand high order schemes with adaptive numerical dissipation controls. Standard high resolution shock-capturing methods are too dissipative to capture the small scales and/or long-time wave propagations without extreme grid refinements and small time steps. An integrated approach for the control of numerical dissipation in high order schemes for the compressible Euler and Navier-Stokes equations has been developed and verified by the authors and collaborators. These schemes are suitable for the problems in question. Basically, the scheme consists of sixth-order or higher non-dissipative spatial difference operators as the base scheme. To control the amount of numerical dissipation, multiresolution wavelets are used as sensors to adaptively limit the amount and to aid the selection and/or blending of the appropriate types of numerical dissipation to be used. Magnetohydrodynamics (MHD) waves play a key role in drag reduction in highly maneuverable high speed combat aircraft, in space weather forecasting, and in the understanding of the dynamics of the evolution of our solar system and the main sequence stars. Although there exist a few well-studied second and third-order high-resolution shock-capturing schemes for the MHD in the literature, these schemes are too diffusive and not practical for turbulence/combustion MHD flows. On the other hand, extension of higher than third-order high-resolution schemes to the MHD system of equations is not straightforward. Unlike the hydrodynamic equations, the inviscid MHD system is non-strictly hyperbolic with non-convex fluxes. The wave structures and shock types are different from their hydrodynamic counterparts. Many of the non-traditional hydrodynamic shocks are not fully understood. Consequently, reliable and highly accurate numerical schemes for multiscale MHD equations pose a great

5. Efficient Low Dissipative High Order Schemes for Multiscale MHD Flows

NASA Technical Reports Server (NTRS)

Sjoegreen, Bjoern; Yee, Helen C.; Mansour, Nagi (Technical Monitor)

2002-01-01

Accurate numerical simulations of complex multiscale compressible viscous flows, especially high speed turbulence combustion and acoustics, demand high order schemes with adaptive numerical dissipation controls. Standard high resolution shock-capturing methods are too dissipative to capture the small scales and/or long-time wave propagations without extreme grid refinements and small time steps. An integrated approach for the control of numerical dissipation in high order schemes for the compressible Euler and Navier-Stokes equations has been developed and verified by the authors and collaborators. These schemes are suitable for the problems in question. Basically, the scheme consists of sixth-order or higher non-dissipative spatial difference operators as the base scheme. To control the amount of numerical dissipation, multiresolution wavelets are used as sensors to adaptively limit the amount and to aid the selection and/or blending of the appropriate types of numerical dissipation to be used. Magnetohydrodynamics (MHD) waves play a key role in drag reduction in highly maneuverable high speed combat aircraft, in space weather forecasting, and in the understanding of the dynamics of the evolution of our solar system and the main sequence stars. Although there exist a few well-studied second and third-order high-resolution shock-capturing schemes for the MHD in the literature, these schemes are too diffusive and not practical for turbulence/combustion MHD flows. On the other hand, extension of higher than third-order high-resolution schemes to the MHD system of equations is not straightforward. Unlike the hydrodynamic equations, the inviscid MHD system is non-strictly hyperbolic with non-convex fluxes. The wave structures and shock types are different from their hydrodynamic counterparts. Many of the non-traditional hydrodynamic shocks are not fully understood. Consequently, reliable and highly accurate numerical schemes for multiscale MHD equations pose a great

6. "Ideal" tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

Del Sarto, Daniele; Pucci, Fulvia; Tenerani, Anna; Velli, Marco

2016-03-01

This paper discusses the transition to fast growth of the tearing instability in thin current sheets in the collisionless limit where electron inertia drives the reconnection process. It has been previously suggested that in resistive MHD there is a natural maximum aspect ratio (ratio of sheet length and breadth to thickness) which may be reached for current sheets with a macroscopic length L, the limit being provided by the fact that the tearing mode growth time becomes of the same order as the Alfvén time calculated on the macroscopic scale. For current sheets with a smaller aspect ratio than critical the normalized growth rate tends to zero with increasing Lundquist number S, while for current sheets with an aspect ratio greater than critical the growth rate diverges with S. Here we carry out a similar analysis but with electron inertia as the term violating magnetic flux conservation: previously found scalings of critical current sheet aspect ratios with the Lundquist number are generalized to include the dependence on the ratio de2/L2, where de is the electron skin depth, and it is shown that there are limiting scalings which, as in the resistive case, result in reconnecting modes growing on ideal time scales. Finite Larmor radius effects are then included, and the rescaling argument at the basis of "ideal" reconnection is proposed to explain secondary fast reconnection regimes naturally appearing in numerical simulations of current sheet evolution.

7. Line-tied MHD modes: effect of plasma pressure, axial boundary condition and axial flow

Arcudi, Francesco; Delzanno, Gian Luca; Finn, John M.

2008-11-01

Recent 3D nonlinear magnetohydrodynamic (MHD) simulations of astrophysical jets [1] showed a narrow jet-like region with very tightly wound magnetic fields, very suggestive of jet observations. These results were unexpected because such tightly wound magnetic fields should be violently MHD unstable. In order to make direct contact with the simulations of Ref. [1], we present a linear stability study in resistive MHD in cylindrical geometry. In this work, stability is studied including axial flows and finite plasma pressure. We also changed the axial boundary conditions to model those typical of astrophysical jets and laboratory experiments, using line-tying at one end of the field lines and non-line-tied boundary conditions at the other end [2]. The numerical results show that pressure strongly shifts the marginal stability threshold relative to the Kruskal-Shafranov threshold and a monotonically increasing pressure profile stabilizes the plasma. On the other hand, non-line-tied boundary conditions have little effect on marginal stability for typical parameters. All the results are supported by analytical studies based on reduced ideal MHD. [1] H. Li, G. Lapenta, J. M. Finn, S. Li, and S. A. Colgate, Astrophys. J. 643, 92 (2006). [2] D. D. Ryutov, I. Furno, T. P. Intrator, S. Abbate, and T. Madziwa-Nussinov, Phys. Plasmas 13, 032105 (2006).

8. Global simulations of protoplanetary disks with net magnetic flux. I. Non-ideal MHD case

Béthune, William; Lesur, Geoffroy; Ferreira, Jonathan

2017-04-01

Context. The planet-forming region of protoplanetary disks is cold, dense, and therefore weakly ionized. For this reason, magnetohydrodynamic (MHD) turbulence is thought to be mostly absent, and another mechanism has to be found to explain gas accretion. It has been proposed that magnetized winds, launched from the ionized disk surface, could drive accretion in the presence of a large-scale magnetic field. Aims: The efficiency and the impact of these surface winds on the disk structure is still highly uncertain. We present the first global simulations of a weakly ionized disk that exhibits large-scale magnetized winds. We also study the impact of self-organization, which was previously demonstrated only in non-stratified models. Methods: We perform numerical simulations of stratified disks with the PLUTO code. We compute the ionization fraction dynamically, and account for all three non-ideal MHD effects: ohmic and ambipolar diffusions, and the Hall drift. Simplified heating and cooling due to non-thermal radiation is also taken into account in the disk atmosphere. Results: We find that disks can be accreting or not, depending on the configuration of the large-scale magnetic field. Magnetothermal winds, driven both by magnetic acceleration and heating of the atmosphere, are obtained in the accreting case. In some cases, these winds are asymmetric, ejecting predominantly on one side of the disk. The wind mass loss rate depends primarily on the average ratio of magnetic to thermal pressure in the disk midplane. The non-accreting case is characterized by a meridional circulation, with accretion layers at the disk surface and decretion in the midplane. Finally, we observe self-organization, resulting in axisymmetric rings of density and associated pressure "bumps". The underlying mechanism and its impact on observable structures are discussed.

9. Impact of ideal MHD stability limits on high-beta hybrid operation

Piovesan, P.; Igochine, V.; Turco, F.; Ryan, D. A.; Cianciosa, M. R.; Liu, Y. Q.; Marrelli, L.; Terranova, D.; Wilcox, R. S.; Wingen, A.; Angioni, C.; Bock, A.; Chrystal, C.; Classen, I.; Dunne, M.; Ferraro, N. M.; Fischer, R.; Gude, A.; Holcomb, C. T.; Lebschy, A.; Luce, T. C.; Maraschek, M.; McDermott, R.; Odstrčil, T.; Paz-Soldan, C.; Reich, M.; Sertoli, M.; Suttrop, W.; Taylor, N. Z.; Weiland, M.; Willensdorfer, M.; The ASDEX Upgrade Team; The DIII-D Team; The EUROfusion MST1 Team

2017-01-01

The hybrid scenario is a candidate for stationary high-fusion gain tokamak operation in ITER and DEMO. To obtain such performance, the energy confinement and the normalized pressure {βN} must be maximized, which requires operating near or above ideal MHD no-wall limits. New experimental findings show how these limits can affect hybrid operation. Even if hybrids are mainly limited by tearing modes, proximity to the no-wall limit leads to 3D field amplification that affects plasma profiles, e.g. rotation braking is observed in ASDEX Upgrade throughout the plasma and peaks in the core. As a result, even the small ASDEX Upgrade error fields are amplified and their effects become visible. To quantify such effects, ASDEX Upgrade measured the response to 3D fields applied by 8× 2 non-axisymmetric coils as {βN} approaches the no-wall limit. The full n  =  1 response profile and poloidal structure were measured by a suite of diagnostics and compared with linear MHD simulations, revealing a characteristic feature of hybrids: the n  =  1 response is due to a global, marginally-stable n  =  1 kink characterized by a large m  =  1, n  =  1 core harmonic due to q min being just above 1. A helical core distortion of a few cm forms and affects various core quantities, including plasma rotation, electron and ion temperature, and intrinsic W density. In similar experiments, DIII-D also measured the effect of this helical core on the internal current profile, providing information useful to understanding of the physics of magnetic flux pumping, i.e. anomalous current redistribution by MHD modes that keeps {{q}\\text{min}}>1 . Thanks to flux pumping, a broad current profile is maintained in DIII-D even with large on-axis current drive, enabling fully non-inductive operation at high {βN} up to 3.5-4.

10. Magnus: A New Resistive MHD Code with Heat Flow Terms

Navarro, Anamaría; Lora-Clavijo, F. D.; González, Guillermo A.

2017-07-01

We present a new magnetohydrodynamic (MHD) code for the simulation of wave propagation in the solar atmosphere, under the effects of electrical resistivity—but not dominant—and heat transference in a uniform 3D grid. The code is based on the finite-volume method combined with the HLLE and HLLC approximate Riemann solvers, which use different slope limiters like MINMOD, MC, and WENO5. In order to control the growth of the divergence of the magnetic field, due to numerical errors, we apply the Flux Constrained Transport method, which is described in detail to understand how the resistive terms are included in the algorithm. In our results, it is verified that this method preserves the divergence of the magnetic fields within the machine round-off error (˜ 1× {10}-12). For the validation of the accuracy and efficiency of the schemes implemented in the code, we present some numerical tests in 1D and 2D for the ideal MHD. Later, we show one test for the resistivity in a magnetic reconnection process and one for the thermal conduction, where the temperature is advected by the magnetic field lines. Moreover, we display two numerical problems associated with the MHD wave propagation. The first one corresponds to a 3D evolution of a vertical velocity pulse at the photosphere-transition-corona region, while the second one consists of a 2D simulation of a transverse velocity pulse in a coronal loop.

11. A simplfied MHD model of solar surface flows

Hurlburt, Neal E.

2017-08-01

Recent work on modeling solar photospheric flows has replaced those based on random-walks with kinematic models based upon observed convective properties. These models have successfully reproduced many aspects of the solar cycle. Here we present a dynamic model of surface flows based upon simplified MHD driven by supergranular-scale sources, along with global-scale differential rotation and meridonal flow. This approach can be used to investigate a variety of stellar and could supplant random walk methods in projecting solar fields outside the visible range of current magnetographs. The resulting self-consistent solutions are compared against observations and other models.

12. Nonlinear Alfvén wave propagating in ideal MHD plasmas

Zheng, Jugao; Chen, Yinhua; Yu, Mingyang

2016-01-01

The behavior of nonlinear Alfvén waves propagating in ideal MHD plasmas is investigated numerically. It is found that in a one-dimensional weakly nonlinear system an Alfvén wave train can excite two longitudinal disturbances, namely an acoustic wave and a ponderomotively driven disturbance, which behave differently for β \\gt 1 and β \\lt 1, where β is the ratio of plasma-to-magnetic pressures. In a strongly nonlinear system, the Alfvén wave train is modulated and can steepen to form shocks, leading to significant dissipation due to appearance of current sheets at magnetic-pressure minima. For periodic boundary condition, we find that the Alfvén wave transfers its energy to the plasma and heats it during the shock formation. In two-dimensional systems, fast magneto-acoustic wave generation due to Alfvén wave phase mixing is considered. It is found that the process depends on the amplitude and frequency of the Alfvén waves, as well as their speed gradients and the pressure of the background plasma.

13. Dynamics of tokamak plasma surface current in 3D ideal MHD model

Galkin, Sergei A.; Svidzinski, V. A.; Zakharov, L. E.

2013-10-01

Interest in the surface current which can arise on perturbed sharp plasma vacuum interface in tokamaks was recently generated by a few papers (see and references therein). In dangerous disruption events with plasma-touching-wall scenarios, the surface current can be shared with the wall leading to the strong, damaging forces acting on the wall A relatively simple analytic definition of δ-function surface current proportional to a jump of tangential component of magnetic field nevertheless leads to a complex computational problem on the moving plasma-vacuum interface, requiring the incorporation of non-linear 3D plasma dynamics even in one-fluid ideal MHD. The Disruption Simulation Code (DSC), which had recently been developed in a fully 3D toroidal geometry with adaptation to the moving plasma boundary, is an appropriate tool for accurate self-consistent δfunction surface current calculation. Progress on the DSC-3D development will be presented. Self-consistent surface current calculation under non-linear dynamics of low m kink mode and VDE will be discussed. Work is supported by the US DOE SBIR grant #DE-SC0004487.

14. MHD flows at astropauses and in astrotails

Nickeler, D. H.; Wiegelmann, T.; Karlický, M.; Kraus, M.

2014-09-01

The geometrical shapes and the physical properties of stellar wind - interstellar medium interaction regions form an important stage for studying stellar winds and their embedded magnetic fields as well as cosmic ray modulation. Our goal is to provide a proper representation and classification of counter-flow configurations and counter-flow interfaces in the frame of fluid theory. In addition we calculate flows and large-scale electromagnetic fields based on which the large-scale dynamics and its role as possible background for particle acceleration, e.g., in the form of anomalous cosmic rays, can be studied. We find that for the definition of the boundaries, which are determining the astropause shape, the number and location of magnetic null points and stagnation points is essential. Multiple separatrices can exist, forming a highly complex environment for the interstellar and stellar plasma. Furthermore, the formation of extended tail structures occur naturally, and their stretched field and streamlines provide surroundings and mechanisms for the acceleration of particles by field-aligned electric fields.

15. MHD mixed convection stagnation point flow over a permeable surface

Abdul Hamid, Rohana; Abu Bakar, Nor Ashikin; Wan Zaimi, Wan Mohd Khairy Adly; Bidin, Biliana

2013-04-01

In this paper, the effects of suction and injection parameters on magnetohydrodynamic (MHD) mixed convection stagnation point flow are studied numerically. Using appropriate similarity transformations, the governing system of partial differential equations is transformed into a system of ordinary differential equations which are then solved using the shooting method. Numerical results are obtained for the velocity, temperature and concentration profiles. The results show that the suction and injection parameters affect the skin friction coefficient as well as the local Nusselt number for both assisting and opposing flows. The suction parameter increases the skin friction coefficient and the local Nusselt number while the opposite behavior is observed for the injection parameter.

16. MHD of accretion-disk flows

Yankova, Krasimira

2015-01-01

Accretion is one of the most important problems of astrophysics concerning the transfer of matter and the transformation of energy into space. Process represents a falling of the substance on a cosmic object from the surrounding area and is a powerful gravitational mechanism for the production of radiation. Accretion disc effectively converts the mass of the substance by viscous friction and released potential energy transformed into radiation by particle collisions. Accretion onto compact object shows high energy efficiency and temporal variability in a broad class of observational data in all ranges. In the disks of these objects are developed a series instabilities and structures that govern the distribution of the energy. They are expressed in many variety non-stationary phenomena that we observe. That is why we propose generalized model of magnetized accretion disk with advection, which preserves the nonlinearity of the problem. We study interaction of the plasmas flow with the magnetic field, and how this affects the self-organizing disk. The aim of the work is to describe the accretion flow in detail, in his quality of the open astrophysical system, to investigate the evolution and to reveal the mechanisms of the structuring the disk-corona system for to interpret correctly the high energy behavior of such sources.

17. MHD Stability Analysis and Flow Controls of Liquid Metal Free Surface Film Flows as Fusion Reactor PFCs

Zhang, Xiujie; Pan, Chuanjie; Xu, Zengyu

2016-12-01

Numerical and experimental investigation results on the magnetohydrodynamics (MHD) film flows along flat and curved bottom surfaces are summarized in this study. A simplified modeling has been developed to study the liquid metal MHD film state, which has been validated by the existing experimental results. Numerical results on how the inlet velocity (V), the chute width (W) and the inlet film thickness (d0) affect the MHD film flow state are obtained. MHD stability analysis results are also provided in this study. The results show that strong magnetic fields make the stable V decrease several times compared to the case with no magnetic field, especially small radial magnetic fields (Bn) will have a significant impact on the MHD film flow state. Based on the above numerical and MHD stability analysis results flow control methods are proposed for flat and curved MHD film flows. For curved film flow we firstly proposed a new multi-layers MHD film flow system with a solid metal mesh to get the stable MHD film flows along the curved bottom surface. Experiments on flat and curved MHD film flows are also carried out and some firstly observed results are achieved. supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2014GB125003 and 2013GB114002), National Natural Science Foundation of China (No. 11105044)

18. Theoretical and Experimental Research of Capabilities of MHD Technology to Control Gas Flow with Non-Equilibrium Ionization

DTIC Science & Technology

2007-11-02

experimental research of capabilities of using of MHD technology to control gas flow with non-equilibrium ionization. Cold gas flows will be considered, where...and MHD generator will be developed. Requirements to ionizer, MHD generator and flow parameters at which self- sustained operational mode of ionizer and...MHD generator is realized will be formulated. Possibilities of using of MHD control in gas-dynamical systems will be considered. Traditional use of

19. Kelvin-Helmholtz Unstable Magnetotail Flow Channels: Deceleration and Radiation of MHD Waves

Turkakin, H.; Mann, I. R.; Rankin, R.

2014-12-01

The Kelvin-Helmholtz instability (KHI) of magnetotail flow channels associated with burstybulk flows (BBFs) is investigated. MHD oscillations of the channel in both kink and sausage modes areinvestigated for KHI, and both the primary and secondary KHIs are found that drive MHD waves. Theseinstabilities are likely to be important for flow channel braking where the KHI removes energy from the flow.At flow speeds above the peak growth rate, the MHD modes excited by KHI develop from surface modesinto propagating modes leading to the radiation of MHD waves from the flow channel. The coupling ofBBF-driven shear flow instabilities to MHD waves presented here represents a new paradigm to explain BBFexcitation of tail flapping. Our model can also explain, for the first time, the generation mechanism for theobservations of waves propagating toward both flanks and emitted from BBF channels in the magnetotail.

20. The inapplicability of ideal MHD stability theory to the dense Z-pinch

Haines, M. G.; Coppins, M.; Culverwell, I. D.

1989-12-01

For many years Z-pinch has been considered to be intrinsically unstable. This followed the theory of Kruskal and Schwarzchild and experiments of Carruthers and Anderson et al. However in the regime of parameter space required for thermonuclear fusion, the ratio of ion Larmor radius to pinch radius is about one third; and the compressional Z-pinch at Imperial College in which the ratio is one tenth has been found to be anomalously stable for sixteen Alfvén transit times. Recent deuterium fibre experiments at NRL and Los Alamos have also reported anomalous stability. The regimes for stability can be classified using a generalization of the work of Friedberg, and using the Bennett relation which describes pressure balance. As a result ideal MHD is found to be confined to a small wedge-shaped region in ln(I4α) versus ln N space, where I, a, and N are the current (A) and pinch radius (m), and line density (m-1) respectively. We have found that a magnetic Lundquist number S below 100 stabilizes the m=0 mode, and S=3.86×1023I4a/N2. The viscous Lundquist number is the inverse of γτi, where γ is the ratio of the Alfvén speed to the pinch radius and τi is the ion-ion collision time. We find that γτi=2.07×1039I4a/N3. Above a value of γτi of unity the perturbed ion pressure will tend to be anisotropic which Coppins11 has shown to be stabilizing. The ratio of ion Larmor radius to pinch radius is 7.1×108/N1/2 and some stabilization is expected when this is in the range 0.1 to 1, though further work in this area is required. A skin-current Vlasov model will be reported by Arber at this meeting.

1. Three-Dimensional MHD Models of Waves and Flows in Coronal Active Region Loops

Ofman, L.; Wang, T.; Davila, J. M.

2011-12-01

Recent observations show that slow magnetosonic waves are present in active region loops, and are often associated with subsonic up-flows of coronal material. In order to study the relation between up-flows and waves we develop a 3D MHD model of an idealized bi-polar active region with flows in coronal loops. The model is initiated with a dipole magnetic field and gravitationally stratified isothermal atmosphere. To model the effects of flares, coronal material is injected in small-scale regions at the base of the model active region. The up-flows have sub-sonic speeds of ˜100 km/s and are steady or periodic, producing higher density loops by filling magnetic flux-tubes with injected material. We find that the up-flows produce fast and slow magnetosonic waves that propagate in the coronal loops. We perform a parametric study of up-flow magnitude and periodicity, and the relation with the resulting waves. As expected, we find that the up-flow speed decreases with loop height due to the diverge of the flux tubes, while the slow magnetosonic speed is independent of height. When the amplitude of the driving pulses is increased above the sound speed, we find that slow shocks are produced in the loops. Using the results of the 3D MHD model we show that observed slow magnetosonic waves in active region loops can be driven by impulsive flare-produced up-flows at the transition region/corona interface of active regions.

2. MHD Simulations of the Plasma Flow in the Magnetic Nozzle

NASA Technical Reports Server (NTRS)

Smith, T. E. R.; Keidar, M.; Sankaran, K.; olzin, K. A.

2013-01-01

The magnetohydrodynamic (MHD) flow of plasma through a magnetic nozzle is simulated by solving the governing equations for the plasma flow in the presence of an static magnetic field representing the applied nozzle. This work will numerically investigate the flow and behavior of the plasma as the inlet plasma conditions and magnetic nozzle field strength are varied. The MHD simulations are useful for addressing issues such as plasma detachment and to can be used to gain insight into the physical processes present in plasma flows found in thrusters that use magnetic nozzles. In the model, the MHD equations for a plasma, with separate temperatures calculated for the electrons and ions, are integrated over a finite cell volume with flux through each face computed for each of the conserved variables (mass, momentum, magnetic flux, energy) [1]. Stokes theorem is used to convert the area integrals over the faces of each cell into line integrals around the boundaries of each face. The state of the plasma is described using models of the ionization level, ratio of specific heats, thermal conductivity, and plasma resistivity. Anisotropies in current conduction due to Hall effect are included, and the system is closed using a real-gas equation of state to describe the relationship between the plasma density, temperature, and pressure.A separate magnetostatic solver is used to calculate the applied magnetic field, which is assumed constant for these calculations. The total magnetic field is obtained through superposition of the solution for the applied magnetic field and the self-consistently computed induced magnetic fields that arise as the flowing plasma reacts to the presence of the applied field. A solution for the applied magnetic field is represented in Fig. 1 (from Ref. [2]), exhibiting the classic converging-diverging field pattern. Previous research was able to demonstrate effects such as back-emf at a super-Alfvenic flow, which significantly alters the shape of the

3. Two-dimensional MHD simulations of tokamak plasmas with poloidal flow

Hu, Bo; Betti, R.

2006-10-01

It has been shown [1] that, according to the ideal MHD equilibrium theory, poloidal flow in a tokamak can give rise to a pedestal structure with the pressure, density and velocity developing sharp discontinuities in their radial profiles. Such a pedestal arises when the poloidal velocity exceeds the poloidal sound speed. Since the poloidal sound speed vanishes at the separatrix, it is conceivable that evena rather slow poloidal flow can become transonic near the plasma edge, thus inducing a pedestal in the hydrodynamic profiles. While equilibrium calculations [1-4] of such a pedestal are well established, only a few two-dimensional time-dependent simulations have been carried out [5]. Here, we show the preliminary results from a two dimensional MHD code that simulates the formation of the pedestal starting from a poloidal velocity profile that becomes supersonic at the plasma edge. This work was supported by US-DOE under Contract DE-FG02-93ER54215. [1] Betti and Freidberg, Phys. Plasmas 7, 2439 (2000). [2] Guazzotto, Betti, Manickam and Kaye, Phys. Plasmas 11, 604 (2004). [3] Guazzotto and Betti, Phys. Plasmas 12, 056107 (2005). [4] Thyagaraja and McClements, Phys. Plasmas 13, 062502 (2006). [5] Gardiner, Betti and Guazzotto, Bull. Am. Phys. Soc. 46, No. 8, 166 (2001).

4. On MHD nonlinear stretching flow of Powell-Eyring nanomaterial

This communication addresses the magnetohydrodynamic (MHD) flow of Powell-Eyring nanomaterial bounded by a nonlinear stretching sheet. Novel features regarding thermophoresis and Brownian motion are taken into consideration. Powell-Eyring fluid is electrically conducted subject to non-uniform applied magnetic field. Assumptions of small magnetic Reynolds number and boundary layer approximation are employed in the mathematical development. Zero nanoparticles mass flux condition at the sheet is selected. Adequate transformation yield nonlinear ordinary differential systems. The developed nonlinear systems have been computed through the homotopic approach. Effects of different pertinent parameters on velocity, temperature and concentration fields are studied and analyzed. Further numerical data of skin friction and heat transfer rate is also tabulated and interpreted.

5. Plasma response measurements of external magnetic perturbations using electron cyclotron emission and comparisons to 3D ideal MHD equilibrium

Willensdorfer, M.; Denk, S. S.; Strumberger, E.; Suttrop, W.; Vanovac, B.; Brida, D.; Cavedon, M.; Classen, I.; Dunne, M.; Fietz, S.; Fischer, R.; Kirk, A.; Laggner, F. M.; Liu, Y. Q.; Odstrčil, T.; Ryan, D. A.; Viezzer, E.; Zohm, H.; Luhmann, I. C.; The ASDEX Upgrade Team; The EUROfusion MST1 Team

2016-11-01

The plasma response from an external n  =  2 magnetic perturbation field in ASDEX Upgrade has been measured using mainly electron cyclotron emission (ECE) diagnostics and a rigid rotating field. To interpret ECE and ECE-imaging (ECE-I) measurements accurately, forward modeling of the radiation transport has been combined with ray tracing. The measured data is compared to synthetic ECE data generated from a 3D ideal magnetohydrodynamics (MHD) equilibrium calculated by VMEC. The measured amplitudes of the helical displacement around the outboard midplane are in reasonable agreement with the one from the synthetic VMEC diagnostics. Both exceed the predictions from the vacuum field calculations and indicate the presence of a kink response at the edge, which amplifies the perturbation. VMEC and MARS-F have been used to calculate the properties of this kink mode. The poloidal mode structure of the magnetic perturbation of this kink mode at the edge peaks at poloidal mode numbers larger than the resonant components |m|>|nq| , whereas the poloidal mode structure of its displacement is almost resonant |m|≈ |nq| . This is expected from ideal MHD in the proximity of rational surfaces. The displacement measured by ECE-I confirms this resonant response.

6. Suppression of Acoustic Fluctuations in a Supersonic MHD Shear Flow

Kimmel, Roger; Adamovich, Igor; Zhong, Xiaolin; Gogineni, Sivaram

2002-11-01

MHD effects on low-temperature ionized supersonic flows have been investigated experimentally. The main objective was to determine whether the Lorentz force produced by permanent magnets in supersonic flows of nonequilibrium plasmas affects the intensity of turbulent boundary layer pressure fluctuations. A combination of transverse RF and transverse non-self-sustained DC discharges generate stable ionization in steady-state M=4 helium flows, and sustain a transverse current that produces a streamwise Lorentz force in the presence of a magnetic field. Changing the polarity of the transverse DC field changes the Lorentz force direction between an accelerating and a retarding force. A miniature microphone placed in the test section wall is used to measure a reproducible effect of the Lorentz force on the pressure fluctuation spectra. In particular, the pressure fluctuation intensity is reduced for a retarding Lorentz force. When the magnetic field direction is reversed, the same effect of reduction of the pressure fluctuation intensity is observed for the opposite DC field polarity, i.e. again for the retarding Lorentz force. Changing the DC field polarity in a non-magnetic supersonic nozzle of the same geometry and at the same plenum and plasma conditions did not produce any detectable effect on the pressure fluctuation spectrum.

7. Heating and current drive requirements for ideal MHD stability and ITB sustainment in ITER steady state scenarios

Poli, Francesca

2012-10-01

Steady state scenarios envisaged for ITER aim at optimizing the bootstrap current, while maintaining sufficient confinement and stability to provide the necessary fusion yield. Non-inductive scenarios will need to operate with Internal Transport Barriers (ITBs) in order to reach adequate fusion gain at typical currents of 9 MA. However, the large pressure gradients associated with ITBs in regions of weak or negative magnetic shear can be conducive to ideal MHD instabilities in a wide range of βN, reducing the no-wall limit. Scenarios are established as relaxed flattop states with time-dependent transport simulations with TSC [1]. Fully non-inductive configurations with current in the range of 7-10 MA and various heating mixes (NB, EC, IC and LH) have been studied against variations of the pressure profile peaking and of the Greenwald fraction. It is found that stable equilibria have qmin> 2 and moderate ITBs at 2/3 of the minor radius [2]. The ExB flow shear from toroidal plasma rotation is expected to be low in ITER, with a major role in the ITB dynamics being played by magnetic geometry. Combinations of H&CD sources that maintain reverse or weak magnetic shear profiles throughout the discharge and ρ(qmin)>=0.5 are the focus of this work. The ITER EC upper launcher, designed for NTM control, can provide enough current drive off-axis to sustain moderate ITBs at mid-radius and maintain a non-inductive current of 8-9MA and H98>=1.5 with the day one heating mix. LH heating and current drive is effective in modifying the current profile off-axis, facilitating the formation of stronger ITBs in the rampup phase, their sustainment at larger radii and larger bootstrap fraction. The implications for steady state operation and fusion performance are discussed.[4pt] [1] Jardin S.C. et al, J. Comput. Phys. 66 (1986) 481[0pt] [2] Poli F.M. et al, Nucl. Fusion 52 (2012) 063027.

8. MHD-flow in the slotted channels with conducting walls

SciTech Connect

Evtushenko, I.; Kirillov, I.; Reed, C.

1994-12-31

The results of the MHD-flow experimental studies performed in the support of the {open_quotes}slotted channel{close_quotes} blanket concept are presented. The test sections were of the rectangular slotted geometry with the aspect ration b/a=10 (the longer side b is parallel to the applied magnetic field). Three test sections had different walls conductivity, two of them had equal conductivity of all four walls and the third one had a thick top wall (simulation of the blanket first wall) while the remaining three walls were made of a thin liner which was electrically insulated from its surrounding strongback ({open_quotes}Laminated{close_quotes} walls). The applied magnetic field in these experiments was from 0.6 to 2 T. The working fluids were In-Ga-Sn and NaK. Comparison of the pressure drop data for each channel with the analytical and numerical solutions showed the necessity to the further development of the theoretical methods, for different channels the difference between theoretical and test data was from 10 to 20%.

9. MHD Simulation of Plasma Flow through the VASIMR Magnetic Nozzle

Tarditi, A. G.; Shebalin, J. V.

2003-10-01

The VASIMR (Variable Specific Impulse Magnetoplasma Rocket, [1]) concept is currently in the experimental development phase at the Advanced Space Propulsion Laboratory, NASA Johnson Space Center. The current experimental effort is mainly focused on the demonstration of the efficient plasma production (light ion helicon source, [2]) and energy boosting (ion cyclotron resonance heating section). Two other critical issues, the plasma detachment process and the collimation of the plasma plume in the magnetic nozzle, are essential for the near term experimental development and are being addressed through an MHD simulation modeling effort with the NIMROD code [3,4]. The model follows the plasma flow up to few meters from the nozzle throat: at that distance the plasma exhaust parameters reach values comparable with the ionospheric plasma background [5]. Results from two-dimensional simulation runs (cylindrical geometry, assuming azimuthal symmetry) aimed in particular at testing the effectiveness of different open-end boundary condition schemes are presented. [1] F. R. Chang-Diaz, Scientific American, p. 90, Nov. 2000 [2] M. D. Carter, et al., Phys. Plasmas 9, 5097-5110, 2002 [3] http://www.nimrodteam.org [4] A. Tarditi et al., 28th Int. Electric Propulsion Conf., IEPC 2003, Toulouse, France, March 2003 [5] A. V. Ilin et al., Proc. 40th AIAA Aerospace Sciences Meeting, Reno, NV, Jan. 2002

10. MHD biconvective flow of Powell Eyring nanofluid over stretched surface

Naseem, Faiza; Shafiq, Anum; Zhao, Lifeng; Naseem, Anum

2017-06-01

The present work is focused on behavioral characteristics of gyrotactic microorganisms to describe their role in heat and mass transfer in the presence of magnetohydrodynamic (MHD) forces in Powell-Eyring nanofluids. Implications concerning stretching sheet with respect to velocity, temperature, nanoparticle concentration and motile microorganism density were explored to highlight influential parameters. Aim of utilizing microorganisms was primarily to stabilize the nanoparticle suspension due to bioconvection generated by the combined effects of buoyancy forces and magnetic field. Influence of Newtonian heating was also analyzed by taking into account thermophoretic mechanism and Brownian motion effects to insinuate series solutions mediated by homotopy analysis method (HAM). Mathematical model captured the boundary layer regime that explicitly involved contemporary non linear partial differential equations converted into the ordinary differential equations. To depict nanofluid flow characteristics, pertinent parameters namely bioconvection Lewis number Lb, traditional Lewis number Le, bioconvection Péclet number Pe, buoyancy ratio parameter Nr, bioconvection Rayleigh number Rb, thermophoresis parameter Nt, Hartmann number M, Grashof number Gr, and Eckert number Ec were computed and analyzed. Results revealed evidence of hydromagnetic bioconvection for microorganism which was represented by graphs and tables. Our findings further show a significant effect of Newtonian heating over a stretching plate by examining the coefficient values of skin friction, local Nusselt number and the local density number. Comparison was made between Newtonian fluid and Powell-Eyring fluid on velocity field and temperature field. Results are compared of with contemporary studies and our findings are found in excellent agreement with these studies.

11. Preliminary Study of Ideal Operational MHD Beta Limit in HL-2A Tokamak Plasmas

Shen, Yong; Dong, Jiaqi; He, Hongda; D. Turnbull, A.

2009-04-01

Magnetohydrodynamic (MHD) n = 1 kink mode with n the toroidal mode number is studied and the operational beta limit, constrained by the mode, is calculated for the equilibrium of HL-2A by using the GATO code. Approximately the same beta limit is obtained for configurations with a value of the axial safety factor q0 both larger and less than 1. Without the stabilization of the conducting wall, the beta limit is found to be 0.821% corresponding to a normalized beta value of βcN = 2.56 for a typical HL-2A discharge with a plasma current Ip = 0.245 MA, and the scaling of βcN ~constant is confirmed.

12. Simulation of two-dimensional fully developed laminar flow for a magneto-hydrodynamic (MHD) pump.

PubMed

Wang, Pei-Jen; Chang, Chia-Yuan; Chang, Ming-Lang

2004-07-30

MHD micro-pumps circumvent the wear and fatigue caused by high pressure-drop across the check valves of mechanical micro-pumps in micro-fluidic systems. Early analyses of the fluid flow for MHD micro-pumps were mostly made possible by the Poiseuille flow theory; however, this conventional laminar approach cannot illustrate the effects of various channel sizes and shapes. This paper, therefore, presents a simplified MHD flow model based upon steady state, incompressible and fully developed laminar flow theory to investigate the characteristics of a MHD pump. Inside the pump, flowing along the channel is the electrically conducting fluid flowing driven by the Lorentz forces in the direction perpendicular to both dc magnetic field and applied electric currents. The Lorentz forces were converted into a hydrostatic pressure gradient in the momentum equations of the MHD channel flow model. The numerical simulations conducted with the explicit finite difference method show that the channel dimensions and the induced Lorentz forces have significant influences on the flow velocity profile. Furthermore, the simulation results agree well with the experimental results published by other researchers.

13. Nonlinear gel electrophoresis: an analogy with ideal fluid flow.

PubMed

Dennison, C; Phillips, A M; Nevin, J M

1983-12-01

The behavior of electrolytes undergoing electrophoresis in various shaped gels was investigated using bromphenol blue as a model electrolyte. The results suggest that during gel electrophoresis, small electrolytes behave in a manner analogous to the flow of ideal, irrotational fluids.

14. Efficient Low Dissipative High Order Schemes for Multiscale MHD Flows, I: Basic Theory

NASA Technical Reports Server (NTRS)

Sjoegreen, Bjoern; Yee, H. C.

2003-01-01

The objective of this paper is to extend our recently developed highly parallelizable nonlinear stable high order schemes for complex multiscale hydrodynamic applications to the viscous MHD equations. These schemes employed multiresolution wavelets as adaptive numerical dissipation controls t o limit the amount of and to aid the selection and/or blending of the appropriate types of dissipation to be used. The new scheme is formulated for both the conservative and non-conservative form of the MHD equations in curvilinear grids. The four advantages of the present approach over existing MHD schemes reported in the open literature are as follows. First, the scheme is constructed for long-time integrations of shock/turbulence/combustion MHD flows. Available schemes are too diffusive for long-time integrations and/or turbulence/combustion problems. Second, unlike exist- ing schemes for the conservative MHD equations which suffer from ill-conditioned eigen- decompositions, the present scheme makes use of a well-conditioned eigen-decomposition obtained from a minor modification of the eigenvectors of the non-conservative MHD equations t o solve the conservative form of the MHD equations. Third, this approach of using the non-conservative eigensystem when solving the conservative equations also works well in the context of standard shock-capturing schemes for the MHD equations. Fourth, a new approach to minimize the numerical error of the divergence-free magnetic condition for high order schemes is introduced. Numerical experiments with typical MHD model problems revealed the applicability of the newly developed schemes for the MHD equations.

15. Experimental investigations of MHD flow tailoring for first wall coolant channels of self-cooled blankets

SciTech Connect

Picologlou, B.F.; Reed, C.B.; Hua, T.Q.; Barleon, L.; Kreuzinger, H.; Walker, J.S.

1989-03-01

Results of experiments on the concept of flow tailoring, the use of salient features of MHD flows in strong magnetic fields to create desirable velocity profiles in the coolant ducts of the first wall and the blanket, are reported. Proof-of-principle testing of flow tailoring has been chosen as the first joint activity on liquid metal MHD between Argonne National Laboratory (ANL) and Kernforschungszentrum Karlsruhe (KfK) because flow tailoring offers the possibility of significant improvement in blanket design and performance. The joint tests are conducted at ANL's ALEX facility on a test article fabricated at KfK. A 3-D MHD thermal hydraulic code developed at ANL is used to demonstrate the increased thermal performance of first wall coolant channels with flow tailoring. Sample results of detailed measurements of velocity and voltage distributions are compared to theoretical predictions provided by analytical tools developed at ANL with the collaboration of the University of Illinois.

16. Velocity, temperature, and electrical conductivity profiles in hydrogen-oxygen MHD duct flows

NASA Technical Reports Server (NTRS)

Greywall, M. S.; Pian, C. C. P.

1978-01-01

Two-dimensional duct flow computations for radial distributions of velocity, temperature, and electrical conductivity are reported. Calculations were carried out for the flow conditions representative of a hydrogen-oxygen combustion driven MHD duct. Results are presented for: profiles of developing flow in a smooth duct, and for profiles of fully developed pipe flow with a specified streamwise shear stress distribution. The predicted temperature and electrical conductivity profiles for the developing flows compare well with available experimental data.

17. Ideal thermodynamic processes of oscillatory-flow regenerative engines will go to ideal stirling cycle?

Luo, Ercang

2012-06-01

This paper analyzes the thermodynamic cycle of oscillating-flow regenerative machines. Unlike the classical analysis of thermodynamic textbooks, the assumptions for pistons' movement limitations are not needed and only ideal flowing and heat transfer should be maintained in our present analysis. Under such simple assumptions, the meso-scale thermodynamic cycles of each gas parcel in typical locations of a regenerator are analyzed. It is observed that the gas parcels in the regenerator undergo Lorentz cycle in different temperature levels, whereas the locus of all gas parcels inside the regenerator is the Ericson-like thermodynamic cycle. Based on this new finding, the author argued that ideal oscillating-flow machines without heat transfer and flowing losses is not the Stirling cycle. However, this new thermodynamic cycle can still achieve the same efficiency of the Carnot heat engine and can be considered a new reversible thermodynamic cycle under two constant-temperature heat sinks.

18. Research and development studies for MHD/coal power flow train components. Part II. Diagnostics and instrumentation MHD channel combutor. Progres report. [Flow calculations for combustors

SciTech Connect

Bloom, M.H.; Lederman, S.; Sforza, P.; Matalon, M.

1980-01-01

This is Part II of the Technical Progress Report on Tasks II-IV of the subject contract. It deals sequentially with Diagnostics and Instrumentation, the MHD Channel and the Combustor. During this period, a significant effort has gone into establishing a schematic design of a laser diagnostic system which can be applied to the flow-train of the MHD system, and to acquiring, assembling and shaking down a laboratory set-up upon which a prototype can be based. With further reference to the MHD Channel, a model analysis has been initiated of the two-dimensional MHD boundary layer between two electrodes in the limit of small magnetic Reynolds numbers with negligible effect of the flow on the applied magnetic field. An objective of this model study is the assessment of variations in initial conditions on the boundary layer behavior. Finally, the problem of combustion modeling has been studied on an initial basis. The open reports on this subject depict a high degree of empiricism, centering attention on global behavior mainly. A quasi-one-dimensional model code has been set-up to check some of the existing estimates. Also a code for equilibrium combustion has been activated.

19. Closed cycle MHD generator with nonuniform gas-plasma flow driving recombinated plasma clots

SciTech Connect

Slavin, V.S.; Danilov, V.V.; Sokolov, V.S.

1996-12-31

A new concept of a closed cycle MHD generator without alkali seed has been suggested. The essence of it is the phenomenon of frozen conductivity for recombined plasma which appears for noble gas at T{sub e} > 4,000 K. At the inlet of the MHD channel in supersonic flow of noble gas (He or Ar) the plasma clots with electron density about 10{sup 15} cm{sup {minus}3} are formed by pulsed intense electron beam with energy about 300 keV. Gas flow drives these clots in a cross magnetic field along the MHD channel which has electrodes connected with the load by Faraday scheme. The gas flow pushes plasma layers and produces electric power at the expense of enthalpy extraction. The numerical simulation has shown that a supersonic gas flow, containing about 4 plasma layers in the MHD channel simultaneously, is braked without shock waves creation. This type of the MHD generator can provide more than 30% enthalpy extraction ratio and about 80% isentropic efficiency. The advantages of the new concept are the following: (a) possibility of working at higher pressure and lower temperature, (b) operation with alkali seed.

20. Cylindrically-Symmetric Equilibria in Ideal MHD with Fractal Pressure Profiles

Kraus, Brian; Hudson, Stuart

2016-10-01

In ideal magnetohydrodynamics, unphysical, pressure-driven currents exist where flux surfaces with rational rotational transform coincide with pressure gradients, a situation Grad termed pathological''. As an alternative, we construct a non-trivial, continuous pressure profile that is flat on sufficiently wide intervals near each rational surface. Such a profile must be self-similar and thus fractal, because intervals of flat pressure exist around high-order rational surfaces at all scales. This infinite-resolution fractal pressure is analyzed as a homeomorphism of the Cantor set. Additionally, an algorithm has been written to numerically produce an approximation of the pressure profile, where only a finite number of rational surfaces are considered. Using this algorithm, we investigate the magnetic field and current profiles associated with the fractal pressure and a given rotational transform in cylindrical geometry. This work was supported by DOE contract DE-AC02-09CH11466.

1. Linear ideal MHD predictions for n = 2 non-axisymmetric magnetic perturbations on DIII-D

DOE PAGES

Haskey, Shaun R.; Lanctot, Matthew J.; Liu, Y. Q.; ...

2014-02-05

Here, an extensive examination of the plasma response to dominantly n = 2 non-axisymmetric magnetic perturbations (MPs) on the DIII-D tokamak shows the potential to control 3D field interactions by varying the poloidal spectrum of the radial magnetic field. The plasma response is calculated as a function of the applied magnetic field structure and plasma parameters, using the linear magnetohydrodynamic code MARS-F. The ideal, single fluid plasma response is decomposed into two main components: a local pitch-resonant response occurring at rational magnetic flux surfaces, and a global kink response. The efficiency with which the field couples to the total plasmamore » response is determined by the safety factor and the structure of the applied field. In many cases, control of the applied field has a more significant effect than control of plasma parameters, which is of particular interest since it can be modified at will throughout a shot to achieve a desired effect. The presence of toroidal harmonics, other than the dominant n = 2 component, is examined revealing a significant n = 4 component in the perturbations applied by the DIII-D MP coils; however, modeling shows the plasma responses to n = 4 perturbations are substantially smaller than the dominant n = 2 responses in most situations.« less

2. Adaptive Low Dissipative High Order Filter Methods for Multiscale MHD Flows

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sjoegreen, Bjoern

2004-01-01

Adaptive low-dissipative high order filter finite difference methods for long time wave propagation of shock/turbulence/combustion compressible viscous MHD flows has been constructed. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field [divergence of B] numerical error in the sense that no standard divergence cleaning is required. For certain 2-D MHD test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved.

3. Adaptive Low Dissipative High Order Filter Methods for Multiscale MHD Flows

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sjoegreen, Bjoern

2004-01-01

Adaptive low-dissipative high order filter finite difference methods for long time wave propagation of shock/turbulence/combustion compressible viscous MHD flows has been constructed. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field [divergence of B] numerical error in the sense that no standard divergence cleaning is required. For certain 2-D MHD test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved.

4. The direct criterion of Newcomb for the ideal MHD stability of an axisymmetric toroidal plasma

Glasser, A. H.

2016-07-01

A method is presented for determining the ideal magnetohydrodynamic stability of an axisymmetric toroidal plasma, based on a toroidal generalization of the method developed by Newcomb for fixed-boundary modes in a cylindrical plasma. For toroidal mode number n ≠ 0 , the stability problem is reduced to the numerical integration of a high-order complex system of ordinary differential equations, the Euler-Lagrange equation for extremizing the potential energy, for the coupled amplitudes of poloidal harmonics m as a function of the radial coordinate ψ in a straight-fieldline flux coordinate system. Unlike the cylindrical case, different poloidal harmonics couple to each other, which introduces coupling between adjacent singular intervals. A boundary condition is used at each singular surface, where m = nq and q ( ψ ) is the safety factor, to cross the singular surface and continue the solutions beyond it. Fixed-boundary instability is indicated by the vanishing of a real determinant of a Hermitian complex matrix constructed from the fundamental matrix of solutions, the generalization of Newcomb's crossing criterion. In the absence of fixed-boundary instabilities, an M × M plasma response matrix W P , with M the number of poloidal harmonics used, is constructed from the Euler-Lagrange solutions at the plasma-vacuum boundary. This is added to a vacuum response matrix W V to form a total response matrix W T . The existence of negative eigenvalues of W T indicates the presence of free-boundary instabilities. The method is implemented in the fast and accurate DCON code.

5. Thermoelectric Generation Using Counter-Flows of Ideal Fluids

Meng, Xiangning; Lu, Baiyi; Zhu, Miaoyong; Suzuki, Ryosuke O.

2017-08-01

Thermoelectric (TE) performance of a three-dimensional (3-D) TE module is examined by exposing it between a pair of counter-flows of ideal fluids. The ideal fluids are thermal sources of TE module flow in the opposite direction at the same flow rate and generate temperature differences on the hot and cold surfaces due to their different temperatures at the channel inlet. TE performance caused by different inlet temperatures of thermal fluids are numerically analyzed by using the finite-volume method on 3-D meshed physical models and then compared with those using a constant boundary temperature. The results show that voltage and current of the TE module increase gradually from a beginning moment to a steady flow and reach a stable value. The stable values increase with inlet temperature of the hot fluid when the inlet temperature of cold fluid is fixed. However, the time to get to the stable values is almost consistent for all the temperature differences. Moreover, the trend of TE performance using a fluid flow boundary is similar to that of using a constant boundary temperature. Furthermore, 3-D contours of fluid pressure, temperature, enthalpy, electromotive force, current density and heat flux are exhibited in order to clarify the influence of counter-flows of ideal fluids on TE generation. The current density and heat flux homogeneously distribute on an entire TE module, thus indicating that the counter-flows of thermal fluids have high potential to bring about fine performance for TE modules.

6. Conical flow near singular rays. [shock generation in ideal gas

NASA Technical Reports Server (NTRS)

Zahalak, G. I.; Myers, M. K.

1974-01-01

The steady flow of an ideal gas past a conical body is investigated by the method of matched asymptotic expansions, with particular emphasis on the flow near the singular ray occurring in linearized theory. The first-order problem governing the flow in this region is formulated, leading to the equation of Kuo, and an approximate solution is obtained in the case of compressive flow behind the main front. This solution is compared with the results of previous investigations with a view to assessing the applicability of the Lighthill-Whitham theories.

7. Computations of ideal and real gas high altitude plume flows

NASA Technical Reports Server (NTRS)

Feiereisen, William J.; Venkatapathy, Ethiraj

1988-01-01

In the present work, complete flow fields around generic space vehicles in supersonic and hypersonic flight regimes are studied numerically. Numerical simulation is performed with a flux-split, time asymptotic viscous flow solver that incorporates a generalized equilibrium chemistry model. Solutions to generic problems at various altitude and flight conditions show the complexity of the flow, the equilibrium chemical dissociation and its effect on the overall flow field. Viscous ideal gas solutions are compared against equilibrium gas solutions to illustrate the effect of equilibrium chemistry. Improved solution accuracy is achieved through adaptive grid refinement.

8. MHD effects on a thermo-solutal stratified nanofluid flow on an exponentially radiating stretching sheet

Hayat, T.; Rashid, M.; Imtiaz, M.; Alsaedi, A.

2017-03-01

This study is focused on the heat and mass transfer effects in a magnetohydrodynamic (MHD) flow of a viscous nanofluid saturating a porous medium past an exponentially radiating stretching sheet. The governing differential equations are transformed to a system of nonlinear ordinary differential equations by suitable transformations. It is noted that stratification affects the local Nusselt and Sherwood numbers.

9. MHD forced convection flow adjacent to a non-isothermal wedge

SciTech Connect

Yih, K.A.

1999-08-01

The problem of magnetohydrodynamic (MHD) incompressible viscous flow has many important engineering applications in devices such as MHD power generator and the cooling of reactors. In this analysis, the effects of viscous dissipation and stress work on the MHD forced convection adjacent to a non-isothermal wedge is numerically analyzed. These partial differential equations are transformed into the nonsimilar boundary layer equations and solved by the Keller box method. Numerical results for the local friction coefficient and the local Nusselt number are presented for the pressure gradient parameter m, the magnetic parameter {xi}, the Prandtl number Pr, and the Eckert number Ec. In general, increasing the pressure gradient parameter m or the magnetic parameter {xi} or the Prandtl number Pr or decreasing the Eckert number EC increases the local Nusselt number.

10. Simulation of 3-D Nonequilibrium Seeded Air Flow in the NASA-Ames MHD Channel

NASA Technical Reports Server (NTRS)

Gupta, Sumeet; Tannehill, John C.; Mehta, Unmeel B.

2004-01-01

The 3-D nonequilibrium seeded air flow in the NASA-Ames experimental MHD channel has been numerically simulated. The channel contains a nozzle section, a center section, and an accelerator section where magnetic and electric fields can be imposed on the flow. In recent tests, velocity increases of up to 40% have been achieved in the accelerator section. The flow in the channel is numerically computed us ing a 3-D parabolized Navier-Stokes (PNS) algorithm that has been developed to efficiently compute MHD flows in the low magnetic Reynolds number regime: The MHD effects are modeled by introducing source terms into the PNS equations which can then be solved in a very efficient manner. The algorithm has been extended in the present study to account for nonequilibrium seeded air flows. The electrical conductivity of the flow is determined using the program of Park. The new algorithm has been used to compute two test cases that match the experimental conditions. In both cases, magnetic and electric fields are applied to the seeded flow. The computed results are in good agreement with the experimental data.

11. Numerical study for MHD peristaltic flow in a rotating frame.

PubMed

Hayat, T; Zahir, Hina; Tanveer, Anum; Alsaedi, A

2016-12-01

The aim of present investigation is to model and analyze the magnetohydrodynamic (MHD) peristaltic transport of Prandtl fluid in a channel with flexible walls. The whole system consisting of fluid and channel are in a rotating frame of reference with uniform angular velocity. Viscous dissipation in thermal equation is not ignored. The channel boundaries satisfy the convective conditions in terms of temperature. The arising complicated problems are reduced in solvable form using large wavelength and small Reynolds number assumptions. Numerical solution for axial and secondary velocities, temperature and heat transfer coefficient are presented. Main emphasis is given to the outcome of rotation and material parameters of Prandtl fluid on the physical quantities of interest.

12. Flow aerodynamics modeling of an MHD swirl combustor - Calculations and experimental verification

NASA Technical Reports Server (NTRS)

Gupta, A. K.; Beer, J. M.; Louis, J. F.; Busnaina, A. A.; Lilley, D. G.

1981-01-01

The paper describes a computer code for calculating the flow dynamics of a constant-density flow in the second-stage trumpet shaped nozzle section of a two-stage MHD swirl combustor for application to a disk generator. The primitive pressure-velocity variable, finite-difference computer code has been developed for the computation of inert nonreacting turbulent swirling flows in an axisymmetric MHD model swirl combustor. The method and program involve a staggered grid system for axial and radial velocities, and a line relaxation technique for the efficient solution of the equations. The code produces as output the flow field map of the nondimensional stream function, axial and swirl velocity. It was found that the best location for seed injection to obtain a uniform distribution at the combustor exit is in the central location for seed injected at the entrance to the second stage combustor.

13. Velocity, temperature, and electrical conductivity profiles in hydrogen-oxygen MHD duct flows

NASA Technical Reports Server (NTRS)

Greywall, M. S.; Pian, C. C. P.

1978-01-01

This paper presents results of two-dimensional duct flow computations for radial distributions of velocity, temperature, and electrical conductivity. Calculations were carried out for the flow conditions representative of NASA Lewis hydrogen-oxygen combustion driven MHD duct. Results are presented for two sets of computations: (1) profiles of developing flow in a smooth duct, and (2) profiles of fully developed pipe flow with a specified streamwise shear stress distribution. The predicted temperature and electrical conductivity profiles for the developing flows compared well with available experimental data.

14. MHD Convective rotating flow past an oscillating porous plate with chemical reaction and Hall effects

Veera Krishna, M.; Gangadhar Reddy, M.

2016-09-01

In this paper, we have considered Hall effects on the unsteady MHD free convective rotating flow of visco-elastic fluid with heat and mass transfer near oscillating porous plate. The equations of the flow are solved by perturbation method for small elastic parameter. The analytical expressions for the velocity, temperature, concentration have been derived and also its behaviour is computationally discussed with the help of graphs. The skin friction, Nusselt number, and Sherwood number are also obtained analytically and their behaviour discussed.

15. On accelerated flow of MHD powell–eyring fluid via homotopy analysis method

Salah, Faisal; Viswanathan, K. K.; Aziz, Zainal Abdul

2017-09-01

The aim of this article is to obtain the approximate analytical solution for incompressible magnetohydrodynamic (MHD) flow for Powell–Eyring fluid induced by an accelerated plate. Both constant and variable accelerated cases are investigated. Approximate analytical solution in each case is obtained by using the Homotopy Analysis Method (HAM). The resulting nonlinear analysis is carried out to generate the series solution. Finally, Graphical outcomes of different values of the material constants parameters on the velocity flow field are discussed and analyzed.

16. DNS of MHD turbulent flow via the HELIOS supercomputer system at IFERC-CSC

Satake, Shin-ichi; Kimura, Masato; Yoshimori, Hajime; Kunugi, Tomoaki; Takase, Kazuyuki

2014-06-01

The simulation plays an important role to estimate characteristics of cooling in a blanket for such high heating plasma in ITER-BA. An objective of this study is to perform large -scale direct numerical simulation (DNS) on heat transfer of magneto hydro dynamic (MHD) turbulent flow on coolant materials assumed from Flibe to lithium. The coolant flow conditions in ITER-BA are assumed to be Reynolds number and Hartmann number of a higher order. The maximum target of the DNS assumed by this study based on the result of the benchmark of Helios at IFERC-CSC for Project cycle 1 is 116 TB (2048 nodes). Moreover, we tested visualization by ParaView to visualize directly the large-scale computational result. If this large-scale DNS becomes possible, an essential understanding and modelling of a MHD turbulent flow and a design of nuclear fusion reactor contributes greatly.

17. Behavior of fast earthward flow near the braking region: Hall MHD simulation

Lu, Xingqiang; Ma, Zhiwei; Guo, Wei

2016-10-01

Behavior of the fast earthward flow near the braking region in the magnetotail during a substorm is investigated using the Hall MHD simulation. The results indicate that the high-speed earthward plasma flow is associated with fast reconnection in the middle tail. The fast flow is mainly confined in the range -1.5RE < z < 1.5RE . In the region of -15RE < x < -9RE , due to intermittent magnetic reconnection, the earthward flow exhibits a fluctuating property, i.e., the flow is localized in space and is bursty in time. The pile-up of the magnetic flux and plasma in the near-Earth region leads to formation of the fast-flow braking region or dipolarization front. After colliding into the fast-flow braking region, a part of the Earth flow bounces back, and leads to an intermittent tailward flow in the near-Earth magnetotail.

18. Physical Model Development and Benchmarking for MHD Flows in Blanket Design

SciTech Connect

Ramakanth Munipalli; P.-Y.Huang; C.Chandler; C.Rowell; M.-J.Ni; N.Morley; S.Smolentsev; M.Abdou

2008-06-05

An advanced simulation environment to model incompressible MHD flows relevant to blanket conditions in fusion reactors has been developed at HyPerComp in research collaboration with TEXCEL. The goals of this phase-II project are two-fold: The first is the incorporation of crucial physical phenomena such as induced magnetic field modeling, and extending the capabilities beyond fluid flow prediction to model heat transfer with natural convection and mass transfer including tritium transport and permeation. The second is the design of a sequence of benchmark tests to establish code competence for several classes of physical phenomena in isolation as well as in select (termed here as “canonical”,) combinations. No previous attempts to develop such a comprehensive MHD modeling capability exist in the literature, and this study represents essentially uncharted territory. During the course of this Phase-II project, a significant breakthrough was achieved in modeling liquid metal flows at high Hartmann numbers. We developed a unique mathematical technique to accurately compute the fluid flow in complex geometries at extremely high Hartmann numbers (10,000 and greater), thus extending the state of the art of liquid metal MHD modeling relevant to fusion reactors at the present time. These developments have been published in noted international journals. A sequence of theoretical and experimental results was used to verify and validate the results obtained. The code was applied to a complete DCLL module simulation study with promising results.

19. MHD Flow of the Micropolar Fluid between Eccentrically Rotating Disks

PubMed Central

Srivastava, Neetu

2014-01-01

This analytical investigation examines the magnetohydrodynamic flow problem of an incompressible micropolar fluid between the two eccentrically placed disks. Employing suitable transformations, the flow governing partial differential equations is reduced to ordinary differential equations. An exact solution representing the different flow characteristic of micropolar fluid has been derived by solving the ordinary differential equations. Analysis of the flow characteristics of the micropolar fluid has been done graphically by varying the Reynolds number and the Hartmann number. This analysis has been carried out for the weak and strong interactions. PMID:27355040

20. Symmetry group analysis of an ideal plastic flow

Lamothe, Vincent

2012-03-01

In this paper, we study a finite-dimensional Lie point symmetry group of a system describing an ideal plastic plane flow in two dimensions in order to find analytical solutions. The infinitesimal generators that span this Lie algebra are given. We completely classify the subalgebras of codimension up to two into conjugacy classes under the action of the symmetry group. Based on invariant forms, we use Ansätze to compute symmetry reductions in such a way that the obtained solutions simultaneously cover many invariant and partially invariant solutions. We calculate solutions of algebraic, trigonometric, inverse trigonometric and elliptic type. Some solutions depending on one or two arbitrary functions of one variable have also been found. In some cases, the shape of a potentially feasible extrusion die corresponding to the solution is deduced. These tools could be used to thin, curve, undulate or shape a ring in an ideal plastic material.

1. A Numerical Study of Resistivity and Hall Effects for a Compressible MHD Model

NASA Technical Reports Server (NTRS)

Yee, H. C.; Sjogreen, B.

2005-01-01

The effect of resistive, Hall, and viscous terms on the flow structure compared with compressible ideal MHD is studied numerically for a one-fluid non-ideal MHD model. The goal of the present study is to shed some light on the emerging area of non-ideal MHD modeling and simulation. Numerical experiments are performed on a hypersonic blunt body flow with future application to plasma aerodynamics flow control in reentry vehicles. Numerical experiments are also performed on a magnetized time-developing mixing layer with possible application to magnetic/turbulence mixing.

2. Three-dimensional predictions of reactive turbulent recirculating flow of a cylindrical MHD type combustor

Lee, J. J.

1990-01-01

A computational procedure is employed to predict the axisymmetric reactive turbulent recirculating flow-field within a cylindrical MHD combustor. The procedure used in the analysis is an extended version of the three-dimensional Combustor Performance Program developed at the Garrett Turbine Engine Company. The separated flow created by four liquid fuel nozzles and 148 oxidizer holes passing through an injector plate is examined. Numerical results for flow, heat/mass transfer and combustion are presented to describe these complex three-dimensional interactions. The detailed analysis achieved by the numerical model is useful for evaluating combustor performance and in the interpretation of laboratory test data.

3. Self-consistent stationary MHD shear flows in the solar atmosphere as electric field generators

Nickeler, D. H.; Karlický, M.; Wiegelmann, T.; Kraus, M.

2014-09-01

Context. Magnetic fields and flows in coronal structures, for example, in gradual phases in flares, can be described by 2D and 3D magnetohydrostatic (MHS) and steady magnetohydrodynamic (MHD) equilibria. Aims: Within a physically simplified, but exact mathematical model, we study the electric currents and corresponding electric fields generated by shear flows. Methods: Starting from exact and analytically calculated magnetic potential fields, we solved the nonlinear MHD equations self-consistently. By applying a magnetic shear flow and assuming a nonideal MHD environment, we calculated an electric field via Faraday's law. The formal solution for the electromagnetic field allowed us to compute an expression of an effective resistivity similar to the collisionless Speiser resistivity. Results: We find that the electric field can be highly spatially structured, or in other words, filamented. The electric field component parallel to the magnetic field is the dominant component and is high where the resistivity has a maximum. The electric field is a potential field, therefore, the highest energy gain of the particles can be directly derived from the corresponding voltage. In our example of a coronal post-flare scenario we obtain electron energies of tens of keV, which are on the same order of magnitude as found observationally. This energy serves as a source for heating and acceleration of particles.

4. MHD Casson nanofluid flow past a wedge with Newtonian heating

Ahmad, Kartini; Hanouf, Zahir; Ishak, Anuar

2017-02-01

The problem of steady Casson nanofluid flow past a wedge is studied in this paper. The presence of magnetic field along with Newtonian heating at the surface is considered. The governing partial differential equations are first transformed into a set of nonlinear ordinary differential equations by similarity transformations, before being solved numerically using the Keller-box method. The effects of the wedge angle Ω from 0° (horizontal plate) to 180° (vertical plate) as well as of as the magnetic parameter M on the non-Newtonian fluid flow and heat transfer characteristics are investigated. It is found that the surface temperature is slightly higher for the flow over a horizontal plate compared to that over a vertical plate. It is also found that the magnetic field decreases the surface temperature but increases the skin friction. The flow of a Newtonian fluid is found to give higher skin friction as compared to that of Casson fluid.

5. Electric flow through an ideal ferromagnet-superconductor junction

Dobrescu, Oana Ancuta; Cune, L. C.; Apostol, M.

2009-04-01

It is investigated the possibility of controlling the electric flow through a ferromagnet-superconductor junction by spin polarization, within a simple, ideal model of a perfect ferromagnetic-superconductor junction. The ferromagnetic and superconducting properties as well as the Andreev reflection are briefly reviewed and the electrical resistance of the junction is computed both in the diffusive and ballistic regime for the ferromagnetic sample. It is shown that the resistance of the junction increases with increasing magnetization, including both positive or negative jumps on passing from the ballistic to the diffusive regime.

6. Two-dimensional magnetohydrodynamic simulations of poloidal flows in tokamaks and MHD pedestal

SciTech Connect

Guazzotto, L.; Betti, R.

2011-09-15

Poloidal rotation is routinely observed in present-day tokamak experiments, in particular near the plasma edge and in the high-confinement mode of operation. According to the magnetohydrodynamic (MHD) equilibrium theory [R. Betti and J. P. Freidberg, Phys. Plasmas 7, 2439 (2000)], radial discontinuities form when the poloidal velocity exceeds the poloidal sound speed (or rather, more correctly, the poloidal magneto-slow speed). Two-dimensional compressible magnetohydrodynamic simulations show that the transonic discontinuities develop on a time scale of a plasma poloidal revolution to form an edge density pedestal and a localized velocity shear layer at the pedestal location. While such an MHD pedestal surrounds the entire core, the outboard side of the pedestal is driven by the transonic discontinuity while the inboard side is caused by a poloidal redistribution of the mass. The MHD simulations use a smooth momentum source to drive the poloidal flow. Soon after the flow exceeds the poloidal sound speed, the density pedestal and the velocity shear layer form and persist into a quasi steady state. These results may be relevant to the L-H transition, the early stages of the pedestal and edge transport barrier formation.

7. Two-dimensional magnetohydrodynamic simulations of poloidal flows in tokamaks and MHD pedestal

Guazzotto, L.; Betti, R.

2011-09-01

Poloidal rotation is routinely observed in present-day tokamak experiments, in particular near the plasma edge and in the high-confinement mode of operation. According to the magnetohydrodynamic (MHD) equilibrium theory [R. Betti and J. P. Freidberg, Phys. Plasmas 7, 2439 (2000)], radial discontinuities form when the poloidal velocity exceeds the poloidal sound speed (or rather, more correctly, the poloidal magneto-slow speed). Two-dimensional compressible magnetohydrodynamic simulations show that the transonic discontinuities develop on a time scale of a plasma poloidal revolution to form an edge density pedestal and a localized velocity shear layer at the pedestal location. While such an MHD pedestal surrounds the entire core, the outboard side of the pedestal is driven by the transonic discontinuity while the inboard side is caused by a poloidal redistribution of the mass. The MHD simulations use a smooth momentum source to drive the poloidal flow. Soon after the flow exceeds the poloidal sound speed, the density pedestal and the velocity shear layer form and persist into a quasi steady state. These results may be relevant to the L-H transition, the early stages of the pedestal and edge transport barrier formation.

8. MHD free convective flow past a vertical plate

Raihan Mohamad Asimoni, Nor; Farahain Mohammad, Nurul; Kasim, Abdul Rahman Mohd; Shafie, Sharidan

2017-09-01

The free convective flow in incompressible viscous fluid past a vertical plate is studied under the presence of magnetic field. The flow is considered along the vertical plate at x – axis in upward direction and y – axis is taken normal to it. The governing equations are written in vector form. Afterwards, the equations are solved numerically using finite element method with automated solution techniques. Later, the effects of magnetic field strength to the velocity and temperature of the fluid are obtained. It is found that for heated plate, the velocity and the temperature of the fluid decreases when the magnetic field strength increases. Meanwhile for cooled plate, the velocity decreases but the temperature increases when the magnetic field strength increases.

9. MHD unsteady squeezing flow over a porous stretching plate

Hayat, T.; Qayyum, A.; Alsaedi, A.

2013-12-01

This article is concerned with the unsteady squeezing flow of non-Newtonian fluid between two parallel plates. A rheological equation of second grade fluid is used. The fluid is electrically conducting in the presence of a magnetic field. A transformation procedure reduces the partial differential equations into the ordinary differential equations. A series solution is developed using a modern mathematical scheme. The solution expressions for velocity components are computed and discussed. In addition, the skin friction coefficient is analyzed through tabulated values.

10. Resonant behaviour of MHD waves on magnetic flux tubes. III - Effect of equilibrium flow

NASA Technical Reports Server (NTRS)

Goossens, Marcel; Hollweg, Joseph V.; Sakurai, Takashi

1992-01-01

The Hollweg et al. (1990) analysis of MHD surface waves in a stationary equilibrium is extended. The conservation laws and jump conditions at Alfven and slow resonance points obtained by Sakurai et al. (1990) are generalized to include an equilibrium flow, and the assumption that the Eulerian perturbation of total pressure is constant is recovered as the special case of the conservation law for an equilibrium with straight magnetic field lines and flow along the magnetic field lines. It is shown that the conclusions formulated by Hollweg et al. are still valid for the straight cylindrical case. The effect of curvature is examined.

11. Numerical Solution of Boundary Layer MHD Flow with Viscous Dissipation

PubMed Central

Mishra, S. R.; Jena, S.

2014-01-01

The present paper deals with a steady two-dimensional laminar flow of a viscous incompressible electrically conducting fluid over a shrinking sheet in the presence of uniform transverse magnetic field with viscous dissipation. Using suitable similarity transformations the governing partial differential equations are transformed into ordinary differential equations and then solved numerically by fourth-order Runge-Kutta method with shooting technique. Results for velocity and temperature profiles for different values of the governing parameters have been discussed in detail with graphical representation. The numerical evaluation of skin friction and Nusselt number are also given in this paper. PMID:24672367

12. Flow Matching Results of an MHD Energy Bypass System on a Supersonic Turbojet Engine Using the Numerical Propulsion System Simulation (NPSS) Environment

NASA Technical Reports Server (NTRS)

Benyo, Theresa L.

2011-01-01

Flow matching has been successfully achieved for an MHD energy bypass system on a supersonic turbojet engine. The Numerical Propulsion System Simulation (NPSS) environment helped perform a thermodynamic cycle analysis to properly match the flows from an inlet employing a MHD energy bypass system (consisting of an MHD generator and MHD accelerator) on a supersonic turbojet engine. Working with various operating conditions (such as the applied magnetic field, MHD generator length and flow conductivity), interfacing studies were conducted between the MHD generator, the turbojet engine, and the MHD accelerator. This paper briefly describes the NPSS environment used in this analysis. This paper further describes the analysis of a supersonic turbojet engine with an MHD generator/accelerator energy bypass system. Results from this study have shown that using MHD energy bypass in the flow path of a supersonic turbojet engine increases the useful Mach number operating range from 0 to 3.0 Mach (not using MHD) to a range of 0 to 7.0 Mach with specific net thrust range of 740 N-s/kg (at ambient Mach = 3.25) to 70 N-s/kg (at ambient Mach = 7). These results were achieved with an applied magnetic field of 2.5 Tesla and conductivity levels in a range from 2 mhos/m (ambient Mach = 7) to 5.5 mhos/m (ambient Mach = 3.5) for an MHD generator length of 3 m.

13. MHD Coal Fired Flow Facility. Quarterly technical progress report, July-September 1980

SciTech Connect

Altstatt, M. C.; Attig, R. C.; Brosnan, D. A.

1980-11-01

Significant activity, task status, planned research, testing, development, and conclusions for the Magnetohydrodynamics (MHD) Coal-Fired Flow Facility (CFFF) and the Energy Conversion Facility (ECF) are described. On Task 1, the first phase of the downstream quench system was completed. On Task 2, all three combustor sections were completed, hydrotested, ASME code stamped, and delivered to UTSI. The nozzle was also delivered. Fabrication of support stands and cooling water manifolds for the combustor and vitiation heater were completed, heat transfer and thermal stress analysis, along with design development, were conducted on the generator and radiant furnace and secondary combustor installation progressed as planned. Under Task 3 an Elemental Analyzer and Atomic Absorption Spectrophotometer/Graphite Furnace were received and installed, sites were prepared for two air monitoring stations, phytoplankton analysis began, and foliage and soil sampling was conducted using all study plots. Some 288 soil samples were combined to make 72 samples which were analyzed. Also, approval was granted to dispose of MHD flyash and slag at the Franklin County landfill. Task 4 effort consisted of completing all component test plans, and establishing the capability of displaying experimental data in graphical format. Under Task 7, a preliminary testing program for critical monitoring of the local current and voltage non-uniformities in the generator electrodes was outlined, electrode metal wear characteristics were documented, boron nitride/refrasil composite interelectrode sealing was improved, and several refractories for downstream MHD applications were evaluated with promising results.

14. Preconditioning methods for ideal and multiphase fluid flows

Gupta, Ashish

The objective of this study is to develop a preconditioning method for ideal and multiphase multispecies compressible fluid flow solver using homogeneous equilibrium mixture model. The mathematical model for fluid flow going through phase change uses density and temperature in the formulation, where the density represents the multiphase mixture density. The change of phase of the fluid is then explicitly determined using the equation of state of the fluid, which only requires temperature and mixture density. The method developed is based on a finite-volume framework in which the numerical fluxes are computed using Roe's approximate Riemann solver and the modified Harten, Lax and Van-leer scheme (HLLC). All speed Roe and HLLC flux based schemes have been developed either by using preconditioning or by directly modifying dissipation to reduce the effect of acoustic speed in its numerical dissipation when Mach number decreases. Preconditioning proposed by Briley, Taylor and Whitfield, Eriksson and Turkel are studied in this research, where as low dissipation schemes proposed by Rieper and Thornber, Mosedale, Drikakis, Youngs and Williams are also considered. Various preconditioners are evaluated in terms of development, performance, accuracy and limitations in simulations at various Mach numbers. A generalized preconditioner is derived which possesses well conditioned eigensystem for multiphase multispecies flow simulations. Validation and verification of the solution procedure are carried out on several small model problems with comparison to experimental, theoretical, and other numerical results. Preconditioning methods are evaluated using three basic geometries; 1) bump in a channel 2) flow over a NACA0012 airfoil and 3) flow over a cylinder, which are then compared with theoretical and numerical results. Multiphase capabilities of the solver are evaluated in cryogenic and non-cryogenic conditions. For cryogenic conditions the solver is evaluated by predicting

15. Simulation of turbulent flow over idealized water waves

Sullivan, Peter P.; McWilliams, James C.; Moeng, Chin-Hoh

2000-02-01

Turbulent flow over idealized water waves with varying wave slope ak and wave age c/u[low asterisk] is investigated using direct numerical simulations at a bulk Reynolds number Re = 8000. In the present idealization, the shape of the water wave and the associated orbital velocities are prescribed and do not evolve dynamically under the action of the wind. The results show that the imposed waves significantly influence the mean flow, vertical momentum fluxes, velocity variances, pressure, and form stress (drag). Compared to a stationary wave, slow (fast) moving waves increase (decrease) the form stress. At small c/u[low asterisk], waves act similarly to increasing surface roughness zo resulting in mean vertical velocity profiles with shorter buffer and longer logarithmic regions. With increasing wave age, zo decreases so that the wavy lower surface is nearly as smooth as a flat lower boundary. Vertical profiles of turbulence statistics show that the wave effects depend on wave age and wave slope but are confined to a region kz < 1 (where k is the wavenumber of the surface undulation and z is the vertical coordinate). The turbulent momentum flux can be altered by as much as 40% by the waves. A region of closed streamlines (or cat's-eye pattern) centred about the critical layer height was found to be dynamically important at low to moderate values of c/u[low asterisk]. The wave-correlated velocity and flux fields are strongly dependent on the variation of the critical layer height and to a lesser extent the surface orbital velocities. Above the critical layer zcr the positions of the maximum and minimum wave-correlated vertical velocity ww occur upwind and downwind of the peak in zcr, like a stationary surface. The wave-correlated flux uwww is positive (negative) above (below) the critical layer height.

16. The effects of differential flow between rational surfaces on toroidal resistive MHD modes

Brennan, Dylan; Halfmoon, Michael; Rhodes, Dov; Cole, Andrew; Okabayashi, Michio; Paz-Soldan, Carlos; Finn, John

2016-10-01

Differential flow between resonant surfaces can strongly affect the coupling and penetration of resonant components of resistive modes, and yet this mechanism is not yet fully understood. This study focuses on the evolution of tearing instabilities and the penetration of imposed resonant magnetic perturbations (RMPs) in tokamak configurations relevant to DIII-D and ITER, including equilibrium flow shear. It has been observed on DIII-D that the onset of tearing instabilities leading to disruption is often coincident with a loss of differential rotation between a higher m/n tearing surface (normally the 4/3 or 3/2) and a lower m/n tearing surface (normally the 2/1). Imposing RMPs can strongly affect this coupling and the torques between the modes. We apply the nonlinear 3-D resistive magnetohydrodynamic (MHD) code NIMROD to study the mechanisms by which these couplings occur. Reduced MHD analyses are applied to study the effects of differential flow between resonant surfaces in the simulations. Interaction between resonant modes can cause significant energy transfer between them, effectively stabilizing one mode while the other grows. The flow mitigates this transfer, but also affects the individual modes. The combination of these effects determines the nonlinear outcome. Supported by US DOE Grants DE-SC0014005 and DE-SC0014119.

17. Study of multi-phase flow characteristics in an MHD power train

SciTech Connect

Chang, S.L.; Lottes, S.A.; Bouillard, J.X.; Petrick, M.

1993-08-01

Computer simulation was used to predict two-phase flow processes in the CDIF MHD power train system. The predictions were used to evaluate the effects of operating and design parameters on the performance of the system and a parametric evaluation provides information to enhance the performance of the system. Major components of the system under investigation are the two-stage combustor, the converging/diverging nozzle, the supersonic MHD channel, and the diffuser. Flow in each component was simulated using a computer code. Integrating the computer codes, the two-phase flow processes in the system was calculated. Recently, the computer codes were used to investigate problems of nozzle erosion and the non-uniform iron oxide coverage on the cathode wall in the channel. A limited parametric study was conducted. The results indicated that (1) among the three nozzle geometries under investigation a {number_sign}5 nozzle has the smoothest flow development in the nozzle and has the lowest droplet deposition on wall and (2) smaller particle size and lower injection velocity tend to disperse the iron oxide particles more uniformly in the nozzle.

18. An absorbing boundary formulation for the stratified, linearized, ideal MHD equations based on an unsplit, convolutional perfectly matched layer

Hanasoge, S. M.; Komatitsch, D.; Gizon, L.

2010-11-01

Perfectly matched layers are a very efficient way to absorb waves on the outer edges of media. We present a stable convolutional unsplit perfectly matched formulation designed for the linearized stratified Euler equations. The technique as applied to the Magneto-hydrodynamic (MHD) equations requires the use of a sponge, which, despite placing the perfectly matched status in question, is still highly efficient at absorbing outgoing waves. We study solutions of the equations in the backdrop of models of linearized wave propagation in the Sun. We test the numerical stability of the schemes by integrating the equations over a large number of wave periods.

19. Theory of the Equilibrium MHD Flow in the Plasma Thruster Exhaust

Novakowski, S. V.; Sagdeev, R. Z.

2000-10-01

Theory and numerical simulation of the plasma flow in the exhaust area of the plasma thruster are presented. The parameters of the VASIMR thruster (being developed by NASA in the Johnson Space Center, Houston, TX) are used for simulation. The plasma in VASIMR is immersed in a strong magnetic field (up to 0.2 T) such that both the ions and electrons are magnetized. Accordingly, an MHD model is used to describe the plasma flow. Simulations show that equilibrium flows with sub-alfvenic velocities are typical near the rocket. Further away, the transition to the super-alfvenic flow takes place, which leads to change in the magnetic configuration and the consequent plasma detachment. The scalings of such detachment will be presented for different magnetic configurations of the external coils and as functions of other plasma parameters.

20. Measurements of the 3D boundary distortion due to external n=2 magnetic perturbations in comparison to ideal MHD

Willensdorfer, Matthias; Suttrop, Wolfgang; Strumberger, Erika; Zohm, Hartmut; Orain, Francois; Kirk, Andrew; Ryan, David; ASDEX Upgrade Team Team

2016-10-01

Best ELM mitigation/suppression at DIII-D and AUG are achieved by external magnetic perturbation (MP) fields, when the applied poloidal mode spectrum is aligned with the mode (kink) at the edge that is most strongly amplified by the plasma. This kink mode causes a 3D displacement of the plasma boundary, which is characterized at AUG using data from toroidally localized high resolution diagnostics and rigid rotating MP-fields with different applied poloidal mode spectra. Various profile and imaging diagnostics, e.g. electron cyclotron emission (ECE), are used to determine the amplitude, the penetration and the poloidal mode structure of the displacement around the outer midplane. The displacement around the X-point/plasma top, which is related to ELM mitigation, is measured using a new steerable ECE and SOFT X-ray. These measurements are compared to MHD codes like JOREK, MARS-F and VMEC. As predicted by MHD, the measured amplitudes clearly exceed the vacuum field calculations. The displacement measured by imaging ECE indicates a resonant response, although the calculated magnetic structure of this edge kink peaks at poloidal mode numbers larger than the resonant components.

1. Identification of standing fronts in steady state fluid flows: exact and approximate solutions for propagating MHD modes

Pantellini, Filippo; Griton, Léa

2016-10-01

The spatial structure of a steady state plasma flow is shaped by the standing modes with local phase velocity exactly opposite to the flow velocity. The general procedure of finding the wave vectors of all possible standing MHD modes in any given point of a stationary flow requires numerically solving an algebraic equation. We present the graphical procedure (already mentioned by some authors in the 1960's) along with the exact solution for the Alfvén mode and approximate analytic solutions for both fast and slow modes. The technique can be used to identify MHD modes in space and laboratory plasmas as well as in numerical simulations.

2. The study of turbulence in MHD flow generated by rotating and traveling magnetic fields

Kolesnichenko, Ilya; Pavlinov, Alexander; Golbraikh, Ephim; Frick, Peter; Kapusta, Arkadii; Mikhailovich, Boris

2015-05-01

We consider a problem of spectral analysis of signals from electromagnetic sensors operating in a turbulent MHD flow generated by rotating and traveling magnetic fields, which create a strong electromagnetic noise. Using a wavelet-based technique for cross-correlation signal analysis and filtration, we show that at frequencies lower than the frequency of the applied magnetic field, the spectral properties of the velocity field can be clearly seen in spite of the fact that the measured fields are much weaker than the driving rotating (or traveling) magnetic field. On the basis of the proposed method, spectra of turbulent velocity fields, measured in the experiment, were studied.

3. MHD stagnation point flow over a stretching cylinder with variable thermal conductivity and joule heating

Jahan, Shah; Sakidin, Hamzah; Nazar, Roslinda Mohd

2016-11-01

The behavior of magnetohydrodynamics (MHD) flow of viscous fluid near the stagnation point over a stretching cylinder with variable thermal conductivity is analyzed. Thermal conductivity is assumed to be linearly related with temperature. The joule heating effects due to magnetic field is also encountered here. Analytical solutions are developed for both momentum and energy equations by using the homotopy analysis method (HAM). The variations of different parameters on the velocity and temperature distributions along with the skin friction coefficient and local Nusselt number are displayed graphically. Numerical values for the skin friction coefficient are calculated and discussed

4. Thin film flow in MHD third grade fluid on a vertical belt with temperature dependent viscosity.

PubMed

Gul, Taza; Islam, Saed; Shah, Rehan Ali; Khan, Ilyas; Shafie, Sharidan

2014-01-01

In this work, we have carried out the influence of temperature dependent viscosity on thin film flow of a magnetohydrodynamic (MHD) third grade fluid past a vertical belt. The governing coupled non-linear differential equations with appropriate boundary conditions are solved analytically by using Adomian Decomposition Method (ADM). In order to make comparison, the governing problem has also been solved by using Optimal Homotopy Asymptotic Method (OHAM). The physical characteristics of the problem have been well discussed in graphs for several parameter of interest.

5. Thin Film Flow in MHD Third Grade Fluid on a Vertical Belt with Temperature Dependent Viscosity

PubMed Central

Gul, Taza; Islam, Saed; Shah, Rehan Ali; Khan, Ilyas; Shafie, Sharidan

2014-01-01

In this work, we have carried out the influence of temperature dependent viscosity on thin film flow of a magnetohydrodynamic (MHD) third grade fluid past a vertical belt. The governing coupled non-linear differential equations with appropriate boundary conditions are solved analytically by using Adomian Decomposition Method (ADM). In order to make comparison, the governing problem has also been solved by using Optimal Homotopy Asymptotic Method (OHAM). The physical characteristics of the problem have been well discussed in graphs for several parameter of interest. PMID:24949988

6. MHD Coal-Fired Flow Facility. Quarterly technical progress report, April-June 1980

SciTech Connect

Altstatt, M. C.; Attig, R. C.; Baucum, W. E.

1980-07-31

Significant activity, task status, planned research, testing, development, and conclusions for the Magnetohydrodynamics (MHD) Coal-Fired Flow Facility (CFFF) and the Energy Conversion Facility (ECF), formerly the Research and Development Laboratory, are reported. CFFF Bid Package construction is now virtually complete. The remaining construction effort is being conducted by UTSI. On the quench system, another Task 1 effort, the cyclone was erected on schedule. On Tasks 2 through 6, vitiation heater and nozzle fabrication were completed, an investigation of a fish kill (in no way attributable to CFFF operations) in Woods Reservoir was conducted, major preparation for ambient air quality monitoring was made, a broadband data acquisition system for enabling broadband data to be correlated with all general performance data was selected, a Coriolis effect coal flow meter was installed at the CFFF. On Task 7, an analytical model of the coal flow combustor configuration was prepared, MHD generator testing which, in part, involved continued materials evaluation and the heat transfer characteristics of capped and uncapped electrodes was conducted, agglomerator utilization was studied, and development of a laser velocimeter system was nearly completed.

7. Localized reconnection in the magnetotail driven by lobe flow channels: Global MHD simulation

Nishimura, Y.; Lyons, L. R.

2016-02-01

Recent ionospheric measurements suggest polar cap flow channels often trigger nightside auroral brightening. However, measurements were limited to the ionosphere, and it was not understood if such flow channels can exist in the lobe and can trigger magnetotail reconnection in a localized cross-tail extent. We examined if localized flow channels can form self-consistently in a global MHD regime, and if so, how such flow channels originate and relate to localized magnetotail reconnection. We show that lobe convection became nonuniform with azimuthally narrow flow channels (enhanced dawn-dusk electric fields) of ~3 RE cross-tail width. The flow channels propagated from the dayside toward the plasma sheet as an interplanetary magnetic field (IMF) discontinuity swept tailward. The plasma sheet around the lobe flow channels became thinner with a similar cross-tail extent and then localized reconnection occurred. These results suggest that localized flow channels can propagate tailward across the lobe and drive localized magnetotail reconnection, that the cross-tail width of reconnection and resulting plasma sheet flow channels and dipolarization fronts are related to the width of inflow from the lobe, and that IMF discontinuities drive lobe flow channels.

8. Periodic MHD flow with temperature dependent viscosity and thermal conductivity past an isothermal oscillating cylinder

Ahmed, Rubel; Rana, B. M. Jewel; Ahmmed, S. F.

2017-06-01

Temperature dependent viscosity and thermal conducting heat and mass transfer flow with chemical reaction and periodic magnetic field past an isothermal oscillating cylinder have been considered. The partial dimensionless equations governing the flow have been solved numerically by applying explicit finite difference method with the help Compaq visual 6.6a. The obtained outcome of this inquisition has been discussed for different values of well-known flow parameters with different time steps and oscillation angle. The effect of chemical reaction and periodic MHD parameters on the velocity field, temperature field and concentration field, skin-friction, Nusselt number and Sherwood number have been studied and results are presented by graphically. The novelty of the present problem is to study the streamlines by taking into account periodic magnetic field.

9. 2D-simulation of stationary MHD flows in the ducts of rectangular cross-section

Khalzov, Ivan; Ilgisonis, Victor

2005-10-01

The numerical code for a calculation of 2D stationary MHD flows of incompressible conducting viscous fluids (liquid metals) in straight and circular ducts of rectangular cross-section is developed. The flows are driven by the electrical current perpendicular both to the duct axis and to the external magnetic field. The code generalizes the well-known iterative Gauss-Seidel method for the case of systems of elliptic equations. The algorithm developed allows us to carry out the calculations of stationary flows in a wide range of Hartmann (Ha=110^3) and Reynolds (Re=110^6) numbers. The numerical results are presented for the experimental device, which is under construction in Russia.

10. Hall effect on MHD flow and heat transfer over a stretching sheet with variable thickness

Prasad, K. V.; Vajravelu, K.; Vaidya, Hanumesh

2016-07-01

We investigate the MHD flow and heat transfer of an electrically conducting fluid over a stretching sheet with variable thickness. The wall temperature and the wall velocity are assumed to vary. The effects of external magnetic field along the sheet and the Hall currents are considered. The governing equations are solved numerically using an implicit finite difference scheme. The obtained numerical results are compared with the available results in the literature for some special cases and the results are found to be in very good agreement. The effects of the physical parameters on the velocity and temperature fields are presented graphically and analyzed. The effect of the Hall current gives rise to a cross flow. Moreover, the Hall current and the magnetic field have strong effect on the flow and heat transfer characteristics, i.e., shear stress and the Nusselt number.

11. Dual Solutions of MHD Boundary Layer Flow of a Micropolar Fluid with Weak Concentration over a Stretching/Shrinking Sheet

Khan, Z. H.; Qasim, M.; Ishfaq, Naeema; Khan, W. A.

2017-04-01

We investigate the dual solutions for the MHD flow of micropolar fluid over a stretching/shrinking sheet with heat transfer. Suitable relations transform the partial differential equations into the ordinary differential equations. Closed forms solutions are also obtained in terms of confluent hypergeometric function. This is the first attempt to determine the exact solutions for the non-linear equations of MHD micropolar fluid model. It is demonstrated that the microrotation parameter helps in increasing Nusselt number and the dual solutions exist for all fluid flow parameters under consideration. The dual behavior of dimensionless velocity, temperature, microrotation, skin-friction coefficient, local Nusselt number is displayed on graphs and examined.

12. Initial Flow Matching Results of MHD Energy Bypass on a Supersonic Turbojet Engine Using the Numerical Propulsion System Simulation (NPSS) Environment

NASA Technical Reports Server (NTRS)

Benyo, Theresa L.

2010-01-01

Preliminary flow matching has been demonstrated for a MHD energy bypass system on a supersonic turbojet engine. The Numerical Propulsion System Simulation (NPSS) environment was used to perform a thermodynamic cycle analysis to properly match the flows from an inlet to a MHD generator and from the exit of a supersonic turbojet to a MHD accelerator. Working with various operating conditions such as the enthalpy extraction ratio and isentropic efficiency of the MHD generator and MHD accelerator, interfacing studies were conducted between the pre-ionizers, the MHD generator, the turbojet engine, and the MHD accelerator. This paper briefly describes the NPSS environment used in this analysis and describes the NPSS analysis of a supersonic turbojet engine with a MHD generator/accelerator energy bypass system. Results from this study have shown that using MHD energy bypass in the flow path of a supersonic turbojet engine increases the useful Mach number operating range from 0 to 3.0 Mach (not using MHD) to an explored and desired range of 0 to 7.0 Mach.

13. Numerical study of a rotational MHD flow containing polydisperse nonconducting inclusions in a cylindrical pipe

SciTech Connect

Blinov, V.I.; Kazachkov, I.V.; Kolesnichenko, A.F.

1988-01-01

Average characteristics are determined for the first stage of MHD flow in a conducting liquid containing nonconducting inclusions in a channel having nonmetallic walls exposed to crossed electric and magnetic fields. For the second stage, a structural approach is used to evaluate particle paths, clumping, and effects on clumping. Using these criteria, the angular velocity of the stationary rotational motion can be approximated. Particle motion in this rotating flow was considered. Particle paths were determined with an M-4030 computer by solving a second-order differential system. The Runge-Kutta method was used. Raising the field frequency and selecting the optimum ratio for the bulk electromagnetic forces was found to increase the particle concentration and the coagulation rate at the center.

14. Approximate analytical solution for MHD stagnation-point flow in porous media

Awang Kechil, S.; Hashim, I.

2009-04-01

In this paper, the steady two-dimensional laminar forced MHD Hiemenz flow against a flat plate with variable wall temperature in a porous medium which was solved numerically using the implicit finite-difference of Keller-box method [Yih KA. The effect of uniform suction/blowing on heat transfer of magnetohydrodynamic Hiemenz flow through porous media. Acta Mech 1998;130:147-58] is revisited. A simple analytic approach of the Adomian decomposition method (ADM) is employed to obtain an approximate analytical solution of the problem. The skin friction coefficient and the rate of heat transfer given by the ADM are in good agreement with the numerical solutions of the Keller-box method.

15. Techniques for measurement of velocity in liquid-metal MHD flows

SciTech Connect

Reed, C.B.; Picologlou, B.F.; Dauzvardis, P.V.; Bailey, J.L.

1986-01-01

Three instruments for measuring local velocities in liquid-metal MHD experiments for fusion blanket applications are being evaluated. The devices are used in room-temperature NaK experiments to measure three-dimensional flow field patterns anticipated in complex blanket geometries. Hot film anemometry, a standard technique in ordinary fluids, is being used, as well as two developmental devices. One is called the Liquid Metal Electromagnetic Velocity Instrument (LEVI), and performs essentially as a local dc electromagnetic flow meter. The third device, a Thermal Transient Anemometer (TTA) is a rugged, yet relatively simple device, which measures local velocity through the mechanism of convective heat transfer, in some ways similar to hot-film anemometry. Results are presented showing the kinds of data collected this far with each instrument. Measurements include both local velocity measurements and some preliminary frequency analyses of the fluctuating signals from both a hot-film sensor and the LEVI device.

16. Magnetohydrodynamic (MHD) flow of Cu-water nanofluid due to a rotating disk with partial slip

SciTech Connect

Hayat, Tasawar; Rashid, Madiha; Imtiaz, Maria; Alsaedi, Ahmed

2015-06-15

This paper investigates MHD steady flow of viscous nanofluid due to a rotating disk. Water is treated as a base fluid and copper as nanoparticle. Nanofluid fills the porous medium. Effects of partial slip, viscous dissipation and thermal radiation are also considered. Similarity transformations reduce the nonlinear partial differential equations to ordinary differential equations. Flow and heat transfer characteristics are computed by HAM solutions. Also computations for skin friction coefficient and Nusselt number are presented and examined for pertinent parameters. It is noted that higher velocity slip parameter decreases the radial and azimuthal velocities while temperature decreases for larger values of the thermal slip parameter. Also the rate of heat transfer enhances when the nanoparticle volume fraction increases.

17. Techniques for measurement of velocity in liquid-metal MHD flows

SciTech Connect

Reed, C.B.; Picologlou, B.F.; Dauzvardis, P.V.; Bailey, J.L.

1986-11-01

Three instruments for measuring local velocities in liquid-metal MHD experiments for fusion blanket applications are being evaluated. The devices are used in room-temperature NaK experiments to measure three-dimensional flow field patterns anticipated in complex blanket geometries. Hot film anemometry, a standard technique in ordinary fluids, is being used, as well as two developmental devices. One is called the Liquid Metal Electromagnetic Velocity Instrument (LEVI), and performs essentially as a local DC electromagnetic flow meter. The third device, a Thermal Transient Anemometer (TTA) is a rugged, yet relatively simple device, which measures local velocity through the mechanism of convective heat transfer, in some ways similar to hot-film anemometry. Results are presented showing the kinds of data collected thus far with each instrument. Measurements include both local velocity measurements and some preliminary frequency analyses of the fluctuating signals from both a hot-film sensor and the LEVI device.

18. Analytical study on two-phase MHD flow of electrically conducting magnetic fluid

SciTech Connect

Okubo, Masaaki; Ishimoto, Jun; Nishiyama, Hideya; Kamiyama, Shinichi

1994-01-01

An energy conversion system using magnetic fluids proposed by Resler and Rosensweig was based on the principle that the magnetization of magnetic fluids changes with temperature. However, significant results have not been obtained up to the present. To overcome this limit and to increase the acceleration of fluid flow the authors have contributed a new energy conversion system using two-phase flow produced by heat addition. This idea came from the two-phase liquid-metal MHD power generation system proposed by Petrick and Branover. If temperature sensitive magnetic fluids are used, such a system can produce a larger force than conventional systems because the properties of apparent magnetization change not only by temperature rise but also by gas inclusion. In the present paper, an analytical study is extended to the case of electrically conducting magnetic fluid as a basic study for demonstrating the possibility of application of electrically conducting magnetic fluid to working fluid in a liquid-metal MHD power generation system. Electrically conducting magnetic fluid is usually prepared by dispersing fine iron particles into a liquid metal such as mercury. To prevent a solidification of particles and keep a homogeneous dispersion, a thin film of tin is attached to the particles surface. Thus the electrically conducting liquid behaves as fluid itself having magnetization. The equations governing a one-dimensional boiling two-phase duct flow of such an electrically conducting magnetic fluid in a traverse magnetic field are numerically solved. The analytical results of the two-phase flow characteristics of the magnetic fluid are compared with ones of an electrically conducting nonmagnetic fluid.

19. Heat enhanced by an exothermic reaction on a fully developed MHD mixed convection flow in a vertical channel

Jayabalan, C.; Sivagnana Prabhu, K. K.; Kandasamy, R.

2016-09-01

The problem of a fully developed MHD mixed convection flow in a vertical channel with the first-order chemical reaction is analyzed. The dimensionless governing ordinary differential equations are solved numerically by using the Maple 18 software. It is observed that dual solutions exist for both velocity and temperature.

20. Chemical solver to compute molecule and grain abundances and non-ideal MHD resistivities in prestellar core-collapse calculations

Marchand, P.; Masson, J.; Chabrier, G.; Hennebelle, P.; Commerçon, B.; Vaytet, N.

2016-07-01

We develop a detailed chemical network relevant to calculate the conditions that are characteristic of prestellar core collapse. We solve the system of time-dependent differential equations to calculate the equilibrium abundances of molecules and dust grains, with a size distribution given by size-bins for these latter. These abundances are used to compute the different non-ideal magneto-hydrodynamics resistivities (ambipolar, Ohmic and Hall), needed to carry out simulations of protostellar collapse. For the first time in this context, we take into account the evaporation of the grains, the thermal ionisation of potassium, sodium, and hydrogen at high temperature, and the thermionic emission of grains in the chemical network, and we explore the impact of various cosmic ray ionisation rates. All these processes significantly affect the non-ideal magneto-hydrodynamics resistivities, which will modify the dynamics of the collapse. Ambipolar diffusion and Hall effect dominate at low densities, up to nH = 1012 cm-3, after which Ohmic diffusion takes over. We find that the time-scale needed to reach chemical equilibrium is always shorter than the typical dynamical (free fall) one. This allows us to build a large, multi-dimensional multi-species equilibrium abundance table over a large temperature, density and ionisation rate ranges. This table, which we make accessible to the community, is used during first and second prestellar core collapse calculations to compute the non-ideal magneto-hydrodynamics resistivities, yielding a consistent dynamical-chemical description of this process. The multi-dimensional multi-species equilibrium abundance table and a copy of the code are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A18

1. A Bayesian study of uncertainty in ultrasonic flow meters under non-ideal flow conditions

Belligoli, Z.; Dwight, R. P.; Kok, G. J. P.; Lucas, P.

2017-08-01

This paper presents an approach for updating the epistemic uncertainty of ultrasonic flow meter measurements under non-ideal flow conditions. Instead of re-calibrating the instrument to correct its behavior in these difficult working conditions, a Bayesian calibration of a computer model of the real process is used. The numerical model is based on computational fluid dynamics (CFD) and a surrogate model is constructed from a limited number of CFD calculations using kriging. The computer model predicts the flow rate dependent on certain parameters including the bulk Reynolds number—which carries information about the true speed of the flow, and is measured only approximately by an ultrasonic flow meter. Bayesian calibration is applied, and the posterior of the true speed can be derived from the marginal posterior of the Reynolds number. This pdf has a smaller uncertainty with respect to the observed data used to fit the model on the condition that sufficiently informative data are available. If this is the case, the proposed approach is capable of reducing not only the uncertainty but also the error associated with the flow meter measurements in non-ideal conditions.

2. MHD stagnation-point flow and heat transfer over a permeable stretching/shrinking sheet

Ali, Fadzilah Md; Nazar, Roslinda; Arifin, Norihan; Pop, Ioan

2014-06-01

The steady magnetohydrodynamic (MHD) two-dimensional stagnation-point boundary layer flow and heat transfer of a viscous, incompressible and electrically conducting fluid over a permeable flat stretching/shrinking sheet in the presence of an externally applied magnetic field of constant strength is studied. The governing partial differential equations are first transformed into a system of ordinary differential equations, which is then been solved numerically using a shooting method built in Maple software. It is found that the heat transfer rate at the surface reduces with the Eckert number and it is also found that dual solutions exist for certain values of the mass flux parameter and the stretching/shrinking parameter.

3. Stability analysis of MHD viscous flow and heat transfer over a permeable shrinking surface

Hafidzuddin, Mohd Ezad Hafidz; Nazar, Roslinda

2015-10-01

In this study, a problem of steady laminar magnetohydrodynamic (MHD) viscous boundary layer flow and heat transfer over a permeable shrinking surface is considered. The governing nonlinear partial differential equations are transformed into a system of nonlinear ordinary differential equations using a similarity transformation. The transformed ordinary differential equations are then solved numerically using the bvp4c function in MATLAB software. Dual solutions are found for a certain range of the suction parameter. A stability analysis has been performed to determine which solution is stable and physically realizable. The effects of the suction parameter, the Hartmann number and the Prandtl number on the skin friction and heat transfer coefficients as well as the velocity and temperature profiles are presented and discussed in detail.

4. Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel.

PubMed

Gul, Aaiza; Khan, Ilyas; Shafie, Sharidan; Khalid, Asma; Khan, Arshad

2015-01-01

This study investigated heat transfer in magnetohydrodynamic (MHD) mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4) was selected as a conventional base fluid. In addition, non-magnetic (Al2O3) aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work.

5. MHD Flow and Heat Transfer between Coaxial Rotating Stretchable Disks in a Thermally Stratified Medium

PubMed Central

Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed

2016-01-01

This paper investigates the unsteady MHD flow of viscous fluid between two parallel rotating disks. Fluid fills the porous space. Energy equation has been constructed by taking Joule heating, thermal stratification and radiation effects into consideration. We convert system of partial differential equations into system of highly nonlinear ordinary differential equations after employing the suitable transformations. Convergent series solutions are obtained. Behavior of different involved parameters on velocity and temperature profiles is examined graphically. Numerical values of skin friction coefficient and Nusselt number are computed and inspected. It is found that tangential velocity profile is increasing function of rotational parameter. Fluid temperature reduces for increasing values of thermal stratification parameter. At upper disk heat transfer rate enhances for larger values of Eckert and Prandtl numbers. PMID:27218651

6. Slip effects on MHD flow and heat transfer of ferrofluids over a moving flat plate

Ramli, Norshafira; Ahmad, Syakila; Pop, Ioan

2017-08-01

In this study, the problem of MHD flow and heat transfer of ferrofluids over a moving flat plate with slip effect and uniform heat flux is considered. The governing ordinary differential equations are solved via shooting method. The effect of slip parameter on the dimensionless velocity, temperature, skin friction and Nusselt numbers are numerically studied for the three selected ferroparticles; magnetite (Fe3O4), cobalt ferrite (CoFe2O4) and Mn-Zn ferrite (Mn-ZnFe2O4) with water-based fluid. The results indicate that dual solutions exist for a plate moving towards the origin. It is found that the slip process delays the boundary layer separation. Moreover, the velocity and thermal boundary-layer thicknesses decrease in the first solution while increase with the increase of the value of slip parameters in second solution.

7. Numerical study of MHD nanofluid flow and heat transfer past a bidirectional exponentially stretching sheet

Ahmad, Rida; Mustafa, M.; Hayat, T.; Alsaedi, A.

2016-06-01

Recent advancements in nanotechnology have led to the discovery of new generation coolants known as nanofluids. Nanofluids possess novel and unique characteristics which are fruitful in numerous cooling applications. Current work is undertaken to address the heat transfer in MHD three-dimensional flow of magnetic nanofluid (ferrofluid) over a bidirectional exponentially stretching sheet. The base fluid is considered as water which consists of magnetite-Fe3O4 nanoparticles. Exponentially varying surface temperature distribution is accounted. Problem formulation is presented through the Maxwell models for effective electrical conductivity and effective thermal conductivity of nanofluid. Similarity transformations give rise to a coupled non-linear differential system which is solved numerically. Appreciable growth in the convective heat transfer coefficient is observed when nanoparticle volume fraction is augmented. Temperature exponent parameter serves to enhance the heat transfer from the surface. Moreover the skin friction coefficient is directly proportional to both magnetic field strength and nanoparticle volume fraction.

8. Hall Effects on Mhd Flow Past an Accelerated Plate with Heat Transfer

Sundarnath, J. K.; Muthucumarswamy, R.

2015-02-01

Hall current and rotation on an MHD flow past an accelerated horizontal plate relative to a rotating fluid, in the presence of heat transfer has been analyzed. The effects of the Hall parameter, Hartmann number, rotation parameter (non-dimensional angular velocity), Grashof's number and Prandtl number on axial and transverse velocity profiles are presented graphically. It is found that with the increase in the Hartmann number, the axial and transverse velocity components increase in a direction opposite to that of obtained by increasing the Hall parameter and rotation parameter. Also, when Ω=M2m /(1 + m2 ) , it is observed that the transverse velocity component vanishes and axial velocity attains a maximum value.

9. Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel

PubMed Central

Gul, Aaiza; Khan, Ilyas; Shafie, Sharidan; Khalid, Asma; Khan, Arshad

2015-01-01

This study investigated heat transfer in magnetohydrodynamic (MHD) mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4) was selected as a conventional base fluid. In addition, non-magnetic (Al2O3) aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work. PMID:26550837

10. MHD Flow and Heat Transfer between Coaxial Rotating Stretchable Disks in a Thermally Stratified Medium.

PubMed

Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed

2016-01-01

This paper investigates the unsteady MHD flow of viscous fluid between two parallel rotating disks. Fluid fills the porous space. Energy equation has been constructed by taking Joule heating, thermal stratification and radiation effects into consideration. We convert system of partial differential equations into system of highly nonlinear ordinary differential equations after employing the suitable transformations. Convergent series solutions are obtained. Behavior of different involved parameters on velocity and temperature profiles is examined graphically. Numerical values of skin friction coefficient and Nusselt number are computed and inspected. It is found that tangential velocity profile is increasing function of rotational parameter. Fluid temperature reduces for increasing values of thermal stratification parameter. At upper disk heat transfer rate enhances for larger values of Eckert and Prandtl numbers.

11. Influence of aligned MHD on convective boundary layer flow of viscoelastic fluid

Aziz, Laila Amera; Kasim, Abdul Rahman Mohd; Al-Sharifi, H. A. M.; Salleh, Mohd Zuki; Mohammad, Nurul Farahain; Shafie, Sharidan; Ali, Anati

2017-05-01

Effects of aligned Magnetohydrodynamics (MHD) on the mixed convection boundary layer flow of viscoelastic fluid past a circular cylinder with Newtonian heating is investigated. Appropriate transformation is applied to the governing partial differential equations to transform them into dimensionless forms which are then solved using finite difference method known as Keller box. For verification purpose, the preliminary numerical solutions of the model are compared with previous study with a particular condition that the magnetic and viscosity effect are both absent. With strong agreement between the previous and current results, the authors believe that the extended outcome produced from the present model is accurate. Findings from the study will be presented in tabular and graphical form.

12. Unsteady Flow of Radiating and Chemically Reacting MHD Micropolar Fluid in Slip-Flow Regime with Heat Generation

Abo-Dahab, S. M.; Mohamed, R. A.

2013-11-01

An analytical study of the problem of unsteady free convection with thermal radiation and heat generation on MHD micropolar fluid flow through a porous medium bounded by a semi-infinite vertical plate in a slip-flow regime has been presented. The Rosseland diffusion approximation is used to describe the radiation heat flux in the energy equation. The homogeneous chemical reaction of first order is accounted for in the mass diffusion equation. A uniform magnetic field acts perpendicular on the porous surface absorbing micropolar fluid with a suction velocity varying with time. A perturbation technique is applied to obtain the expressions for the velocity, microrotation, temperature, and concentration distributions. Expressions for the skin-friction, Nusselt number, and Sherwood number are also obtained. The results are discussed graphically for different values of the parameters entered into the equations of the problem.

13. Output from MHD Models

Vlahakis, Nektarios

2010-03-01

Outflows emanating from the environment of stellar or galactic objects are a widespread phenomenon in astrophysics. Their morphology ranges from nearly spherically symmetric winds to highly collimated jets. In some cases, e.g., in jets associated with young stellar objects, the bulk outflow speeds are nonrelativistic, while in others, e.g., in jets associated with active galactic nuclei or gamma-ray bursts, it can even be highly relativistic. The main driving mechanism of collimated outflows is likely related to magnetic fields. These fields are able to tap the rotational energy of the compact object or disk, accelerate, and collimate matter ejecta. To zeroth order these outflows can be described by the highly intractable theory of magnetohydrodynamics (MHD). Even in systems where the assumptions of zero resistivity (ideal MHD), steady state, axisymmetry, one fluid description, and polytropic equation of state are applicable, the problem remains difficult. In this case the problem reduces to only two equations, corresponding to the two components of the momentum equation along the flow and in the direction perpendicular to the magnetic field (transfield direction). The latter equation is the most difficult to solve, but also the most important. It answers the question on the degree of the collimation, but also crucially affects the solution of the first, the acceleration efficiency and the bulk velocity of the flow. The first and second parts of this chapter refer to nonrelativistic and relativistic flows, respectively. These Parts can be read independently. In each one, the governing equations are presented and discussed, focusing on the case of flows that are magnetically dominated near the central source. The general characteristics of the solutions in relation to the acceleration and collimation mechanisms are analyzed. As specific examples of exact solutions of the full system of the MHD equations that satisfy all the analyzed general characteristics, self

14. Vorticity transport in shock driven plasma flows: A comparison of MHD and two-fluid models

Bond, Daryl; Wheatley, Vincent; Pullin, Dale; Samtaney, Ravi

2015-11-01

Suppression of the Richtmyer-Meshkov instability in a plasma, through the application of a seed magnetic field, has been studied in the framework of ideal magnetohydrodymanics. These studies have shown that suppression is achieved through the transport of vorticity by magnetohydrodynamic waves away from a perturbed fluid-fluid interface where it was baroclinically generated by shock impact. The implementation of a more physically accurate, fully electromagnetic, two-fluid plasma representation allows a more realistic investigation of vorticity transport in shock driven plasma flows. Results comparing ideal one-dimensional two-fluid and magnetohydrodymanic flows are presented. Substantial increases in the complexity of the flow field and vorticity transport dynamics are observed with important ramifications for the stabilization of shock driven interfaces. This work was partially supported by the KAUST Office of Sponsored Research under Award URF/1/2162-01.

15. MHD three-dimensional flow of viscoelastic fluid over an exponentially stretching surface with variable thermal conductivity

2016-09-01

This study models the magnetohydrodynamic (MHD) three-dimensional boundary layer flow of viscoelastic fluid. The flow is due to the exponentially stretching surface. The heat transfer analysis is performed through prescribed surface temperature (PST) and prescribed surface heat flux (PHF). The thermal conductivity is taken temperature dependent. Series solutions of velocities and temperatures are constructed. Graphical results for PST and PHF cases are plotted and analyzed. Numerical values of skin-friction coefficients and Nusselt numbers are presented and discussed.

16. Linear ideal MHD predictions for n = 2 non-axisymmetric magnetic perturbations on DIII-D

SciTech Connect

Haskey, Shaun R.; Lanctot, Matthew J.; Liu, Y. Q.; Blackwell, B. D.; Nazikian, Raffi

2014-02-05

Here, an extensive examination of the plasma response to dominantly n = 2 non-axisymmetric magnetic perturbations (MPs) on the DIII-D tokamak shows the potential to control 3D field interactions by varying the poloidal spectrum of the radial magnetic field. The plasma response is calculated as a function of the applied magnetic field structure and plasma parameters, using the linear magnetohydrodynamic code MARS-F. The ideal, single fluid plasma response is decomposed into two main components: a local pitch-resonant response occurring at rational magnetic flux surfaces, and a global kink response. The efficiency with which the field couples to the total plasma response is determined by the safety factor and the structure of the applied field. In many cases, control of the applied field has a more significant effect than control of plasma parameters, which is of particular interest since it can be modified at will throughout a shot to achieve a desired effect. The presence of toroidal harmonics, other than the dominant n = 2 component, is examined revealing a significant n = 4 component in the perturbations applied by the DIII-D MP coils; however, modeling shows the plasma responses to n = 4 perturbations are substantially smaller than the dominant n = 2 responses in most situations.

17. 3D Euler equations and ideal MHD mapped to regular systems: Probing the finite-time blowup hypothesis

Bustamante, Miguel D.

2011-06-01

We prove by an explicit construction that solutions to incompressible 3D Euler equations defined in the periodic cube Ω=[0 can be mapped bijectively to a new system of equations whose solutions are globally regular. We establish that the usual Beale-Kato-Majda criterion for finite-time singularity (or blowup) of a solution to the 3D Euler system is equivalent to a condition on the corresponding regular solution of the new system. In the hypothetical case of Euler finite-time singularity, we provide an explicit formula for the blowup time in terms of the regular solution of the new system. The new system is amenable to being integrated numerically using similar methods as in Euler equations. We propose a method to simulate numerically the new regular system and describe how to use this to draw robust and reliable conclusions on the finite-time singularity problem of Euler equations, based on the conservation of quantities directly related to energy and circulation. The method of mapping to a regular system can be extended to any fluid equation that admits a Beale-Kato-Majda type of theorem, e.g. 3D Navier-Stokes, 2D and 3D magnetohydrodynamics, and 1D inviscid Burgers. We discuss briefly the case of 2D ideal magnetohydrodynamics. In order to illustrate the usefulness of the mapping, we provide a thorough comparison of the analytical solution versus the numerical solution in the case of 1D inviscid Burgers equation.

18. Two-Dimensional MHD Simulations of Tokamak Plasmas with Poloidal Flow

Guazzotto, L.; Betti, R.

2002-11-01

A two- dimensional MHD code has been developed to simulate the temporal evolution of Tokamak plasmas with an imposed poloidal flow. The code is fully compressible and can resolve the shock structures arising when the poloidal velocity is of the order of the poloidal sound speed (V_θ ˜ Cs B_θ/B) near the plasma edge, where the plasma is cold and the sound speed is low. The poloidal flow is assigned as an initial condition with a velocity profile ranging from subsonic to supersonic near the edge. It is found that a continuous band of shocks is formed near the edge. Such shocks travel poloidally, leaving behind a pedestal structure similar to the one predicted in Ref. 1 [R. Betti and J. P. Freidberg, Phys. Plasmas 7, 2439 (2000)]. Here, the pedestal is defined as a sharp discontinuity in the pressure, temperature, and density profiles. The pedestal height is modulated in the poloidal angle; it is maximum on the outboard side (θ = 0) and minimum on the inboard (θ = π). Furthermore, both poloidal and toroidal flows develop a shear layer at the location of the pedestal. The large velocity shear (both poloidal and toroidal) occurring in the pedestal region is likely to suppress turbulent eddies and reduce anomalous transport. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

19. Initial Characterization of V-4Cr-4Ti and MHD Coatings Exposed to Flowing Li

SciTech Connect

Pint, Bruce A; Pawel, Steven J; Howell, Michael; Moser, Jeremy L; Garner, George Walter; Santella, Michael L; Tortorelli, Peter F; Wiffen, Frederick W; Distefano, James R

2009-01-01

Conduct an experiment with flowing Li in a thermal gradient to determine the compatibility of V-4Cr-4Ti and a multi-layer electrically-insulating coating needed to reduce the magneto hydrodynamic (MHD) force in the first wall of a lithium cooled blanket. A mono-metallic V-4Cr-4Ti thermal convection loop was operated in vacuum ({approx}10{sup -5}Pa) at a maximum Li temperature of 700 C for 2,355h and Li flow rate of 2-3 cm/s. Two-layer, physical vapor deposited Y{sub 2}O{sub 3}-vanadium, electrically-insulating coatings on V-4Cr-4Ti substrates as well as uncoated tensile and sheet specimens were located in the flow path in the hot and cold legs. After exposure, specimens at the top of the hot leg showed a maximum mass loss equivalent to {approx}1.3 {micro}m of uniform metal loss. Elsewhere, small mass gains were observed on the majority of specimens that also showed an increase in hardness and room temperature yield stress and a decrease in ductility consistent with interstitial uptake. Specimens that lost mass showed a decrease in yield stress and hardness. Profilometry showed no significant thickness loss from the coatings.

20. A Method to Simulate Linear Stability of Impulsively Accelerated Density Interfaces in Ideal-MHD and Gas Dynamics

SciTech Connect

Ravi Samtaney

2009-02-10

We present a numerical method to solve the linear stability of impulsively accelerated density interfaces in two dimensions such as those arising in the Richtmyer-Meshkov instability. The method uses an Eulerian approach, and is based on an unwind method to compute the temporally evolving base state and a flux vector splitting method for the perturbations. The method is applicable to either gas dynamics or magnetohydrodynamics. Numerical examples are presented for cases in which a hydrodynamic shock interacts with a single or double density interface, and a doubly shocked single density interface. Convergence tests show that the method is spatially second order accurate for smooth flows, and between first and second order accurate for flows with shocks.

1. Impact of E × B shear flow on low-n MHD instabilities

Chen, J. G.; Xu, X. Q.; Ma, C. H.; Xi, P. W.; Kong, D. F.; Lei, Y. A.

2017-05-01

Recently, the stationary high confinement operations with improved pedestal conditions have been achieved in DIII-D [K. H. Burrell et al., Phys. Plasmas 23, 056103 (2016)], accompanying the spontaneous transition from the coherent edge harmonic oscillation (EHO) to the broadband MHD turbulence state by reducing the neutral beam injection torque to zero. It is highly significant for the burning plasma devices such as ITER. Simulations about the effects of E × B shear flow on the quiescent H-mode (QH-mode) are carried out using the three-field two-fluid model in the field-aligned coordinate under the BOUT++ framework. Using the shifted circular cross-section equilibriums including bootstrap current, the results demonstrate that the E × B shear flow strongly destabilizes low-n peeling modes, which are mainly driven by the gradient of parallel current in peeling-dominant cases and are sensitive to the Er shear. Adopting the much more general shape of E × B shear ( ω E = E r / R B θ ) profiles, the linear and nonlinear BOUT++ simulations show qualitative consistence with the experiments. The stronger shear flow shifts the most unstable mode to lower-n and narrows the mode spectrum. At the meantime, the nonlinear simulations of the QH-mode indicate that the shear flow in both co- and counter directions of diamagnetic flow has some similar effects. The nonlinear mode interaction is enhanced during the mode amplitude saturation phase. These results reveal that the fundamental physics mechanism of the QH-mode may be shear flow and are significant for understanding the mechanism of EHO and QH-mode.

2. First results from different investigations on MHD flow in multichannel U-Bends

SciTech Connect

Reimann, J.; Barleon, L.; Molokov, S.

1995-04-01

In electrically coupled multichannel ducts with a U-bend geometry, MHD effects can result in strongly non-uniform distributions of flow rates Q{sub i} and pressure drops {Delta}p{sub i} in the individual channels. A multichannel U-bend geometry is part of the KfK self-cooled Pb-17Li blanket design for a fusion reactor (radial-toroidal-radial channels). However, inserts are proposed which decouple electrically the radial channels. The multi-channel effects (MCDs) were investigated by (i) Screening test with InGaSn at LAS, Riga, and (ii) more detailed experiments with NaK at KfK, Karlsruhe. Different flow channel geometries and channel numbers between 1 and 5 were used. Hartmann numbers and interaction parameters were varied between O {le} M {le} 2300 and O {le} N {le} 40000. In parallel, a theoretical analysis was performed, based on the method of core flow approximation (CFA) which is valid for M {r_arrow} {infinity} and N {r_arrow} {infinity}. Significant MCEs occur in all ducts with totally electrically coupled channels. For the mode {Delta}p{sub i} = const, the flow rates in the outer channels can become significantly larger than those in the inner channels. For Q{sub i} = const, the highest pressure drop occurs in the middle channel and the lowest in the outer channels. The CFA predicts correctly the ratios of the pressure drops of the single channels but gives lower values than observed experimentally. No marked MCE was found for flow geometry which is similar to the KfK design, i.e., a fairly uniform flow rate and pressure drop distribution was observed for all values of M and N.

3. Effects of Magnetic Field on the Turbulent Wake of a Cylinder in MHD Channel Flow

SciTech Connect

John Rhoads; Edlundd, Eric; Ji, Hantao

2013-04-01

Results from a free-surface MHD flow experiment are presented detailing the modi cation of vortices in the wake of a circular cylinder with its axis parallel to the applied magnetic fi eld. Experiments were performed with a Reynolds number near Re ~ 104 as the interaction parameter, N = |j x B| / |ρ (υ • ∇), was increased through unity. By concurrently sampling the downstream fluid velocity at sixteen cross-stream locations in the wake, it was possible to extract an ensemble of azimuthal velocity profi les as a function of radius for vortices shed by the cylinder at varying strengths of magnetic field. Results indicate a signi cant change in vortex radius and rotation as N is increased. The lack of deviations from the vortex velocity pro file at high magnetic fi elds suggests the absence of small-scale turbulent features. By sampling the wake at three locations downstream in subsequent experiments, the decay of the vortices was examined and the effective viscosity was found to decrease as N-049±0.4. This reduction in effective viscosity is due to the modi cation of the small-scale eddies by the magnetic fi eld. The slope of the energy spectrum was observed to change from a k-1.8 power-law at low N to a k-3.5 power-law for N > 1. Together, these results suggest the flow smoothly transitioned to a quasi-two-dimensional state in the range 0 < N < 1.

4. MHD pressure drop of NaK flow in stainless steel pipe

SciTech Connect

Miyazaki, K.; Kotake, S.

1983-09-01

An experiment on electric potential and pressure drop for NaK flow in uniform transverse magnetic fields was conducted. A test channel was constructed using 45.3 mm (or 28 mm) I.D. and 1.65 mm thick 304-SS circular pipe in the NaK-Blowdown MHD Experimental Facility of Osaka University. The experimental range covered had a driving gas pressure <8 bar, an applied magnetic flux density: B/sub 0/=0.3 about1.75 T, a mean flow velocity of NaK: U/sub 0/=2 about 15 m/sec, a Reynolds number Re = 8 X 10/sup 4/ about6.2 X 10/sup 5/ and a Hartmann number: Ha = 740 about4150. A theoretical analysis is given on the basis of a uniform-velocity thick-wall model. Good agreement between the theory and the experiment were obtained both for the potential and for the pressure drop, except a small deviation of the experimental pressure drop towards values lying above the theoretical ones in a weak B/sub 0/ and high U/sub 0/ region (Ha/sup 2//Re <15).

5. Boundary layer flow of MHD tangent hyperbolic nanofluid over a stretching sheet: A numerical investigation

Khan, Mair; Hussain, Arif; Malik, M. Y.; Salahuddin, T.; Khan, Farzana

This article presents the two-dimensional flow of MHD hyperbolic tangent fluid with nanoparticles towards a stretching surface. The mathematical modelling of current flow analysis yields the nonlinear set of partial differential equations which then are reduce to ordinary differential equations by using suitable scaling transforms. Then resulting equations are solved by using shooting technique. The behaviour of the involved physical parameters (Weissenberg number We , Hartmann number M , Prandtl number Pr , Brownian motion parameter Nb , Lewis number Le and thermophoresis number Nt) on velocity, temperature and concentration are interpreted in detail. Additionally, local skin friction, local Nusselt number and local Sherwood number are computed and analyzed. It has been explored that Weissenberg number and Hartmann number are decelerate fluid motion. Brownian motion and thermophoresis both enhance the fluid temperature. Local Sherwood number is increasing function whereas Nusselt number is reducing function for increasing values of Brownian motion parameter Nb , Prandtl number Pr , thermophoresis parameter Nt and Lewis number Le . Additionally, computed results are compared with existing literature to validate the accuracy of solution, one can see that present results have quite resemblance with reported data.

6. Chemical reaction and radiation effects on MHD flow past an exponentially stretching sheet with heat sink

Nur Wahida Khalili, Noran; Aziz Samson, Abdul; Aziz, Ahmad Sukri Abdul; Ali, Zaileha Md

2017-09-01

In this study, the problem of MHD boundary layer flow past an exponentially stretching sheet with chemical reaction and radiation effects with heat sink is studied. The governing system of PDEs is transformed into a system of ODEs. Then, the system is solved numerically by using Runge-Kutta-Fehlberg fourth fifth order (RKF45) method available in MAPLE 15 software. The numerical results obtained are presented graphically for the velocity, temperature and concentration. The effects of various parameters are studied and analyzed. The numerical values for local Nusselt number, skin friction coefficient and local Sherwood number are tabulated and discussed. The study shows that various parameters give significant effect on the profiles of the fluid flow. It is observed that the reaction rate parameter affected the concentration profiles significantly and the concentration thickness of boundary layer decreases when reaction rate parameter increases. The analysis found is validated by comparing with the results previous work done and it is found to be in good agreement.

7. Unsteady MHD Mixed Convection Flow of a Micropolar Fluid Over a Vertical Wedge

Roy, N. C.; Gorla, R. S. R.

2017-05-01

An analysis is presented to investigate the unsteady magnetohydrodynamic (MHD) mixed convection boundary-layer flow of a micropolar fluid over a vertical wedge in the presence of thermal radiation and heat generation or absorption. The free-stream velocity and surface temperature are assumed to be oscillating in magnitude but not in the direction of the oncoming flow velocity. The governing equations have been solved by two distinct methods, namely, the finite difference method for the entire frequency range, and the series solution for low frequency range and the asymptotic series expansion method for the high frequency range. Numerical solutions provide a good agreement with the series solutions. The amplitudes of skin friction and couple stress coefficients are found to be strongly dependent on the Richardson number and the vortex viscosity parameter. The Prandtl number, the conduction-radiation parameter, the surface temperature parameter and the pressure gradient parameter significantly affect the amplitudes of skin friction, couple stress and surface heat transfer rates. However, the amplitudes of skin friction coefficient are considerably affected by the magnetic field parameter, whereas the amplitudes of heat transfer rate are appreciably changed with the heat generation or absorption parameter. In addition, results are presented for the transient skin friction, couple stress and heat transfer rate with the variations of the Richardson number, the vortex viscosity parameter, the pressure gradient parameter and the magnetic field parameter.

8. Optimal homotopy perturbation method for nonlinear differential equations governing MHD Jeffery-Hamel flow with heat transfer problem

Marinca, Vasile; Ene, Remus-Daniel

2017-01-01

In this paper, the Optimal Homotopy Perturbation Method (OHPM) is employed to determine an analytic approximate solution for the nonlinear MHD Jeffery-Hamel flow and heat transfer problem. The Navier-Stokes equations, taking into account Maxwell's electromagnetism and heat transfer, lead to two nonlinear ordinary differential equations. The results obtained by means of OHPM show very good agreement with numerical results and with Homotopy Perturbation Method (HPM) results.

9. Influence of radiation on MHD peristaltic blood flow through a tapered channel in presence of slip and joule heating

Ahamad, N. Ameer; Ravikumar, S.; Govindaraju, Kalimuthu

2017-07-01

The aim of the present attempt was to investigate an effect of slip and joule heating on MHD peristaltic Newtonian fluid through an asymmetric vertical tapered channel under influence of radiation. The Mathematical modeling is investigated by utilizing long wavelength and low Reynolds number assumptions. The effects of Hartmann number, porosity parameter, volumetric flow rate, radiation parameter, non uniform parameter, shift angle, Prandtl number, Brinkman number, heat source/sink parameter on temperature characteristics are presented graphically and discussed in detail.

10. Soret and Dufour Effects on MHD Peristaltic Flow of Jeffrey Fluid in a Rotating System with Porous Medium

PubMed Central

Hayat, Tasawar; Rafiq, Maimona; Ahmad, Bashir

2016-01-01

The objective of present paper is to examine the peristaltic flow of magnetohydrodynamic (MHD) Jeffrey fluid saturating porous space in a channel through rotating frame. Unlike the previous attempts, the flow formulation is based upon modified Darcy's law porous medium effect in Jeffrey fluid situation. In addition the impacts due to Soret and Dufour effects in the radiative peristaltic flow are accounted. Rosseland’s approximation has been utilized for the thermal radiative heat flux. Lubrication approach is implemented for the simplification. Resulting problems are solved for the stream function, temperature and concentration. Graphical results are prepared and analyzed for different parameters of interest entering into the problems. PMID:26808387

11. Soret and Dufour Effects on MHD Peristaltic Flow of Jeffrey Fluid in a Rotating System with Porous Medium.

PubMed

Hayat, Tasawar; Rafiq, Maimona; Ahmad, Bashir

2016-01-01

The objective of present paper is to examine the peristaltic flow of magnetohydrodynamic (MHD) Jeffrey fluid saturating porous space in a channel through rotating frame. Unlike the previous attempts, the flow formulation is based upon modified Darcy's law porous medium effect in Jeffrey fluid situation. In addition the impacts due to Soret and Dufour effects in the radiative peristaltic flow are accounted. Rosseland's approximation has been utilized for the thermal radiative heat flux. Lubrication approach is implemented for the simplification. Resulting problems are solved for the stream function, temperature and concentration. Graphical results are prepared and analyzed for different parameters of interest entering into the problems.

12. Hall effects on MHD flow of heat generating/absorbing fluid through porous medium in a rotating parallel plate channel

Swarnalathamma, B. V.; Krishna, M. Veera

2017-07-01

We studied heat transfer on MHD convective flow of viscous electrically conducting heat generating/absorbing fluid through porous medium in a rotating channel under uniform transverse magnetic field normal to the channel and taking Hall current. The flow is governed by the Brinkman's model. The diagnostic solutions for the velocity and temperature are obtained by perturbation technique and computationally discussed with respect to flow parameters through the graphs. The skin friction and Nusselt number are also evaluated and computationally discussed with reference to pertinent parameters in detail.

13. MHD Modelling of Coronal Loops: Injection of High-Speed Chromospheric Flows

NASA Technical Reports Server (NTRS)

Petralia, A.; Reale, F.; Orlando, S.; Klimchuk, J. A.

2014-01-01

Context. Observations reveal a correspondence between chromospheric type II spicules and bright upward-moving fronts in the corona observed in the extreme-ultraviolet (EUV) band. However, theoretical considerations suggest that these flows are probably not the main source of heating in coronal magnetic loops. Aims. We investigate the propagation of high-speed chromospheric flows into coronal magnetic flux tubes and the possible production of emission in the EUV band. Methods. We simulated the propagation of a dense 104 K chromospheric jet upward along a coronal loop by means of a 2D cylindrical MHD model that includes gravity, radiative losses, thermal conduction, and magnetic induction. The jet propagates in a complete atmosphere including the chromosphere and a tenuous cool (approximately 0.8 MK) corona, linked through a steep transition region. In our reference model, the jet initial speed is 70 km per second, its initial density is 10(exp 11) per cubic centimeter, and the ambient uniform magnetic field is 10 G. We also explored other values of jet speed and density in 1D and different magnetic field values in 2D, as well as the jet propagation in a hotter (approximately 1.5 MK) background loop. Results. While the initial speed of the jet does not allow it to reach the loop apex, a hot shock-front develops ahead of it and travels to the other extreme of the loop. The shock front compresses the coronal plasma and heats it to about 10(exp 6) K. As a result, a bright moving front becomes visible in the 171 Angstrom channel of the SDO/AIA mission. This result generally applies to all the other explored cases, except for the propagation in the hotter loop. Conclusions. For a cool, low-density initial coronal loop, the post-shock plasma ahead of upward chromospheric flows might explain at least part of the observed correspondence between type II spicules and EUV emission excess.

14. Thermo-Diffusion and Diffuso-Thermo Effects on MHD Squeezing Flow Between Parallel Disks

Khan, Sheikh Irfanullah; Mohyud-Din, Syed Tauseef; Bin-Mohsin, Bandar

In this article, Magnetohydrodynamic (MHD) squeezing flow between two parallel disks is considered. The upper disk is taken to be solid and the lower one is permeable. Soret and Dufour effects are measured to explore the thermal-diffusion and diffusion-thermo effects. Governing PDEs are converted into system of ODEs with the support of suitable similarity transforms. Homotopy analysis method (HAM) has been employed to obtain the expressions for velocity, temperature and concentration profiles. Effects of different emerging parameters such as squeezing number S, Hartman number M, Prandtl number Pr, Eckert number Ec, dimensionless length δ and Schmidt number Sc on the flow are also discussed with the help of graphs for velocity, temperature and concentration. The local Nusselt and Sherwood numbers along with convergence of the series solutions are presented with the help of graphs. From the results obtained, we observed that the physical quantities like skin friction coefficient increases with increasing value of Hartmann number M in the blowing case (A<0) whereas a fall is observed in the suction case (A>0). However, the rate of heat transfer at upper wall increases with increasing values of Dufour number Du and Soret number Sr for both the suction (A>0) and blowing flow (A<0), whereas, for the larger values of Dufour number Du and smaller values of Soret number Sr, a rapid fall is observed in Sherwood number Sh for both the suction (A>0) and blowing (A<0) cases. A numerical solution is obtained by employing Runge-Kutta method of order four (RK-4) to check the validity and reliability of the developed algorithm. A well agreement is found between both the solutions.

15. Reactive transport in stratified flow fields with idealized heterogeneity

Carleton, James N.; Montas, Hubert J.

2009-06-01

A two-dimensional equation governing the steady state spatial concentration distribution of a reactive constituent within a heterogeneous advective-dispersive flow field is solved analytically. The solution which is developed for the case of a single point source can be generalized to represent analogous situations with any number of separate point sources. A limiting case of special interest has a line source of constant concentration spanning the domain's upstream boundary. The work has relevance for improving understanding of reactive transport within various kinds of advection-dominated natural or engineered environments including rivers and streams, and bioreactors such as treatment wetlands. Simulations are used to examine quantitatively the impact that transverse dispersion (deviations from purely stochastic-convective flow) can have on mean concentration decline in the direction of flow. Results support the contention that transverse mixing serves to enhance the overall rate of reaction in such systems.

16. Efficient Low Dissipative High Order Schemes for Multiscale MHD Flows. II; Minimization of Delta * B Numerical Error

NASA Technical Reports Server (NTRS)

Sjoegreen, Bjoern; Yee, H. C.

2003-01-01

The generalization of a class of low-dissipative high order filter finite difference schemes for long time wave propagation of shock/turbulence/combustion compressible viscous gas dynamic flows to compressible MHD equations for structured curvilinear grids has been developed. The new scheme consists 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. Several variants of the filter approach that cater to different flow types are proposed. These filters provide a natural and efficient way for the minimization of the divergence of the magnetic field (Delta * B) numerical error in the sense that no standard divergence cleaning is required. Performance evaluation of these variants, and the key role that the proper treatment of their corresponding numerical boundary conditions can play will be illustrated. Many levels of grid refinement and detailed comparison with several commonly used compressible MHD shock-capturing schemes will be sought. For certain MHD 2-D test problems, divergence free preservation of the magnetic fields of these filter schemes has been achieved.

17. A consistent and conservative scheme for MHD flows with complex boundaries on an unstructured Cartesian adaptive system

SciTech Connect

Zhang, Jie; Ni, Ming-Jiu

2014-01-01

The numerical simulation of Magnetohydrodynamics (MHD) flows with complex boundaries has been a topic of great interest in the development of a fusion reactor blanket for the difficulty to accurately simulate the Hartmann layers and side layers along arbitrary geometries. An adaptive version of a consistent and conservative scheme has been developed for simulating the MHD flows. Besides, the present study forms the first attempt to apply the cut-cell approach for irregular wall-bounded MHD flows, which is more flexible and conveniently implemented under adaptive mesh refinement (AMR) technique. It employs a Volume-of-Fluid (VOF) approach to represent the fluid–conducting wall interface that makes it possible to solve the fluid–solid coupling magnetic problems, emphasizing at how electric field solver is implemented when conductivity is discontinuous in cut-cell. For the irregular cut-cells, the conservative interpolation technique is applied to calculate the Lorentz force at cell-center. On the other hand, it will be shown how consistent and conservative scheme is implemented on fine/coarse mesh boundaries when using AMR technique. Then, the applied numerical schemes are validated by five test simulations and excellent agreement was obtained for all the cases considered, simultaneously showed good consistency and conservative properties.

18. MHD heat and mass transfer flow over a permeable stretching/shrinking sheet with radiation effect

Mat Yasin, Mohd Hafizi; Ishak, Anuar; Pop, Ioan

2016-06-01

The steady two-dimensional magnetohydrodynamic (MHD) flow past a permeable stretching/shrinking sheet with radiation effects is investigated. The similarity transformation is introduced to transform the governing partial differential equations into a system of ordinary differential equations before being solved numerically using a shooting method. The results are obtained for the skin friction coefficient, the local Nusselt number and the local Sherwood number as well as the velocity, temperature and the concentration profiles for some values of the governing parameters, namely, suction/injection parameter S, stretching/shrinking parameter λ, magnetic parameter M, radiation parameter R, heat source/sink Q and chemical rate parameter K. For the shrinking case, there exist two solutions for a certain range of parameters, but the solution is unique for the stretching case. The stability analysis verified that the upper branch solution is linearly stable and physically reliable while the lower branch solution is not. For the reliable solution, the skin friction coefficient increases in the present of magnetic field. The heat transfer rate at the surface decreases in the present of radiation.

19. Thermophysical effects of carbon nanotubes on MHD flow over a stretching surface

Ul Haq, Rizwan; Khan, Zafar Hayat; Khan, Waqar Ahmed

2014-09-01

This article is intended for investigating the effects of magnetohydrodynamics (MHD) and volume fraction of carbon nanotubes (CNTs) on the flow and heat transfer in two lateral directions over a stretching sheet. For this purpose, three types of base fluids specifically water, ethylene glycol and engine oil with single and multi-walled carbon nanotubes are used in the analysis. The convective boundary condition in the presence of CNTs is presented first time and not been explored so far. The transformed nonlinear differential equations are solved by the Runge-Kutta-Fehlberg method with a shooting technique. The dimensionless velocity and shear stress are obtained in both directions. The dimensionless heat transfer is determined on the surface. Three different models of thermal conductivity are comparable for both CNTs and it is found that the Xue [1] model gives the best approach to guess the superb thermal conductivity in comparison with the Maxwell [2] and Hamilton and Crosser [3] models. And finally, another finding suggests the engine oil provides the highest skin friction and heat transfer rates.

20. Particle simulation algorithms with short-range forces in MHD and fluid flow

SciTech Connect

Cable, S.; Tajima, T.; Umegaki, K.

1992-07-01

Attempts are made to develop numerical algorithms for handling fluid flows involving liquids and liquid-gas mixtures. In these types of systems, the short-range intermolecular interactions are important enough to significantly alter behavior predicted on the basis of standard fluid mechanics and magnetohydrodynamics alone. We have constructed a particle-in-cell (PIC) code for the purpose of studying the effects of these interactions. Of the algorithms considered, the one which has been successfully implemented is based on a MHD particle code developed by Brunel et al. In the version presented here, short range forces are included in particle motion by, first, calculating the forces between individual particles and then, to prevent aliasing, interpolating these forces to the computational grid points, then interpolating the forces back to the particles. The code has been used to model a simple two-fluid Rayleigh-Taylor instability. Limitations to the accuracy of the code exist at short wavelengths, where the effects of the short-range forces would be expected to be most pronounced.

1. Effect of Induced Magnetic Field on MHD Mixed Convection Flow in Vertical Microchannel

Jha, B. K.; Aina, B.

2017-08-01

The present work presents a theoretical investigation of an MHD mixed convection flow in a vertical microchannel formed by two electrically non-conducting infinite vertical parallel plates. The influence of an induced magnetic field arising due to motion of an electrically conducting fluid is taken into consideration. The governing equations of the motion are a set of simultaneous ordinary differential equations and their exact solutions in dimensionless form have been obtained for the velocity field, the induced magnetic field and the temperature field. The expressions for the induced current density and skin friction have also been obtained. The effects of various non-dimensional parameters such as rarefaction, fluid wall interaction, the Hartmann number and the magnetic Prandtl number on the velocity, the induced magnetic field, the temperature, the induced current density, and skin friction have been presented in a graphical form. It is found that the effect of the Hartmann number and magnetic Prandtl number on the induced current density is found to have a decreasing nature at the central region of the microchannel.

2. Flow-Induced New Channels of Energy Exchange in Multi-Scale Plasma Dynamics - Revisiting Perturbative Hybrid Kinetic-MHD Theory.

PubMed

Shiraishi, Junya; Miyato, Naoaki; Matsunaga, Go

2016-05-10

It is found that new channels of energy exchange between macro- and microscopic dynamics exist in plasmas. They are induced by macroscopic plasma flow. This finding is based on the kinetic-magnetohydrodynamic (MHD) theory, which analyses interaction between macroscopic (MHD-scale) motion and microscopic (particle-scale) dynamics. The kinetic-MHD theory is extended to include effects of macroscopic plasma flow self-consistently. The extension is realised by generalising an energy exchange term due to wave-particle resonance, denoted by δ WK. The first extension is generalisation of the particle's Lagrangian, and the second one stems from modification to the particle distribution function due to flow. These extensions lead to a generalised expression of δ WK, which affects the MHD stability of plasmas.

3. Flow-Induced New Channels of Energy Exchange in Multi-Scale Plasma Dynamics – Revisiting Perturbative Hybrid Kinetic-MHD Theory

PubMed Central

Shiraishi, Junya; Miyato, Naoaki; Matsunaga, Go

2016-01-01

It is found that new channels of energy exchange between macro- and microscopic dynamics exist in plasmas. They are induced by macroscopic plasma flow. This finding is based on the kinetic-magnetohydrodynamic (MHD) theory, which analyses interaction between macroscopic (MHD-scale) motion and microscopic (particle-scale) dynamics. The kinetic-MHD theory is extended to include effects of macroscopic plasma flow self-consistently. The extension is realised by generalising an energy exchange term due to wave-particle resonance, denoted by δ WK. The first extension is generalisation of the particle’s Lagrangian, and the second one stems from modification to the particle distribution function due to flow. These extensions lead to a generalised expression of δ WK, which affects the MHD stability of plasmas. PMID:27160346

4. Spin-Up Instability of a Levitated Molten Drop in MHD-Flow Transition to Turbulence

NASA Technical Reports Server (NTRS)

Abedian, B.; Hyers, R. W.; Curreri, Peter A. (Technical Monitor)

2002-01-01

When an alternating magnetic field interacts with induced eddy currents in a conducting body, there will be a repulsive force between the body and the driving coil system generating the field. This repulsive force is the basis of electromagnetic levitation, which allows containerless processing of different materials. The eddy currents in the conducting body also generate Joule heating. Axial rotation of electromagnetically levitated objects is a common observation in levitation systems and often an undesirable side effect of such experiments on 1-g and -g. There have been recent efforts to use magnetic damping and suppress this tendency of body rotation. The first report of rotation in EML drops was attributed to a slight asymmetry of the shape and location of the levitation coils could change the axis and speed of rotation. Other theories of sample rotation include a frequency difference in the traveling electromagnetic waves and a phase difference in two different applied fields of the same frequency. All of these different mechanisms share the following characteristics: the torque is small, constant for constant field strength, and very weakly dependent on the sample's temperature and phase (solid or liquid). During experiments on the MSL-1 (First Microgravity Science Laboratory) mission of the Space Shuttle (STS-83 and STS-94, April and July 1997), a droplet of palladium-silicon alloy was electromagnetically levitated for viscosity measurements. For the non-deforming droplet, the resultant MHD flow inside the drop is inferred from motion of impurities on the surface. These observations indicate formation of a pair of co-rotating toroidal flow structures inside the spheroidal levitated drop that undergo secondary flow instabilities. As rise in the fluid temperature rises, the viscosity falls and the internal flow accelerates and becomes oscillatory; and beyond a point in the experiments, the surface impurities exhibit non-coherent chaotic motion signifying

5. MHD coal-fired flow facility baseline water-quality study. Woods Reservoir, May 1979-April 1980

SciTech Connect

Cooper, J.

1980-12-01

The Department of Energy (DOE) Magnetohydrodynamics (MHD) Coal-Fired Flow Facility (CFFF) is located on Woods Reservoir at The University of Tennessee Space Institute (UTSI). Part of the role of UTSI, as participants in the DOE program, is to document environmental aspects of coal-fired MHD. In early 1979, prior to operation of the CFFF, a water quality program was initiated to establish baseline conditions for the reservoir. The study was designed to provide an accurate assessment of water quality which could be used as a basis for comparison to evaluate the impact, if any, of the plant operation on the aquatic environment. Results of a one year baseline study of water quality on Woods Reservoir are presented in this report. The key findings are that this reservoir is a eutrophic lake. Its predominant ions are calcium and bicarbonate and its pH is circumneutral.

6. Unsteady heat and mass transfer in MHD flow over an oscillatory stretching surface with Soret and Dufour effects

Zheng, Lian-Cun; Jin, Xin; Zhang, Xin-Xin; Zhang, Jun-Hong

2013-10-01

In this paper, we study the unsteady coupled heat and mass transfer of two-dimensional MHD fluid over a moving oscillatory stretching surface with Soret and Dufour effects. Viscous dissipation effects are adopted in the energy equation. A uniform magnetic field is applied vertically to the flow direction. The governing equations are reduced to non-linear coupled partial differential equations and solved by means of homotopy analysis method (HAM). The effects of some physical parameters such as magnetic parameter, Dufour number, Soret number, the Prandtl number and the ratio of the oscillation frequency of the sheet to its stretching rate on the flow and heat transfer characteristics are illustrated and analyzed.

7. Convective heat and mass transfer on MHD peristaltic flow of Williamson fluid with the effect of inclined magnetic field

Veera Krishna, M.; Swarnalathamma, B. V.

2016-05-01

In this paper, we discussed the peristaltic MHD flow of an incompressible and electrically conducting Williamson fluid in a symmetric planar channel with heat and mass transfer under the effect of inclined magnetic field. Viscous dissipation and Joule heating are also taken into consideration. Mathematical model is presented by using the long wavelength and low Reynolds number approximations. The differential equations governing the flow are highly nonlinear and thus perturbation solution for small Weissenberg number (We < 1) is presented. Effects of the heat and mass transfer on the longitudinal velocity, temperature and concentration are studied in detail. Main observations are presented in the concluding section. The streamlines pattern is also given due attention.

8. Fractional boundary layer flow and radiation heat transfer of MHD viscoelastic fluid over an unsteady stretching surface

SciTech Connect

Shen, Bingyu; Zheng, Liancun Chen, Shengting

2015-10-15

This paper presents an investigation for magnetohydrodynamic (MHD) viscoelastic fluid boundary layer flow and radiation heat transfer over an unsteady stretching sheet in presence of heat source. Time dependent fractional derivative is first introduced in formulating the boundary layer equations. Numerical solutions are obtained by using the finite difference scheme and L1-algorithm approximation. Results indicate that the proposed model describes a basic delaying times framework for viscoelastic flow and radiation heat transfer. The effects of involved parameters on velocity and temperature fields are shown graphically and analyzed in detail.

9. Melting heat transfer in the MHD flow of a third-grade fluid over a variable-thickness surface

Hayat, Tasawar; Kiran, Asmara; Imtiaz, Maria; Alsaedi, Ahmed; Ayub, M.

2017-06-01

The present study addresses the magnetohydrodynamic (MHD) flow of a third-grade fluid over a nonlinear stretched surface with variable thickness. The heat transfer phenomenon is discussed through melting. The system of nonlinear ordinary differential equations is attained by considering proper transformations. Convergent series solutions of velocity and temperature are developed. Fluid flow, temperature, skin friction coefficient and Nusselt number are examined through graphs for different parameters. It is noted that velocity and temperature decrease with decreasing the wall thickness parameter. It is also revealed that the temperature distribution enhances for increasing values of the Prandtl number. Here the velocity field reduces for increasing values of the melting parameter.

10. Selected topics on the topology of ideal fluid flows

Peralta-Salas, Daniel

2016-08-01

This is a survey of certain geometric aspects of inviscid and incompressible fluid flows, which are described by the solutions to the Euler equations. We will review Arnold’s theorem on the topological structure of stationary fluids in compact manifolds, and Moffatt’s theorem on the topological interpretation of helicity in terms of knot invariants. The recent realization theorem by Enciso and Peralta-Salas of vortex lines of arbitrarily complicated topology for stationary solutions to the Euler equations will also be introduced. The aim of this paper is not to provide detailed proofs of all the stated results but to introduce the main ideas and methods behind certain selected topics of the subject known as Topological Fluid Mechanics. This is the set of lecture notes, the author gave at the XXIV International Fall Workshop on Geometry and Physics held in Zaragoza (Spain) during September 2015.

11. Multiple convection patterns and thermohaline flow in an idealized OGCM

SciTech Connect

Rahmstorf, S.

1995-12-01

This paper investigates how multiple steady states arise in an ocean general circulation model, caused by the fact that many different convection patterns can be stable under the same surface boundary conditions. Two alternative boundary conditions are used in the experiments: classical mixed boundary conditions and a diffusive atmospheric heat balance combined with fixed salt fluxes. In both cases, transitions between different quasi-steady convection patterns can be triggered by briefly adding fresh water at convection sites. Either a large-scale freshwater anomaly is used to completely erase the previous convection pattern or a {open_quotes}surgical{close_quotes} anomaly is added to single grid points to turn off convection there. Under classical mixed-boundary conditions, different convection sites can lead to different overturning rates of deep water. The dynamics of the convection-driven flow is analyzed in some detail. With an energy balance atmosphere, in contrast, the overturning rate is very robust, apparently regulated by a negative thermal feedback. In spite of this, different convection patterns are associated with very different climatic states, since the heat transport of the deep circulation depends strongly on where convection takes place. It is suggested that considerable climate variability in the North Atlantic could be caused by changes in high-latitude convection.

12. Heat transfer at microscopic level in a MHD fractional inertial flow confined between non-isothermal boundaries

2017-07-01

Heat transfer through a Forchheimer medium in an unsteady magnetohydrodynamic (MHD) developed differential-type fluid flow is analyzed numerically in this study. The boundary layer flow is modeled with the help of the fractional calculus approach. The fluid is confined between infinite parallel plates and flows by motion of the plates in their own plane. Both the plates have variable surface temperature. Governing partial differential equations with appropriate initial and boundary conditions are solved by employing a finite-difference scheme to discretize the fractional time derivative and finite-element discretization for spatial variables. Coefficients of skin friction and local Nusselt numbers are computed for the fractional model. The flow behavior is presented for various values of the involved parameters. The influence of different dimensionless numbers on skin friction and Nusselt number is discussed by tabular results. Forchheimer medium flows that involve catalytic converters and gas turbines can be modeled in a similar manner.

13. MHD-IPS analysis of relationship among solar wind density, temperature, and flow speed

Hayashi, Keiji; Tokumaru, Munetoshi; Fujiki, Ken'ichi

2016-08-01

The solar wind properties near the Sun are a decisive factor of properties in the rest of heliosphere. As such, determining realistic plasma density and temperature near the Sun is very important in models for solar wind, specifically magnetohydrodynamics (MHD) models. We had developed a tomographic analysis to reconstruct three-dimensional solar wind structures that satisfy line-of-sight-integrated solar wind speed derived from the interplanetary scintillation (IPS) observation data and nonlinear MHD equations simultaneously. In this study, we report a new type of our IPS-MHD tomography that seeks three-dimensional MHD solution of solar wind, matching additionally near-Earth and/or Ulysses in situ measurement data for each Carrington rotation period. In this new method, parameterized relation functions of plasma density and temperature at 50 Rs are optimized through an iterative forward model minimizing discrepancy with the in situ measurements. Satisfying three constraints, the derived 50 Rs maps of plasma quantities provide realistic observation-based information on the state of solar wind near the Sun that cannot be well determined otherwise. The optimized plasma quantities exhibit long-term variations over the solar cycles 21 to 24. The differences in plasma quantities derived from the optimized and original IPS-MHD tomography exhibit correlations with the source-surface magnetic field strength, which can in future give new quantitative constrains and requirements to models of coronal heating and acceleration.

14. Closed cycle MHD generator with nonuniform gas-plasma flow driving recombinated plasma clots formed by high-energy electron beams

SciTech Connect

Danilov, V.V.; Laptev, S.S.; Slavin, V.S.

1996-12-31

A new concept of a closed cycle MHD generator without alkali seed has been suggested. The essence of it is the use of the high-energy electron beams technology for a nonuniform gas-plasma flow in MHD channel creation. At the inlet of MHD channel in supersonic flow of noble gas (He) the plasma clots with a density about 10{sup 15} cm{sup {minus}3} are formed by pulsed intense electron beams with energy about 100 keV. Gas flow drives these clots in a cross magnetic field along the MHD channel which has electrodes connected with a load by Faradays scheme. Because the nonuniform gas-plasma flow has not the conductivity in the Halls EMF direction a Faradays current can flow only through the narrow plasma layers. The energy dissipation and Joules heating in MHD channel support the nonequilibrium conductivity in these plasma layers. a gas flow pushes current layers and produces electric power at the expense of enthalpy extraction. The key element is a question of plasma layers stability in MHD channel. The most dangerous instability is the overheating instability. it is shown that taking into account the phenomenon of frozen conductivity for recombinated plasma which appears for noble gas at T{sub e} > 4,000 K the regime with {partial_derivative}{sigma}/{partial_derivative}T{sub e} < 0 can be realized. Due to the fulfillment of this condition the overheating instability is effectively suppressed. The numerical simulation has shown that a supersonic gas flow, containing about 4 current layers in MHD channel simultaneously, is braked without shock waves creation. Current layers provide no less than 30% enthalpy extraction and about 80% isentropic efficiency.

15. Blood Flow in Idealized Vascular Access for Hemodialysis: A Review of Computational Studies.

PubMed

Ene-Iordache, Bogdan; Remuzzi, Andrea

2017-06-29

Although our understanding of the failure mechanism of vascular access for hemodialysis has increased substantially, this knowledge has not translated into successful therapies. Despite advances in technology, it is recognized that vascular access is difficult to maintain, due to complications such as intimal hyperplasia. Computational studies have been used to estimate hemodynamic changes induced by vascular access creation. Due to the heterogeneity of patient-specific geometries, and difficulties with obtaining reliable models of access vessels, idealized models were often employed. In this review we analyze the knowledge gained with the use of computational such simplified models. A review of the literature was conducted, considering studies employing a computational fluid dynamics approach to gain insights into the flow field phenotype that develops in idealized models of vascular access. Several important discoveries have originated from idealized model studies, including the detrimental role of disturbed flow and turbulent flow, and the beneficial role of spiral flow in intimal hyperplasia. The general flow phenotype was consistent among studies, but findings were not treated homogeneously since they paralleled achievements in cardiovascular biomechanics which spanned over the last two decades. Computational studies in idealized models are important for studying local blood flow features and evaluating new concepts that may improve the patency of vascular access for hemodialysis. For future studies we strongly recommend numerical modelling targeted at accurately characterizing turbulent flows and multidirectional wall shear disturbances.

16. Classical MHD shocks: theory and numerical simulation

SciTech Connect

Pogorelov, Nikolai V.

2005-08-01

Recent results are surveyed in the investigation of the behavior of shocks in ideal magnetohydrodynamics (MHD) and corresponding structures in dissipative/resistive plasma flows. In contrast to evolutionary shocks, a solution of the problem of the nonevolutionary shock interaction with small perturbations is either nonunique or does not exist. The peculiarity of non-ideal MHD is in that some nonevolutionary shocks have dissipative structures. Since this structure is always non-plane, it can reveal itself in problems where transverse perturbations do not exist due to symmetries restrictions. We discuss the numerical behavior of nonevolutionary shocks and argue that they necessarily disappear once the problem is solved in a genuinely three-dimensional statement.

17. SU2: the Open-Source Software for Non-ideal Compressible Flows

Pini, M.; Vitale, S.; Colonna, P.; Gori, G.; Guardone, A.; Economon, T.; Alonso, J. J.; Palacios, F.

2017-03-01

The capabilities of the open-source SU2 software suite for the numerical simulation of viscous flows over unstructured grid are extended to non-ideal compressible-fluid dynamics (NICFD). A built-in thermodynamic library is incorporated to account for the non-ideal thermodynamic characteristics of fluid flows evolving in the close proximity of the liquid-vapour saturation curve and critical point. The numerical methods, namely the Approximate Riemann Solvers (ARS), viscous fluxes and boundary conditions are generalised to non-ideal fluid properties. Quantities of interest for turbomachinery cascades, as loss coefficients and flow angles, can be automatically determined and used for design optimization. A variety of test cases are carried out to assess the performance of the solver. At first, numerical methods are verified against analytical solution of reference NICFD test cases, including steady shock reflection and unsteady shock tube. Then, non-ideal gas effects in planar nozzles and past turbine cascades, typically encountered in Organic Rankine Cycle applications, are investigated and debated. The obtained results demonstrate that SU2 is highly suited for the analysis and the automatic design of internal flow devices operating in the non-ideal compressible-fluid regime.

18. Peristaltic MHD Convective flow of Walter’s-B Fluid through a Biddable walled channel with Slip Effect

Veera Krishna, M.; Swarnalathamma, B. V.

2017-08-01

The combined effects on peristaltic MHD Convective flow of an electrically conducting Walters-B fluid through a biddable walled channel have been studied. Using small wave number move towards, the nonlinear model differential equations are obtained and tackled analytically by regular perturbation method. Expressions for the stream function, velocity, temperature, skin-friction coefficient and heat transfer coefficient are constructed. Pertinent results are presented graphically and discussed quantitatively. It is found that the velocity distribution depresses while the fluid temperature rises with an increase in Hartmann number. The trapping phenomenon is observed and the size of trapped bolus increases with an increase in Hartmann number.

19. Hall effects on unsteady MHD reactive flow of second grade fluid through porous medium in a rotating parallel plate channel

Krishna, M. Veera; Swarnalathamma, B. V.

2017-07-01

We considered the transient MHD flow of a reactive second grade fluid through porous medium between two infinitely long horizontal parallel plates when one of the plate is set into uniform accelerated motion in the presence of a uniform transverse magnetic field under Arrhenius reaction rate. The governing equations are solved by Laplace transform technique. The effects of the pertinent parameters on the velocity, temperature are discussed in detail. The shear stress and Nusselt number at the plates are also obtained analytically and computationally discussed with reference to governing parameters.

20. Soret and Dufour effects on MHD viscoelastic fluid flow through a vertical flat plate with constant suction

Hossain, Sheikh Imamul; Alam, Md. Mahmud

2016-07-01

An attempt is made to represent the numerical solution of magnetohydrodynamics (MHD) viscoelastic fluid flow through an infinite vertical flat plate with constant suction in the presence of Soret and Dufour effects. The expressions of non-dimensional, coupled partial momentum, energy and concentration differential equations are obtained with the help of the usual non-dimensional variables. Implicit finite difference method is imposed to obtain the non-dimensional equations. Also the stability conditions and convergence criteria are analyzed. The effects of the various parameters entering into the problem on shear stress, Nusselt number, and Sherwood number are demonstrated graphically with physical interpretation.

1. Numerical Simulation for the Unsteady MHD Flow and Heat Transfer of Couple Stress Fluid over a Rotating Disk

PubMed Central

2014-01-01

The present work is devoted to study the numerical simulation for unsteady MHD flow and heat transfer of a couple stress fluid over a rotating disk. A similarity transformation is employed to reduce the time dependent system of nonlinear partial differential equations (PDEs) to ordinary differential equations (ODEs). The Runge-Kutta method and shooting technique are employed for finding the numerical solution of the governing system. The influences of governing parameters viz. unsteadiness parameter, couple stress and various physical parameters on velocity, temperature and pressure profiles are analyzed graphically and discussed in detail. PMID:24835274

2. Viscous dissipation and thermal radiation effects on the magnetohydrodynamic (MHD) flow and heat transfer over a stretching slender cylinder

2016-05-01

An axisymmetric magnetohydrodynamic (MHD) boundary layer flow and heat transfer of a fluid over a slender cylinder are investigated numerically. The effects of viscous dissipation, thermal radiation, and surface transverse curvature are taken into account in the simulations. For this purpose, the governing partial differential equations are transformed to ordinary differential equations by using appropriate similarity transformations. The resultant ordinary differential equations along with appropriate boundary conditions are solved by the fourth-order Runge-Kutta method combined with the shooting technique. The effects of various parameters on the velocity and temperature profiles, local skin friction coefficient, and Nusselt number are analyzed.

3. Proceedings of the workshop on nonlinear MHD and extended MHD

SciTech Connect

1998-12-01

Nonlinear MHD simulations have proven their value in interpreting experimental results over the years. As magnetic fusion experiments reach higher performance regimes, more sophisticated experimental diagnostics coupled with ever expanding computer capabilities have increased both the need for and the feasibility of nonlinear global simulations using models more realistic than regular ideal and resistive MHD. Such extended-MHD nonlinear simulations have already begun to produce useful results. These studies are expected to lead to ever more comprehensive simulation models in the future and to play a vital role in fully understanding fusion plasmas. Topics include the following: (1) current state of nonlinear MHD and extended-MHD simulations; (2) comparisons to experimental data; (3) discussions between experimentalists and theorists; (4) /equations for extended-MHD models, kinetic-based closures; and (5) paths toward more comprehensive simulation models, etc. Selected papers have been indexed separately for inclusion in the Energy Science and Technology Database.

4. MHD Effect on Unsteady Mixed Convection Boundary Layer Flow past a Circular Cylinder with Constant Wall Temperature

Ismail, M. A.; Mohamad, N. F.; Ilias, M. R.; Shafie, S.

2017-09-01

Magnetohydrodynamic (MHD) effect is a study on motion of electrical-conducting fluid under magnetic fields. This effect has great intention due to its applications such as design of heat exchanger and nuclear reactor. In the problem in fluid motion, flow of separation can reduced the effectiveness of the system as well as can increased the energy lost. This study will present the results on reducing the flow separation by considering magnetic effect. In this study, unsteady mixed convection boundary layer flow past a circular cylinder is given attention. Focus of study is on the separation times that affected by the magnetic fields. The mathematical models in the form of partial differential equations are transformed into nonlinear coupled ordinary differential equations and solved numerically using an implicit finite-difference scheme known as Keller-box method. The effect of magnetic parameter on velocity and temperature profiles as well as skin friction and Nusselt number are studied.

5. Unsteady MHD free convection flow of rotating Jeffrey fluid embedded in a porous medium with ramped wall temperature

Zin, N. A. Mohd; Khan, I.; Shafie, S.

2017-09-01

The effect of radiative heat transfer on unsteady magnetohydrodynamic (MHD) free convection flow of rotating Jeffrey fluid past an infinite vertical plate saturated in a porous medium with ramped wall temperature is investigated. The incompressible fluid is taken electrically conducting under influence of transverse magnetic field which perpendicular to the flow. An appropriate dimensionless variables are employed to the governing equations and solved analytically by Laplace transform technique. The results of several controlling parameters for both ramped wall temperature and an isothermal plate are presented graphically with comprehensive discussions. It has been observed that, an increase in rotation parameter, reduced the primary velocity, but an opposite behaviour is noticed for the secondary velocity. Moreover, large values of Hartmann number tends to retard the fluid flow due to the Lorentz force.

6. Enthalpy, Entropy, and Exergy Flows — Real Gas Effects in Ideal Pulse Tube Cryocoolers

Kittel, P.

2006-04-01

The enthalpy, entropy, and exergy flows in ideal pulse tube cryocoolers and some of the losses in non-ideal pulse tube cryocoolers have been described previously. This paper will describe how these flows are affected by real gas phenomena in ideal pulse tube cryocoolers. Frequently such descriptions take an energy-centric view, concentrating on the first law of thermodynamics, the conservation of energy. This approach can result in a complex description of the cooler in terms of energy and enthalpy flows. An alternative is to take an entropy-centric approach. Closely related to this is the exergy-centric approach. These descriptions concentrate on the second law of thermodynamics, the generation of entropy or the destruction of exergy. Both the energy-centric and exergy/entropy-centric approaches make use of both the laws of thermodynamics and both approaches give equivalent descriptions of a cryocooler. However, the latter approach can be more useful as it can yield a simpler description, one that emphasis loss mechanisms. This paper applies the second law approach to pulse tube cryocoolers. The non-ideal gas effects in the various components on the exergy, entropy, and enthalpy flows are discussed. The discussion applies to basic, orifice, and inertance type pulse tubes and can be easily extended to other types of regenerative cryocoolers such as Gifford-McMahon and Stirling cryocoolers.

7. MHD Control of the Separation Phenomenon in a Supersonic Xenon Plasma Flow

DTIC Science & Technology

2007-11-02

Series connection of the resistor R11im in the LC circuit is caused by the necessity to have a voltage applied to the electrode which would be sufficient...heat release in the electrode vicinity. In the course of an inspection of the electrodes after a series of experiments, traces of erosion of the brass... electromotive force (e.m.f) For implementation of an MHD interaction in the BST a magnetic system is applied which provides a discharge of a

8. Simulation of Cold Flow in a Truncated Ideal Nozzle with Film Cooling

NASA Technical Reports Server (NTRS)

Braman, Kalen; Ruf, Joseph

2015-01-01

Flow transients during rocket start-up and shut-down can lead to significant side loads on rocket nozzles. The capability to estimate these side loads computationally can streamline the nozzle design process. Towards this goal, the flow in a truncated ideal contour (TIC) nozzle has been simulated for a range of nozzle pressure ratios (NPRs) aimed to match a series of cold flow experiments performed at the NASA MSFC Nozzle Test Facility. These simulations were performed with varying turbulence model choices and with four different versions of the TIC nozzle model geometry, each of which was created with a different simplification to the test article geometry.

9. Cattaneo-Christov Heat Flux Model for MHD Three-Dimensional Flow of Maxwell Fluid over a Stretching Sheet

PubMed Central

Rubab, Khansa; Mustafa, M.

2016-01-01

This letter investigates the MHD three-dimensional flow of upper-convected Maxwell (UCM) fluid over a bi-directional stretching surface by considering the Cattaneo-Christov heat flux model. This model has tendency to capture the characteristics of thermal relaxation time. The governing partial differential equations even after employing the boundary layer approximations are non linear. Accurate analytic solutions for velocity and temperature distributions are computed through well-known homotopy analysis method (HAM). It is noticed that velocity decreases and temperature rises when stronger magnetic field strength is accounted. Penetration depth of temperature is a decreasing function of thermal relaxation time. The analysis for classical Fourier heat conduction law can be obtained as a special case of the present work. To our knowledge, the Cattaneo-Christov heat flux model law for three-dimensional viscoelastic flow problem is just introduced here. PMID:27093542

10. Cattaneo-Christov Heat Flux Model for MHD Three-Dimensional Flow of Maxwell Fluid over a Stretching Sheet.

PubMed

Rubab, Khansa; Mustafa, M

2016-01-01

This letter investigates the MHD three-dimensional flow of upper-convected Maxwell (UCM) fluid over a bi-directional stretching surface by considering the Cattaneo-Christov heat flux model. This model has tendency to capture the characteristics of thermal relaxation time. The governing partial differential equations even after employing the boundary layer approximations are non linear. Accurate analytic solutions for velocity and temperature distributions are computed through well-known homotopy analysis method (HAM). It is noticed that velocity decreases and temperature rises when stronger magnetic field strength is accounted. Penetration depth of temperature is a decreasing function of thermal relaxation time. The analysis for classical Fourier heat conduction law can be obtained as a special case of the present work. To our knowledge, the Cattaneo-Christov heat flux model law for three-dimensional viscoelastic flow problem is just introduced here.

11. A study of heat and mass transfer in a fractional MHD flow over an infinite oscillating plate.

PubMed

Shahid, N

2015-01-01

Exact expressions of velocity, temperature and mass concentration have been calculated for free convective flow of fractional MHD viscous fluid over an oscillating plate. Expressions of velocity have been obtained both for sine and cosine oscillations of plate. Corresponding fractional differential equations have been solved by using Laplace transform and inverse Laplace transform. The expression of temperature and mass concentration have been presented in the form of Fox-H function and in the form of general Wright function, respectively and velocity is presented in the form of integral solutions using Generalized function. Some limiting cases of fluid and fractional parameters have been discussed to retrieve some solutions present in literature. The influence of thermal radiation, mass diffusion and fractional parameters on fluid flow has been analyzed through graphical illustrations.

12. Viscous Dissipation and Thermal Radiation effects in MHD flow of Jeffrey Nanofluid through Impermeable Surface with Heat Generation/Absorption

Sharma, Kalpna; Gupta, Sumit

2017-06-01

This paper investigates steady two dimensional flow of an incompressible magnetohydrodynamic (MHD) boundary layer flow and heat transfer of nanofluid over an impermeable surface in presence of thermal radiation and viscous dissipation. By using similarity transformation, the arising governing equations of momentum, energy and nanoparticle concentration are transformed into coupled nonlinear ordinary differential equations, which are than solved by homotopy analysis method (HAM). The effect of different physical parameters, namely, Prandtl number Pr, Eckert number Ec, Magnetic parameter M, Brownian motion parameter Nb, Thermophoresis parameter Nt, Lewis parameter Le and Radiation parameter Rd on the velocity, temperature and concentration profiles along with the Nusselt number and skin friction coefficient are discussed graphically and in tabular form in details. The present results are also compared with existing limiting solutions.

13. Mechanisms for non-ideal flow in low-power arc-heated supersonic nozzles

Wu, Cheng-Kang; Pan, Wen-Xia; Meng, Xian; Wang, Hai-Xing

2015-08-01

The flow in a low-powered arc gas heater combined with a supersonic nozzle of throat diameter less than 1 mm is quite complicated and difficult to describe in quantitative detail. Experiments on arc-heated supersonic jet thrusters of monatomic gases argon and helium have been carried out and their performance measured. The flow characteristics are analyzed with the help of numerical simulation. Results show that the viscous effect is the most important factor causing the large difference between ideal and real performance. A large outer section of the exit flow is slow-moving. This is especially pronounced in helium, where 70 % of the exit area of the nozzle might be in subsonic flow. Friction forces can be much larger than the net thrust, reaching several times higher in helium, resulting in very low efficiencies. Other factors causing the differences between ideal and real flow include: complex flow in the throat region, electric arc extending to the nozzle expansion section, heat transfer to the inlet gas and from the hot plasma, and environmental pressure in the vacuum chamber. It is recognized that the ordinary concepts of supersonic nozzle flow must be greatly modified when dealing with such complicated situations. The general concepts presented in this paper could be helpful in guiding the design and operation of this equipment.

14. Multi-region relaxed magnetohydrodynamics with flow

SciTech Connect

Dennis, G. R. Dewar, R. L.; Hole, M. J.; Hudson, S. R.

2014-04-15

We present an extension of the multi-region relaxed magnetohydrodynamics (MRxMHD) equilibrium model that includes plasma flow. This new model is a generalization of Woltjer's model of relaxed magnetohydrodynamics equilibria with flow. We prove that as the number of plasma regions becomes infinite, our extension of MRxMHD reduces to ideal MHD with flow. We also prove that some solutions to MRxMHD with flow are not time-independent in the laboratory frame, and instead have 3D structure which rotates in the toroidal direction with fixed angular velocity. This capability gives MRxMHD potential application to describing rotating 3D MHD structures such as 'snakes' and long-lived modes.

15. On the accuracy of Whitham's method. [for steady ideal gas flow past cones

NASA Technical Reports Server (NTRS)

Zahalak, G. I.; Myers, M. K.

1974-01-01

The steady flow of an ideal gas past a conical body is studied by the method of matched asymptotic expansions and by Whitham's method in order to assess the accuracy of the latter. It is found that while Whitham's method does not yield a correct asymptotic representation of the perturbation field to second order in regions where the flow ahead of the Mach cone of the apex is disturbed, it does correctly predict the changes of the second-order perturbation quantities across a shock (the first-order shock strength). The results of the analysis are illustrated by a special case of a flat, rectangular plate at incidence.

16. Complex blood flow patterns in an idealized left ventricle: A numerical study

Tagliabue, Anna; Dedè, Luca; Quarteroni, Alfio

2017-09-01

In this paper, we study the blood flow dynamics in a three-dimensional (3D) idealized left ventricle of the human heart whose deformation is driven by muscle contraction and relaxation in coordination with the action of the mitral and aortic valves. We propose a simplified but realistic mathematical treatment of the valves function based on mixed time-varying boundary conditions (BCs) for the Navier-Stokes equations modeling the flow. These switchings in time BCs, from natural to essential and vice versa, model either the open or the closed configurations of the valves. At the numerical level, these BCs are enforced by means of the extended Nitsche's method (Tagliabue et al., Int. J. Numer. Methods Fluids, 2017). Numerical results for the 3D idealized left ventricle obtained by means of Isogeometric Analysis are presented, discussed in terms of both instantaneous and phase-averaged quantities of interest and validated against those available in the literature, both experimental and computational. The complex blood flow patterns are analysed to describe the characteristic fluid properties, to show the transitional nature of the flow, and to highlight its main features inside the left ventricle. The sensitivity of the intraventricular flow patterns to the mitral valve properties is also investigated.

17. On the MHD squeeze flow between two parallel disks with suction or injection via HAM and HPM

Ganji, D. D.; Abbasi, M.; Rahimi, J.; Gholami, M.; Rahimipetroudi, I.

2014-09-01

An analysis has been performed to study the problem of magneto-hydrodynamic (MHD) squeeze flow of an electrically conducting fluid between two infinite, parallel disks. The analytical methods called Homotopy Analysis Method (HAM) and Homotopy Perturbation Method (HPM) have been used to solve nonlinear differential equations. It has been attempted to show the capabilities and wide-range applications of the proposed methods in comparison with a type of numerical analysis as Boundary Value Problem (BVP) in solving this problem. Also, the velocity fields have been computed and shown graphically for various values of physical parameters. The objective of the present work is to investigate the effect of squeeze Reynolds number, Hartmann number and the suction/injection parameter on the velocity field. Furthermore, the results reveal that HAM and HPM are very effective and convenient.

18. Thermal radiation and mass transfer effects on unsteady MHD free convection flow past a vertical oscillating plate

Rana, B. M. Jewel; Ahmed, Rubel; Ahmmed, S. F.

2017-06-01

Unsteady MHD free convection flow past a vertical porous plate in porous medium with radiation, diffusion thermo, thermal diffusion and heat source are analyzed. The governing non-linear, partial differential equations are transformed into dimensionless by using non-dimensional quantities. Then the resultant dimensionless equations are solved numerically by applying an efficient, accurate and conditionally stable finite difference scheme of explicit type with the help of a computer programming language Compaq Visual Fortran. The stability and convergence analysis has been carried out to establish the effect of velocity, temperature, concentration, skin friction, Nusselt number, Sherwood number, stream lines and isotherms line. Finally, the effects of various parameters are presented graphically and discussed qualitatively.

19. Application of Caputo-Fabrizio derivatives to MHD free convection flow of generalized Walters'-B fluid model

2016-10-01

The present article applies the idea of Caputo-Fabrizio time fractional derivatives to magnetohydrodynamics (MHD) free convection flow of generalized Walters'-B fluid over a static vertical plate. Free convection is caused due to combined gradients of temperature and concentration. Hence, heat and mass transfers are considered together. The fractional model of Walters'-B fluid is used in the mathematical formulation of the problem. The problem is solved via the Laplace transform method. Exact solutions for velocity, temperature and concentration are obtained. The physical quantities of interest are examined through plots for various values of fractional parameter: α, Walters'-B parameter Γ, magnetic parameter M , Prandtl number Pr, Schmidt number Sc, thermal Grashof number Gr and mass Grashof number Gm. As a special case, the published results from open literature are recovered.

20. Thermal radiation effect on MHD flow and heat transfer of Williamson nanofluids over a stretching sheet with Newtonian heating

Bing, Kho Yap; Hussanan, Abid; Mohamed, Muhammad Khairul Anuar; Sarif, Norhafizah Mohd; Ismail, Zulkhibri; Salleh, Mohd Zuki

2017-04-01

In this paper, the boundary layer magnetohydrodynamics (MHD) flow of Williamson nanofluids over a stretching sheet with Newtonian heating in the presence of thermal radiation effect is analyzed. Using a similarity transformation, the governing equations are reduced to a set of nonlinear ordinary differential equations (ODEs). These equations are solved numerically using a shooting method. The effects of Williamson parameter, magnetic parameter, radiation parameter, Prandtl number, Lewis number, Schmidt number, heat capacities ratio, thermophoretic diffusivity and conjugate parameter on velocity, temperature and concentration fields are shown graphically and discussed. It is found that the rate of heat transfer is higher for Williamson nanofluids compared to the classical viscous fluid. Also, the comparisons with existing results are provided in the literature.

1. Impact of thermal radiation on MHD slip flow of a ferrofluid over a non-isothermal wedge

2017-01-01

This article is concerned with the problem of magnetohydrodynamic (MHD) mixed convection flow of Cobalt-kerosene ferrofluid adjacent a non-isothermal wedge under the influence of thermal radiation and partial slip. Such type of problems are posed by electric generators and biomedical enforcement. The governing equations are solved using the Thomas algorithm with finite-difference type and solutions for a wide range of magnet parameter are presented. It is found that local Nusselt number manifests a considerable diminishing for magnetic parameter and magnifies intensively in case of slip factor, thermal radiation and surface temperature parameters. Further, the skin friction coefficient visualizes a sufficient enhancement for the parameters thermal radiation, surface temperature and magnetic field, but a huge reduction is recorded by promoting the slip factor.

2. Simulation of Cold Flow in a Truncated Ideal Nozzle with Film Cooling

NASA Technical Reports Server (NTRS)

Braman, K. E.; Ruf, J. H.

2015-01-01

Flow transients during rocket start-up and shut-down can lead to significant side loads on rocket nozzles. The capability to estimate these side loads computationally can streamline the nozzle design process. Towards this goal, the flow in a truncated ideal contour (TIC) nozzle has been simulated using RANS and URANS for a range of nozzle pressure ratios (NPRs) aimed to match a series of cold flow experiments performed at the NASA MSFC Nozzle Test Facility. These simulations were performed with varying turbulence model choices and for four approximations of the supersonic film injection geometry, each of which was created with a different simplification of the test article geometry. The results show that although a reasonable match to experiment can be obtained with varying levels of geometric fidelity, the modeling choices made do not fully represent the physics of flow separation in a TIC nozzle with film cooling.

3. Ideal and resistive magnetohydrodynamic instabilities in cylindrical geometry with a sheared flow along the axis

Brunetti, D.; Lazzaro, E.; Nowak, S.

2017-05-01

The problem of the linear stability of internal magnetohydrodynamic modes in a cylindrical plasma with a sheared longitudinal flow is addressed. A Newcomb-like equation describing the perturbation is derived and exactly solved for a class of analytic profiles for rotational transform, equilibrium flow and pressure. A dispersion relation for ideal modes is then derived and analysed for different limits of the poloidal mode number (viz. m = 1, m> 1 and m\\gg 1). In the resistive case, a simple and exact expression for the tearing stability index {{Δ }}\\prime is derived using the same class of equilibrium profiles. It is found that a small flow shear has a destabilising effect, while if the flow shear is dominant over the magnetic shear the tearing mode is stabilised. Implications on the stability of the m = 1 resistive mode are also discussed.

4. Research and development studies for MHD/coal power flow train components. Technical progress report, 1 September 1979-31 August 1980

SciTech Connect

Bloom, M. H.

1980-01-01

The aim of this program is to contribute to certain facets of the development of the MHD/coal power system, and particularly the CDIF of DOE with regard to its flow train. Consideration is given specifically to the electrical power take-off, the diagnostic and instrumentation systems, the combustor and MHD channel technology, and electrode alternatives. Within the constraints of the program, high priorities were assigned to the problems of power take-off and the related characteristics of the MHD channel, and to the establishment of a non-intrusive, laser-based diagnostic system. The next priority was given to the combustor modeling and to a significantly improved analysis of particle combustion. Separate abstracts were prepared for nine of the ten papers included. One paper was previously included in the data base. (WHK)

5. MHD flows of UCM fluids above porous stretching sheets using two-auxiliary-parameter homotopy analysis method

2009-02-01

The performance of a two-auxiliary-parameter homotopy analysis method (HAM) is investigated in solving laminar MHD flow of an upper-convected Maxwell fluid (UCM) above a porous isothermal stretching sheet. The analysis is carried out up to the 20th-order of approximation, and the effect of parameters such as elasticity number, suction/injection velocity, and magnetic number are studied on the velocity field above the sheet. The results will be contrasted with those reported recently by Hayat et al. [Hayat T, Abbas Z, Sajid M. Series solution for the upper-convected Maxwell fluid over a porous stretching plate. Phys Lett A 358;2006:396-403] obtained using a third-order one-auxiliary-parameter homotopy analysis method. It is concluded that the flow reversal phenomenon as predicted by Hayat et al. (2006) may have arisen because of the inadequacies of using just one-auxiliary-parameter in their analysis. That is, no flow reversal is predicted to occur if instead of using one-auxiliary-parameter use is made of two auxiliary parameters together with a more convenient set of base functions to assure the convergence of the series used to solve the highly nonlinear ODE governing the flow.

6. MHD mixed convection analysis in an open channel by obstructed Poiseuille flow of non-Newtonian power law fluid

Rabbi, Khan Md.; Rakib, Tawfiqur; Das, Sourav; Mojumder, Satyajit; Saha, Sourav

2016-07-01

This paper demonstrates magneto-hydrodynamic (MHD) mixed convection flow through a channel with a rectangular obstacle at the entrance region using non-Newtonian power law fluid. The obstacle is kept at uniformly high temperature whereas the inlet and top wall of the channel are maintained at a temperature lower than obstacle temperature. Poiseuille flow is implemented as the inlet velocity boundary condition. Grid independency test and code validation are performed to justify the computational accuracy before solving the present problem. Galerkin weighted residual method has been appointed to solve the continuity, momentum and energy equations. The problem has been solved for wide range of pertinent parameters like Richardson number (Ri = 0.1 - 10) at a constant Reynolds number (Re = 100), Hartmann number (Ha = 0 - 100), power index (n = 0.6 - 1.6). The flow and thermal field have been thoroughly discussed through streamline and isothermal lines respectively. The heat transfer performance of the given study has been illustrated by average Nusselt number plots. It is observed that increment of Hartmann number (Ha) tends to decrease the heat transfer rate up to a critical value (Ha = 20) and then let increase the heat transfer performance. Thus maximum heat transfer rate has been recorded for higher Hartmann number and Rayleigh number in case of pseudo-plastic (n = 0.6) non-Newtonian fluid flow.

7. Experimental investigations of the steady flow through an idealized model of a femoral artery bypass

Giurgea, Corina; Bode, Florin; Ioan Budiu, Octavian; Nascutiu, Lucian; Banyai, Daniel; Damian, Mihai

2014-03-01

The present paper presents the steps taken by the authors in the first stage of an experimental program within a larger national research project whose objective is to characterize the flow through a femoral artery bypass with a view to finding solutions for its optimization. The objective of the stage is to investigate by means of the PIV method the stationary flow through a bypass model with an idealized geometry. A bypass assembly which reunites the idealized geometry models of the proximal and distal anastomoses, and which respects the lengths of a femoral artery bypass was constructed on the basis of data for a real patient provided by medical investigations. With the aim of testing the model and the established experimental set-up with regard to their suitability for the assessment of the velocity field associated to the steady flow through the bypass, three zones that can restore the whole distal anastomosis were PIV investigated. The measurements were taken in the conditions of maintained inflow at the bypass entry of 0.9 l / min (Re = 600). The article presents comparatively the flow spectra and the velocity fields for each zone obtained in two situations: with the femoral artery completely occluded and completely open.

8. MHD flow of Powell-Eyring nanofluid over a non-linear stretching sheet with variable thickness

Hayat, T.; Ullah, Ikram; Alsaedi, A.; Farooq, M.

This research explores the magnetohydrodynamic (MHD) boundary layer flow of Powell-Eyring nanofluid past a non-linear stretching sheet of variable thickness. An electrically conducting fluid is considered under the characteristics of magnetic field applied transverse to the sheet. The mathematical expressions are accomplished via boundary layer access, Brownian motion and thermophoresis phenomena. The flow analysis is subjected to a recently established conditions requiring zero nanoparticles mass flux. Adequate transformations are implemented for the reduction of partial differential systems to the ordinary differential systems. Series solutions for the governing nonlinear flow of momentum, temperature and nanoparticles concentration have been executed. Physical interpretation of numerous parameters is assigned by graphical illustrations and tabular values. Moreover the numerical data of drag coefficient and local heat transfer rate are executed and discussed. It is investigated that higher wall thickness parameter results in the reduction of velocity distribution. Effects of thermophoresis parameter on temperature and concentration profiles are qualitatively similar. Both the temperature and concentration profiles are enhanced for higher values of thermophoresis parameter.

9. Derivation and Application of Idealized Flow Conditions in River Network Simulation

Afshari Tork, S.; Fekete, B. M.

2015-12-01

Stream flow information is essential for many applications across broad range of scales, e.g. global water balances, engineering design, flood forecasting, environmental management, etc. Quantitative assessment of flow dynamics of natural streams, requires detailed knowledge of all the geometrical and geophysical variables (e.g. bed-slope, bed roughness, etc.) along river reaches. Simplifying the river bed geometries could reduce both the computational burden implementing flow simulations and challenges in assembling the required data, especially for large domains. Average flow conditions expressed as empirical "at-a-station" hydraulic geometry relationships between key channel components, (i.e. water depth, top-width, flow velocity, flow area against discharge) have been studied since 60's. Recent works demonstrated that power-function as idealized riverbed geometry whose parameters are correlated to those of exponential relationship between mean water depth and top-width, are consistent with empirical "at-a-station" relations.US Geological Surveys' National Water Information System web-interface provides huge amount of river discharge and corresponding stage height data from several thousands of streamflow monitoring stations over United States accompanied by river survey summaries providing additional flow informations (width, mean velocity, cross-sectional area). We conducted a series of analyses to indentify consistent data daily monitoring and corresponding survey records that are suitable to refine our current understanding of how the "at-a-station" properties of river channels relate to channel forming characteristics (e.g. riverbed slope, flow regime, geology, etc.). The resulting ~1,200 actively operating USGS stations with over ~225,000 corresponding survery records (almost 200 survey per gauge on average) is the largest river survey database ever studied in the past.Our presentation will show our process assembling our river monitoring and survey data

10. RIS4E at Kilauea's December 1974 (D1974) Flow: Establishing the D1974 Flow as an Ideal Mars Analog

Young, K. E.; Bleacher, J. E.; Rogers, D.; McAdam, A.; Garry, W. B.; Scheidt, S. P.; Carter, L. M.; Glotch, T. D.

2015-12-01

The Kīlauea December 1974 (D1974) flow was emplaced from a series of en echelon fissures southwest of Kīlauea Caldera. In 6.5 hours the D1974 flow was emplaced over the Keanakākoi ash member as a rapidly emplaced sheet flow. This flow has previously been used as a location for radar roughness studies due to the exposure of abrupt changes in surface texture ranging between smooth pāhoehoe, rubbly and slabby lavas and ´áā lava. When viewed in visible remote sensing images, this flow field displays dark and light toned areas that reveal sinuous patterns, streamlined islands, and rafted lava slabs and plates. The flow is an ideal location to study lava textures, textural relationships and the formation of non-traditional channels and associated features as analogs to characterizing the formation of channel networks on the flanks of martian volcanoes or rilles in the lunar mare. The D1974 flow is also positioned downwind from Kīlauea Caldera along the volcano's SW rift zone. D1974 lavas flowed across older, active fumaroles and have since been exposed to acid fog, rain, and other plume related processes. In 2008 the Kīlauea Caldera experienced an explosive event along the wall of Halemáumáu and has since displayed an active lava lake, thereby elevating the flow's exposure to processes related to volcanic gasses. Alteration products have therefore formed both in and around the older fumaroles (at the solfatara site) as well as being deposited as thin coatings over the entire length of the flow. These products are reminiscent of sulfate-rich materials that have been identified on Mars by several groups. Though these martian deposits have been identified and analyzed, their formation mechanism remains somewhat ambiguous. The D1974 flow represents an ideal analog with which to test various formation scenarios using a variety of field portable technologies, designed to analyze the alteration products in situ (thereby preserving their initial structures and

11. MHD Free Convective Boundary Layer Flow of a Nanofluid past a Flat Vertical Plate with Newtonian Heating Boundary Condition

PubMed Central

Uddin, Mohammed J.; Khan, Waqar A.; Ismail, Ahmed I.

2012-01-01

Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement. PMID:23166688

12. Analysis of heat transfer for unsteady MHD free convection flow of rotating Jeffrey nanofluid saturated in a porous medium

Mohd Zin, Nor Athirah; Khan, Ilyas; Shafie, Sharidan; Alshomrani, Ali Saleh

In this article, the influence of thermal radiation on unsteady magnetohydrodynamics (MHD) free convection flow of rotating Jeffrey nanofluid passing through a porous medium is studied. The silver nanoparticles (AgNPs) are dispersed in the Kerosene Oil (KO) which is chosen as conventional base fluid. Appropriate dimensionless variables are used and the system of equations is transformed into dimensionless form. The resulting problem is solved using the Laplace transform technique. The impact of pertinent parameters including volume fraction φ , material parameters of Jeffrey fluid λ1 , λ , rotation parameter r , Hartmann number Ha , permeability parameter K , Grashof number Gr , Prandtl number Pr , radiation parameter Rd and dimensionless time t on velocity and temperature profiles are presented graphically with comprehensive discussions. It is observed that, the rotation parameter, due to the Coriolis force, tends to decrease the primary velocity but reverse effect is observed in the secondary velocity. It is also observed that, the Lorentz force retards the fluid flow for both primary and secondary velocities. The expressions for skin friction and Nusselt number are also evaluated for different values of emerging parameters. A comparative study with the existing published work is provided in order to verify the present results. An excellent agreement is found.

13. Simultaneous effects of MHD and partial slip on peristaltic flow of Jeffery fluid in a rectangular duct

Ellahi, R.; Hussain, F.

2015-11-01

The purpose of this paper is to study the closed-form solutions of peristaltic flow of Jeffery fluid under the simultaneous effects of magnetohydrodynamics (MHD) and partial slip conditions in a rectangular duct. The influence of wave train propagation is also taken into account. The analysis of mathematical model consists of continuity and the momentum equations are carried out under long wavelength (0 < < → ∞) and low Reynolds number (Re → 0) assumptions. The governing equations are first reduced to the dimensionless system of partial differential equation using the appropriate variables and afterwards exact solutions are obtained by applying the method of separation of variables. The role of pertinent parameters such as Hartmann number M, slip parameter β1, volumetric flow rate Q, Jeffery parameter λ1 and the aspect ratio β against the velocity profile, pressure gradient and pressure rise is illustrated graphically. The streamlines have also been presented to discuss the trapping bolus discipline. Comparison with the existing studies is made as a limiting case of the considered problem.at the end.

14. MHD free convective boundary layer flow of a nanofluid past a flat vertical plate with Newtonian heating boundary condition.

PubMed

Uddin, Mohammed J; Khan, Waqar A; Ismail, Ahmed I

2012-01-01

Steady two dimensional MHD laminar free convective boundary layer flows of an electrically conducting Newtonian nanofluid over a solid stationary vertical plate in a quiescent fluid taking into account the Newtonian heating boundary condition is investigated numerically. A magnetic field can be used to control the motion of an electrically conducting fluid in micro/nano scale systems used for transportation of fluid. The transport equations along with the boundary conditions are first converted into dimensionless form and then using linear group of transformations, the similarity governing equations are developed. The transformed equations are solved numerically using the Runge-Kutta-Fehlberg fourth-fifth order method with shooting technique. The effects of different controlling parameters, namely, Lewis number, Prandtl number, buoyancy ratio, thermophoresis, Brownian motion, magnetic field and Newtonian heating on the flow and heat transfer are investigated. The numerical results for the dimensionless axial velocity, temperature and nanoparticle volume fraction as well as the reduced Nusselt and Sherwood number have been presented graphically and discussed. It is found that the rate of heat and mass transfer increase as Newtonian heating parameter increases. The dimensionless velocity and temperature distributions increase with the increase of Newtonian heating parameter. The results of the reduced heat transfer rate is compared for convective heating boundary condition and found an excellent agreement.

15. An accurate, stable and efficient domain-type meshless method for the solution of MHD flow problems

SciTech Connect

Bourantas, G.C. Skouras, E.D. Loukopoulos, V.C. Nikiforidis, G.C.

2009-11-20

The aim of the present paper is the development of an efficient numerical algorithm for the solution of magnetohydrodynamics flow problems for regular and irregular geometries subject to Dirichlet, Neumann and Robin boundary conditions. Toward this, the meshless point collocation method (MPCM) is used for MHD flow problems in channels with fully insulating or partially insulating and partially conducting walls, having rectangular, circular, elliptical or even arbitrary cross sections. MPC is a truly meshless and computationally efficient method. The maximum principle for the discrete harmonic operator in the meshfree point collocation method has been proven very recently, and the convergence proof for the numerical solution of the Poisson problem with Dirichlet boundary conditions have been attained also. Additionally, in the present work convergence is attained for Neumann and Robin boundary conditions, accordingly. The shape functions are constructed using the Moving Least Squares (MLS) approximation. The refinement procedure with meshless methods is obtained with an easily handled and fully automated manner. We present results for Hartmann number up to 10{sup 5}. The numerical evidences of the proposed meshless method demonstrate the accuracy of the solutions after comparing with the exact solution and the conventional FEM and BEM, for the Dirichlet, Neumann and Robin boundary conditions of interior problems with simple or complex boundaries.

16. The migration and growth of nuclei in an ideal vortex flow

Zhang, Lingxin; Chen, Linya; Shao, Xueming

2016-12-01

Tip vortex cavitation occurs on ship propellers which can cause significant noise compared to the wet flow. In order to predict the inception of tip vortex cavitation, numerous researches have been investigated about the detailed flow field around the tip. According to informed studies, the inception of tip vortex cavitation is affected by many factors. To understand the effect of water quality on cavitation inception, the motion of nuclei in an ideal vortex flow, i.e., the Rankine vortex flow, was investigated. The one-way coupling point-particle tracking model was employed to simulate the trajectory of nuclei. Meanwhile, Rayleigh-Plesset equation was introduced to describe the growth of nuclei. The results show that the nucleus size has a significant effect on nucleus' trajectory. The capture time of a nucleus is approximately inversely proportional to its radius. The growth of nucleus accelerates its migration in the vortex flow and shortens its capture time, especially for the case of explosive growth.

17. Heat-flow equation motivated by the ideal-gas shock wave.

PubMed

2010-08-01

We present an equation for the heat-flux vector that goes beyond Fourier's Law of heat conduction, in order to model shockwave propagation in gases. Our approach is motivated by the observation of a disequilibrium among the three components of temperature, namely, the difference between the temperature component in the direction of a planar shock wave, versus those in the transverse directions. This difference is most prominent near the shock front. We test our heat-flow equation for the case of strong shock waves in the ideal gas, which has been studied in the past and compared to Navier-Stokes solutions. The new heat-flow treatment improves the agreement with nonequilibrium molecular-dynamics simulations of hard spheres under strong shockwave conditions.

18. MHD channel performance for potential early commercial MHD power plants

NASA Technical Reports Server (NTRS)

Swallom, D. W.

1981-01-01

The commercial viability of full and part load early commercial MHD power plants is examined. The load conditions comprise a mass flow of 472 kg/sec in the channel, Rosebud coal, 34% by volume oxygen in the oxidizer preheated to 922 K, and a one percent by mass seeding with K. The full load condition is discussed in terms of a combined cycle plant with optimized electrical output by the MHD channel. Various electrical load parameters, pressure ratios, and magnetic field profiles are considered for a baseload MHD generator, with a finding that a decelerating flow rate yields slightly higher electrical output than a constant flow rate. Nominal and part load conditions are explored, with a reduced gas mass flow rate and an enriched oxygen content. An enthalpy extraction of 24.6% and an isentropic efficiency of 74.2% is predicted for nominal operation of a 526 MWe MHD generator, with higher efficiencies for part load operation.

19. MHD channel performance for potential early commercial MHD power plants

NASA Technical Reports Server (NTRS)

Swallom, D. W.

1981-01-01

The commercial viability of full and part load early commercial MHD power plants is examined. The load conditions comprise a mass flow of 472 kg/sec in the channel, Rosebud coal, 34% by volume oxygen in the oxidizer preheated to 922 K, and a one percent by mass seeding with K. The full load condition is discussed in terms of a combined cycle plant with optimized electrical output by the MHD channel. Various electrical load parameters, pressure ratios, and magnetic field profiles are considered for a baseload MHD generator, with a finding that a decelerating flow rate yields slightly higher electrical output than a constant flow rate. Nominal and part load conditions are explored, with a reduced gas mass flow rate and an enriched oxygen content. An enthalpy extraction of 24.6% and an isentropic efficiency of 74.2% is predicted for nominal operation of a 526 MWe MHD generator, with higher efficiencies for part load operation.

20. Large-eddy simulation of flows over idealized urban areas in thermal stratification

Chan, Mr.; Liu, Dr.

2012-04-01

Large-eddy simulation (LES) equipped with the one-equation subgrid-scale model was employed to investigate the mean wind and turbulence over idealized two-dimensional (2D) street canyons in various thermal stratifications. The prevailing wind is driven by a background pressure gradient above the roof level that is perpendicular to the axis of street canyons. The building-height-to-street-width (aspect) ratio is kept unity so the flows fall into the skimming flow regime. Cyclic boundary conditions are assigned to the domain inlet and outlet, simulating the infinite horizontally homogenous building structures. The buoyancy force is modeled by Boussinesq approximation. Building geometry is the key factor governing the wind flow behaviors aloft. Its effects on the flow structures in isothermal conditions are widely studied. Whereas, thermal stratification, which is caused by the temperature difference between the urban fabrics and the prevailing wind, plays another important role in the wind flow behaviors. The presence of buoyancy force drives/suppresses convective flows that substantially modify the vertical transport processes. In stable stratification, e.g. nighttime, a cooler urban surface favors subsidence that reduces turbulence intensities subsequently. While in unstable stratification, e.g. daytime, a hotter urban surface induces buoyancy and convective current that in turn promotes turbulence. In isothermal conditions, it is well known that the mean flows exhibit a log-law region over an aerodynamically smooth surface where the mean wind profile is in a logarithmic form (law of the wall). The logarithmic wind profile is also observed over homogenously rough surfaces, such as the idealized two-dimensional street canyons used in this study. However, in thermal stratification (both stable and unstable), the mean wind profile deviates from the isothermal one whose extent depends on the intensity of thermal stratification compared with the mean wind (measured by

1. Transport and heat transfer of time dependent MHD slip flow of nanofluids in solar collectors with variable thermal conductivity and thermal radiation

In this paper, the unsteady magnetohydrodynamic (MHD) boundary layer slip flow and heat transfer of nanofluid in a solar collector, modeled mathematically as a nonlinear stretching sheet is investigated numerically. The variable thermal conductivity is assumed as a function of temperature and the wall-slip conditions are utilized at the boundary. The similarity transformation technique is used to reduce the governing boundary value problem to a system of nonlinear ordinary differential equations (ODEs) and then solved numerically. The numerical values obtained for the velocity and temperature depend on nanofluid volume concentration parameter, unsteadiness parameter, suction/injection parameter, thermal conductivity parameter, slip parameters, MHD parameter and thermal radiation parameter. The effects of various parameters on the flow and heat transfer characteristics are presented and discussed through graphs and tables.

2. MHD flow past a parabolic flow past an infinite isothermal vertical plate in the presence of thermal radiation and chemical reaction

Muthucumaraswamy, R.; Sivakumar, P.

2016-02-01

The problem of MHD free convection flow with a parabolic starting motion of an infinite isothermal vertical plate in the presence of thermal radiation and chemical reaction has been examined in detail in this paper. The fluid considered here is a gray, absorbing emitting radiation but a non-scattering medium. The dimensionless governing coupled linear partial differential equations are solved using the Laplace transform technique. A parametric study is performed to illustrate the influence of the radiation parameter, magnetic parameter, chemical reaction parameter, thermal Grashof number, mass Grashof number, Schmidt number and time on the velocity, temperature, concentration. The results are discussed graphically and qualitatively. The numerical results reveal that the radiation induces a rise in both the velocity and temperature, and a decrease in the concentration. The model finds applications in solar energy collection systems, geophysics and astrophysics, aerospace and also in the design of high temperature chemical process systems.

3. Modeling and Simulation of Mucus Flow in Human Bronchial Epithelial Cell Cultures - Part I: Idealized Axisymmetric Swirling Flow.

PubMed

Vasquez, Paula A; Jin, Yuan; Palmer, Erik; Hill, David; Forest, M Gregory

2016-08-01

A multi-mode nonlinear constitutive model for mucus is constructed directly from micro- and macro-rheology experimental data on cell culture mucus, and a numerical algorithm is developed for the culture geometry and idealized cilia driving conditions. This study investigates the roles that mucus rheology, wall effects, and HBE culture geometry play in the development of flow profiles and the shape of the air-mucus interface. Simulations show that viscoelasticity captures normal stress generation in shear leading to a peak in the air-mucus interface at the middle of the culture and a depression at the walls. Linear and nonlinear viscoelastic regimes can be observed in cultures by varying the hurricane radius and mean rotational velocity. The advection-diffusion of a drug concentration dropped at the surface of the mucus flow is simulated as a function of Peclet number.

4. Modeling and Simulation of Mucus Flow in Human Bronchial Epithelial Cell Cultures – Part I: Idealized Axisymmetric Swirling Flow

PubMed Central

Vasquez, Paula A.; Jin, Yuan; Palmer, Erik; Hill, David; Forest, M. Gregory

2016-01-01

A multi-mode nonlinear constitutive model for mucus is constructed directly from micro- and macro-rheology experimental data on cell culture mucus, and a numerical algorithm is developed for the culture geometry and idealized cilia driving conditions. This study investigates the roles that mucus rheology, wall effects, and HBE culture geometry play in the development of flow profiles and the shape of the air-mucus interface. Simulations show that viscoelasticity captures normal stress generation in shear leading to a peak in the air-mucus interface at the middle of the culture and a depression at the walls. Linear and nonlinear viscoelastic regimes can be observed in cultures by varying the hurricane radius and mean rotational velocity. The advection-diffusion of a drug concentration dropped at the surface of the mucus flow is simulated as a function of Peclet number. PMID:27494700

5. Heat transfer characteristics of rectangular coolant channels with various aspect ratios in the plasma-facing components under fully developed MHD laminar flow

SciTech Connect

Takase, K.; Hasan, M.Z.

1995-12-31

Convective heat transfer in MHD laminar flow through rectangular channels in the plasma-facing components of a fusion reactor has been analyzed numerically to investigate the effects of channel aspect ratio, defined as the ratio of the lengths of the plasma-facing side to the other side. The adverse effect of the nonuniformity of surface heat flus on Nusselt number (Nu) at the plasma-facing side can be alleviated by increasing the aspect ratio of a rectangular duct. At the center and corner of the plasma-facing side of a square duct, the Nu of non-MHD flow are 6.8 and 2.2, respectively, for uniform surface heat flux. In the presence of a strong magnetic field, Nu at the center and corner increases to 22 and 3.6, respectively. However, when the heat flux is highly nonuniform, as in the plasma-facing components, Nu decreases from 22 to 3.1 at the center and from 3.6 to 3.1 at the corner. When the aspect ratio is increased to 4, Nu at the center and corner increase to 5 and 4.7. Along the circumference of a rectangular channel, there are locations where the wall temperature is equal to or less than the bulk coolant temperature, thus making the Nu with conventional definition infinity or negative. The ratio between Nu of MHD flow and Nu of non-MHD flow for various aspect ratios is constant in the region of Hartmann number of more than 200 at least. On the other hand, its ratio increases monotonously with increasing the aspect ratio.

6. Heat and mass transfer for natural convection MHD flow over a permeable moving vertical plate with convective boundary condition in the presence of viscous dissipation

Shateyi, Stanford

2017-07-01

The spectral relaxation method is employed to examine natural convective heat and mass transfer, MHD flow over a permeable moving vertical plate with convective boundary condition in the presence of viscous dissipation, thermal radiation and chemical reaction. The governing partial differential equations were transformed into a system of nonlinear ordinary differential equations by using a similarity approach. The pertinent results are then displayed in tabular form and graphically.

7. The dynamics of idealized katabatic flow over a moderate slope and ice shelf

Renfrew, A. Ian

2004-04-01

A non-hydrostatic numerical weather prediction model has been employed to simulate idealized katabatic flows over a moderate slope and adjoining ice shelf. The topography of Coats Land and the adjoining Brunt Ice Shelf, Antarctica, has been used; this is typical of much of the Antarctic coastline. The Regional Atmospheric Modeling System Version 4.3 has been adapted for simulations over compacted snow, most notably through changes to the multi-layer soil model. The simulations are initialized using clear-sky conditions and at rest. On the slope, a shallow katabatic flow develops, the winds becoming approximately steady on the slope by ~ 12 h. The peak downslope winds are about 7 m s-1 at 30 m above the snow surface. The katabatic flow depth ranges from 50 to 100 m down the slope. Over the ice shelf the katabatic flow peters out, while a pool of cold air develops, primarily through sensible-heat loss into the surface and partially balancing the net radiative-heat loss to space. Near-surface and sounding data from the model simulations compare well with archetypal and typical katabatic flow observations, especially after some tuning of the model's turbulence parametrization. An analysis of the downslope flow dynamics shows the buoyancy force is generally balanced by the inertial force, except towards the foot of the slope where it is balanced by upslope forces related to gradients in the potential-temperature deficit and katabatic-layer height, caused by the pool of cold air over the ice shelf. Over time, the cooling of the ice shelf boundary layer leads to an apparent retreat of the katabatic flow from the ice shelf and some way up the slope. The dynamical analysis explains the surface climatology observed, such that the persistent katabatic winds of Coats Land rarely reach the Brunt Ice Shelf. The simulated katabatic flow moves from 'shooting' to 'tranquil' towards the foot of the slope. This transition acts to trigger a train of internal gravity waves which

8. International Conference on MHD Electrical Power Generation, 7th, Massachusetts Institute of Technology, Cambridge, MA, June 16-20, 1980, Proceedings. Volumes 1, 2 & 3

Dawson, A. M.; Overlan, D.

The first volume of this conference on magnetohydrodynamics (MHD) for electrical power generation covers: (1) MHD pilot plants; (2) MHD generator experiments and modeling; (3) the performance of various MHD generator types; (4) MHD channel design considerations; (5) MHD channel materials considerations; (6) MHD system components, heat recovery and emissions; and (7) MHD oxidizers and inverters. The second volume deals with (8) MHD system magnets and combustors; (9) MHD field, flow and chemical processes; (10) MHD fluid dynamics; (11) MHD electrical power plant design; (12) current transfer and diagnostics; and (13) MHD power plant systems considerations.

9. MHD Stagnation point flows in the presence of resistivity and viscosity

SciTech Connect

Gratton, F.T.; Heyn, M.F.; Biernat, H.K.; Rijnbeek, R.P.; Gnavi, G. )

1988-07-01

The authors analyze the steady state situation in which two separate and counterstreaming plasmas (assumed to be incompressible) carrying antiparallel magnetic fields are separated by a resistive current layer. Exact solutions are presented which describe the stagnation point flow pattern and magnetic field behavior which result. They incorporate the effects of viscosity, which enables us to model flows with vorticity. The uniform plasma flow which is obtained at large distances from the current layer allows us to specify finite values of the asymptotic magnetic field. The exact solutions complement those of a different type obtained by B.U.O. Sonnerup and E.R. Priest (1975) which assume potential flow, i.e., zero vorticity. The results they obtain are discussed in relation to observational features at the Earth's magnetopause.

10. Reorienting MHD colliding flows: a shock physics mechanism for generating filaments normal to magnetic fields

Fogerty, Erica; Carroll-Nellenback, Jonathan; Frank, Adam; Heitsch, Fabian; Pon, Andy

2017-09-01

We present numerical simulations of reorienting oblique shocks that form in the collision layer between magnetized colliding flows. Reorientation aligns post-shock filaments normal to the background magnetic field. We find that reorientation begins with pressure gradients between the collision region and the ambient medium. This drives a lateral expansion of post-shock gas, which reorients the growing filament from the outside-in (i.e. from the flow/ambient boundary, towards the colliding flows axis). The final structures of our simulations resemble polarization observations of filaments in Taurus and Serpens South, as well as the integral-shaped filament in Orion A. Given the ubiquity of colliding flows in the interstellar medium, shock reorientation may be relevant to the formation of filaments normal to magnetic fields.

11. MHD flow through a porous medium adjacent to a stretching sheet: Numerical and an approximate solution

Chauhan, D. S.; Agrawal, R.

2011-05-01

A viscous incompressible electrically conducting fluid flow through a porous medium over a stretching sheet is considered in the presence of a magnetic field. Such flow problems have relevance in the process of a polymer sheet extrusion from a dye, and the numerical and approximate solutions of these problems are of great interest as these solutions serve practical purposes. By using the technique of stretching variables of the flow concern in porous medium and minimizing the residual of the resulting governing differential equations by the least squares method, we obtained an approximate solution for this problem of flow through porous medium near a stretching sheet. The results are also compared to a numerical solution determined by using the shooting method along with the Runge-Kutta method. The effects of various pertinent parameters on the velocity distribution and the residual function are investigated. The results are depicted graphically and discussed.

12. MHD boundary layer radiative, heat generating and chemical reacting flow past a wedge moving in a nanofluid.

PubMed

Khan, Md Shakhaoath; Karim, Ifsana; Islam, Md Sirajul; Wahiduzzaman, Mohammad

2014-01-01

The present study analyzed numerically magneto-hydrodynamics (MHD) laminar boundary layer flow past a wedge with the influence of thermal radiation, heat generation and chemical reaction. This model used for the momentum, temperature and concentration fields. The principal governing equations is based on the velocity uw (x) in a nanofluid and with a parallel free stream velocity ue (x) and surface temperature and concentration. Similarity transformations are used to transform the governing nonlinear boundary layer equations for momentum, thermal energy and concentration to a system of nonlinear ordinary coupled differential equations with fitting boundary conditions. The transmuted model is shown to be controlled by a number of thermo-physical parameters, viz. the magnetic parameter, thermal convective parameter, mass convective parameter, radiation-conduction parameter, heat generation parameter, Prandtl number, Lewis number, Brownian motion parameter, thermophoresis parameter, chemical reaction parameter and pressure gradient parameter. Numerical elucidations are obtained with the legendary Nactsheim-Swigert shooting technique together with Runge-Kutta six order iteration schemes. Comparisons with previously published work are accomplished and proven an excellent agreement.

13. MHD Boundary Layer Slip Flow and Heat Transfer of Ferrofluid along a Stretching Cylinder with Prescribed Heat Flux

PubMed Central

2014-01-01

This study investigates the magnetohydrodynamic (MHD) flow of ferrofluid along a stretching cylinder. The velocity slip and prescribed surface heat flux boundary conditions are employed on the cylinder surface. Water as conventional base fluid containing nanoparticles of magnetite (Fe3O4) is used. Comparison between magnetic (Fe3O4) and non-magnetic (Al2O3) nanoparticles is also made. The governing non-linear partial differential equations are reduced to non-linear ordinary differential equations and then solved numerically using shooting method. Present results are compared with the available data in the limiting cases. The present results are found to be in an excellent agreement. It is observed that with an increase in the magnetic field strength, the percent difference in the heat transfer rate of magnetic nanoparticles with Al2O3 decreases. Surface shear stress and the heat transfer rate at the surface increase as the curvature parameter increases, i.e curvature helps to enhance the heat transfer. PMID:24465388

14. MHD boundary layer radiative, heat generating and chemical reacting flow past a wedge moving in a nanofluid

Khan, Md Shakhaoath; Karim, Ifsana; Islam, Md Sirajul; Wahiduzzaman, Mohammad

2014-07-01

The present study analyzed numerically magneto-hydrodynamics (MHD) laminar boundary layer flow past a wedge with the influence of thermal radiation, heat generation and chemical reaction. This model used for the momentum, temperature and concentration fields. The principal governing equations is based on the velocity u w (x) in a nanofluid and with a parallel free stream velocity u e (x) and surface temperature and concentration. Similarity transformations are used to transform the governing nonlinear boundary layer equations for momentum, thermal energy and concentration to a system of nonlinear ordinary coupled differential equations with fitting boundary conditions. The transmuted model is shown to be controlled by a number of thermo-physical parameters, viz. the magnetic parameter, thermal convective parameter, mass convective parameter, radiation-conduction parameter, heat generation parameter, Prandtl number, Lewis number, Brownian motion parameter, thermophoresis parameter, chemical reaction parameter and pressure gradient parameter. Numerical elucidations are obtained with the legendary Nactsheim-Swigert shooting technique together with Runge-Kutta six order iteration schemes. Comparisons with previously published work are accomplished and proven an excellent agreement.

15. MHD boundary layer slip flow and heat transfer of ferrofluid along a stretching cylinder with prescribed heat flux.

PubMed

2014-01-01

This study investigates the magnetohydrodynamic (MHD) flow of ferrofluid along a stretching cylinder. The velocity slip and prescribed surface heat flux boundary conditions are employed on the cylinder surface. Water as conventional base fluid containing nanoparticles of magnetite (Fe3O4) is used. Comparison between magnetic (Fe3O4) and non-magnetic (Al2O3) nanoparticles is also made. The governing non-linear partial differential equations are reduced to non-linear ordinary differential equations and then solved numerically using shooting method. Present results are compared with the available data in the limiting cases. The present results are found to be in an excellent agreement. It is observed that with an increase in the magnetic field strength, the percent difference in the heat transfer rate of magnetic nanoparticles with Al2O3 decreases. Surface shear stress and the heat transfer rate at the surface increase as the curvature parameter increases, i.e curvature helps to enhance the heat transfer.

16. Forward and Inverse Modeling of Helioseismic Holography Measurements of MHD Simulations of Convection and Sunspot Flows

DeGrave, Kyle; Braun, Douglas; Birch, Aaron; Crouch, Ashley D.; Javornik, Brenda; Rempel, Matthias D.

2016-05-01

We test and validate newly-developed, empirically-derived sensitivity kernels for use in helioseismic analysis. These kernels are based on the Born approximation and derived from applying direct measurements to artificial realizations of incoming and scattered wavefields. These kernels are employed in a series of forward and inverse modeling of flows from the near-surface layers of two publicly available magnetohydrodynamic (MURaM-based) solar simulations - a quiet-Sun simulation, and one containing a sunspot. Forward travel times computed using the kernels generally compare favorably in non-magnetic regions. One finding of note is the presence of flow-like artifacts in the sunspot measurements which appear when the spot umbra or penumbra falls within the measurement pupils. Inversions for the horizontal flow components are able to reproduce the large-scale supergranule-sized flows in the upper 3Mm of both domains, but are compromised by noise at greater depths. In spite of the magnetic artifact, the moat flow surrounding the spot is at least qualitatively recovered. This work is supported by the NASA Heliophysics Division through NNH12CF68C, NNH12CF23C, and NNX16AG88G, and by the NSF Solar-Terrestrial Program through grant AGS-1127327.

17. Buoyancy effects on the 3D MHD stagnation-point flow of a Newtonian fluid

Borrelli, A.; Giantesio, G.; Patria, M. C.; Roşca, N. C.; Roşca, A. V.; Pop, I.

2017-02-01

This work examines the steady three-dimensional stagnation-point flow of an electrically conducting Newtonian fluid in the presence of a uniform external magnetic field H0 under the Oberbeck-Boussinesq approximation. We neglect the induced magnetic field and examine the three possible directions of H0 which coincide with the directions of the axes. In all cases it is shown that the governing nonlinear partial differential equations admit similarity solutions. We find that the flow has to satisfy an ordinary differential problem whose solution depends on the Hartmann number M, the buoyancy parameter λ and the Prandtl number Pr. The skin-friction components along the axes are computed and the stagnation-point is classified. The numerical integration shows the existence of dual solutions and the occurrence of the reverse flow for some values of the parameters.

18. Magnetite micropolar nanofluid non-aligned MHD flow with mixed convection

Tabassum, Rabil; Mehmood, R.; Akbar, N. S.

2017-06-01

The magnetite micropolar nanofluid ( Fe3O4 /water) oblique flow in the presence of mixed convection and magnetic field is considered in the present investigation. Magnetite nanoparticles are added to water in order to examine the temperature and velocity characteristics of the flow. Appropriate transformations are employed to obtain the governing equations. Numerical solutions are attained by the Range-Kutta-Fehlberg integration scheme with the shooting method. Characteristics of flow velocity profiles, temperature distribution, micro-rotation, shear stress and heat flux are remarkably influenced by magnetic parameter, magnetite nanoparticles volume fraction and mixed convection parameter. The obtained results indicate that the shear stress at the wall decreases but the local heat flux increases with increase in the nanoparticles volume fraction. Moreover, an increase in the magnetic field strength consequently enhances the shear stress at the surface but decreases the local heat transfer rate at the surface.

19. 2-D MHD numerical simulations of EML plasma armatures with ablation

Boynton, G. C.; Huerta, M. A.; Thio, Y. C.

1993-01-01

We use a 2-D) resistive MHD code to simulate an EML plasma armature. The energy equation includes Ohmic heating, radiation heat transport and the ideal gas equation of state, allowing for variable ionization using the Saha equations. We calculate rail ablation taking into account the flow of heat into the interior of the rails. Our simulations show the development of internal convective flows and secondary arcs. We use an explicit Flux Corrected Transport algorithm to advance all quantities in time.

20. Simulation of MHD CuO-water nanofluid flow and convective heat transfer considering Lorentz forces

Sheikholeslami, Mohsen; Bandpy, Mofid Gorji; Ellahi, R.; Zeeshan, A.

2014-11-01

Magnetic field effect on CuO-water nanofluid flow and heat transfer in an enclosure which is heated from below is investigated. Lattice Boltzmann method is applied to solve the governing equations. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo-Kleinstreuer-Li) correlation. In this model effect of Brownian motion on the effective thermal conductivity is considered. Effect of active parameter such as: Hartmann number, heat source length, nanoparticle volume fraction and Rayleigh numbers on the flow and heat transfer characteristics have been examined. The results reveal that the enhancement in heat transfer increases as Hartmann number and heat source length increase but it decreases with increase of Rayleigh number. Also it can be found that effect of Hartmann number and heat source length is more pronounced at high Rayleigh number.

1. Numerical investigation of entropy generation in unsteady MHD generalized Couette flow with variable electrical conductivity.

PubMed

Chinyoka, T; Makinde, O D

2013-01-01

The thermodynamic second law analysis is utilized to investigate the inherent irreversibility in an unsteady hydromagnetic generalized Couette flow with variable electrical conductivity in the presence of induced electric field. Based on some simplified assumption, the model nonlinear governing equations are obtained and solved numerically using semidiscretization finite difference techniques. Effects of various thermophysical parameters on the fluid velocity, temperature, current density, skin friction, the Nusselt number, entropy generation number, and the Bejan number are presented graphically and discussed quantitatively.

2. Numerical Investigation of Entropy Generation in Unsteady MHD Generalized Couette Flow with Variable Electrical Conductivity

PubMed Central

Chinyoka, T.; Makinde, O. D.

2013-01-01

The thermodynamic second law analysis is utilized to investigate the inherent irreversibility in an unsteady hydromagnetic generalized Couette flow with variable electrical conductivity in the presence of induced electric field. Based on some simplified assumption, the model nonlinear governing equations are obtained and solved numerically using semidiscretization finite difference techniques. Effects of various thermophysical parameters on the fluid velocity, temperature, current density, skin friction, the Nusselt number, entropy generation number, and the Bejan number are presented graphically and discussed quantitatively. PMID:23956691

3. Numerical investigation of the turbulent MHD flow in a circular pipe with transverse magnetic field

Dechamps, Xavier; Rasquin, Michel; Degrez, Gérard

2012-11-01

In modern industrial metallurgical processes, external magnetic fields are often applied to control the motion of liquid metals by a non-intrusive means. The desired results are for example the damping of unwanted motions or the homogenization of a liquid zone in a partially solidified ingot. Because of the commonly appearing parameters in these processes, one can assume the quasi-static assumption for the magnetohydrodynamic equations. Here we are interested in the numerical study of the turbulent flow of a liquid metal inside an electrically insulated pipe with a transverse uniform magnetic field. For this purpose, we will use a hybrid spectral/finite element solver, which allows to study complex flows in Cartesian and axisymmetric geometries. For the case of interest, we consider a bulk Reynolds number of 8200 and a Hartmann number ranging between 5 and 30. Here, the main points of interest are the evolution of the skin friction coefficient as a function of the ratio of the Hartmann number Ha over the Reynolds number Re (with 0 < Ha/Re < 75 × 10-4) as well as the energy budget (viscous, Joule and numerical dissipations, kinetic energy production) in a cross-section. These results will determine the transition point between laminar and turbulent flows. Support of the Fonds Nationals de la Recherche Scientifique (FNRS) is aknowledged.

4. Electro-osmotically driven MHD flow and heat transfer in micro-channel

Shit, G. C.; Mondal, A.; Sinha, A.; Kundu, P. K.

2016-05-01

A theoretical analysis is presented for electro-osmotic flow (EOF) of blood in a hydrophobic micro-channel with externally applied magnetic field. The lumen of micro-channels is assumed to be porous medium in addition to the consideration of permeability of the channel walls. The effects of slip velocity and thermal-slip are taken into consideration. The governing equations in the electrical double layer (EDL) together with the Poisson-Boltzmann equation and the body force exerted by the applied potential are furthermore considered. The flow is governed by the non-Newtonian viscoelastic fluid model. These equations along with the thermal energy equation are approximated by assuming that the channel height is much greater than the thickness of electrical double layer consisting the stern and diffusive layers. The problem is solved analytically and the computed results have presented graphically for various values of the dimensionless parameters. The results presented here have significant impact on the therapeutic treatment in hyperthermia as well as in controlling blood flow and heat transfer in micro-channels.

5. Numerical investigation of MHD flow of blood and heat transfer in a stenosed arterial segment

Majee, Sreeparna; Shit, G. C.

2017-02-01

A numerical investigation of unsteady flow of blood and heat transfer has been performed with an aim to provide better understanding of blood flow through arteries under stenotic condition. The blood is treated as Newtonian fluid and the arterial wall is considered to be rigid having deposition of plaque in its lumen. The heat transfer characteristic has been analyzed by taking into consideration of the dissipation of energy due to applied magnetic field and the viscosity of blood. The vorticity-stream function formulation has been adopted to solve the problem using implicit finite difference method by developing well known Peaceman-Rachford Alternating Direction Implicit (ADI) scheme. The quantitative profile analysis of velocity, temperature and wall shear stress as well as Nusselt number is carried out over the entire arterial segment. The streamline and temperature contours have been plotted to understand the flow pattern in the diseased artery, which alters significantly in the downstream of the stenosis in the presence of magnetic field. Both the wall shear stress and Nusselt number increases with increasing magnetic field strength. However, wall shear stress decreases and Nusselt number enhances with Reynolds number. The results show that with an increase in the magnetic field strength upto 8 T, does not causes any damage to the arterial wall, but the study is significant for assessing temperature rise during hyperthermic treatment.

6. Experimental investigation of heat transfer in free-surface MHD flow

Rhoads, J.; Katzenstein, A.; Edlund, E.; Sloboda, P.; Spence, E.; Ji, H.

2012-11-01

The presence of a strong external magnetic field can significantly alter the dynamics of large and small scale features within the flow. In particular, turbulent eddies with vorticity non-parallel to the magnetic field are strongly damped. This anisotropization of the turbulence may be critically important for heat transport in flowing liquid metal walls in a fusion reactor. Experiments have been conducted in the Liquid Metal Experiment (LMX) using a GaInSn eutectic alloy as a working fluid to investigate these effects. These experiments considered free-surface, wide aspect-ratio flows up to 20 cm/s through a channel situated in a magnetic field up to 2 kG, corresponding to a Reynolds number up to Re ~104 and a Hartmann number up to Ha ~ 50 . Resistive heaters were placed on the free surface and the fluid temperature downstream was monitored by an array of thermocouples and an infrared camera. The relationship between Nusselt number and Hartmann number will be presented. Work supported under contract DE-AC02-09CH11466.

7. Orbital Advection by Interpolation: A Fast and Accurate Numerical Scheme for Super-Fast MHD Flows

SciTech Connect

Johnson, B M; Guan, X; Gammie, F

2008-04-11

In numerical models of thin astrophysical disks that use an Eulerian scheme, gas orbits supersonically through a fixed grid. As a result the timestep is sharply limited by the Courant condition. Also, because the mean flow speed with respect to the grid varies with position, the truncation error varies systematically with position. For hydrodynamic (unmagnetized) disks an algorithm called FARGO has been developed that advects the gas along its mean orbit using a separate interpolation substep. This relaxes the constraint imposed by the Courant condition, which now depends only on the peculiar velocity of the gas, and results in a truncation error that is more nearly independent of position. This paper describes a FARGO-like algorithm suitable for evolving magnetized disks. Our method is second order accurate on a smooth flow and preserves {del} {center_dot} B = 0 to machine precision. The main restriction is that B must be discretized on a staggered mesh. We give a detailed description of an implementation of the code and demonstrate that it produces the expected results on linear and nonlinear problems. We also point out how the scheme might be generalized to make the integration of other supersonic/super-fast flows more efficient. Although our scheme reduces the variation of truncation error with position, it does not eliminate it. We show that the residual position dependence leads to characteristic radial variations in the density over long integrations.

8. Numerical simulation of MHD free convection flow in a differentially heated square enclosure with tilted obstacle

Ali, M. M.; Alim, M. A.; Maleque, M. A.; Ahmed, Syed Sabbir

2017-06-01

A numerical study has been carried out to analyze the flow and heat transfer characteristics due to the effects of magnetohydrodynamic free convection flow in a differentially heated enclosure having a hot tilted square block. The vertical and horizontal walls of the cavity are non-uniformly heated while the walls of the tilted block are uniformly heated. The basic partial differential equations of the physical problem are solved numerically using finite element technique along with Galerkin's weighted residual simulation. Calculations have been performed for different values of buoyancy parameter (102 ≤ Ra ≤ 105) and magnetic field parameter (0 ≤ Ha ≤ 60) and obtained results are illustrated in terms of streamlines, isotherms, average Nusselt number and average temperature. The results show that the flow pattern and temperature distributions affected noticeably for the effect of aforementioned parameters. In addition, an increase in average Nusselt number is found for the whole range of Rayleigh number and average temperature decreased for increasing Rayleigh number. Comparison between the obtained results and the previously published results on the basis of special case is a good agreement.

9. Flow Shear Effects in the Onset Physics of Resistive MHD Instabilities in Tokamaks. Final report

SciTech Connect

Brennan, Dylan P.

2013-04-24

The progress in this research centers around the computational analysis of flow shear effects in the onset of a 3/2 mode driven by a 1/1 mode in DIII-D equilibria. The initial idea was to try and calculate, via nonlinear simulations with NIMROD, the effects of rotation shear on driven 3/2 and 2/1 seed island physics, in experimentally relevant DIIID equilibria. The simulations indicated that very small seed islands were directly driven, as shielding between the sawtooth and the surfaces is significant at the high Lundquist numbers of the experiment. Instead, long after the initial crash the difference in linear stability of the 3/2, which remained prevalent despite the flattening of the core profiles from the sawtooth, contributed to a difference in the eventual seed island evolution. Essentially the seed islands grew or decayed long after the sawtooth crash, and not directly from it. Effectively the dominant 1/1 mode was found to be dragging the coupled modes surrounding it at a high rate through the plasma at their surfaces. The 1/1 mode is locked to the local frame of the plasma in the core, where the flow rate is greatest. The resonant perturbations at the surrounding surfaces propagate in the 'high slip regime' in the language of Fitzpatrick. Peaked flux averaged jxb forces (see Figs. 1 and 2) agree with localized flow modifications at the surfaces in analogy with Ebrahimi, PRL 2007. We track the mode into nonlinear saturation and have found oscillatory states in the evolution. During a visit (11/09) to Tulsa by R.J. LaHaye (GA), it became clear that similar oscillatory states are observed in DIII-D for these types of discharges.

10. Effect of melting on an MHD micropolar fluid flow toward a shrinking sheet with thermal radiation

Das, K.; Sarkar, A.

2016-07-01

The effect of melting on a steady boundary layer stagnation-point flow and heat transfer of an electrically conducting micropolar fluid toward a horizontal shrinking sheet in the presence of a uniform transverse magnetic field and thermal radiation is studied. A similarity transformation technique is adopted to obtain self-similar ordinary differential equations, which are solved numerically. The present results are found to be in good agreement with previously published data. Numerical results for the dimensionless velocity and temperature profiles, as well as for the skin friction and the rate of heat transfer are obtained.

11. The effect of wall suction/injection on MHD Marangoni convection boundary layer flow in nanofluid

Hamid, Rohana Abdul; Arifin, Norihan Md.

2014-07-01

The problem of Marangoni-driven boundary layer flow over a permeable flat surface in an electrically conducting nanofluid is considered in the present paper. Numerical solutions of the similarity equations are obtained using the shooting method. Three types of nanoparticles, namely copper (Cu), alumina (Al2O3) and titania (TiO2) are considered by using a water-based fluid to investigate the effect of nanoparticle volume fraction parameter φ of the nanofluid. It is found that the wall suction or injection has the significant effect on the velocity and temperature profiles.

12. MHD Oldroyd-B fluid flow across a melting surface with cross diffusion and double stratification

Sandeep, N.; Gnaneswara Reddy, M.

2017-03-01

In this study, we analyzed the Oldroyd-B flow across a horizontal melting surface with cross-diffusion and double stratification (thermal and solutal) effects. We reconstructed the controlling equations as a group of nonlinear ODEs and solved by employing the RK-based shooting technique. The influence of important specifications on the three common profiles (velocity, temperature and concentration) is discussed through the plots. Tables are utilized to discuss the heat and mass transfer rates. We verified that the thermal stratification improves the heat transfer rate. Cross diffusion regulates the concentration and thermal fields.

13. MHD Flow with Hall current and Joule Heating Effects over an Exponentially Stretching Sheet

2017-06-01

The aim of the present paper is to study the influence of Hall current and Joule heating on flow, heat and mass transfer over an exponentially stretching sheet in a viscous fluid. Using similarity transformations the governing nonlinear coupled equations are converted into ordinary differential equations. These equations are linearized using the successive linearization method and then solved using the Chebyshev pseudo spectral method. The influence of magnetic parameter, Hall parameter, suction/injection parameter and slip parameter on the physical quantities are presented graphically. The obtained results are compared with the previously published results for special cases.

14. Oscillatory MHD Convective Flow of Second Order Fluid Through Porous Medium in a Vertical Rotating Channel in Slip-Flow Regime with Heat Radiation

Garg, B. P.; Singh, K. D.; Bansal, A. K.

2015-02-01

An analysis of an oscillatory magnetohydrodynamic (MHD) convective flow of a second order (viscoelastic), incompressible, and electrically conducting fluid through a porous medium bounded by two infinite vertical parallel porous plates is presented. The two porous plates with slip-flow condition and the no-slip condition are subjected respectively to a constant injection and suction velocity. The pressure gradient in the channel varies periodically with time. A magnetic field of uniform strength is applied in the direction perpendicular to the planes of the plates. The induced magnetic field is neglected due to the assumption of a small magnetic Reynolds number. The temperature of the plate with no-slip condition is non-uniform and oscillates periodically with time and the temperature difference of the two plates is assumed high enough to induce heat radiation. The entire system rotates in unison about the axis perpendicular to the planes of the plates. Adopting complex variable notations, a closed form solution of the problem is obtained. The analytical results are evaluated numerically and then presented graphically to discuss in detail the effects of different parameters of the problem. The velocity, temperature and the skin-friction in terms of its amplitude and phase angle have been shown graphically to observe the effects of the viscoelastic parameter γ, rotation parameter Ω, suction parameter λ , Grashof number Gr, Hartmann number M, the pressure A, Prandtl number Pr, radiation parameter N and the frequency of oscillation ω .

15. Quantifying residual, eddy, and mean flow effects on mixing in an idealized circumpolar current

DOE PAGES

Wolfram, Phillip J.; Ringler, Todd D.

2017-05-23

Meridional diffusivity is assessed in this paper for a baroclinically unstable jet in a high-latitudeIdealized Circumpolar Current (ICC) using the Model for Prediction Across Scales-Ocean (MPAS-O) and the online Lagrangian In-situ Global High-performance particle Tracking (LIGHT) diagnostic via space-time dispersion of particle clusters over 120 monthly realizations of O(106) particles on 11 potential density surfaces. Diffusivity in the jet reaches values of O(6000 m2 s-1) and is largest near the critical layer supporting mixing suppression and critical layer theory. Values in the vicinity of the shelf break are suppressed to O(100 m2 s-1) due to the presence of westward slopemore » front currents. Diffusivity attenuates less rapidly with depth in the jet than both eddy velocity and kinetic energy scalings would suggest. Removal of the mean flow via high-pass filtering shifts the nonlinear parameter (ratio of the eddy velocity to eddy phase speed) into the linear wave regime by increasing the eddy phase speed via the depth-mean flow. Low-pass filtering, in contrast, quantifies the effect of mean shear. Diffusivity is decomposed into mean flow shear, linear waves, and the residual nonhomogeneous turbulence components, where turbulence dominates and eddy-produced filamentation strained by background mean shear enhances mixing, accounting for ≥ 80% of the total diffusivity relative to mean shear [O(100 m2 s-1)], linear waves [O(1000 m2 s-1)], and undecomposed full diffusivity [O(6000 m2 s-1)]. Finally, diffusivity parameterizations accounting for both the nonhomogeneous turbulence residual and depth variability are needed.« less

16. Slip Analysis at Fluid-Solid Interface in MHD Squeezing Flow of Casson Fluid through Porous Medium

Qayyum, Mubashir; Khan, Hamid; Khan, Omar

An unsteady squeezing flow of Casson fluid having Magneto Hydro Dynamic effect and passing through porous medium channel with slip at the boundaries has been modelled and analyzed. Similarity transformations are applied to the governing partial differential equations of the Casson model to get a highly non-linear fourth order ordinary differential equation. The obtained equation is then solved analytically using the Homotopy Perturbation Method (HPM) for uniform and non-uniform slip at the boundaries. Five cases of boundary conditions, representing slip at upper wall only, uniform slip at both walls, non-uniform slip where slip at upper wall is greater than that of lower wall, non-uniform slip where slip at lower wall is greater than that of upper wall, and slip at lower wall only are considered and thoroughly investigated. Validation is performed by solving the equation numerically using fourth order explicit Runge Kutta method (ERK4). Both analytical and numerical results show good agreement. Lastly, the effects of various fluid parameters on the velocity profile are investigated for each case graphically. Analysis of these plots show that the positive and negative squeeze numbers have opposite effect on the velocity profile throughout all the cases. It is also observed that various fluid parameters like Casson, MHD, and Permeability have similar effects on the velocity profile in the cases when slip is occurring at the upper wall only, and non-uniform slip at both the boundaries with slip at lower wall is greater than upper wall. Furthermore, similar effects have been observed when slip is uniform at both the boundaries, and in case of non-uniform slip with slip at lower wall is less than the upper wall.

17. Computational modelling and analysis of heat and mass transfer in MHD flow past the upper part of a paraboloid of revolution

Gnaneswara Reddy, M.; Sandeep, N.

2017-05-01

The flow and heat transfer nature of MHD dissipative flow past the upper part of a non-melting paraboloid of revolution with non-uniform heat source/sink, thermophoresis and Brownian moment effects are investigated numerically. The buoyancy induced on the flow is considered in such way that the surface is neither vertical/horizontal nor wedge/cone. The equations governing the flow are solved numerically by employing the RKF integration scheme after suitable transformations. Graphical results are obtained to discuss the behaviour of flow, temperature and concentration fields at various parameters of interest. The reduced wall friction, local Nusselt and Sherwood numbers are computed. It is found that the non-uniform heat source/sink parameters regulate the thermal boundary layer. Thermophoresis and Brownian moment parameters act as controlling parameters of heat and mass transfer rate.

18. The analysis of MHD blood flows through porous arteries using a locally modified homogenous nanofluids model.

PubMed

2016-05-12

In this paper, magneto-hydrodynamic blood flows through porous arteries are numerically simulated using a locally modified homogenous nanofluids model. Blood is taken into account as the third-grade non-Newtonian fluid containing nanoparticles. In the modified nanofluids model, the viscosity, density, and thermal conductivity of the solid-liquid mixture (nanofluids) which are commonly utilized as an effective value, are locally combined with the prevalent single-phase model. The modified governing equations are solved numerically using Newton's method and a block tridiagonal matrix solver. The results are compared to the prevalent nanofluids single-phase model. In addition, the efficacies of important physical parameters such as pressure gradient, Brownian motion parameter, thermophoresis parameter, magnetic-field parameter, porosity parameter, and etc. on temperature, velocity and nanoparticles concentration profiles are examined.

19. Effects of Porosity and Mixed Convection on MHD Two Phase Fluid Flow in an Inclined Channel

PubMed Central

Hasnain, Jafar; Abbas, Zaheer; Sajid, Muhammad

2015-01-01

The present study deals with the flow and heat transfer analysis of two immiscible fluids in an inclined channel embedded in a porous medium. The channel is divided in two phases such that a third grade fluid occupies the phase I and a viscous fluid occupies the phase II. Both viscous and third grade fluids are electrically conducting. A constant magnetic field is imposed perpendicular to the channel walls. The mathematical model is developed by using Darcy's and modified Darcy's laws for viscous and third grade fluids respectively. The transformed ordinary differential equations are solved numerically using a shooting method. The obtained results are presented graphically and influence of emerging parameters is discussed in detail. PMID:25803360

20. Effects of prescribed heat flux and transpiration on MHD axisymmetric flow impinging on stretching cylinder

Mabood, Fazle; Lorenzini, Giulio; Pochai, Nopparat; Ibrahim, Sheikh Muhammad

2016-11-01

A numerical treatment for axisymmetric flow and heat transfer due to a stretching cylinder under the influence of a uniform magnetic field and prescribed surface heat flux is presented. Numerical results are obtained for dimensionless velocity, temperature, skin friction coefficient and Nusselt number for several values of the suction/injection, magnetic and curvature parameters as well as the Prandtl number. The present study reveals that the controlling parameters have strong effects on the physical quantities of interest. It is seen that the magnetic field enhances the dimensionless temperature inside the thermal boundary layer, whereas it reduces the dimensionless velocity inside the hydrodynamic boundary layer. Heat transfer rate reduces, while the skin friction coefficient increases with magnetic field.

1. Effects of porosity and mixed convection on MHD two phase fluid flow in an inclined channel.

PubMed

Hasnain, Jafar; Abbas, Zaheer; Sajid, Muhammad

2015-01-01

The present study deals with the flow and heat transfer analysis of two immiscible fluids in an inclined channel embedded in a porous medium. The channel is divided in two phases such that a third grade fluid occupies the phase I and a viscous fluid occupies the phase II. Both viscous and third grade fluids are electrically conducting. A constant magnetic field is imposed perpendicular to the channel walls. The mathematical model is developed by using Darcy's and modified Darcy's laws for viscous and third grade fluids respectively. The transformed ordinary differential equations are solved numerically using a shooting method. The obtained results are presented graphically and influence of emerging parameters is discussed in detail.

2. Radiation effects on the MHD flow near the stagnation point of a stretching sheet: revisited

Pop, Ioan; Ishak, Anuar; Aman, Fazlina

2011-10-01

This paper considers the effects of radiation on the flow near the two-dimensional stagnation point of a stretching sheet immersed in a viscous and incompressible electrically conducting fluid in the presence of an applied constant magnetic field. The external velocity and the stretching velocity of the sheet are assumed to vary linearly with the distance from the stagnation point. The governing partial differential equations are transformed into a system of ordinary differential equations using a similarity transformation, before being solved numerically by the Keller-box method. The features of the heat transfer characteristics for different values of the governing parameters are analyzed and discussed. The results indicate that the heat transfer rate at the surface decreases in the presence of radiation.

3. MHD Energy Bypass Scramjet Engine

NASA Technical Reports Server (NTRS)

Mehta, Unmeel B.; Bogdanoff, David W.; Park, Chul; Arnold, Jim (Technical Monitor)

2001-01-01

Revolutionary rather than evolutionary changes in propulsion systems are most likely to decrease cost of space transportation and to provide a global range capability. Hypersonic air-breathing propulsion is a revolutionary propulsion system. The performance of scramjet engines can be improved by the AJAX energy management concept. A magneto-hydro-dynamics (MHD) generator controls the flow and extracts flow energy in the engine inlet and a MHD accelerator downstream of the combustor accelerates the nozzle flow. A progress report toward developing the MHD technology is presented herein. Recent theoretical efforts are reviewed and ongoing experimental efforts are discussed. The latter efforts also include an ongoing collaboration between NASA, the US Air Force Research Laboratory, US industry, and Russian scientific organizations. Two of the critical technologies, the ionization of the air and the MHD accelerator, are briefly discussed. Examples of limiting the combustor entrance Mach number to a low supersonic value with a MHD energy bypass scheme are presented, demonstrating an improvement in scramjet performance. The results for a simplified design of an aerospace plane show that the specific impulse of the MHD-bypass system is better than the non-MHD system and typical rocket over a narrow region of flight speeds and design parameters. Equilibrium ionization and non-equilibrium ionization are discussed. The thermodynamic condition of air at the entrance of the engine inlet determines the method of ionization. The required external power for non-equilibrium ionization is computed. There have been many experiments in which electrical power generation has successfully been achieved by magneto-hydrodynamic (MHD) means. However, relatively few experiments have been made to date for the reverse case of achieving gas acceleration by the MHD means. An experiment in a shock tunnel is described in which MHD acceleration is investigated experimentally. MHD has several

4. Non-Ideal Compressible-Fluid Dynamics of Fast-Response Pressure Probes for Unsteady Flow Measurements in Turbomachinery

Gori, G.; Molesini, P.; Persico, G.; Guardone, A.

2017-03-01

The dynamic response of pressure probes for unsteady flow measurements in turbomachinery is investigated numerically for fluids operating in non-ideal thermodynamic conditions, which are relevant for e.g. Organic Rankine Cycles (ORC) and super-critical CO2 applications. The step response of a fast-response pressure probe is investigated numerically in order to assess the expected time response when operating in the non-ideal fluid regime. Numerical simulations are carried out exploiting the Non-Ideal Compressible Fluid-Dynamics (NICFD) solver embedded in the open-source fluid dynamics code SU2. The computational framework is assessed against available experimental data for air in dilute conditions. Then, polytropic ideal gas (PIG), i.e. constant specific heats, and Peng-Robinson Stryjek-Vera (PRSV) models are applied to simulate the flow field within the probe operating with siloxane fluid octamethyltrisiloxane (MDM). The step responses are found to depend mainly on the speed of sound of the working fluid, indicating that molecular complexity plays a major role in determining the promptness of the measurement devices. According to the PRSV model, non-ideal effects can increase the step response time with respect to the acoustic theory predictions. The fundamental derivative of gas-dynamic is confirmed to be the driving parameter for evaluating non-ideal thermodynamic effects related to the dynamic calibration of fast-response aerodynamic pressure probes.

5. Numerical solutions of ideal quantum gas dynamical flows governed by semiclassical ellipsoidal-statistical distribution

PubMed Central

Yang, Jaw-Yen; Yan, Chih-Yuan; Diaz, Manuel; Huang, Juan-Chen; Li, Zhihui; Zhang, Hanxin

2014-01-01

The ideal quantum gas dynamics as manifested by the semiclassical ellipsoidal-statistical (ES) equilibrium distribution derived in Wu et al. (Wu et al. 2012 Proc. R. Soc. A 468, 1799–1823 (doi:10.1098/rspa.2011.0673)) is numerically studied for particles of three statistics. This anisotropic ES equilibrium distribution was derived using the maximum entropy principle and conserves the mass, momentum and energy, but differs from the standard Fermi–Dirac or Bose–Einstein distribution. The present numerical method combines the discrete velocity (or momentum) ordinate method in momentum space and the high-resolution shock-capturing method in physical space. A decoding procedure to obtain the necessary parameters for determining the ES distribution is also devised. Computations of two-dimensional Riemann problems are presented, and various contours of the quantities unique to this ES model are illustrated. The main flow features, such as shock waves, expansion waves and slip lines and their complex nonlinear interactions, are depicted and found to be consistent with existing calculations for a classical gas. PMID:24399919

6. Numerical solutions of ideal quantum gas dynamical flows governed by semiclassical ellipsoidal-statistical distribution.

PubMed

Yang, Jaw-Yen; Yan, Chih-Yuan; Diaz, Manuel; Huang, Juan-Chen; Li, Zhihui; Zhang, Hanxin

2014-01-08

The ideal quantum gas dynamics as manifested by the semiclassical ellipsoidal-statistical (ES) equilibrium distribution derived in Wu et al. (Wu et al. 2012 Proc. R. Soc. A468, 1799-1823 (doi:10.1098/rspa.2011.0673)) is numerically studied for particles of three statistics. This anisotropic ES equilibrium distribution was derived using the maximum entropy principle and conserves the mass, momentum and energy, but differs from the standard Fermi-Dirac or Bose-Einstein distribution. The present numerical method combines the discrete velocity (or momentum) ordinate method in momentum space and the high-resolution shock-capturing method in physical space. A decoding procedure to obtain the necessary parameters for determining the ES distribution is also devised. Computations of two-dimensional Riemann problems are presented, and various contours of the quantities unique to this ES model are illustrated. The main flow features, such as shock waves, expansion waves and slip lines and their complex nonlinear interactions, are depicted and found to be consistent with existing calculations for a classical gas.

7. Reactive flow modeling of small scale detonation failure experiments for a baseline non-ideal explosive

Kittell, David E.; Cummock, Nick R.; Son, Steven F.

2016-08-01

Small scale characterization experiments using only 1-5 g of a baseline ammonium nitrate plus fuel oil (ANFO) explosive are discussed and simulated using an ignition and growth reactive flow model. There exists a strong need for the small scale characterization of non-ideal explosives in order to adequately survey the wide parameter space in sample composition, density, and microstructure of these materials. However, it is largely unknown in the scientific community whether any useful or meaningful result may be obtained from detonation failure, and whether a minimum sample size or level of confinement exists for the experiments. In this work, it is shown that the parameters of an ignition and growth rate law may be calibrated using the small scale data, which is obtained from a 35 GHz microwave interferometer. Calibration is feasible when the samples are heavily confined and overdriven; this conclusion is supported with detailed simulation output, including pressure and reaction contours inside the ANFO samples. The resulting shock wave velocity is most likely a combined chemical-mechanical response, and simulations of these experiments require an accurate unreacted equation of state (EOS) in addition to the calibrated reaction rate. Other experiments are proposed to gain further insight into the detonation failure data, as well as to help discriminate between the role of the EOS and reaction rate in predicting the measured outcome.

8. Reactive flow modeling of small scale detonation failure experiments for a baseline non-ideal explosive

SciTech Connect

Kittell, David E.; Cummock, Nick R.; Son, Steven F.

2016-08-14

Small scale characterization experiments using only 1–5 g of a baseline ammonium nitrate plus fuel oil (ANFO) explosive are discussed and simulated using an ignition and growth reactive flow model. There exists a strong need for the small scale characterization of non-ideal explosives in order to adequately survey the wide parameter space in sample composition, density, and microstructure of these materials. However, it is largely unknown in the scientific community whether any useful or meaningful result may be obtained from detonation failure, and whether a minimum sample size or level of confinement exists for the experiments. In this work, it is shown that the parameters of an ignition and growth rate law may be calibrated using the small scale data, which is obtained from a 35 GHz microwave interferometer. Calibration is feasible when the samples are heavily confined and overdriven; this conclusion is supported with detailed simulation output, including pressure and reaction contours inside the ANFO samples. The resulting shock wave velocity is most likely a combined chemical-mechanical response, and simulations of these experiments require an accurate unreacted equation of state (EOS) in addition to the calibrated reaction rate. Other experiments are proposed to gain further insight into the detonation failure data, as well as to help discriminate between the role of the EOS and reaction rate in predicting the measured outcome.

9. The Effects of Thermal Radiation on an Unsteady MHD Axisymmetric Stagnation-Point Flow over a Shrinking Sheet in Presence of Temperature Dependent Thermal Conductivity with Navier Slip

PubMed Central

Mondal, Sabyasachi; Haroun, Nageeb A. H.; Sibanda, Precious

2015-01-01

In this paper, the magnetohydrodynamic (MHD) axisymmetric stagnation-point flow of an unsteady and electrically conducting incompressible viscous fluid in with temperature dependent thermal conductivity, thermal radiation and Navier slip is investigated. The flow is due to a shrinking surface that is shrunk axisymmetrically in its own plane with a linear velocity. The magnetic field is imposed normally to the sheet. The model equations that describe this fluid flow are solved by using the spectral relaxation method. Here, heat transfer processes are discussed for two different types of wall heating; (a) a prescribed surface temperature and (b) a prescribed surface heat flux. We discuss and evaluate how the various parameters affect the fluid flow, heat transfer and the temperature field with the aid of different graphical presentations and tabulated results. PMID:26414006

10. The Effects of Thermal Radiation on an Unsteady MHD Axisymmetric Stagnation-Point Flow over a Shrinking Sheet in Presence of Temperature Dependent Thermal Conductivity with Navier Slip.

PubMed

Mondal, Sabyasachi; Haroun, Nageeb A H; Sibanda, Precious

2015-01-01

In this paper, the magnetohydrodynamic (MHD) axisymmetric stagnation-point flow of an unsteady and electrically conducting incompressible viscous fluid in with temperature dependent thermal conductivity, thermal radiation and Navier slip is investigated. The flow is due to a shrinking surface that is shrunk axisymmetrically in its own plane with a linear velocity. The magnetic field is imposed normally to the sheet. The model equations that describe this fluid flow are solved by using the spectral relaxation method. Here, heat transfer processes are discussed for two different types of wall heating; (a) a prescribed surface temperature and (b) a prescribed surface heat flux. We discuss and evaluate how the various parameters affect the fluid flow, heat transfer and the temperature field with the aid of different graphical presentations and tabulated results.

11. Multi-region relaxed Hall magnetohydrodynamics with flow

SciTech Connect

Lingam, Manasvi; Abdelhamid, Hamdi M.; Hudson, Stuart R.

2016-08-15

The recent formulations of multi-region relaxed magnetohydrodynamics (MRxMHD) have generalized the famous Woltjer-Taylor states by incorporating a collection of “ideal barriers” that prevent global relaxation and flow. In this paper, we generalize MRxMHD with flow to include Hall effects, and thereby obtain the partially relaxed counterparts of the famous double Beltrami states as a special subset. The physical and mathematical consequences arising from the introduction of the Hall term are also presented. We demonstrate that our results (in the ideal MHD limit) constitute an important subset of ideal MHD equilibria, and we compare our approach against other variational principles proposed for deriving the partially relaxed states.

12. Effects of thermophoresis and heat generation/absorption on MHD flow due to an oscillatory stretching sheet with chemically reactive species

Sheikh, Mariam; Abbas, Zaheer

2015-12-01

The effects of chemical reaction and heat generation/absorption on MHD flow over an oscillatory stretching surface in a viscous fluid have been studied in the presence of thermophoresis. The porous plate is oscillated back and forth in its own plane and suction/injection is also taking into account. The similarity solution of the developed non-linear governing partial differential equations is constructed in the form of series using homotopy analysis method. The convergence of the obtained series solutions is discussed in the whole domain (0 ≤ η ≤ ∞) . A parametric study of the all governing parameters is accomplished and the physical results are shown graphically.

13. Mathematical modelling of unsteady MHD natural convection flow past a vertical plate with variable surface temperature and mass flux in the presence of radiation and chemical reaction

Raju, S. Suresh Kumar; Narahari, Marneni; Pendyala, Rajashekhar

2016-11-01

In the present study, a numerical analysis is made for unsteady magnetohydrodynamic (MHD) natural convective boundary-layer flow past an impulsively started semi-infinite vertical plate with variable surface temperature and mass flux in the presence of thermal radiation and chemical reaction. The Crank-Nicolson implicit finite difference technique is implemented to solve the system of governing equations. Numerical results are obtained for different values of system parameters and analyzed through graphs. The velocity profiles of the present study have been compared with the available results for the limiting case and a good agreement is found between the results.

14. Exact analysis of MHD flow of a Walters'-B fluid over an isothermal oscillating plate embedded in a porous medium

2017-02-01

This paper carries out an exact analysis of the MHD free convection flow of a Walters'-B fluid over an oscillating isothermal vertical plate embedded in a porous medium. Exact solutions are produced for velocity, temperature and concentration with the aid of the Laplace transform technique. Similarly, at the wall, the corresponding shear stress is also calculated from the velocity expression. The obtained results confirm an excellent agreement with previously published work. The influence of various pertinent parameters is plotted and illustrated graphically. Finally, the numerical results for the skin friction are exhibited in tabular form.

15. Non-linear heat and mass transfer in a MHD Homann nanofluid flow through a porous medium with chemical reaction, heat generation and uniform inflow

EL-Dabe, N. T.; Attia, H. A.; Essawy, M. A. I.; Ramadan, A. A.; Abdel-Hamid, A. H.

2016-11-01

The steady MHD axisymmetric flow of an incompressible viscous electrically conducting nanofluid impinging on a permeable plate is investigated with heat and mass transfer. An external uniform magnetic field as well as a uniform inflow, in the presence of either suction or injection, are applied normal to the plate. The effects of heat (generation/absorption) and chemical reaction have been accentuated. This study indicates the incorporated influence of both the thermophoresis phenomenon and the Brownian behavior. Numerical solutions for the governing non-linear momentum, energy and nanoparticle equations have been obtained. The rates of heat and mass transfer are presented and discussed.

16. Effects of ion-slip current on MHD free convection flow in a temperature stratified porous medium in a rotating system

Hossain, Delowar; Samad, Abdus; Alam, Mahmud

2017-06-01

The ion-slip effects on unsteady MHD free convection flow past an infinite vertical porous plate with the effect of temperature stratified porous medium in a rotating system with viscous dissipation and Joule heating has been studied numerically. Introducing a time dependent suction to the plate, a similarity procedure has been adopted by taking a time dependent similarity parameter. The governing differential equations are transformed by introducing usual similarity variables. The resultant equations are solved numerically using Runge-Kutta method along with shooting technique. Resulting non-dimensional velocity and temperature profiles are then presented graphically for different values of the parameters entering into the problem.

17. MHD boundary layer flow and heat transfer due to an exponentially shrinking sheet in a nanofluid with thermal radiation and chemical reaction

Hamid, Rohana Abdul; Nazar, Roslinda

2017-08-01

In this paper, the problem of magnetohydrodynamic (MHD) boundary layer flow and heat transfer of a nanofluid with the influences of the chemical reaction and thermal radiation over an exponentially shrinking sheet is studied numerically. The model used for the nanofluid is called the Buongiorno model which incorporates the effects of the Brownian motion and thermophoresis. The governing dimensionless ordinary differential equations are solved using the bvp4c method. The effects of the magnetic field parameter, thermal radiation parameter and chemical reaction parameter on the velocity, temperature and concentration profiles of the nanofluid over an exponentially permeable shrinking sheet are discussed and presented through graphs and tables.

18. High-magnetic-field MHD-generator program

Kruger, C. H.; Eustis, R. H.; Mitchner, M.; Self, S. A.; Koester, J. K.; Nakamura, T.

1981-04-01

Channel phenomena which are important at high magnetic fields are investigated. Nonuniformity effects, boundary layers, hall field breakdown, the effects of electrode configuration and current concentrations, and studies of steady state combustion disk and linear channels in a 6 Tesla magnet of small dimensions were studied. A multi-channel fiber optics diagnostic system is described. A one dimensional model to describe the performance of a non-ideal MHD generator was developed. A two dimensional MHD computer code was developed which predicts the dependence on electrode and insulator dimensions of the onset of interelectrode Hall field breakdown. Calculations of the effects of nonuniformities on the flow and electrical behavior of baseload-sized disk generators were performed.

19. Real-gas effects 1: Simulation of ideal gas flow by cryogenic nitrogen and other selected gases

NASA Technical Reports Server (NTRS)

Hall, R. M.

1980-01-01

The thermodynamic properties of nitrogen gas do not thermodynamically approximate an ideal, diatomic gas at cryogenic temperatures. Choice of a suitable equation of state to model its behavior is discussed and the equation of Beattie and Bridgeman is selected as best meeting the needs for cryogenic wind tunnel use. The real gas behavior of nitrogen gas is compared to an ideal, diatomic gas for the following flow processes: isentropic expansion; normal shocks; boundary layers; and shock wave boundary layer interactions. The only differences in predicted pressure ratio between nitrogen and an ideal gas that may limit the minimum operating temperatures of transonic cryogenic wind tunnels seem to occur at total pressures approaching 9atmospheres and total temperatures 10 K below the corresponding saturation temperature, where the differences approach 1 percent for both isentropic expansions and normal shocks. Several alternative cryogenic test gases - air, helium, and hydrogen - are also analyzed. Differences in air from an ideal, diatomic gas are similar in magnitude to those of nitrogen. Differences for helium and hydrogen are over an order of magnitude greater than those for nitrogen or air. Helium and hydrogen do not approximate the compressible flow of an ideal, diatomic gas.

20. Real-gas effects 1: Simulation of ideal gas flow by cryogenic nitrogen and other selected gases

NASA Technical Reports Server (NTRS)

Hall, R. M.

1980-01-01

The thermodynamic properties of nitrogen gas do not thermodynamically approximate an ideal, diatomic gas at cryogenic temperatures. Choice of a suitable equation of state to model its behavior is discussed and the equation of Beattie and Bridgeman is selected as best meeting the needs for cryogenic wind tunnel use. The real gas behavior of nitrogen gas is compared to an ideal, diatomic gas for the following flow processes: isentropic expansion; normal shocks; boundary layers; and shock wave boundary layer interactions. The only differences in predicted pressure ratio between nitrogen and an ideal gas that may limit the minimum operating temperatures of transonic cryogenic wind tunnels seem to occur at total pressures approaching 9atmospheres and total temperatures 10 K below the corresponding saturation temperature, where the differences approach 1 percent for both isentropic expansions and normal shocks. Several alternative cryogenic test gases - air, helium, and hydrogen - are also analyzed. Differences in air from an ideal, diatomic gas are similar in magnitude to those of nitrogen. Differences for helium and hydrogen are over an order of magnitude greater than those for nitrogen or air. Helium and hydrogen do not approximate the compressible flow of an ideal, diatomic gas.

1. MHD Turbulence and Magnetic Dynamos

NASA Technical Reports Server (NTRS)

Shebalin, John V

2014-01-01

Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much

2. A comparative CFD study on the hemodynamics of flow through an idealized symmetric and asymmetric stenosed arteries

Prashantha, B.; Anish, S.

2017-04-01

The aim of the present study is to numerically evaluate the hemodynamic factors which affect the formation of atherosclerosis and plaque rupture in the human artery. An increase of atherosclerosis in the artery causes geometry changes, which results in hemodynamic changes such as flow separation, reattachment and adhesion of new cells (chemotactic) in the artery. Hence, geometry plays an important role in the determining the nature of hemodynamic patterns. Influence of stenosis in the non-bifurcating artery, under pulsatile flow condition has been studied on an idealized geometry. Analysis of flow through symmetric and asymmetric stenosis in the artery revealed the significance of oscillating shear index (OSI), flow separation, low wall shear stress (WSS) zones and secondary flow patterns on plaque formation. The observed characteristic of flow in the post-stenotic region highlight the importance of plaque eccentricity on the formation of secondary stenosis on the arterial wall.

3. Analysis of the Magneto-Hydrodynamic (MHD) Energy Bypass Engine for High-Speed Air-Breathing Propulsion

NASA Technical Reports Server (NTRS)

Riggins, David W.

2002-01-01

The performance of the MHD energy bypass air-breathing engine for high-speed propulsion is analyzed in this investigation. This engine is a specific type of the general class of inverse cycle engines. In this paper, the general relationship between engine performance (specific impulse and specific thrust) and the overall total pressure ratio through an engine (from inlet plane to exit plane) is first developed and illustrated. Engines with large total pressure decreases, regardless of cause or source, are seen to have exponentially decreasing performance. The ideal inverse cycle engine (of which the MHD engine is a sub-set) is then demonstrated to have a significant total pressure decrease across the engine; this total pressure decrease is cycle-driven, degrades rapidly with energy bypass ratio, and is independent of any irreversibility. The ideal MHD engine (inverse cycle engine with no irreversibility other than that inherent in the MHD work interaction processes) is next examined and is seen to have an additional large total pressure decrease due to MHD-generated irreversibility in the decelerator and the accelerator. This irreversibility mainly occurs in the deceleration process. Both inherent total pressure losses (inverse cycle and MHD irreversibility) result in a significant narrowing of the performance capability of the MHD bypass engine. The fundamental characteristics of MHD flow acceleration and flow deceleration from the standpoint of irreversibility and second-law constraints are next examined in order to clarify issues regarding flow losses and parameter selection in the MM modules. Severe constraints are seen to exist in the decelerator in terms of allowable deceleration Mach numbers and volumetric (length) required for meaningful energy bypass (work interaction). Considerable difficulties are also encountered and discussed due to thermal/work choking phenomena associated with the deceleration process. Lastly, full engine simulations utilizing inlet

4. An MHD model of the earth's magnetosphere

NASA Technical Reports Server (NTRS)

Wu, C. C.

1985-01-01

It is pointed out that the earth's magnetosphere arises from the interaction of the solar wind with the earth's geomagnetic field. A global magnetohydrodynamics (MHD) model of the earth's magnetosphere has drawn much attention in recent years. In this model, MHD equations are used to describe the solar wind interaction with the magnetosphere. In the present paper, some numerical aspects of the model are considered. Attention is given to the ideal MHD equations, an equation of state for the plasma, the model as an initial- and boundary-value problem, the shock capturing technique, computational requirements and techniques for global MHD modeling, a three-dimensional mesh system employed in the global MHD model, and some computational results.

5. Global MHD model of the earth's magnetosphere

NASA Technical Reports Server (NTRS)

Wu, C. C.

1983-01-01

A global MHD model of the earth's magnetosphere is defined. An introduction to numerical methods for solving the MHD equations is given with emphasis on the shock-capturing technique. Finally, results concerning the shape of the magnetosphere and the plasma flows inside the magnetosphere are presented.

6. Simulation of ideal-gas flow by nitrogen and other selected gases at cryogenic temperatures. [transonic flow in cryogenic wind tunnels

NASA Technical Reports Server (NTRS)

Hall, R. M.; Adcock, J. B.

1981-01-01

The real gas behavior of nitrogen, the gas normally used in transonic cryogenic tunnels, is reported for the following flow processes: isentropic expansion, normal shocks, boundary layers, and interactions between shock waves and boundary layers. The only difference in predicted pressure ratio between nitrogen and an ideal gas which may limit the minimum operating temperature of transonic cryogenic wind tunnels occur at total pressures approaching 9 atm and total temperatures 10 K below the corresponding saturation temperature. These pressure differences approach 1 percent for both isentropic expansions and normal shocks. Alternative cryogenic test gases were also analyzed. Differences between air and an ideal diatomic gas are similar in magnitude to those for nitrogen and should present no difficulty. However, differences for helium and hydrogen are over an order of magnitude greater than those for nitrogen or air. It is concluded that helium and cryogenic hydrogen would not approximate the compressible flow of an ideal diatomic gas.

7. Energy Transfer in Mixed Convection MHD Flow of Nanofluid Containing Different Shapes of Nanoparticles in a Channel Filled with Saturated Porous Medium.

PubMed

Aaiza, Gul; Khan, Ilyas; Shafie, Sharidan

2015-12-01

Energy transfer in mixed convection unsteady magnetohydrodynamic (MHD) flow of an incompressible nanofluid inside a channel filled with saturated porous medium is investigated. The channel with non-uniform walls temperature is taken in a vertical direction under the influence of a transverse magnetic field. Based on the physical boundary conditions, three different flow situations are discussed. The problem is modelled in terms of partial differential equations with physical boundary conditions. Four different shapes of nanoparticles of equal volume fraction are used in conventional base fluids, ethylene glycol (EG) (C 2 H 6 O 2 ) and water (H 2 O). Solutions for velocity and temperature are obtained discussed graphically in various plots. It is found that viscosity and thermal conductivity are the most prominent parameters responsible for different results of velocity and temperature. Due to higher viscosity and thermal conductivity, C 2 H 6 O 2 is regarded as better convectional base fluid compared to H 2 O.

8. Homotopy analysis method for chemical reaction and thermophoresis effects on heat and mass transfer for mhd hiemenz flow over a porous wedge in the presence of heat radiation

Kandasamy, R.; Muhaimin, I.; Puvi Arasu, P.; Loganathan, P.

2011-05-01

An analytical technique, namely, the homotopy analysis method, is applied to analyze the effect of chemical reaction and thermophoresis particle deposition on the MHD mixed convective heat and mass transfer for a Hiemenz flow over a porous wedge in the presence of heat radiation. The fluid is assumed to be viscous and incompressible. Analytical and numerical calculations are carried out for different values of dimensionless parameters, and an analysis of the results obtained shows that the flow field is influenced appreciably by the buoyancy ratio as well as by the thermal diffusion and suction/injection parameters. The effects of these parameters on the process characteristics are investigated methodically, and typical results are illustrated. An explicit, totally analytical, and uniformly valid solution is derived which agrees well with numerical results.

9. On ideals and idealization.

PubMed

Morrison, Andrew P

2009-04-01

This chapter repositions ideals away from their role as defensive structures restraining aggressive and lustful drives (as traditionally viewed) toward their place in shaping creativity and love. We select and mold our particular ideals in providing meaning and in this manner help to create those selfobjects needed to resolve or soothe our needs. This creative process may include "reshaping" of the available object to represent the "idealized other." From this perspective, Kohut's view of idealization and the idealized parental imago will be considered, including my own notion of a one-and-a-half person psychology. Our ideals inevitably conflict and clash, leading to internal self-conflicts that generate what I call the dialectic of narcissism. Narcissism is here considered broadly, reflecting all attributes of self-experience. Shame plays an important role in this dialectic, relating to failure with regard to ideals and to falling short of cherished goals. Ultimately, it is the shaping of, and approximation to, flexible and meaningful ideals that comprise that lofty, ineffable, human ideal--wisdom. Clinical vignettes will be offered to illustrate these themes.

10. MHD turbulent processes

NASA Technical Reports Server (NTRS)

Montgomery, David

1988-01-01

Three areas of study in MHD turbulence are considered. These are the turbulent relaxation of the toroidal Z pinch, density fluctuations in MHD fluids, and MHD cellular automata. A Boolean computer game that updates a cellular representation in parallel and that has macroscopic averages converging to solutions of the two-dimensional MHD equations is discussed.

11. High-order conservative finite difference GLM-MHD schemes for cell-centered MHD

Mignone, Andrea; Tzeferacos, Petros; Bodo, Gianluigi

2010-08-01

We present and compare third- as well as fifth-order accurate finite difference schemes for the numerical solution of the compressible ideal MHD equations in multiple spatial dimensions. The selected methods lean on four different reconstruction techniques based on recently improved versions of the weighted essentially non-oscillatory (WENO) schemes, monotonicity preserving (MP) schemes as well as slope-limited polynomial reconstruction. The proposed numerical methods are highly accurate in smooth regions of the flow, avoid loss of accuracy in proximity of smooth extrema and provide sharp non-oscillatory transitions at discontinuities. We suggest a numerical formulation based on a cell-centered approach where all of the primary flow variables are discretized at the zone center. The divergence-free condition is enforced by augmenting the MHD equations with a generalized Lagrange multiplier yielding a mixed hyperbolic/parabolic correction, as in Dedner et al. [J. Comput. Phys. 175 (2002) 645-673]. The resulting family of schemes is robust, cost-effective and straightforward to implement. Compared to previous existing approaches, it completely avoids the CPU intensive workload associated with an elliptic divergence cleaning step and the additional complexities required by staggered mesh algorithms. Extensive numerical testing demonstrate the robustness and reliability of the proposed framework for computations involving both smooth and discontinuous features.

12. Generalized Hall effect as a modification of ideal magnetohydrodynamics

SciTech Connect

Goodman, M.L.

1986-01-01

The generalized Hall effect (GHE) in the generalized Hall model (GHM) is studied as a correction to ideal magnetohydrodynamics (MHD) in the context of how it affects the linear stability of cylindrically symmetric equilibria and how it changes helically symmetric equilibria. The GHM differs from what is usually called the Hall model by including the electron pressure in the electron-momentum equations. This gives the GHM some aspects of a two-fluid model, whereas the Hall model is a one-fluid model. In both cases of cylindrical and helical symmetry, the presence of the electron pressure gradient as part of the GHE gives rise to an electric field tangent to the boundary of the plasma. This introduces an additional boundary condition in the case of a perfectly conducting plasma boundary. In the case of helical symmetry, the equilibrium equations are a generalization of the Grad-Shafranov equation to equilibria with flow and GHE. In the case of cylindrical symmetry, a class of Alfven-wave solutions that do not exist in ideal MHD is obtained and the accumulation point, with respect to large radial wavenumber, of the slow magnetoacoustic wave is shown to be changed from a finite nonzero value in ideal MHD to infinity by the GHE>

13. Double-layer optical fiber coating analysis in MHD flow of an elastico-viscous fluid using wet-on-wet coating process

Khan, Zeeshan; Islam, Saeed; Shah, Rehan Ali; Khan, Muhammad Altaf; Bonyah, Ebenezer; Jan, Bilal; Khan, Aurangzeb

Modern optical fibers require a double-layer coating on the glass fiber in order to provide protection from signal attenuation and mechanical damage. The most important plastic resins used in wires and optical fibers are plastic polyvinyl chloride (PVC) and low and high density polyethylene (LDPE/HDPE), nylon and Polysulfone. One of the most important things which affect the final product after processing is the design of the coating die. In the present study, double-layer optical fiber coating is performed using melt polymer satisfying Oldroyd 8-constant fluid model in a pressure type die with the effect of magneto-hydrodynamic (MHD). Wet-on-wet coating process is applied for double-layer optical fiber coating. The coating process in the coating die is modeled as a simple two-layer Couette flow of two immiscible fluids in an annulus with an assigned pressure gradient. Based on the assumptions of fully developed laminar and MHD flow, the Oldroyd 8-constant model of non-Newtonian fluid of two immiscible resin layers is modeled. The governing nonlinear equations are solved analytically by the new technique of Optimal Homotopy Asymptotic Method (OHAM). The convergence of the series solution is established. The results are also verified by the Adomian Decomposition Method (ADM). The effect of important parameters such as magnetic parameter Mi , the dilatant constant α , the Pseodoplastic constant β , the radii ratio δ , the pressure gradient Ω , the speed of fiber optics V , and the viscosity ratio κ on the velocity profiles, thickness of coated fiber optics, volume flow rate, and shear stress on the fiber optics are investigated. At the end the result of the present work is also compared with the experimental results already available in the literature by taking non-Newtonian parameters tends to zero.

14. MHD-EMP protection guidelines

Barnes, P. R.; Vance, E. F.

A nuclear detonation at altitudes several hundred kilometers above the earth will severely distort the earth's magnetic field and result in a strong magnetohydrodynamic electromagnetic pulse (MHD-EMP). The geomagnetic disturbance interacts with the soil to induce current and horizontal electric gradients. MHD-EMP, also called E3 since it is the third component of the high-altitude EMP (HEMP), lasts over 100 s after an exoatmospheric burst. MHD-EMP is similar to solar geomagnetic storms in it's global and low frequency (less than 1 Hz) nature except that E3 can be much more intense with a far shorter duration. When the MHD-EMP gradients are integrated over great distances by power lines, communication cables, or other long conductors, the induced voltages are significant. (The horizontal gradients in the soil are too small to induce major responses by local interactions with facilities.) The long pulse waveform for MHD-EMP-induced currents on long lines has a peak current of 200 A and a time-to-half-peak of 100 s. If this current flows through transformer windings, it can saturate the magnetic circuit and cause 60 Hz harmonic production. To mitigate the effects of MHD-EMP on a facility, long conductors must be isolated from the building and the commercial power harmonics and voltage swings must be addressed. The transfer switch would be expected to respond to the voltage fluctuations as long as the harmonics have not interfered with the switch control circuitry. The major sources of MHD-EMP induced currents are the commercial power lines and neutral; neutral current indirect coupling to the facility power or ground system via the metal fence, powered gate, parking lights, etc; metal water pipes; phone lines; and other long conductors that enter or come near the facility. The major source of harmonics is the commercial power system.

15. MHD-EMP protection guidelines

SciTech Connect

Barnes, P.R.; Vance, E.F.

1992-01-01

A nuclear detonation at altitudes several hundred kilometers above the earth will severely distort the earth's magnetic field and result in a strong magnetohyrodynamic electromagnetic pulse (MHD-EMP). The geomagnetic disturbance interacts with the soil to induce current and horizontal electric gradients. The geomagnetic disturbance interacts with the soil to induced current and horizontal electric gradients in the earth. MHD-EMP, also called E3 since it is the third component of the high-altitude EMP (HEMP), lasts over 100 s after the exoatmospheric burst. MHD-EMP is similar to solar geomagnetic storms in it's global and low frequency (less than 1 Hz) nature except that E3 can be much more intense with a far shorter duration. When the MHD-EMP gradients are integrated over great distances by power lines, communication cables, or other long conductors, the induced voltages are significant. (The horizontal gradients in the soil are too small to induce major responses by local interactions with facilities.) The long pulse waveform for MHD-EMP-induced currents on long lines has a peak current of 200 A and a time-to-half-peak of 100 s. If this current flows through transformer windings, it can saturate the magnetic circuit and cause 60 Hz harmonic production. To mitigate the effects of MHD-EMP on a facility, long conductors must be isolated from the building and the commercial power harmonics and voltage swings must be addressed. The transfer switch would be expected to respond to the voltage fluctuations as long as the harmonics have not interfered with the switch control circuitry. The major sources of MHD-EMP induced currents are the commercial power lines and neutral; neutral current indirect coupling to the facility power or ground system via the metal fence, powered gate, parking lights, etc; metal water pipes; phone lines; and other long conductors that enter or come near the facility. The major source of harmonics is the commercial power system.

16. Conjugate effects of heat and mass transfer on MHD free convection flow over an inclined plate embedded in a porous medium.

PubMed

Ali, Farhad; Khan, Ilyas; Samiulhaq; Shafie, Sharidan

2013-01-01

The aim of this study is to present an exact analysis of combined effects of radiation and chemical reaction on the magnetohydrodynamic (MHD) free convection flow of an electrically conducting incompressible viscous fluid over an inclined plate embedded in a porous medium. The impulsively started plate with variable temperature and mass diffusion is considered. The dimensionless momentum equation coupled with the energy and mass diffusion equations are analytically solved using the Laplace transform method. Expressions for velocity, temperature and concentration fields are obtained. They satisfy all imposed initial and boundary conditions and can be reduced, as special cases, to some known solutions from the literature. Expressions for skin friction, Nusselt number and Sherwood number are also obtained. Finally, the effects of pertinent parameters on velocity, temperature and concentration profiles are graphically displayed whereas the variations in skin friction, Nusselt number and Sherwood number are shown through tables.

17. Conjugate Effects of Heat and Mass Transfer on MHD Free Convection Flow over an Inclined Plate Embedded in a Porous Medium

PubMed Central

Ali, Farhad; Khan, Ilyas; Samiulhaq; Shafie, Sharidan

2013-01-01

The aim of this study is to present an exact analysis of combined effects of radiation and chemical reaction on the magnetohydrodynamic (MHD) free convection flow of an electrically conducting incompressible viscous fluid over an inclined plate embedded in a porous medium. The impulsively started plate with variable temperature and mass diffusion is considered. The dimensionless momentum equation coupled with the energy and mass diffusion equations are analytically solved using the Laplace transform method. Expressions for velocity, temperature and concentration fields are obtained. They satisfy all imposed initial and boundary conditions and can be reduced, as special cases, to some known solutions from the literature. Expressions for skin friction, Nusselt number and Sherwood number are also obtained. Finally, the effects of pertinent parameters on velocity, temperature and concentration profiles are graphically displayed whereas the variations in skin friction, Nusselt number and Sherwood number are shown through tables. PMID:23840321

18. Numerical solutions of MHD stagnation-point flow and heat transfer past a stretching/shrinking sheet with chemical reaction and transpiration

Naganthran, Kohilavani; Nazar, Roslinda

2017-08-01

In this study, the influence of the first order chemical reaction towards the magnetohydrodynamics (MHD) stagnation-point boundary layer flow past a permeable stretching/shrinking surface (sheet) is considered numerically. The governing boundary layer equations are transformed into a system of ordinary differential equations from the system of partial differential equations by using a proper similarity transformation so that it can be solved numerically by the "bvp4c" function in Matlab software. The main numerical solutions are presented graphically and discussed in the relevance of the governing parameters. It is found that dual solutions exist when the sheet is stretched and shrunk. Stability analysis is done to determine which solution is stable and valid physically. The results of the stability analysis show that the first solution (upper branch) is physically stable and realizable while the second solution (lower branch) is impracticable.

19. Simultaneous effects of heat generation/absorption and thermal radiation in magnetohydrodynamics (MHD) flow of Maxwell nanofluid towards a stretched surface

Hayat, Tasawar; Qayyum, Sajid; Shehzad, Sabir Ali; Alsaedi, Ahmed

Mathematical analysis of magnetohydrodynamic (MHD) three-dimensional nonlinear convective flow of Maxwell nanofluid towards a stretching surface is made in this article. Characteristics of heat transfer are examined under thermal radiation, heat generation/absorption and prescribed heat flux condition. Nanofluid model includes Brownian motion and thermophoresis. Dimensional nonlinear expressions of momentum, energy and concentration are converted into dimensionless systems by invoking suitable similarity variables. A well-known homotopic technique is implemented for dimensionless expressions. Impact of different quantities on velocities, temperature and concentration are scrutinized graphically and discussed in detail. The expressions of Nusselt and Sherwood numbers are calculated and addressed comprehensively. It is also seen that thermal radiation parameter enhances the temperature field and heat transfer rate.

20. MHD Marangoni boundary layer flow and heat transfer of pseudo-plastic nanofluids over a porous medium with a modified model

Lin, Yanhai; Zheng, Liancun; Zhang, Xinxin

2015-11-01

We present a research for the MHD Marangoni boundary layer flow and heat transfer in pseudo-plastic power law nanofluids over a porous medium driven by temperature gradient. A variable magnetic field is considered. Four different types of nanoparticles, copper, aluminum oxide, copper oxide, and titanium oxide are considered with pseudo-plastic power-law carboxy methyl cellulose (CMC)-water used as base fluids. A generalized Fourier law proposed by Zheng for varying thermal conductivity of nanofluids is taken into account, and the surface tension is assumed a quadratic function of the temperature. The governing partial differential equations (PDEs) are formulated, and similarity solutions are obtained numerically using shooting technique combined with Runge-Kutta iteration program and Newton's scheme. The effects of various physical parameters on horizontal velocity component and temperature curves are discussed and graphically illustrated in details.

1. Effect of hall current on MHD flow of a nanofluid with variable properties due to a rotating disk with viscous dissipation and nonlinear thermal radiation

Abdel-Wahed, Mohamed; Akl, Mohamed

2016-09-01

Analysis of the MHD Nanofluid boundary layer flow over a rotating disk with a constant velocity in the presence of hall current and non-linear thermal radiation has been covered in this work. The variation of viscosity and thermal conductivity of the fluid due to temperature and nanoparticles concentration and size is considered. The problem described by a system of P.D.E that converted to a system of ordinary differential equations by the similarity transformation technique, the obtained system solved analytically using Optimal Homotopy Asymptotic Method (OHAM) with association of mathematica program. The velocity profiles and temperature profiles of the boundary layer over the disk are plotted and investigated in details. Moreover, the surface shear stress, rate of heat transfer explained in details.

2. Forced Reconnection in the Near Magnetotail: Onset and Energy Conversion in PIC and MHD Simulations

NASA Technical Reports Server (NTRS)

Birn, J.; Hesse, Michael

2014-01-01

Using two-dimensional particle-in-cell (PIC) together with magnetohydrodynamic (MHD) Q1 simulations of magnetotail dynamics, we investigate the evolution toward onset of reconnection and the subsequent energy transfer and conversion. In either case, reconnection onset is preceded by a driven phase, during which magnetic flux is added to the tail at the high-latitude boundaries, followed by a relaxation phase, during which the configuration continues to respond to the driving. The boundary deformation leads to the formation of thin embedded current sheets, which are bifurcated in the near tail, converging to a single sheet farther out in the MHD simulations. The thin current sheets in the PIC simulation are carried by electrons and are associated with a strong perpendicular electrostatic field, which may provide a connection to parallel potentials and auroral arcs and an ionospheric signal even prior to the onset of reconnection. The PIC simulation very well satisfies integral entropy conservation (intrinsic to ideal MHD) during this phase, supporting ideal ballooning stability. Eventually, the current intensification leads to the onset of reconnection, the formation and ejection of a plasmoid, and a collapse of the inner tail. The earthward flow shows the characteristics of a dipolarization front: enhancement of Bz, associated with a thin vertical electron current sheet in the PIC simulation. Both MHD and PIC simulations show a dominance of energy conversion from incoming Poynting flux to outgoing enthalpy flux, resulting in heating of the inner tail. Localized Joule dissipation plays only a minor role.

3. Translationally symmetric extended MHD via Hamiltonian reduction: Energy-Casimir equilibria

Kaltsas, D. A.; Throumoulopoulos, G. N.; Morrison, P. J.

2017-09-01

The Hamiltonian structure of ideal translationally symmetric extended MHD (XMHD) is obtained by employing a method of Hamiltonian reduction on the three-dimensional noncanonical Poisson bracket of XMHD. The existence of the continuous spatial translation symmetry allows the introduction of Clebsch-like forms for the magnetic and velocity fields. Upon employing the chain rule for functional derivatives, the 3D Poisson bracket is reduced to its symmetric counterpart. The sets of symmetric Hall, Inertial, and extended MHD Casimir invariants are identified, and used to obtain energy-Casimir variational principles for generalized XMHD equilibrium equations with arbitrary macroscopic flows. The obtained set of generalized equations is cast into Grad-Shafranov-Bernoulli (GSB) type, and special cases are investigated: static plasmas, equilibria with longitudinal flows only, and Hall MHD equilibria, where the electron inertia is neglected. The barotropic Hall MHD equilibrium equations are derived as a limiting case of the XMHD GSB system, and a numerically computed equilibrium configuration is presented that shows the separation of ion-flow from electro-magnetic surfaces.

4. Lie group analysis for MHD boundary layer flow and heat transfer over stretching sheet in presence of viscous dissipation and uniform heat source/sink

Metri, Prashant G.; Guariglia, Emanuel; Silvestrov, Sergei

2017-01-01

An analysis for the MHD boundary layer flow and heat transfer towards stretching sheet is carried out via symmetry analysis. A steady two dimensional flow of an electrically conducting incompressible fluid flow over a stretching sheet. The flow is permeated by a uniform transverse magnetic field. The governing partial differential equations are reduced to a system of ordinary differential equations by the scaling symmetries. The symmetry groups admitted by the corresponding boundary value problem are obtained by using special Lie group transformations. The scaling of group transformations is applied to the governing equations. The system remains invariant due to some relation among the parameters of the transformations. After finding two absolute invariants a third order ordinary differential equation corresponding to momentum equation and second order differential equation corresponding to energy equation are derived. The equations along with boundary conditions solved numerically. Numerical solutions of these equations are obtained by using Runge-Kutta-Fehlberg scheme. Further more attention is paid to the effects of some physical parameters magnetic field (Mn), Prandtl number (Pr), Eckert number (Ec) and uniform heat source/sink, on velocity and thermal boundary layer. The results thus obtained are presented graphically and discussed.

5. Time Dependent MHD Nano-Second Grade Fluid Flow Induced by Permeable Vertical Sheet with Mixed Convection and Thermal Radiation.

PubMed

2015-01-01

The aim of present paper is to study the series solution of time dependent MHD second grade incompressible nanofluid towards a stretching sheet. The effects of mixed convection and thermal radiation are also taken into account. Because of nanofluid model, effects Brownian motion and thermophoresis are encountered. The resulting nonlinear momentum, heat and concentration equations are simplified using appropriate transformations. Series solutions have been obtained for velocity, temperature and nanoparticle fraction profiles using Homotopy Analysis Method (HAM). Convergence of the acquired solution is discussed critically. Behavior of velocity, temperature and concentration profiles on the prominent parameters is depicted and argued graphically. It is observed that temperature and concentration profiles show similar behavior for thermophoresis parameter Νt but opposite tendency is noted in case of Brownian motion parameter Νb. It is further analyzed that suction parameter S and Hartman number Μ depict decreasing behavior on velocity profile.

6. Influence of Newtonian Heating on Three Dimensional MHD Flow of Couple Stress Nanofluid with Viscous Dissipation and Joule Heating

PubMed Central

2015-01-01

The present exploration discusses the influence of Newtonian heating on the magnetohydrodynamic (MHD) three dimensional couple stress nanofluid past a stretching surface. Viscous dissipation and Joule heating effects are also considered. Moreover, the nanofluid model includes the combined effects of thermophoresis and Brownian motion. Using an appropriate transformation, the governing non linear partial differential equations are converted into nonlinear ordinary differential equations. Series solutions using Homotopy Analysis method (HAM) are computed. Plots are presented to portrait the arising parameters in the problem. It is seen that an increase in conjugate heating parameter results in considerable increase in the temperature profile of the stretching wall. Skin friction coefficient, local Nusselt and local Sherwood numbers tabulated and analyzed. Higher values of conjugate parameter, Thermophoresis parameter and Brownian motion parameter result in enhancement of temperature distribution. PMID:25874800

7. Time Dependent MHD Nano-Second Grade Fluid Flow Induced by Permeable Vertical Sheet with Mixed Convection and Thermal Radiation

PubMed Central

2015-01-01

The aim of present paper is to study the series solution of time dependent MHD second grade incompressible nanofluid towards a stretching sheet. The effects of mixed convection and thermal radiation are also taken into account. Because of nanofluid model, effects Brownian motion and thermophoresis are encountered. The resulting nonlinear momentum, heat and concentration equations are simplified using appropriate transformations. Series solutions have been obtained for velocity, temperature and nanoparticle fraction profiles using Homotopy Analysis Method (HAM). Convergence of the acquired solution is discussed critically. Behavior of velocity, temperature and concentration profiles on the prominent parameters is depicted and argued graphically. It is observed that temperature and concentration profiles show similar behavior for thermophoresis parameter Νt but opposite tendency is noted in case of Brownian motion parameter Νb. It is further analyzed that suction parameter S and Hartman number Μ depict decreasing behavior on velocity profile. PMID:25962063

8. Influence of Newtonian heating on three dimensional MHD flow of couple stress nanofluid with viscous dissipation and Joule heating.

PubMed

2015-01-01

The present exploration discusses the influence of Newtonian heating on the magnetohydrodynamic (MHD) three dimensional couple stress nanofluid past a stretching surface. Viscous dissipation and Joule heating effects are also considered. Moreover, the nanofluid model includes the combined effects of thermophoresis and Brownian motion. Using an appropriate transformation, the governing non linear partial differential equations are converted into nonlinear ordinary differential equations. Series solutions using Homotopy Analysis method (HAM) are computed. Plots are presented to portrait the arising parameters in the problem. It is seen that an increase in conjugate heating parameter results in considerable increase in the temperature profile of the stretching wall. Skin friction coefficient, local Nusselt and local Sherwood numbers tabulated and analyzed. Higher values of conjugate parameter, Thermophoresis parameter and Brownian motion parameter result in enhancement of temperature distribution.

9. MHD Spectroscopy

SciTech Connect

Heeter, R F; Fasoli, A; Testa, D; Sharapov, S; Berk, H L; Breizman, B; Gondhalekar, A; Mantsinen, M

2004-03-23

Experiments are conducted on the JET tokamak to assess the diagnostic potential of MHD active and passive spectroscopy, for the plasma bulk and its suprathermal components, using Alfv{acute e}n Eigenmodes (AEs) excited by external antennas and by energetic particles. The measurements of AE frequencies and mode numbers give information on the bulk plasma. Improved equilibrium reconstruction, in particular in terms of radial profiles of density and safety factor, is possible from the comparison between the antenna driven spectrum and that calculated theoretically. Details of the time evolution of the non-monotonic safety factor profile in advanced scenarios can be reconstructed from the frequency of ICRH-driven energetic particle modes. The plasma effective mass can be inferred from the resonant frequency of externally driven AEs in discharges with similar equilibrium profiles. The stability thresholds and the nonlinear development of the instabilities can give clues on energy and spatial distribution of the fast particle population. The presence of unstable AEs provides lower limits in the energy of ICRH generated fast ion tails. Fast ion pressure gradients and their evolution can be inferred from the stability of AEs at different plasma radial positions. Finally, the details of the AE spectrum in the nonlinear stage can be used to obtain information about the fast particle velocity space diffusion.

10. Cometary MHD and chemistry

NASA Technical Reports Server (NTRS)

Wegmann, R.; Schmidt, H. U.; Huebner, W. F.; Boice, D. C.

1987-01-01

An MHD and chemical comet-coma model was developed, applying the computer program of Huebner (1985) for the detailed chemical evolution of a spherically expanding coma and the program of Schmidt and Wegman (1982) and Wegman (1987) for the MHD flow of plasma and magnetic field in a comet to the Giotto-mission data on the ion abundances measured by the HIS ion mass spectrometer. The physics and chemistry of the coma are modeled in great detail, including photoprocesses, gas-phase chemical kinetics, energy balance with a separate electron temperature, multifluid hydrodynamics with a transition to free molecular flow, fast-streaming atomic and molecular hydrogen, counter and cross streaming of the ionized species relative to the neutral species in the coma-solar wind interaction region with momentum exchange by elastic collisions, mass-loading through ion pick-up, and Lorentz forces of the advected magnetic field. The results, both inside and outside of the contact surface, are discussed and compared with the relevant HIS ion mass spectra.

11. Three-dimensional modeling of flow and deformation in idealized mild and moderate arterial vessels.

PubMed

Gu, Xi; Yeoh, Guan Heng; Timchenko, Victoria

2016-10-01

Three-dimensional numerical calculations of mild and moderate stenosed blood vessels have been performed. Large eddy simulation through a dynamic subgrid scale Smagorinsky model is applied to model the transitional and turbulent pulsatile flow. For the compliant stenosed model, fluid-structure interaction is realized through a two-way coupling between the fluid flow and the deforming vessel through the change in the external diameter due to the increment of circumferential pressure via a novel moving boundary approach. Model predictions compare very well against measured and numerical data for the centerline velocities, thickness of the flow separation zones and radial wall displacements.

12. Dipole Alignment in Rotating MHD Turbulence

NASA Technical Reports Server (NTRS)

Shebalin, John V.; Fu, Terry; Morin, Lee

2012-01-01

We present numerical results from long-term CPU and GPU simulations of rotating, homogeneous, magnetohydrodynamic (MHD) turbulence, and discuss their connection to the spherically bounded case. We compare our numerical results with a statistical theory of geodynamo action that has evolved from the absolute equilibrium ensemble theory of ideal MHD turbulence, which is based on the ideal MHD invariants are energy, cross helicity and magnetic helicity. However, for rotating MHD turbulence, the cross helicity is no longer an exact invariant, although rms cross helicity becomes quasistationary during an ideal MHD simulation. This and the anisotropy imposed by rotation suggests an ansatz in which an effective, nonzero value of cross helicity is assigned to axisymmetric modes and zero cross helicity to non-axisymmetric modes. This hybrid statistics predicts a large-scale quasistationary magnetic field due to broken ergodicity , as well as dipole vector alignment with the rotation axis, both of which are observed numerically. We find that only a relatively small value of effective cross helicity leads to the prediction of a dipole moment vector that is closely aligned (less than 10 degrees) with the rotation axis. We also discuss the effect of initial conditions, dissipation and grid size on the numerical simulations and statistical theory.

13. Steady Subsonic Ideal Flows Through an Infinitely Long Nozzle with Large Vorticity

Du, Lili; Xie, Chunjing; Xin, Zhouping

2014-05-01

In this paper, the existence, uniqueness, and far field behavior of a class of subsonic flows with large vorticity for the steady Euler equations in infinitely long nozzles are established. More precisely, for any given convex horizontal velocity of incoming flow in the upstream, there exists a critical value m cr , if the mass flux is larger than m cr , then there exists a unique smooth subsonic Euler flow through the infinitely long nozzle. This well-posedness result is proved by a new observation for the method developed in Xie and Xin (SIAM J Math Anal 42:751-784, 2010) to deal with the Euler system. Furthermore, the optimal convergence rates of the subsonic flows at far fields are obtained via the maximum principle and an elaborate choice of the comparison functions.

14. Choking of ideal-gas flow in convergent nozzles and integral nozzle characteristics

SciTech Connect

Yagudin, S.V.

1995-05-01

The results of a numerical and theoretical investigation of the local and integral characteristics of convergent nozzles are presented. It is shown that self-similar (choked) nozzle flow, when the gas flow rate does not depend on the external pressure, may occur at subcritical values of the pressure ratio {pi}{sub c} this nozzle will have a higher thrust coefficient than the initial conical nozzle.

15. Heat and mass transfer on unsteady MHD free convection rotating flow through a porous medium over an infinite vertical plate with hall effects

Babu, D. Dastagiri; Venkateswarlu, S.; Reddy, E. Keshava

2017-07-01

In this paper, we have considered the unsteady MHD free convection flow of an incompressible electrically conducting fluid through porous medium bounded by an infinite vertical porous surface in the presence of heat source and chemical reaction in a rotating system taking hall current into account. The flow through porous medium is governed by Brinkman's model for the momentum equation. In the undisturbed state, both the plate and fluid in porous medium are in solid body rotation with the same angular velocity about normal to the infinite vertical plane surface. The vertical surface is subjected to the uniform constant suction perpendicular to it and the temperature on the surface varies with time about a non-zero constant mean while the temperature of free stream is taken to be constant. The exact solutions for the velocity, temperature and concentration are obtained making use of perturbation technique. The velocity expression consists steady state and oscillatory state. It reveals that, the steady part of the velocity field has three layer characters while the oscillatory part of the fluid field exhibits a multi-layer character. The influence of various flow parameters on the velocity, temperature and concentration is analysed graphically, and computational results for the skin friction, Nusselt number and Sherwood number are also obtained in the tabular forms.

16. Effects of temperature dependent conductivity and absorptive/generative heat transfer on MHD three dimensional flow of Williamson fluid due to bidirectional non-linear stretching surface

Bilal, S.; Khalil-ur-Rehman; Malik, M. Y.; Hussain, Arif; Khan, Mair

Present work is communicated to identify characteristics of magnetohydrodynamic (MHD) three dimensional boundary layer flow of Williamson fluid confined by a bidirectional stretched surface. Conductivity of working fluid is assumed to be temperature dependent. Generative/absorptive heat transfer is also taken into account. Mathematical model is formulated in the form of partial expressions and then transmuted into ordinary differential equations with the help of newfangled set of similarity transformations. The resulting non-linear differential system of equations is solved numerically with the aid of Runge-Kutta algorithm supported by shooting method. Flow features are exemplified quantitatively through graphs. Scintillating results for friction factor and convective heat transfer are computed and scrutinized tabularly. Furthermore, the accuracy of present results is tested with existing literature and we found an excellent agreement. It is inferred that velocity along x-direction mounts whereas along y-direction depreciates for incrementing values of stretching ratio parameter. Moreover, it is also elucidated that non-linearity index tends to decrement the velocity and thermal distributions of fluid flow.

17. MHD Power Generation

ERIC Educational Resources Information Center

Kantrowitz, Arthur; Rosa, Richard J.

1975-01-01

Explains the operation of the Magnetohydrodynamic (MHD) generator and advantages of the system over coal, oil or nuclear powered generators. Details the development of MHD generators in the United States and Soviet Union. (CP)

18. MHD Power Generation

ERIC Educational Resources Information Center

Kantrowitz, Arthur; Rosa, Richard J.

1975-01-01

Explains the operation of the Magnetohydrodynamic (MHD) generator and advantages of the system over coal, oil or nuclear powered generators. Details the development of MHD generators in the United States and Soviet Union. (CP)

19. Large-eddy simulation of atmospheric boundary layer flow and passive scalar dispersion over idealized urban surfaces

Cheng, Wai Chi; Porté-Agel, Fernando

2015-04-01

Accurate prediction of atmospheric boundary layer (ABL) flow and its interaction with urban surfaces is critical for understanding the transport of momentum and scalars within and above cities. This, in turn, is essential for predicting the local climate and pollutant dispersion patterns in urban areas. Large-eddy simulation (LES) explicitly resolves the large-scale turbulent eddy motions and, therefore, can potentially provide improved understanding and prediction of flows and scalar transport inside and above urban canopies. In this study, LES is used to simulate the dispersion of passive scalar over idealized urban surfaces represented by uniform arrays of cubes. A modulated gradient subgird-scale (SGS) model is used to parametrize the SGS fluxes of momentum and scalar, and an immersed boundary method is used to model the presence of cubes. A similar LES framework for flow was validated in our previous studies in simulations of turbulent boundary-layer flow past a 2D block and a uniform array of cubes. Here, the LES framework is further validated with wind tunnel experimental data of passive scalar dispersion within and above a staggered array of cubes with a localized scalar source at ground level. Good agreement between the simulation results and experimental data are found in the vertical and horizontal profiles of scalar concentration in different streamwise locations. After the validation, the LES framework is used to simulate the scalar transport at rural-to-urban flow transition region and the results obtained are presented.

20. Effects of objectifying gaze on female cognitive performance: The role of flow experience and internalization of beauty ideals.

PubMed

2016-11-01

Although previous research has demonstrated that objectification impairs female cognitive performance, no research to date has investigated the mechanisms underlying such decrement. Therefore, we tested the role of flow experience as one mechanism leading to performance decrement under sexual objectification. Gaze gender was manipulated by having male versus female experimenters take body pictures of female participants (N = 107) who then performed a Sustained Attention to Response Task. As predicted, a moderated mediation model showed that under male versus female gaze, higher internalization of beauty ideals was associated with lower flow, which in turn decreased performance. The implications of these results are discussed in relation to objectification theory and strategies to prevent sexually objectifying experiences.

1. Integral Constraints and MHD Stability

Jensen, T. H.

2003-10-01

Determining stability of a plasma in MHD equilibrium, energetically isolated by a conducting wall, requires an assumption on what governs the dynamics of the plasma. One example is the assumption that the plasma obeys ideal MHD, leading to the well known δ W" criteria [I. Bernstein, et al., Proc. Roy. Soc. London A244, 17 (1958)]. A radically different approach was used by Taylor [J.B. Taylor, Rev. Mod. Phys. 58, 741 (1986)] in assuming that the dynamics of the plasma is restricted only by the requirement that helicity, an integral constant associated with the plasma, is conserved. The relevancy of Taylor's assumption is supported by the agreement between resulting theoretical results and experimental observations. Another integral constraint involves the canonical angular momentum of the plasma particles. One consequence of using this constraint is that tokamak plasmas have no poloidal current in agreement with some current hole tokamak observations [T.H. Jensen, Phys. Lett. A 305, 183 (2002)].

2. Idealized debris flow in flume with bed driven by a conveyor belt

USGS Publications Warehouse

Ling, Chi-Hai; Chen, Cheng-lung

1989-01-01

The generalized viscoplastic fluid (GVF) model is used to derive the theoretical expressions of two-dimensional velocities and surface profile for debris flow established in a flume with bed driven by a conveyor belt. The rheological parameters of the GVF model are evaluated through the comparison of theoretical results with measured data. A slip velocity of the established (steady) nonuniform flow on the moving bed (i.e., the conveyor belt) is observed, and a relation between the slip velocity and the velocity gradient at the bed is derived. Two belts, one rough and the other smooth, were tested. The flow profile in the flume is found to be linear and dependent on the roughness of the belt, but not much on its speed.

3. The ideal oxygen/nitrous oxide fresh gas flow sequence with the Anesthesia Delivery Unit machine.

PubMed

Hendrickx, Jan F A; Cardinael, Sara; Carette, Rik; Lemmens, Hendrikus J M; De Wolf, Andre M

2007-06-01

To determine whether early reduction of oxygen and nitrous oxide fresh gas flow from 6 L/min to 0.7 L/min could be accomplished while maintaining end-expired nitrous oxide concentration > or =50% with an Anesthesia Delivery Unit anesthesia machine. Prospective, randomized clinical study. Large teaching hospital in Belgium. 53 ASA physical status I and II patients requiring general endotracheal anesthesia and controlled mechanical ventilation. Patients were randomly assigned to one of 4 groups depending on the duration of high oxygen/nitrous oxide fresh gas flow (two and 4 L/min, respectively) before lowering total fresh gas flow to 0.7 L/min (0.3 and 0.4 L/min oxygen and nitrous oxide, respectively): one, two, three, or 5 minutes (1-minute group, 2-minute group, 3-minute group, and 5-minute group), with n = 10, 12, 13, and 8, respectively. The course of the end-expired nitrous oxide concentration and bellows volume deficit at end-expiration was compared among the 4 groups during the first 30 minutes. At the end of the high-flow period the end-expired nitrous oxide concentration was 35.6 +/- 6.2%, 48.4 +/- 4.8%, 53.7 +/- 8.7%, and 57.3 +/- 1.6% in the 4 groups, respectively. Thereafter, the end-expired nitrous oxide concentration decreased to a nadir of 36.1 +/- 4.5%, 45.4 +/- 3.8%, 50.9 +/- 6.1%, and 55.4 +/- 2.8% after three, 4, 6, and 8 minutes after flows were lowered in the 1- to 5-minute groups, respectively. A decrease in bellows volume was observed in most patients, but was most pronounced in the 2-minute group. The bellows volume deficit gradually faded within 15 to 20 minutes in all 4 groups. A 3-minute high-flow period (oxygen and nitrous oxide fresh gas flow of 2 and 4 L/min, respectively) suffices to attain and maintain end-expired nitrous oxide concentration > or =50% and ensures an adequate bellows volume during the ensuing low-flow period.

4. Equilibrium operating performance of axial-flow turbojet engines by means of idealized analysis

NASA Technical Reports Server (NTRS)

Sanders, John C; Chapin, Edward C

1950-01-01

A method of predicting equilibrium operating performance of turbojet engines has been developed, with the assumption of simple model processes for the components. Results of the analysis are plotted in terms of dimensionless parameters comprising critical engine dimensions and over-all operating variables. This investigation was made of an engine in which the ratio of axial inlet-air velocity to compressor-tip velocity is constant, which approximates turbojet engines with axial-flow compressors. Experimental correlation of the theory with data from several existing axial-flow-type engines was good and showed close correlation between calculated and measured performance.

5. Stability Results for Idealized Shear Flows on a Rectangular Periodic Domain

Dullin, Holger R.; Worthington, Joachim

2017-06-01

We present a new linearly stable solution of the Euler fluid flow on a torus. On a two-dimensional rectangular periodic domain [0,2π )× [0,2π / κ) for κ \\in R^+ , the Euler equations admit a family of stationary solutions given by the vorticity profiles Ω ^*(x)= Γ cos (p_1x_1+ κ p_2x_2) . We show linear stability for such flows when p_2=0 and κ ≥ |p_1| (equivalently p_1=0 and κ {|p_2|}≤ {1} ). The classical result due to Arnold is that for p_1 = 1, p_2 = 0 and κ ≥ 1 the stationary flow is nonlinearly stable via the energy-Casimir method. We show that for κ ≥ |p_1| ≥ 2, p_2 = 0 the flow is linearly stable, but one cannot expect a similar nonlinear stability result. Finally we prove nonlinear instability for all steady states satisfying p_1^2+κ ^2{p_2^2}>{3(κ ^2+1)}/4(7-4√{3)} . The modification and application of a structure-preserving Hamiltonian truncation is discussed for the anisotropic case κ ≠ 1 . This leads to an explicit Lie-Poisson integrator for the approximate system, which is used to illustrate our analytical results.

6. MHD dissipative flow and heat transfer of Casson fluids due to metachronal wave propulsion of beating cilia with thermal and velocity slip effects under an oblique magnetic field

Akbar, Noreen Sher; Tripathi, D.; Bég, O. Anwar; Khan, Z. H.

2016-11-01

A theoretical investigation of magnetohydrodynamic (MHD) flow and heat transfer of electrically-conducting viscoplastic fluids through a channel is conducted. The robust Casson model is implemented to simulate viscoplastic behavior of fluids. The external magnetic field is oblique to the fluid flow direction. Viscous dissipation effects are included. The flow is controlled by the metachronal wave propagation generated by cilia beating on the inner walls of the channel. The mathematical formulation is based on deformation in longitudinal and transverse velocity components induced by the ciliary beating phenomenon with cilia assumed to follow elliptic trajectories. The model also features velocity and thermal slip boundary conditions. Closed-form solutions to the non-dimensional boundary value problem are obtained under physiological limitations of low Reynolds number and large wavelength. The influence of key hydrodynamic and thermo-physical parameters i.e. Hartmann (magnetic) number, Casson (viscoplastic) fluid parameter, thermal slip parameter and velocity slip parameter on flow characteristics are investigated. A comparative study is also made with Newtonian fluids (corresponding to massive values of plastic viscosity). Stream lines are plotted to visualize trapping phenomenon. The computations reveal that velocity increases with increasing the magnitude of Hartmann number near the channel walls whereas in the core flow region (center of the channel) significant deceleration is observed. Temperature is elevated with greater Casson parameter, Hartmann number, velocity slip, eccentricity parameter, thermal slip and also Brinkmann (dissipation) number. Furthermore greater Casson parameter is found to elevate the quantity and size of the trapped bolus. In the pumping region, the pressure rise is reduced with greater Hartmann number, velocity slip, and wave number whereas it is enhanced with greater cilia length.

7. Broken Symmetry and Coherent Structure in MHD Turbulence

NASA Technical Reports Server (NTRS)

Shebalin, John V.

2007-01-01

Absolute equilibrium ensemble theory for ideal homogeneous magnetohydrodynamic (MHD) turbulence is fairly well developed. Theory and Simulation indicate that ideal MHD turbulence non-ergodic and contains coherent structure. The question of applicability real (i.e., dissipative) MHD turbulence is examined. Results from several very long time numerical simulations on a 64(exp 3) grid are presented. It is seen that coherent structure begins to form before decay dominates over nonlinearity. The connection with inverse spectral cascades and selective decay will also be discussed.

8. Steady Secondary Flows Generated by Periodic Compression and Expansion of an Ideal Gas in a Pulse Tube

NASA Technical Reports Server (NTRS)

Lee, Jeffrey M.

1999-01-01

This study establishes a consistent set of differential equations for use in describing the steady secondary flows generated by periodic compression and expansion of an ideal gas in pulse tubes. Also considered is heat transfer between the gas and the tube wall of finite thickness. A small-amplitude series expansion solution in the inverse Strouhal number is proposed for the two-dimensional axisymmetric mass, momentum and energy equations. The anelastic approach applies when shock and acoustic energies are small compared with the energy needed to compress and expand the gas. An analytic solution to the ordered series is obtained in the strong temperature limit where the zeroth-order temperature is constant. The solution shows steady velocities increase linearly for small Valensi number and can be of order I for large Valensi number. A conversion of steady work flow to heat flow occurs whenever temperature, velocity or phase angle gradients are present. Steady enthalpy flow is reduced by heat transfer and is scaled by the Prandtl times Valensi numbers. Particle velocities from a smoke-wire experiment were compared with predictions for the basic and orifice pulse tube configurations. The theory accurately predicted the observed steady streaming.

9. MHD Flow and Heat Transfer of a Generalized Burgers’ Fluid Due to an Exponential Accelerating Plate with Effects of the Second Order Slip and Viscous Dissipation

Zhang, Yan; Zhao, Hao-Jie; Bai, Yu

2017-06-01

In classical study on generalized viscoelastic fluid, the momentum equation was derived by considering the fractional constitutive model, while the energy equation was ignored its effect. This paper presents an investigation for the magnetohydrodynamic (MHD) flow and heat transfer of an incompressible generalized Burgers’ fluid due to an exponential accelerating plate with the effect of the second order velocity slip. The energy equation and momentum equation are coupled by the fractional Burgers’ fluid constitutive model. Numerical solutions for velocity, temperature and shear stress are obtained using the modified implicit finite difference method combined with the G1-algorithm, whose validity is confirmed by the comparison with the analytical solution. Our results show that the influences of the fractional parameters α and β on the flow are opposite each other, which is just like the effects of the two parameters on the temperature. Moreover, the impact trends of the relaxation time λ 1 and retardation time λ 3 on the velocity are opposite each other. Increasing the boundary parameter will promote the temperature, but has little effect on the temperature boundary layer thickness. Supported by the National Natural Science Foundations of China under Grant Nos. 21576023, 51406008, and the National Key Research Program of China under Grant Nos. 2016YFC0700601, 2016YFC0700603, and 2016YFE0115500

10. Combined Influence of Thermal Diffusion and Diffusion Thermo on Unsteady MHD Free Convective Fluid Flow Past an Infinite Vertical Porous Plate in Presence of Chemical Reaction

Srinivasa Raju, Rallabandi

2016-10-01

The present investigation is concerned with the effects of thermal diffusion (Soret) and diffusion thermo (Dufour) on an unsteady MHD free convective flow with heat and mass transfer of an electrically conducting fluid in the presence of chemical reaction. A uniform magnetic field acts perpendicular to the porous surface, which absorbs the fluid with a suction velocity varying with time. The problem is governed by coupled non-linear partial differential equations with appropriate boundary conditions. A finite element numerical solution is developed to solve the resulting well-posed two-point boundary value problem. The present numerical results are compared with available data and are found in an excellent agreement. The expressions for velocity, temperature and concentration fields are obtained. With the aid of these, the expressions for the coefficient of skin-friction, the rate of heat transfer in the form of Nusselt number and the rate of mass transfer in the form of Sherwood number are derived. Finally the effects of various physical parameters of the flow quantities are studied with the help of graphs and tables.

11. Study of MHD Corrosion and Transport of Corrosion Products of Ferritic/Martensitic Steels in the Flowing PbLi and its Application to Fusion Blanket

Saeidi, Sheida

Two important components of a liquid breeder blanket of a fusion power reactor are the liquid breeder/coolant and the steel structure that the liquid is enclosed in. One candidate combination for such components is Lead-Lithium (PbLi) eutectic alloy and advanced Reduced Activation Ferritic/Martensitic (RAFM) steel. The research performed here is aimed at: (1) better understanding of corrosion processes in the system including RAFM steel and flowing PbLi in the presence of a strong magnetic field and (2) prediction of corrosion losses in conditions of a Dual Coolant Lead Lithium (DCLL) blanket, which is at present the key liquid metal blanket concept in the US. To do this, numerical and analytical tools have been developed and then applied to the analysis of corrosion processes. First, efforts were taken to develop a computational suite called TRANSMAG (Transport phenomena in Magnetohydrodynamic Flows) as an analysis tool for corrosion processes in the PbLi/RAFM system, including transport of corrosion products in MHD laminar and turbulent flows. The computational approach in TRANSMAG is based on simultaneous solution of flow, energy and mass transfer equations with or without a magnetic field, assuming mass transfer controlled corrosion and uniform dissolution of iron in the flowing PbLi. Then, the new computational tool was used to solve an inverse mass transfer problem where the saturation concentration of iron in PbLi was reconstructed from the experimental data resulting in the following correlation: CS = e 13.604--12975/T, where T is the temperature of PbLi in K and CS is in wppm. The new correlation for saturation concentration was then used in the analysis of corrosion processes in laminar flows in a rectangular duct in the presence of a strong transverse magnetic field. As shown in this study, the mass loss increases with the magnetic field such that the corrosion rate in the presence of a magnetic field can be a few times higher compared to purely

12. Ideal hydrodynamics and elliptic flow at CERN Super Proton Synchrotron (SPS) energies: Importance of the initial conditions

SciTech Connect

Petersen, Hannah; Bleicher, Marcus

2009-05-15

The elliptic flow excitation function calculated in a full (3+1) dimensional hybrid Boltzmann approach with an intermediate hydrodynamic stage for heavy ion reactions from GSI Schwerionen Synchrotron to the highest CERN Super Proton Synchrotron (SPS) energies is discussed in the context of the experimental data. In this study, we employ a hadron gas equation of state to investigate the differences in the dynamics and viscosity effects. The specific event-by-event setup with initial conditions and freeze-out from a nonequilibrium transport model allows for a direct comparison between ideal fluid dynamics and transport simulations. At higher SPS energies, where the pure transport calculation cannot account for the high elliptic flow values, the smaller mean free path in the hydrodynamic evolution leads to higher elliptic flow values. In contrast to previous studies within pure hydrodynamics, the more realistic initial conditions employed here and the inclusion of a sequential final state hadronic decoupling provides results that are in line with the experimental data almost over the whole energy range from E{sub lab}=2-160A GeV. Thus, this new approach leads to a substantially different shape of the v{sub 2}/{epsilon} scaling curve as a function of (1/SdN{sub ch}/dy) in line with the experimental data compared to previous ideal hydrodynamic calculations. This hints at a strong influence of the initial conditions for the hydrodynamic evolution on the finally observed v{sub 2} values, thus questioning the standard interpretation that the hydrodynamic limit is only reached at BNL Relativistic Heavy Ion Collider energies.

13. The impact of uncertainty on shape optimization of idealized bypass graft models in unsteady flow

Sankaran, Sethuraman; Marsden, Alison L.

2010-12-01

It is well known that the fluid mechanics of bypass grafts impacts biomechanical responses and is linked to intimal thickening and plaque deposition on the vessel wall. In spite of this, quantitative information about the fluid mechanics is not currently incorporated into surgical planning and bypass graft design. In this work, we use a derivative-free optimization technique for performing systematic design of bypass grafts. The optimization method is coupled to a three-dimensional pulsatile Navier-Stokes solver. We systematically account for inevitable uncertainties that arise in cardiovascular simulations, owing to noise in medical image data, variable physiologic conditions, and surgical implementation. Uncertainties in the simulation input parameters as well as shape design variables are accounted for using the adaptive stochastic collocation technique. The derivative-free optimization framework is coupled with a stochastic response surface technique to make the problem computationally tractable. Two idealized numerical examples, an end-to-side anastomosis, and a bypass graft around a stenosis, demonstrate that accounting for uncertainty significantly changes the optimal graft design. Results show that small changes in the design variables from their optimal values should be accounted for in surgical planning. Changes in the downstream (distal) graft angle resulted in greater sensitivity of the wall-shear stress compared to changes in the upstream (proximal) angle. The impact of cost function choice on the optimal solution was explored. Additionally, this work represents the first use of the stochastic surrogate management framework method for robust shape optimization in a fully three-dimensional unsteady Navier-Stokes design problem.

14. The Impact of Dry Midlevel Air on Hurricane Intensity in Idealized Simulations with No Mean Flow

NASA Technical Reports Server (NTRS)

Braun, Scott A.; Sippel, Jason A.; Nolan, David S.

2012-01-01

This study examines the potential negative influences of dry midlevel air on the development of tropical cyclones (specifically, its role in enhancing cold downdraft activity and suppressing storm development). The Weather Research and Forecasting model is used to construct two sets of idealized simulations of hurricane development in environments with different configurations of dry air. The first set of simulations begins with dry air located north of the vortex center by distances ranging from 0 to 270 km, whereas the second set of simulations begins with dry air completely surrounding the vortex, but with moist envelopes in the vortex core ranging in size from 0 to 150 km in radius. No impact of the dry air is seen for dry layers located more than 270 km north of the initial vortex center (approximately 3 times the initial radius of maximum wind). When the dry air is initially closer to the vortex center, it suppresses convective development where it entrains into the storm circulation, leading to increasingly asymmetric convection and slower storm development. The presence of dry air throughout the domain, including the vortex center, substantially slows storm development. However, the presence of a moist envelope around the vortex center eliminates the deleterious impact on storm intensity. Instead, storm size is significantly reduced. The simulations suggest that dry air slows intensification only when it is located very close to the vortex core at early times. When it does slow storm development, it does so primarily by inducing outward- moving convective asymmetries that temporarily shift latent heating radially outward away from the high-vorticity inner core.

15. Numerical Solutions for Supersonic Flow of an Ideal Gas Around Blunt Two-Dimensional Bodies

NASA Technical Reports Server (NTRS)

Fuller, Franklyn B.

1961-01-01

The method described is an inverse one; the shock shape is chosen and the solution proceeds downstream to a body. Bodies blunter than circular cylinders are readily accessible, and any adiabatic index can be chosen. The lower limit to the free-stream Mach number available in any case is determined by the extent of the subsonic field, which in turn depends upon the body shape. Some discussion of the stability of the numerical processes is given. A set of solutions for flows about circular cylinders at several Mach numbers and several values of the adiabatic index is included.

16. Computational Methods for Ideal Magnetohydrodynamics

Kercher, Andrew D.

Numerical schemes for the ideal magnetohydrodynamics (MHD) are widely used for modeling space weather and astrophysical flows. They are designed to resolve the different waves that propagate through a magnetohydro fluid, namely, the fast, Alfven, slow, and entropy waves. Numerical schemes for ideal magnetohydrodynamics that are based on the standard finite volume (FV) discretization exhibit pseudo-convergence in which non-regular waves no longer exist only after heavy grid refinement. A method is described for obtaining solutions for coplanar and near coplanar cases that consist of only regular waves, independent of grid refinement. The method, referred to as Compound Wave Modification (CWM), involves removing the flux associated with non-regular structures and can be used for simulations in two- and three-dimensions because it does not require explicitly tracking an Alfven wave. For a near coplanar case, and for grids with 213 points or less, we find root-mean-square-errors (RMSEs) that are as much as 6 times smaller. For the coplanar case, in which non-regular structures will exist at all levels of grid refinement for standard FV schemes, the RMSE is as much as 25 times smaller. A multidimensional ideal MHD code has been implemented for simulations on graphics processing units (GPUs). Performance measurements were conducted for both the NVIDIA GeForce GTX Titan and Intel Xeon E5645 processor. The GPU is shown to perform one to two orders of magnitude greater than the CPU when using a single core, and two to three times greater than when run in parallel with OpenMP. Performance comparisons are made for two methods of storing data on the GPU. The first approach stores data as an Array of Structures (AoS), e.g., a point coordinate array of size 3 x n is iterated over. The second approach stores data as a Structure of Arrays (SoA), e.g. three separate arrays of size n are iterated over simultaneously. For an AoS, coalescing does not occur, reducing memory efficiency

17. Supersonic MHD generator system

SciTech Connect

Rahman, M.A.

1983-11-29

An improved MHD electrical power generating system of the type having a MHD topping cycle and a steam generating bottoming cycle is disclosed. The system typically includes a combustion system, a conventional MHD generator and a first diffuser radiant boiler. The improvement comprises a first supersonic MHD generator and ramjet engine configuration operatively connected in series with each other and with the conventional MHD generator. The first supersonic MHD generator and ramjet engine configuration increase the power output and improve the operating efficiency of the electrical generating system. A diffuser system is also disclosed which is in fluid communication with the supersonic MHD generator and the ramjet engine for collecting bypass plasma gas to be used for heating a second radiant boiler adapted for powering a steam turbine generator.

18. HAM solutions on MHD squeezing axisymmetric flow of water nanofluid through saturated porous medium between two parallel disks

Reddy, B. Siva Kumar; Rao, K. V. Surya Narayana; Vijaya, R. Bhuvana

2017-07-01

In this paper, we have considered the unsteady magnetohydrodynamic squeezing axi-symmetric flow of water-nanofluid through saturated porous medium between two parallel disks. The equations for the governing flow are solved by Galerkin optimal Homotopy asymptotic method. The effects of non-dimensional parameters on velocity, temperature and concentration have been discussed with the help of graphs. Also we obtained local Nusselt number and computationally discussed with reference to flow parameters.

19. Superheater/intermediate temperature air heater tube corrosion tests in the MHD coal fired flow facility (Montana Rosebud POC tests)

SciTech Connect

White, M.

1996-01-01

Nineteen alloys have been exposed for approximately 1000 test hours as candidate superheater and intermediate temperature air heater tubes in a U.S. DOE facility dedicated to demonstrating Proof of Concept for the bottoming or heat and seed recovery portion of coal fired magnetohydrodynamic (MHD) electrical power generating plants. Corrosion data have been obtained from a test series utilizing a western United States sub-bituminous coal, Montana Rosebud. The test alloys included a broad range of compositions ranging from carbon steel to austenitic stainless steels to high chromium nickel-base alloys. The tubes, coated with K{sub 2}SO-containing deposits, developed principally, oxide scales by an oxidation/sulfidation mechanism. In addition to being generally porous, these scales were frequently spalled and/or non-compact due to a dispersed form of outward growth by oxide precipitation in the adjacent deposit. Austenitic alloys generally had internal penetration as trans Tranular and/or intergranular oxides and sulfides. While only two of the alloys had damage visible without magnification as a result of the relatively short exposure, there was some concern about Iona-term corrosion performance owing to the relatively poor quality scales formed. Comparison of data from these tests to those from a prior series of tests with Illinois No. 6, a high sulfur bituminous coal, showed less corrosion in the present test series with the lower sulfur coal. Although K{sub 2}SO{sub 4}was the principal corrosive agent as the supplier of sulfur, which acted to degrade alloy surface scales, tying up sulfur as K{sub 2}SO{sub 4} prevented the occurrence of complex alkali iron trisulfates responsible for severe or catastrophic corrosion in conventional power plants with certain coals and metal temperatures.

20. Magnetotail dynamics: MHD simulations of driven and spontaneous dynamic changes

SciTech Connect

Birn, J.; Schindler, K.; Hesse, M.

1994-05-01

The dynamic evolution of the magnetotail during growth phase and expansion phase of a substorm is studied through threedimensional time-dependent MHD simulations. To model growth phase effects, an external electric field with an equatorward inflow is applied at the boundaries over a finite time period. This leads to the formation of a thin current sheet with greatly enhanced current density in the near tail, embedded in the wider plasma/current sheet, which becomes diminished in strength. A faster, spontaneous current sheet formation occurs when entropy conservation is released in an isobaric model, while the ideal MHD constraint persists. This may be a suitable model for the late, explosive part of the growth phase. The transition to the substorm expansive phase is modeled by an increase in anomalous resistivity, using either uniform resistivity or a current density dependent resistivity which is turned on when the current density exceeds a certain threshold. In both cases the violation of ideal MHD leads to resistive instability and the formation of a near-Earth neutral line, fast flow, and plasmoid ejection, together with the dipolarization and current reduction in the region further earthward. The spontaneous increase in total region 1 type field-aligned currents associated with the disruptions of the thin current sheets is less significant than that found in earlier simulations of the disruption of a wider current sheet, whereas the driven increase in the region 1 type current is substantial. The results demonstrate that the same dynamic process which appears spontaneous in the behavior of some quantities might be interpreted as entirely driven from the observation of others.

1. Computational fluid dynamics of blood flow in coil-embolized aneurysms: effect of packing density on flow stagnation in an idealized geometry.

PubMed

Otani, Tomohiro; Nakamura, Masanori; Fujinaka, Toshiyuki; Hirata, Masayuki; Kuroda, Junko; Shibano, Katsuhiko; Wada, Shigeo

2013-08-01

Coil embolization is performed to induce flow stagnation in cerebral aneurysms and enhance blood clot formation, thus preventing rupture and further growth. We investigated hemodynamics in differently positioned aneurysms coiled at various packing densities to determine the effective packing density in terms of flow stagnation. As a first step, hemodynamic simulations were conducted for idealized geometries of both terminal- and sidewall-type aneurysms. Porous media modeling was employed to describe blood flow in coil-embolized aneurysms. The stagnant volume ratio (SVR) was analyzed to quantify the efficacy of coil embolization. Regardless of aneurysm type and angle, SVR increased with increasing packing density, but the increase in SVR varied depending on type. For sidewall-type aneurysms, the packing density required to achieve 60 % SVR was 20 %, roughly independent of aneurysm angle; flow stagnation was achieved at low packing density. In contrast, in terminal-type aneurysms, the packing density required to achieve 60 % SVR was highly dependent on aneurysm angle, accomplishing a 20 % packing density only for lower angles. Indications are that a relatively high packing density would be required, particularly when these aneurysms are angled against the parent artery. The packing density required for flow stagnation varies depending on aneurysm type and relative position.

2. MHD slip flow of a dissipative Casson fluid over a moving geometry with heat source/sink: A numerical study

Raju, C. S. K.; Sandeep, N.

2017-04-01

A Mathematical model is developed for investigating the heat and mass transfer of magnetohydrodynamic Casson fluid over a moving wedge with slip, nonlinear thermal radiation, uniform heat source/sink and chemical reaction. For regulating the momentum and concentration gradients we also considered the viscous dissipation and cross diffusion effects. Numerical solutions are carried out by employing Runge-Kutta and Newton's methods. The effects of the physical governing factors on the flow, temperature and concentration profiles are illustrated graphically for accelerating and decelerating flow cases. We also computed the local Nusselt and Sherwood numbers along with friction factor for the same cases. It is found that increasing the temperature jump parameter encourages the heat transfer rate. It is also concluded that the local Nusselt number is high in accelerating flow case when equated with the decelerating flow case.

3. Haar wavelet solution of the MHD Jeffery-Hamel flow and heat transfer in Eyring-Powell fluid

Khan, Najeeb Alam; Sultan, Faqiha; Shaikh, Amber; Ara, Asmat; Rubbab, Qammar

2016-11-01

This study deals with the numerical investigation of Jeffery-Hamel flow and heat transfer in Eyring-Powell fluid in the presence of an outer magnetic field by using Haar wavelet method. Jeffery-Hamel flows occur in various practical situations involving flow between two non-parallel walls. Applications of such fluids in biological and industrial sciences brought a great concern to the investigation of flow characteristics in converging and diverging channels. A suitable similarity transformation is applied to transform the nonlinear coupled partial differential equations (PDEs) into nonlinear coupled ordinary differential equations (ODEs), which govern the momentum and heat transfer properties of the fluid. Due to the high nonlinearity of resulting coupled ODEs, the exact solution is unlikely. Thus, the solution is approximated using a numerical scheme based on Haar wavelets and the results are verified by comparing with 4th order Runge-Kutta results.

4. Metal/gas MHD conversion

Thibault, J. P.; Joussellin, F.; Alemany, A.; Dupas, A.

1982-09-01

Operation features, theory, performance, and possible spatial applications of metal/gas MHD electrical generators are described. The working principle comprises an MHD channel, surrounded by a magnet, filled with a molten, highly conductive metal into which gas is pumped. The heat of the metal expands the gas, forcing a flow through the magnetic field crossing the channel, thus creating an electrical current conducted by the metal. The gas and metal are separated by a centrifugal device and both are redirected into the channel, forming thereby a double closed circuit when the heat of the molten metal is returned to the flow. Necessary characteristics for the gas such as a fairly low vaporization temperature and nonmiscibility with the metal, are outlined, and a space system using Li-Cs or Z-K as the heat carrier kept molten by a parabolic dish system is sketched. Equations governing the fluid mechanics, thermodynamics, and the electrical generation are defined. The construction of a prototype MHD generator using a tin-water flow operating at 250 C, a temperature suitable for coupling to solar heat sources, is outlined, noting expected efficiencies of 20-30 percent.

5. Heat and Mass Transfer Analysis of MHD Nanofluid Flow with Radiative Heat Effects in the Presence of Spherical Au-Metallic Nanoparticles.

PubMed

2016-12-01

Energy generation is currently a serious concern in the progress of human civilization. In this regard, solar energy is considered as a significant source of renewable energy. The purpose of the study is to establish a thermal energy model in the presence of spherical Au-metallic nanoparticles. It is numerical work which studies unsteady magnetohydrodynamic (MHD) nanofluid flow through porous disks with heat and mass transfer aspects. Shaped factor of nanoparticles is investigated using small values of the permeable Reynolds number. In order to scrutinize variation of thermal radiation effects, a dimensionless Brinkman number is introduced. The results point out that heat transfer significantly escalates with the increase of Brinkman number. Partial differential equations that govern this study are reduced into nonlinear ordinary differential equations by means of similarity transformations. Then using a shooting technique, a numerical solution of these equations is constructed. Radiative effects on temperature and mass concentration are quite opposite. Heat transfer increases in the presence of spherical Au-metallic nanoparticles.

6. Heat and Mass Transfer Analysis of MHD Nanofluid Flow with Radiative Heat Effects in the Presence of Spherical Au-Metallic Nanoparticles

2016-10-01

Energy generation is currently a serious concern in the progress of human civilization. In this regard, solar energy is considered as a significant source of renewable energy. The purpose of the study is to establish a thermal energy model in the presence of spherical Au-metallic nanoparticles. It is numerical work which studies unsteady magnetohydrodynamic (MHD) nanofluid flow through porous disks with heat and mass transfer aspects. Shaped factor of nanoparticles is investigated using small values of the permeable Reynolds number. In order to scrutinize variation of thermal radiation effects, a dimensionless Brinkman number is introduced. The results point out that heat transfer significantly escalates with the increase of Brinkman number. Partial differential equations that govern this study are reduced into nonlinear ordinary differential equations by means of similarity transformations. Then using a shooting technique, a numerical solution of these equations is constructed. Radiative effects on temperature and mass concentration are quite opposite. Heat transfer increases in the presence of spherical Au-metallic nanoparticles.

7. Steady MHD free convection heat and mass transfer flow about a vertical porous surface with thermal diffusion and induced magnetic field

Touhid Hossain, M. M.; Afruz-Zaman, Md.; Rahman, Fouzia; Hossain, M. Arif

2013-09-01

In this study the thermal diffusion effect on the steady laminar free convection flow and heat transfer of viscous incompressible MHD electrically conducting fluid above a vertical porous surface is considered under the influence of an induced magnetic field. The governing non-dimensional equations relevant to the problem, containing the partial differential equations, are transformed by usual similarity transformations into a system of coupled non-linear ordinary differential equations and will be solved analytically by using the perturbation technique. On introducing the non-dimensional concept and applying Boussinesq's approximation, the solutions for velocity field, temperature distribution and induced magnetic field to the second order approximations are obtained for large suction with different selected values of the established dimensionless parameters. The influences of these various establish parameters on the velocity and temperature fields and on the induced magnetic fields are exhibited under certain assumptions and are studied graphically in the present analysis. It is observed that the effects of thermal-diffusion and large suction have great importance on the velocity, temperature and induced magnetic fields and mass concentration for several fluids considered, so that their effects should be taken into account with other useful parameters associated. It is also found that the dimensionless Prandtl number, Grashof number, Modified Grashof number and magnetic parameter have an appreciable influence on the concerned independent variables.

8. Effect of multiple slip on a chemically reactive MHD non-Newtonian nanofluid power law fluid flow over a stretching sheet with microorganism

Basir, Mohammad Faisal Mohd; Ismail, Fazreen Amira; Amirsom, Nur Ardiana; Latiff, Nur Amalina Abdul; Ismail, Ahmad Izani Md.

2017-04-01

The effect of multiple slip on a chemically reactive magnetohydrodynamic (MHD) non-Newtonian power law fluid flow over a stretching sheet with microorganism was numerically investigated. The governing partial differential equations were transformed into nonlinear ordinary differential equations using the similarity transformations developed by Lie group analysis. The reduced governing nonlinear ordinary differential equations were then numerically solved using the Runge-Kutta-Fehlberg fourth-fifth order method. Good agreement was found between the present numerical solutions with the existing published results to support the validity and the accuracy of the numerical computations. The influences of the velocity, thermal, mass and microorganism slips, the magnetic field parameter and the chemical reaction parameter on the dimensionless velocity, temperature, nanoparticle volume fraction, microorganism concentration, the distribution of the density of motile microorganisms have been illustrated graphically. The effects of the governing parameters on the physical quantities, namely, the local heat transfer rate, the local mass transfer rate and the local microorganism transfer rate were analyzed and discussed.

9. Hall Effects And Rotation Effects On MHD Flow Past An Exponentially Accelerated Vertical Plate With Combined Heat And Mass Transfer Effects

Thamizhsudar, M.; Pandurangan, J.; Muthucumaraswamy, R.

2015-08-01

A theoretical solution of flow past an exponentially accelerated vertical plate in the presence of Hall current and MHD relative to a rotating fluid with uniform temperature and mass diffusion is presented. The dimensionless equations are solved using the Laplace method. The axial and transverse velocity, temperature and concentration fields are studied for different parameters such as the Hall parameter (m), Hartmann number (M), Rotation parameter (Ω), Schmidt number, Prandtl number, thermal Grashof number (Gr) and mass Grashof number (Gc). It has been observed that the temperature of the plate decreases with increasing values of the Prandtl number and the concentration near the plate increases with decreasing values of Schmidt number. It is also observed that both axial and transverse velocities increase with decreasing values of the magnetic field parameter or rotation parameter, but the trend gets reversed with respect to the Hall parameter. The effects of parameters m, M, Ω, Gr and Gc on the axial and transverse velocity profiles are shown graphically.

10. O the Generalized Hall Effect as a Modification of Ideal Magnetohydrodynamics

Goodman, Michael Lee

The generalized Hall effect (GHE) in the generalized Hall model (GHM) is studied as a correction to ideal magnetohydrodynamics (MHD) in the context of how it affects the linear stability of cylindrically symmetric equilibria and how it changes helically symmetric equilibria. The GHM differs from what is usually called the Hall model by including the electron pressure in the electron momentum equation. This gives the GHM some aspects of a two fluid model whereas the Hall model is a one fluid model. In both cases of cyclindrical and helical symmetry the presence of the electron pressure gradient as part of the GHE gives rise to an electric field tangent to the boundary of the plasma. This introduces an additional boundary condition in the case of a perfectly conducting plasma boundary. In the case of helical symmetry the equilibrium equations are a generalization of the Grad-Schafranov equation to equilibria with flow and GHE. The classification of these partial differential equations is independent of the component of the ion fluid velocity parallel to the helical direction which may allow for transonic or supersonic flows which are governed by elliptic equations. In the case of cylindrical symmetry a class of Alfven wave solutions that do not exist in ideal MHD is obtained and the accumulation point, with respect to large radial wavenumber, of the slow magnetoacoustic wave is shown to be changed from a finite nonzero value in ideal MHD to infinity by the GHE.

11. Revisiting MHD stability comparison theorems: Some surprising new results

Cerfon, Antoine; Freidberg, Jeffrey

2009-05-01

The classic MHD stability comparison theorems (Kruskal-Oberman, Rosenbluth-Rostoker) show that ideal MHD yields the most stringent stability limits according to the hierarchy δWCGL>δWKIN>δWMHD. This has long justified the use of ideal MHD for conservative predictions of MHD stability boundaries. We reexamine these theorems, with the following conclusions:(1) It is crucial to distinguish between ergodic and closed field line systems.(2) It is essential to account for resonant particles in the kinetic MHD model.(3) For ergodic systems the original kinetic MHD analysis over-estimates stability: δWKIN>δWMHD. Our new result predicts δWKIN=δWMHD.(4) For closed line systems plasma compressibility effects become important, and resonant particle effects vanish. Both the original and new analysis predict δWKIN>δWMHD. However, using a Vlasov-Fluid model with Vlasov ions and fluid electrons we show that both δWKIN and δWMHD, while mathematically correct, yield the wrong physical result. The V-F model shows that at marginal stability the compressibility stabilization term vanishes identically! For ergodic systems, marginal stability is always incompressible, so δWKIN=δWMHD=δWVF. For compressible modes in closed line systems, however, perpendicular resonant particle effects cancel the stabilizing effect of plasma compressibility predicted by ideal and kinetic MHD: δWKIN>δWMHD>δWVF.

12. Study of extended MHD effects on interchange modes in spheromak equilibria

Howell, E. C.; Sovinec, C. R.

2014-10-01

A study of extended MHD effects on linear interchange modes is performed using the NIMROD code [Sovinec & King JCP 2010]. A linear cylindrical equilibrium model is adapted from [Jardin NF 1982] to allow finite toroidal current at the edge. These equilibria are representative of SSPX discharges where currents are driven on the open field to keep the safety factor above 1/2 across the profile [McLean et al., POP 2006]. These spheromaks have weak magnetic shear, and interchange stability is an important consideration. The Suydam parameter, D, is scaled to study resistive and ideal interchange modes. The calculated MHD growth rate increases with D. The resistive interchange scaling γ ~η 1 / 3 is observed for D <1/4 . Calculations using the full extended MHD model are performed for a range of hall parameters Λ. This model includes gyro-viscosity, the hall term, equilibrium diamagnetic flows, and the cross-field diamagnetic heat flux. Two fluid effects in the full model are always destabilizing at large Λ. However, some cases exhibit a range of Λ where the growth rate for the full model is reduced relative to the MHD growth rate. Work supported by US DOE.

13. Saturnian Local Time Effects in Titan's Interaction- A multi-fluid MHD study

Ma, Yingjuan; Russell, Chris; Nagy, Andrew; Toth, Gabor; Dougherty, Michele; Cravens, Tom

2013-04-01

We use a multi-fluid MHD model to study the effects of Saturnian Local Time(SLT). The multi-fluid model improves the previously used 7-species single-fluid MHD model by solving the density, velocity and pressure equations for each of the seven ion fluids. This model allows the motion of the different ion fluids to be decoupled. The model is first applied to an idealized case and the results are compared in detail with that of the 7-species single-fluid MHD model to illustrate the importance of the multi-fluid effects. Simulation results show that the multi-fluid model is able to reproduce asymmetric results along the convection electric field direction. The velocities patterns are different for different mass ion fluids. The heavier the ion is, the more significant is the flow along the convection electric field direction. Also the multi-fluid MHD model predicts that more heavy ions are escaping from the satellite as compared with the single-fluid model. We also apply the model to test the effects of SLT and find that the escaping fluxes of heavy ions vary significantly with SLT.

14. MHD-EMP protection guidelines

SciTech Connect

Barnes, P.R.; Vance, E.F.

1992-03-01

A nuclear detonation at altitudes several hundred kilometers above the earth will severely distort the earths magnetic field and result in a strong magnetohyrodynamic electromagnetic pulse (MHD-EMP). The geomagnetic disturbance interacts with the soil to induce current and horizontal electric gradients. The geomagnetic disturbance interacts with the soil to induced current and horizontal electric gradients in the earth. MHD-EMP, also called E3 since it is the third component of the high-altitude EMP (HEMP), lasts over 100 s after the exoatmospheric burst. MHD-EMP is similar to solar geomagnetic storms in its global and low frequency (less than 1 Hz) nature except that E3 can be much more intense with a far shorter duration. When the MHD-EMP gradients are integrated over great distances by power lines, communication cables, or other long conductors, the induced voltages are significant. (The horizontal gradients in the soil are too small to induce major responses by local interactions with facilities.) The long pulse waveform for MHD-EMP-induced currents on long lines has a peak current of 200 A and a time-to-half-peak of 100 s. If this current flows through transformer windings, it can saturate the magnetic circuit and cause 60 Hz harmonic production. To mitigate the effects of MHD-EMP on a facility, long conductors must be isolated from the building and the commercial power harmonics and voltage swings must be addressed. The transfer switch would be expected to respond to the voltage fluctuations as long as the harmonics have not interfered with the switch control circuitry. The major sources of MHD-EMP induced currents are the commercial power lines and neutral; neutral current indirect coupling to the facility power or ground system via the metal fence, powered gate, parking lights, etc; metal water pipes; phone lines; and other long conductors that enter or come near the facility. The major source of harmonics is the commercial power system.

15. Effect of thermal radiation on MHD flow of blood and heat transfer in a permeable capillary in stretching motion

Misra, J. C.; Sinha, A.

2013-05-01

In this paper, a theoretical analysis is presented for magnetohydrodynamic flow of blood in a capillary, its lumen being porous and wall permeable. The unsteadiness in the flow and temperature fields is caused by the time-dependence of the stretching velocity and the surface temperature. Thermal radiation, velocity slip and thermal slip conditions are taken into account. In order to study the flow field as well as the temperature field, the problem is formulated as a boundary value problem consisting of a system of nonlinear coupled partial differential equations. The problem is analysed by using similarity transformation and boundary layer approximation. Solution of the problem is achieved by developing a suitable numerical method and using high speed computers. Computational results for the variation in velocity, temperature, skin-friction co-efficient and Nusselt number are presented in graphical/tabular form. Effects of different parameters are adequately discussed. Since the study takes care of thermal radiation in blood flow, the results reported here are likely to have an important bearing on the therapeutic procedure of hyperthermia, particularly in understanding/regulating blood flow and heat transfer in capillaries.

16. Advanced development of diagnostics for non-ideal blast flows. Technical report 1 Apr 89-1 Jun 91

SciTech Connect

Modarress, D.; Hoeft, T.

1992-07-01

Investigations of non-ideal airblast are performed at the Ernst Mach Institute in a shock tube that simulates a radiation-induced thermal layer. Visualization techniques were adequate for overall study of the flow, but did not provide the detailed data for validation of computer codes. Under this contract three tasks were performed to provide needed data. The first task was to develop a software package for analysis of interferogram fringes. This package translates fringes shift due to the presence of helium into densities over the image area. This package was installed at EMI. The second task was to evaluate and test techniques for direct time-varying measurement of gas species concentration. Absorption spectroscopy of NO2 was selected to be used, but had corrosion problems and was abandoned. As a replacement, filtered Rayleigh scattering from Freon gas was identified. The third task was to fabricate and install a multi-location laser Doppler velocimeter system for the shock tube. This unit was installed in the shock tube and preliminary velocity measurements of flow over a rough surface were made.

17. Numerical Simulation of MHD Hiemenz Flow of a Micropolar Fluid towards a Nonlinear Stretching Surface through a Porous Medium

Sharma, Rajesh; Bhargava, Rama

2015-07-01

In this article, the two-dimensional boundary layer problem of Hiemenz flow (two-dimensional flow of a fluid near a stagnation point) of an incompressible micropolar fluid towards a nonlinear stretching surface placed in a porous medium in the presence of transverse magnetic field is examined. The resulting nonlinear differential equations governing the problem have been transformed by a similarity transformation into a system of nonlinear ordinary differential equations which are solved numerically by the Element Free Galerkin method. The influence of various parameters on the velocity, microrotation, temperature, and concentration is shown. Some of the results are compared with the Finite Element Method. Finally, validation of the numerical results is demonstrated for local skin friction ? for hydrodynamic micropolar fluid flow on a linearly stretching surface.

18. MHD waves and instabilities for gravitating, magnetized configurations in motion

Keppens, Rony; Goedbloed, Hans J. P.

Seismic probing of equilibrium configurations is of course well-known from geophysics, but has also been succesfully used to determine the internal structure of the Sun to an amazing accuracy. The results of helioseismology are quite impressive, although they only exploit an equilibrium structure where inward gravity is balanced by a pressure gradient in a 1D radial fashion. In principle, one can do the same for stationary, gravitating, magnetized plasma equilibria, as needed to perform MHD seismology in astrophysical jets or accretion disks. The introduction of (sheared) differential rotation does require the important switch from diagnosing static to stationary equilibrium configurations. The theory to describe all linear waves and instabilities in ideal MHD, given an exact stationary, gravitating, magnetized plasma equilibrium, in any dimensionality (1D, 2D, 3D) has been known since 1960, and is governed by the Frieman-Rotenberg equation. The full (mathematical) power of spectral theory governing physical eigenmode determination comes into play when using the Frieman-Rotenberg equation for moving equilibria, as applicable to astrophysical jets, accretion disks, but also solar flux ropes with stationary flow patterns. I will review exemplary seismic studies of flowing equilibrium configurations, covering solar to astrophysical configurations in motion. In that case, even essentially 1D configurations require quantification of the spectral web of eigenmodes, organizing the complex eigenfrequency plane.

19. Dual solutions of radiative MHD nanofluid flow over an exponentially stretching sheet with heat generation/absorption

Naramgari, Sandeep; Sulochana, C.

2016-01-01

In this study, we analyzed the heat and mass transfer in thermophoretic radiative hydromagnetic nanofluid flow over an exponentially stretching porous sheet embedded in porous medium with internal heat generation/absorption, viscous dissipation and suction/injection effects. The governing partial differential equations of the flow are converted into nonlinear coupled ordinary differential equations by using similarity transformation. Runge-Kutta-based shooting technique is employed to yield the numerical solutions for the model. The effect of non-dimensional parameters on velocity, temperature and concentration profiles are discussed and presented through graphs. The physical quantities of interest local skin friction coefficient, Nusselt and Sherwood numbers are calculated and presented through tables.

20. Experimental and Computational Study of the Effect of MHD Forces on Stability and Separation of Nonequilibrium Ionized Supersonic Flow

DTIC Science & Technology

2005-07-21

to M=3-4, and mass flow rates of up to 45 g/sec at a stagnation pressure of 1 atm. Pitot tube and schlieren measurements in a M=3 test section showed...section / diffuser assembly is attached to a vacuum system connected to a 1200 ft3 dump tank pumped out by an Allis-Chalmers 1300 cfm rotary vane vacuum...test section also has several Pitot ports, also shown in Fig. 1. The Pitot tube probes can be moved in and out of the flow during the experiment, which

1. Explosive MHD Generators

Lebedev, E. F.; Ostashev, V. E.; Fortov, V. E.

2004-11-01

Explosive driven MHD generators (EMHD) occupy an intermediate position between destroyed Explosive Flux Compression Generators and solid-propellant- pulsed MHD generators. Studies revealed the negative consequences of destroying a plasma liner through Rayleigh-Taylor instability. The real efficiency of conversion of condensed HE charge chemical energy reaches ~10% if the magnetic field in a MHD channel is approximately 8-10 T. Accommodation of 20-30 linear MHD channels into a toroidal magnet seems to be optimal for EMHD generator design. This device may operate repeatedly with a frequency of up to 6.5×103pps.

2. Selective decay and dynamic alignment in the MHD turbulence: The role of the rugged invariants

Telloni, Daniele; Perri, Silvia; Carbone, Vincenzo; Bruno, Roberto

2016-03-01

In the evolving MagnetoHydroDynamic (MHD) turbulence a key role is played by the relaxation processes, which drive a magnetized fluid towards self-organized, stable configurations, like a force-free state (resulting from a selective decay) or a dynamic alignment (anti-alignment) between the plasma flow velocity and magnetic field. The evolution of the three MHD rugged invariants, namely of the magnetic helicity Hm, the cross-helicity Hc and the total energy E, is of particular importance in interpreting the asymptotic solutions of the MHD decay. It is thus prominent to investigate the magnetic and cross-helicity content carried by the solar wind and by magnetic structures advected by the flowing plasma, and particularly their radial evolution throughout the inner heliosphere, in order to offer a rather complete picture of the phenomenological aspect of the relaxation phenomena occurring in the solar wind turbulence. The results presented in this paper show that within some solar wind streams, the ideal MHD decays towards a state with maximal cross-helicity, where the magnetic and velocity fluctuations are (anti-)aligned with a high correlation degree. The maximal magnetic helicity state, say the force-free configuration, is instead observed in interplanetary flux ropes, a particular class of magnetic objects advected by the solar wind. However, it is worth noting that in some peculiar flux ropes, the competitive action of both rugged invariants drives the MHD configuration of these structures to intermediate states, where both the magnetic and cross-helicity significantly deviate from zero, without, however, reaching a maximum value.

3. Ideal Magnetohydrodynamic Solution to the σ Problem in Crab-like Pulsar Winds and General Asymptotic Analysis of Magnetized Outflows

Vlahakis, Nektarios

2004-01-01

Using relativistic, steady, axisymmetric, ideal magnetohydrodynamics (MHD), we analyze the super-Alfvénic regime of a pulsar wind by solving the momentum equation along the flow, as well as in the transfield direction. Employing a self-similar model, we demonstrate that ideal MHD can account for the full acceleration from high (>>1) to low (<<1) values of σ, the Poynting-to-matter energy flux ratio. The solutions also show a transition from a current-carrying to a return-current regime, partly satisfying the current-closure condition. We discuss the kind of boundary conditions near the base of the ideal MHD regime that are necessary in order to have the required transition from high to low σ in realistic distances and argue that this is a likely case for an equatorial wind. Examining the MHD asymptotics in general, we extend the analysis of Heyvaerts & Norman and Chiueh, Li, & Begelman by including two new elements: classes of quasi-conical and parabolic field line shapes that do not preclude an efficient and much faster than logarithmic acceleration, and the transition σ=σc after which the centrifugal forces (poloidal and azimuthal) are the dominant terms in the transfield force-balance equation.

4. Numerical study of unsteady MHD oblique stagnation point flow and heat transfer due to an oscillating stream

Javed, T.; Ghaffari, A.; Ahmad, H.

2016-05-01

The unsteady stagnation point flow impinging obliquely on a flat plate in presence of a uniform applied magnetic field due to an oscillating stream has been studied. The governing partial differential equations are transformed into dimensionless form and the stream function is expressed in terms of Hiemenz and tangential components. The dimensionless partial differential equations are solved numerically by using well-known implicit finite difference scheme named as Keller-box method. The obtained results are compared with those available in the literature. It is observed that the results are in excellent agreement with the previous studies. The effects of pertinent parameters involved in the problem namely magnetic parameter, Prandtl number and impinging angle on flow and heat transfer characteristics are illustrated through graphs. It is observed that the influence of magnetic field strength increases the fluid velocity and by the increase of obliqueness parameter, the skin friction increases.

5. Marangoni convective MHD flow of SWCNT and MWCNT nanoliquids due to a disk with solar radiation and irregular heat source

Mahanthesh, B.; Gireesha, B. J.; Shashikumar, N. S.; Shehzad, S. A.

2017-10-01

Present study addresses the Marangoni transport of dissipating SWCNT and MWCNT nanofluids under the influence of magnetic force and radiation. A novel exponential space dependent heat source is considered. The flow is generated due to a disk with surface tension created by thermal gradient. The partial differential equations system governing the flow of carbon-water nanoliquids and heat transfer through Marangoni convection is established. Subsequent system is reduced to nonlinear ordinary boundary value problem via generalized Karman transformations. Numerical solutions are developed of the arising nonlinear problem via Runge-Kutta based shooting approach. Impacts of embedded parameters are focused on Nusselt number, velocity and heat transport distributions through graphical illustrations. Our simulations figured out that the heat transfer rate increased via Marangoni convection; however it is decayed by applied magnetic force. The temperature of SWCNT-H2O nanoliquid dominates MWCNT-H2O nanoliquid.

6. Heat Transfer Analysis of MHD Thin Film Flow of an Unsteady Second Grade Fluid Past a Vertical Oscillating Belt

PubMed Central

Gul, Taza; Islam, Saeed; Shah, Rehan Ali; Khan, Ilyas; Khalid, Asma; Shafie, Sharidan

2014-01-01

This article aims to study the thin film layer flowing on a vertical oscillating belt. The flow is considered to satisfy the constitutive equation of unsteady second grade fluid. The governing equation for velocity and temperature fields with subjected initial and boundary conditions are solved by two analytical techniques namely Adomian Decomposition Method (ADM) and Optimal Homotopy Asymptotic Method (OHAM). The comparisons of ADM and OHAM solutions for velocity and temperature fields are shown numerically and graphically for both the lift and drainage problems. It is found that both these solutions are identical. In order to understand the physical behavior of the embedded parameters such as Stock number, frequency parameter, magnetic parameter, Brinkman number and Prandtl number, the analytical results are plotted graphically and discussed. PMID:25383797

7. Influence of heat transfer on Poiseuille flow of MHD Jeffrey fluid through porous medium with slip boundary conditions

Ramesh, K.

2017-07-01

In the current article, we have discussed the Poiseuille flow of an incompressible magnetohydrodynamic Jeffrey fluid between parallel plates through homogeneous porous medium using slip boundary conditions under the effect of heat transfer. The equations governing the fluid flow are modeled in Cartesian coordinate system. The energy equation is considered under the effects viscous dissipation and heat generation. Analytical solutions for the velocity and temperature profiles are obtained. The effects of the various involved parameters on the velocity and temperature profiles are studied and the results are presented through the graphs. It is observed from our analysis that, with increase of slip parameter and pressure gradient increase the velocity. The temperature is an increasing function of heat generation parameter, Brinkman number, thermal slip parameter and non-Newtonian fluid parameter.

8. Joule heating effect on a continuously moving thin needle in MHD Sakiadis flow with thermophoresis and Brownian moment

Sulochana, C.; Ashwinkumar, G. P.; Sandeep, N.

2017-09-01

In the current study, we investigated the impact of thermophoresis and Brownian moment on the boundary layer 2D forced convection flow of a magnetohydrodynamic nanofluid along a persistently moving horizontal needle with frictional heating effect. The various pertinent parameters are taken into account in the present analysis, namely, the thermophoresis and Brownian moment, uneven heat source/sink, Joule heating and frictional heating effects. To check the variation in the boundary layer behavior, we considered two distinct nanoparticles namely Al50Cu50 (alloy with 50% alumina and 50% copper) and Cu with water as base liquid. Numerical solutions are derived for the reduced system of governing PDEs by employing the shooting process. Computational results of the flow, energy and mass transport are interpreted with the support of tables and graphical illustrations. The obtained results indicate that the increase in the needle size significantly reduces the flow and thermal fields. In particular, the velocity field of the Cu-water nanofluid is highly affected when compared with the Al50Cu50 -water nanofluid. Also, we showed that the thermophoresis and Brownian moment parameters are capable of enhancing the thermal conductivity to a great extent.

9. Test of an MHD code for cosmological applications

Stasyszyn, F.; Dolag, K.

2009-08-01

We build up a comprehensive MHD test suit containing various shock tube tests and different planar MHD test problems (like the Orzang-Tang Vortex, Blast Waves and a Rotor test). To test the MHD implementation (Dolag & Stasyszyn, in prep.) within the cosmological SPH code Gadget 13, we performed fully consistently three dimensional setups to test the code under the same conditions as used the cosmological applications. The results were compared with the idealized solutions obtained in 1D/2D using Athena 3.0 (Gardiner & Stone 2006), showing us that the SPH MHD implementation performs very well. We also compare different regularization schemes of SPH MHD suggested in the literature, and calibrate theses schemes inferring optimal values for the numerical parameters involved. The Implementation of a Hyperbolic/Parabolic divergence cleaning scheme as suggested by Dedner (Dedner et al. 2002) have been also tested, finding good agreement with the results reported in the literature (Price & Monaghan 2005).

10. Towards Integrated Pulse Detonation Propulsion and MHD Power

NASA Technical Reports Server (NTRS)

Litchford, Ron J.; Thompson, Bryan R.; Lineberry, John T.

1999-01-01

The interest in pulse detonation engines (PDE) arises primarily from the advantages that accrue from the significant combustion pressure rise that is developed in the detonation process. Conventional rocket engines, for example, must obtain all of their compression from the turbopumps, while the PDE provides additional compression in the combustor. Thus PDE's are expected to achieve higher I(sub sp) than conventional rocket engines and to require smaller turbopumps. The increase in I(sub sp) and the decrease in turbopump capacity must be traded off against each other. Additional advantages include the ability to vary thrust level by adjusting the firing rate rather than throttling the flow through injector elements. The common conclusion derived from these aggregated performance attributes is that PDEs should result in engines which are smaller, lower in cost, and lighter in weight than conventional engines. Unfortunately, the analysis of PDEs is highly complex due to their unsteady operation and non-ideal processes. Although the feasibility of the basic PDE concept has been proven in several experimental and theoretical efforts, the implied performance improvements have yet to be convincingly demonstrated. Also, there are certain developmental issues affecting the practical application of pulse detonation propulsion systems which are yet to be fully resolved. Practical detonation combustion engines, for example, require a repetitive cycle of charge induction, mixing, initiation/propagation of the detonation wave, and expulsion/scavenging of the combustion product gases. Clearly, the performance and power density of such a device depends upon the maximum rate at which this cycle can be successfully implemented. In addition, the electrical energy required for direct detonation initiation can be significant, and a means for direct electrical power production is needed to achieve self-sustained engine operation. This work addresses the technological issues associated

11. Kinetics of osmotic water flow across cell membranes in non-ideal solutions during freezing and thawing.

PubMed

Weng, Lindong; Li, Weizhong; Zuo, Jianguo

2010-10-01

Cryopreservation requires quantitatively analytical models to simulate the biophysical responses of biomaterials during cryopreservation. The Mazur model and other improved ones, such as Karlsson model concerning solutions containing cryoprotectants (CPA), are somehow precluded by some minor points, particularly, the assumption of ideal solutions. To avoid the ideal solution assumption, in this study a new method is developed to simulate water transport across cell membranes in non-ideal solutions during cooling and thawing. The comparison between osmolalities calculated by the linear freezing-point depression used in this new method and other non-ideal ones is conducted and a good agreement is achieved. In addition, in an ideal case, besides a theoretical agreement, this new approach has been validated by its numerical simulation results. Comparisons between this new approach and the traditional ones with an ideal solution assumption have been conducted based on a spherical hypothetical cell. The main results are (1) the predicted non-ideal intracellular water content is larger than the ideal results; (2) the concentration of CPA solutions is directly proportional to the deviation between the non-ideal and ideal curves. In the end, this study presents a direct description of the degree of subcooling of the protoplasm during dynamic cooling. This study demonstrates that our experimental data-based method is a valid one with clear physical interpretations, convenient expressions and a more extensive application room than traditional ones. Copyright © 2010 Elsevier Inc. All rights reserved.

12. Symmetry, Statistics and Structure in MHD Turbulence

NASA Technical Reports Server (NTRS)

Shebalin, John V.

2007-01-01

Here, we examine homogeneous MHD turbulence in terms of truncated Fourier series. The ideal MHD equations and the associated statistical theory of absolute equilibrium ensembles are symmetric under P, C and T. However, the presence of invariant helicities, which are pseudoscalars under P and C, dynamically breaks this symmetry. This occurs because the surface of constant energy in phase space has disjoint parts, called components: while ensemble averages are taken over all components, a dynamical phase trajectory is confined to only one component. As the Birkhoff-Khinchin theorem tells us, ideal MHD turbulence is thus non-ergodic. This non-ergodicity manifests itself in low-wave number Fourier modes that have large mean values (while absolute ensemble theory predicts mean values of zero). Therefore, we have coherent structure in ideal MHD turbulence. The level of non-ergodicity and amount of energy contained in the associated coherent structure depends on the values of the helicities, as well as on the presence, or not, of a mean magnetic field and/or overall rotation. In addition to the well known cross and magnetic helicities, we also present a new invariant, which we call the parallel helicity, since it occurs when mean field and rotation axis are aligned. The question of applicability of these results to real (i.e., dissipative) MHD turbulence is also examined. Several long-time numerical simulations on a 64(exp 3) grid are given as examples. It is seen that coherent structure begins to form before decay dominates over nonlinearity. The connection of these results with inverse spectral cascades, selective decay, and magnetic dynamos is also discussed.

13. MHD heat and seed recovery technology project

SciTech Connect

Petrick, M.; Johnson, T. R.

1980-08-01

The MHD Heat and Seed Recovery Technology Project at Argonne National Laboratory is obtaining information for the design and operation of the steam plant downstream of the MHD channel-diffuser, and of the seed regeneration process. The project goal is to supply the engineering data required in the design of components for prototype and demonstration MHD facilities. The work is being done in close cooperation with the Heat Recovery-Seed Recovery facility, which will be a 20-MW pilot plant of the MHD steam bottoming system. The primary effort of the HSR Technology Project is directed toward experimental investigations of critical issues, such as 1) NO/sub x/ behavior in the radiant boiler and secondary combustor; 2) radiant boiler design to meet the multiple requirements of steam generation, NO/sub x/ decomposition, and seed slag separation; 3) effects of solid or liquid seed deposits on heat transfer and gas flow in the steam and air heaters; 4) formation, growth, and deposition of seed-slag particles, 5) character of the combustion gas effluents, and 6) the corrosion and erosion of ceramic and metallic materials of construction. These investigations are performed primarily in a 2-MW test facility, Argonne MHD Process Engineering Laboratory (AMPEL). Other project activities are related to studies of the thermochemistry of the seed-slag combustion gas system, identification of ceramic and metallic materials for service in the MHD-steam plant, and evaluation of seed regeneration processes. Progress is reported.

14. Numerical investigation of MHD stagnation point flow and heat transfer over a permeable shrinking sheet with external magnetic field, viscous dissipation and Joule heating

Jafar, Khamisah; Nazar, Roslinda; Ishak, Anuar; Pop, Ioan

2012-05-01

The present study considers the steady laminar magnetohydrodynamic (MHD) boundary layer flow of a viscous and incompressible electrically conducting fluid near the stagnation point on a horizontal continuously shrinking surface, with variable wall temperature and a constant magnetic field applied normal to the surface of the sheet. The surface is assumed to be permeable, allowing either suction or injection at the wall. By introducing an appropriate similarity transformation, the governing system of partial differential equations is first transformed into a system of ordinary differential equations, which is then solved numerically using an implicit finite-difference scheme known as the Keller-box method for some values of the selected parameters. The effects of the governing parameters, namely the shrinking parameter λ, the suction parameter f0 and the magnetic parameter M on the skin friction coefficient, the local Nusselt number as well as the velocity and temperature profiles are determined and discussed. For the present study, the analysis is limited to the case where the Prandtl number is fixed at unity, i.e. Pr = 1 and the Eckert number, Ec = 0.5. It is found that solutions for the shrinking sheet only exist when the magnitude of the shrinking parameter is less than some limiting critical value λc. Where solutions do exist, they are either a unique solution or dual solutions, and for large enough suction at the wall, there may even be triple solutions. For the shrinking sheet, in the presence of viscous dissipation and Joule heating, the magnetic field increases the surface shear stress and slightly increases the surface heat transfer rate.

15. Explosively-driven magnetohydrodynamic (MHD) generator studies

SciTech Connect

Agee, F.J.; Lehr, F.M.; Vigil, M.; Kaye, R.; Gaudet, J.; Shiffler, D.

1995-08-01

Plasma jet generators have been designed and tested which used an explosive driver and shocktube with a rectangular cross section that optimize the flow velocity and electrical conductivity. The latest in a series of designs has been tested using a reactive load to diagnose the electrical properties of the MHD generator/electromagnet combination. The results of these tests indicate that the plasma jet/MHD generator design does generate a flow velocity greater than 25 km/s and produces several gigawatts of pulsed power in a very small package size. A larger, new generator design is also presented.

16. Adjustment of a turbulent boundary layer flow to idealized urban surfaces: A large-eddy simulation study

Cheng, Wai Chi; Porté-Agel, Fernando

2014-05-01

Accurate prediction of atmospheric boundary layer (ABL) flow and its interaction with urban surfaces is critical for understanding the transport of momentum and scalars within and above cities. This, in turn, is essential for predicting the local climate and pollutant dispersion patterns in urban areas. Large-eddy simulation (LES) explicitly resolves the large-scale turbulent eddy motions and, therefore, can potentially provide improved understanding and prediction of flows inside and above urban canopies. This study focuses on the validation and the use of a recently-developed LES framework to simulate a turbulent boundary layer flow through idealized urban canopies represented by uniform arrays of cubes. The LES framework is first validated with wind tunnel experimental data. Good agreement between the simulation results and the experimental data are found in the vertical and spanwise profiles of mean velocities and velocity standard deviations at different streamwise locations. Next, the model is used to simulate ABL flows over surface transitions from a flat homogeneous terrain to aligned and staggered arrays of cubes with height h. For both configurations, five different frontal area densities (Λf), equal to 0.028, 0.063, 0.111, 0.174 and 0.250, are considered. Within the arrays, the flow is found to adjust quickly and shows similar structure of the wake of the cubes after the second row. Above the arrays, an internal boundary layer (IBL) is identified. No significant difference in the depth of the IBL among different cases is observed. The drag exerted by the cubes on the flow (Df) and the drag coefficients of the cubes (Cd) are calculated explicitly using the LES results. For the downstream cubes, Df is found to increases with decreasing density for both configurations, and larger values of Cd are found for the cubes of staggered arrays than those of the aligned arrays with the same Λf. At a downstream location where the flow immediately above the cube

17. MHD Stagnation-Point Flow and Heat Transfer with Effects of Viscous Dissipation, Joule Heating and Partial Velocity Slip

Mat Yasin, Mohd Hafizi; Ishak, Anuar; Pop, Ioan

2015-12-01

The steady two-dimensional stagnation-point flow and heat transfer past a permeable stretching/shrinking sheet with effects of viscous dissipation, Joule heating and partial velocity slip in the presence of a magnetic field is investigated. The partial differential equations are reduced to nonlinear ordinary differential equations by using a similarity transformation, before being solved numerically by shooting technique. Results indicate that the skin friction coefficient and the local Nusselt number increase as magnetic parameter increases. It is found that for the stretching sheet the solution is unique while for the shrinking sheet there exist nonunique solutions (dual solutions) in certain range of parameters. The stability analysis shows that the upper branch solution is stable while the lower branch solution is unstable.

18. Double Diffusive Magnetohydrodynamic (MHD) Mixed Convective Slip Flow along a Radiating Moving Vertical Flat Plate with Convective Boundary Condition

PubMed Central

Rashidi, Mohammad M.; Kavyani, Neda; Abelman, Shirley; Uddin, Mohammed J.; Freidoonimehr, Navid

2014-01-01

In this study combined heat and mass transfer by mixed convective flow along a moving vertical flat plate with hydrodynamic slip and thermal convective boundary condition is investigated. Using similarity variables, the governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved using a semi-numerical/analytical method called the differential transform method and results are compared with numerical results. Close agreement is found between the present method and the numerical method. Effects of the controlling parameters, including convective heat transfer, magnetic field, buoyancy ratio, hydrodynamic slip, mixed convective, Prandtl number and Schmidt number are investigated on the dimensionless velocity, temperature and concentration profiles. In addition effects of different parameters on the skin friction factor, , local Nusselt number, , and local Sherwood number are shown and explained through tables. PMID:25343360

19. Heat and Mass Transfer on MHD Flow of a Viscoelastic Fluid through Porous Media over a Shrinking Sheet

PubMed Central

Bhukta, D.; Dash, G. C.; Mishra, S. R.

2014-01-01

An attempt has been made to study the heat and mass transfer effect in a boundary layer flow through porous medium of an electrically conducting viscoelastic fluid over a shrinking sheet subject to transverse magnetic field in the presence of heat source. Effects of radiation, viscous dissipation, and uniform heat sink on the heat transfer have been considered. The method of solution involves similarity transformation. The coupled nonlinear partial differential equations representing momentum, concentration, and nonhomogenous heat equation are reduced into a set of nonlinear ordinary differential equations. The transformed equations are solved by applying Kummer's function. The exact solution of temperature field is obtained for power-law surface temperature (PST) as well as power-law heat flux (PHF) boundary condition. The interaction of magnetic field is proved to be counterproductive in enhancing velocity and concentration distribution, whereas presence of porous matrix reduces the temperature field at all points. PMID:27379316

20. MHD Convective Flow of Jeffrey Fluid Due to a Curved Stretching Surface with Homogeneous-Heterogeneous Reactions.

PubMed

Imtiaz, Maria; Hayat, Tasawar; Alsaedi, Ahmed

2016-01-01

This paper looks at the flow of Jeffrey fluid due to a curved stretching sheet. Effect of homogeneous-heterogeneous reactions is considered. An electrically conducting fluid in the presence of applied magnetic field is considered. Convective boundary conditions model the heat transfer analysis. Transformation method reduces the governing nonlinear partial differential equations into the ordinary differential equations. Convergence of the obtained series solutions is explicitly discussed. Characteristics of sundry parameters on the velocity, temperature and concentration profiles are analyzed by plotting graphs. Computations for pressure, skin friction coefficient and surface heat transfer rate are presented and examined. It is noted that fluid velocity and temperature through curvature parameter are enhanced. Increasing values of Biot number correspond to the enhancement in temperature and Nusselt number.

1. MHD Stagnation-Point Flow and Heat Transfer with Effects of Viscous Dissipation, Joule Heating and Partial Velocity Slip

PubMed Central

Mat Yasin, Mohd Hafizi; Ishak, Anuar; Pop, Ioan

2015-01-01

The steady two-dimensional stagnation-point flow and heat transfer past a permeable stretching/shrinking sheet with effects of viscous dissipation, Joule heating and partial velocity slip in the presence of a magnetic field is investigated. The partial differential equations are reduced to nonlinear ordinary differential equations by using a similarity transformation, before being solved numerically by shooting technique. Results indicate that the skin friction coefficient and the local Nusselt number increase as magnetic parameter increases. It is found that for the stretching sheet the solution is unique while for the shrinking sheet there exist nonunique solutions (dual solutions) in certain range of parameters. The stability analysis shows that the upper branch solution is stable while the lower branch solution is unstable. PMID:26647651

2. MHD Convective Flow of Jeffrey Fluid Due to a Curved Stretching Surface with Homogeneous-Heterogeneous Reactions

PubMed Central

Imtiaz, Maria; Hayat, Tasawar; Alsaedi, Ahmed

2016-01-01

This paper looks at the flow of Jeffrey fluid due to a curved stretching sheet. Effect of homogeneous-heterogeneous reactions is considered. An electrically conducting fluid in the presence of applied magnetic field is considered. Convective boundary conditions model the heat transfer analysis. Transformation method reduces the governing nonlinear partial differential equations into the ordinary differential equations. Convergence of the obtained series solutions is explicitly discussed. Characteristics of sundry parameters on the velocity, temperature and concentration profiles are analyzed by plotting graphs. Computations for pressure, skin friction coefficient and surface heat transfer rate are presented and examined. It is noted that fluid velocity and temperature through curvature parameter are enhanced. Increasing values of Biot number correspond to the enhancement in temperature and Nusselt number. PMID:27583457

3. MHD Stagnation-Point Flow and Heat Transfer with Effects of Viscous Dissipation, Joule Heating and Partial Velocity Slip.

PubMed

Yasin, Mohd Hafizi Mat; Ishak, Anuar; Pop, Ioan

2015-12-09

The steady two-dimensional stagnation-point flow and heat transfer past a permeable stretching/shrinking sheet with effects of viscous dissipation, Joule heating and partial velocity slip in the presence of a magnetic field is investigated. The partial differential equations are reduced to nonlinear ordinary differential equations by using a similarity transformation, before being solved numerically by shooting technique. Results indicate that the skin friction coefficient and the local Nusselt number increase as magnetic parameter increases. It is found that for the stretching sheet the solution is unique while for the shrinking sheet there exist nonunique solutions (dual solutions) in certain range of parameters. The stability analysis shows that the upper branch solution is stable while the lower branch solution is unstable.

4. Effects of variable electrical conductivity and thermal conductivity on unsteady MHD free convection flow past an exponential accelerated inclined plate

Rana, B. M. Jewel; Ahmed, Rubel; Ahmmed, S. F.

2017-06-01

An analysis is carried out to investigate the effects of variable viscosity, thermal radiation, absorption of radiation and cross diffusion past an inclined exponential accelerated plate under the influence of variable heat and mass transfer. A set of suitable transformations has been used to obtain the non-dimensional coupled governing equations. Explicit finite difference technique has been used to solve the obtained numerical solutions of the present problem. Stability and convergence of the finite difference scheme have been carried out for this problem. Compaq Visual Fortran 6.6a has been used to calculate the numerical results. The effects of various physical parameters on the fluid velocity, temperature, concentration, coefficient of skin friction, rate of heat transfer, rate of mass transfer, streamlines and isotherms on the flow field have been presented graphically and discussed in details.

5. Heat line analysis for MHD mixed convection flow of nanofluid within a driven cavity containing heat generating block

Parvin, Salma; Siddiqua, Ayesha

2016-07-01

Mixed convective flow and heat transfer characteristics of nanofluid inside a double lid driven cavity with a square heat generating block is analyzed numerically based on heat line approach. The water- alumina nanofluid is chosen as the operational fluid through the enclosure. The governing partial differential equations with proper boundary conditions are solved by Finite Element Method using Galerkin's weighted residual scheme. Calculations are performed for different solid volume fraction (χ) of nanoparticles 0 ≤ χ ≤ 0.15. Results are shown in terms of stream lines, isothermal lines, heat lines, average Nusselt number, average velocity and average temperature. An enhancement in heat transfer rate is observed with the increase of nanoparticles volume fraction.

6. Double diffusive magnetohydrodynamic (MHD) mixed convective slip flow along a radiating moving vertical flat plate with convective boundary condition.

PubMed

Rashidi, Mohammad M; Kavyani, Neda; Abelman, Shirley; Uddin, Mohammed J; Freidoonimehr, Navid

2014-01-01

In this study combined heat and mass transfer by mixed convective flow along a moving vertical flat plate with hydrodynamic slip and thermal convective boundary condition is investigated. Using similarity variables, the governing nonlinear partial differential equations are converted into a system of coupled nonlinear ordinary differential equations. The transformed equations are then solved using a semi-numerical/analytical method called the differential transform method and results are compared with numerical results. Close agreement is found between the present method and the numerical method. Effects of the controlling parameters, including convective heat transfer, magnetic field, buoyancy ratio, hydrodynamic slip, mixed convective, Prandtl number and Schmidt number are investigated on the dimensionless velocity, temperature and concentration profiles. In addition effects of different parameters on the skin friction factor, [Formula: see text], local Nusselt number, [Formula: see text], and local Sherwood number [Formula: see text] are shown and explained through tables.

7. MHD Stagnation Point Flow of Williamson Fluid over a Stretching Cylinder with Variable Thermal Conductivity and Homogeneous/Heterogeneous Reaction

Bilal, M.; Sagheer, M.; Hussain, S.; Mehmood, Y.

2017-06-01

The present study reveals the effect of homogeneous/hetereogeneous reaction on stagnation point flow of Williamson fluid in the presence of magnetohydrodynamics and heat generation/absorption coefficient over a stretching cylinder. Further the effects of variable thermal conductivity and thermal stratification are also considered. The governing partial differential equations are converted to ordinary differential equations with the help of similarity transformation. The system of coupled non-linear ordinary differential equations is then solved by shooting technique. MATLAB shooting code is validated by comparison with the previously published work in limiting case. Results are further strengthened when the present results are compared with MATLAB built-in function bvp4c. Effects of prominent parameters are deliberated graphically for the velocity, temperature and concentration profiles. Skin-friction coefficient and Nusselt number for the different parameters are investigated with the help of tables.

8. Heat and Mass Transfer on MHD Flow of a Viscoelastic Fluid through Porous Media over a Shrinking Sheet.

PubMed

Bhukta, D; Dash, G C; Mishra, S R

2014-01-01

An attempt has been made to study the heat and mass transfer effect in a boundary layer flow through porous medium of an electrically conducting viscoelastic fluid over a shrinking sheet subject to transverse magnetic field in the presence of heat source. Effects of radiation, viscous dissipation, and uniform heat sink on the heat transfer have been considered. The method of solution involves similarity transformation. The coupled nonlinear partial differential equations representing momentum, concentration, and nonhomogenous heat equation are reduced into a set of nonlinear ordinary differential equations. The transformed equations are solved by applying Kummer's function. The exact solution of temperature field is obtained for power-law surface temperature (PST) as well as power-law heat flux (PHF) boundary condition. The interaction of magnetic field is proved to be counterproductive in enhancing velocity and concentration distribution, whereas presence of porous matrix reduces the temperature field at all points.

9. Reduced MHD Equations For Low Aspect Ratio Tokamaks

Callen, J. D.; Hegna, C. C.; Kruger, S. E.

1997-11-01

The usual derivations [1] of reduced MHD equations for describing tokamak plasmas use a large aspect ratio expansion to remove, to lowest order, the compressional Alfven wave response that enforces the axisymmetric ideal MHD (Grad-Shafranov) equilibrium. For very low aspect ratio tokamaks such an approach is invalid, even though [2] the radially localized compressional Alfven waves that enforce ideal MHD equilibrium still have higher frequencies than the shear Alfven waves that appear in reduced MHD descriptions. We are beginning to explore and will discuss a multiple time scale approach that does not explicitly require a large aspect ratio expansion in order to develop a reduced MHD description appropriate for low aspect ratio tokamak plasmas. The relationship of this approach to geometric-properties-based formulations of the ideal MHD energy principle [3] will also be discussed. [1] H.R. Strauss, Phys. Fluids 19, 134 (1976); 20, 1354 (1977). [2] R.D. Hazeltine and J.D. Meiss, Plasma Confinement (Addison-Wesley, Redwood City, CA, 1992), Chapter 7. [3] R.L. Dewar, D.A. Monticello, W.N.-C. Sy, Phys. Fluids 27, 1723 (1984); J.M. Greene, Phys. Plasmas 3, 8(1996).

10. MHD Forced Convective Laminar Boundary Layer Flow from a Convectively Heated Moving Vertical Plate with Radiation and Transpiration Effect

PubMed Central

Uddin, Md. Jashim; Khan, Waqar A.; Ismail, A. I. Md.

2013-01-01

A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to whilst the magnetic field and mass transfer velocity are taken to be proportional to where is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory. PMID:23741295

11. MHD Stagnation-Point Flow of a Carreau Fluid and Heat Transfer in the Presence of Convective Boundary Conditions

PubMed Central

Khan, Masood; Hashim; Alshomrani, Ali Saleh

2016-01-01

In the present investigation we analyze the impact of magnetic field on the stagnation-point flow of a generalized Newtonian Carreau fluid. The convective surface boundary conditions are considered to investigate the thermal boundary layer. The leading partial differential equations of the current problem are altered to a set of ordinary differential equations by picking local similarity transformations. The developed non-linear ordinary differential equations are then numerically integrated via Runge-Kutta Fehlberg method after changing into initial value problems. This investigation explores that the momentum and thermal boundary layers are significantly influenced by various pertinent parameters like the Hartmann number M, velocity shear ratio parameter α, Weissenberg number We, power law index n, Biot number γ and Prandtl number Pr. The analysis further reveals that the fluid velocity as well as the skin friction is raised by the velocity shear ratio parameter. Moreover, strong values of the Hartmann number correspond to thinning of the momentum boundary layer thickness while quite the opposite is true for the thermal boundary layer thickness. Additionally, it is seen that the numerical computations are in splendid consent with previously reported studies. PMID:27322600

12. Effects of partial slip boundary condition and radiation on the heat and mass transfer of MHD-nanofluid flow

Abd Elazem, Nader Y.; Ebaid, Abdelhalim

2017-07-01

In this paper, the effect of partial slip boundary condition on the heat and mass transfer of the Cu-water and Ag-water nanofluids over a stretching sheet in the presence of magnetic field and radiation. Such partial slip boundary condition has attracted much attention due to its wide applications in industry and chemical engineering. The flow is basically governing by a system of partial differential equations which are reduced to a system of ordinary differential equations. This system has been exactly solved, where exact analytical expression has been obtained for the fluid velocity in terms of exponential function, while the temperature distribution, and the nanoparticles concentration are expressed in terms of the generalized incomplete gamma function. In addition, explicit formulae are also derived from the rates of heat transfer and mass transfer. The effects of the permanent parameters on the skin friction, heat transfer coefficient, rate of mass transfer, velocity, the temperature profile, and concentration profile have been discussed through tables and graphs.

13. MHD Stagnation-Point Flow of a Carreau Fluid and Heat Transfer in the Presence of Convective Boundary Conditions.

PubMed

Khan, Masood; Hashim; Alshomrani, Ali Saleh

2016-01-01

In the present investigation we analyze the impact of magnetic field on the stagnation-point flow of a generalized Newtonian Carreau fluid. The convective surface boundary conditions are considered to investigate the thermal boundary layer. The leading partial differential equations of the current problem are altered to a set of ordinary differential equations by picking local similarity transformations. The developed non-linear ordinary differential equations are then numerically integrated via Runge-Kutta Fehlberg method after changing into initial value problems. This investigation explores that the momentum and thermal boundary layers are significantly influenced by various pertinent parameters like the Hartmann number M, velocity shear ratio parameter α, Weissenberg number We, power law index n, Biot number γ and Prandtl number Pr. The analysis further reveals that the fluid velocity as well as the skin friction is raised by the velocity shear ratio parameter. Moreover, strong values of the Hartmann number correspond to thinning of the momentum boundary layer thickness while quite the opposite is true for the thermal boundary layer thickness. Additionally, it is seen that the numerical computations are in splendid consent with previously reported studies.

14. MHD Natural Convection Flow of Casson Nanofluid over Nonlinearly Stretching Sheet Through Porous Medium with Chemical Reaction and Thermal Radiation

Ullah, Imran; Khan, Ilyas; Shafie, Sharidan

2016-11-01

In the present work, the effects of chemical reaction on hydromagnetic natural convection flow of Casson nanofluid induced due to nonlinearly stretching sheet immersed in a porous medium under the influence of thermal radiation and convective boundary condition are performed numerically. Moreover, the effects of velocity slip at stretching sheet wall are also examined in this study. The highly nonlinear-coupled governing equations are converted to nonlinear ordinary differential equations via similarity transformations. The transformed governing equations are then solved numerically using the Keller box method and graphical results for velocity, temperature, and nanoparticle concentration as well as wall shear stress, heat, and mass transfer rate are achieved through MATLAB software. Numerical results for the wall shear stress and heat transfer rate are presented in tabular form and compared with previously published work. Comparison reveals that the results are in good agreement. Findings of this work demonstrate that Casson fluids are better to control the temperature and nanoparticle concentration as compared to Newtonian fluid when the sheet is stretched in a nonlinear way. Also, the presence of suspended nanoparticles effectively promotes the heat transfer mechanism in the base fluid.

15. MHD forced convective laminar boundary layer flow from a convectively heated moving vertical plate with radiation and transpiration effect.

PubMed

Uddin, Md Jashim; Khan, Waqar A; Ismail, A I Md

2013-01-01

A two-dimensional steady forced convective flow of a Newtonian fluid past a convectively heated permeable vertically moving plate in the presence of a variable magnetic field and radiation effect has been investigated numerically. The plate moves either in assisting or opposing direction to the free stream. The plate and free stream velocities are considered to be proportional to x(m) whilst the magnetic field and mass transfer velocity are taken to be proportional to x((m-1)/2) where x is the distance along the plate from the leading edge of the plate. Instead of using existing similarity transformations, we use a linear group of transformations to transform the governing equations into similarity equations with relevant boundary conditions. Numerical solutions of the similarity equations are presented to show the effects of the controlling parameters on the dimensionless velocity, temperature and concentration profiles as well as on the friction factor, rate of heat and mass transfer. It is found that the rate of heat transfer elevates with the mass transfer velocity, convective heat transfer, Prandtl number, velocity ratio and the magnetic field parameters. It is also found that the rate of mass transfer enhances with the mass transfer velocity, velocity ratio, power law index and the Schmidt number, whilst it suppresses with the magnetic field parameter. Our results are compared with the results existing in the open literature. The comparisons are satisfactory.

16. MHD Natural Convection Flow of Casson Nanofluid over Nonlinearly Stretching Sheet Through Porous Medium with Chemical Reaction and Thermal Radiation.

PubMed

Ullah, Imran; Khan, Ilyas; Shafie, Sharidan

2016-12-01

In the present work, the effects of chemical reaction on hydromagnetic natural convection flow of Casson nanofluid induced due to nonlinearly stretching sheet immersed in a porous medium under the influence of thermal radiation and convective boundary condition are performed numerically. Moreover, the effects of velocity slip at stretching sheet wall are also examined in this study. The highly nonlinear-coupled governing equations are converted to nonlinear ordinary differential equations via similarity transformations. The transformed governing equations are then solved numerically using the Keller box method and graphical results for velocity, temperature, and nanoparticle concentration as well as wall shear stress, heat, and mass transfer rate are achieved through MATLAB software. Numerical results for the wall shear stress and heat transfer rate are presented in tabular form and compared with previously published work. Comparison reveals that the results are in good agreement. Findings of this work demonstrate that Casson fluids are better to control the temperature and nanoparticle concentration as compared to Newtonian fluid when the sheet is stretched in a nonlinear way. Also, the presence of suspended nanoparticles effectively promotes the heat transfer mechanism in the base fluid.

17. Nonlinear Dynamics of Non-uniform Current-Vortex Sheets in Magnetohydrodynamic Flows

Matsuoka, C.; Nishihara, K.; Sano, T.

2017-04-01

A theoretical model is proposed to describe fully nonlinear dynamics of interfaces in two-dimensional MHD flows based on an idea of non-uniform current-vortex sheet. Application of vortex sheet model to MHD flows has a crucial difficulty because of non-conservative nature of magnetic tension. However, it is shown that when a magnetic field is initially parallel to an interface, the concept of vortex sheet can be extended to MHD flows (current-vortex sheet). Two-dimensional MHD flows are then described only by a one-dimensional Lagrange parameter on the sheet. It is also shown that bulk magnetic field and velocity can be calculated from their values on the sheet. The model is tested by MHD Richtmyer-Meshkov instability with sinusoidal vortex sheet strength. Two-dimensional ideal MHD simulations show that the nonlinear dynamics of a shocked interface with density stratification agrees fairly well with that for its corresponding potential flow. Numerical solutions of the model reproduce properly the results of the ideal MHD simulations, such as the roll-up of spike, exponential growth of magnetic field, and its saturation and oscillation. Nonlinear evolution of the interface is found to be determined by the Alfvén and Atwood numbers. Some of their dependence on the sheet dynamics and magnetic field amplification are discussed. It is shown by the model that the magnetic field amplification occurs locally associated with the nonlinear dynamics of the current-vortex sheet. We expect that our model can be applicable to a wide variety of MHD shear flows.

18. Field topologies in ideal and near-ideal magnetohydrodynamics and vortex dynamics

Low, B. C.

2015-01-01

Magnetic field topology frozen in ideal magnetohydrodynamics (MHD) and its breakage in near-ideal MHD are reviewed in two parts, clarifying and expanding basic concepts. The first part gives a physically complete description of the frozen field topology derived from magnetic flux conservation as the fundamental property, treating four conceptually related topics: Eulerian and Lagrangian descriptions of three dimensional (3D) MHD, Chandrasekhar-Kendall and Euler-potential field representations, magnetic helicity, and inviscid vortex dynamics as a fluid system in physical contrast to ideal MHD. A corollary of these developments clarifies the challenge of achieving a high degree of the frozen-in condition in numerical MHD. The second part treats field-topology breakage centered around the Parker Magnetostatic Theorem on a general incompatibility of a continuous magnetic field with the dual demand of force-free equilibrium and an arbitrarily prescribed, 3D field topology. Preserving field topology as a global constraint readily results in formation of tangential magnetic discontinuities, or, equivalently, electric current-sheets of zero thickness. A similar incompatibility is present in the steady force-thermal balance of a heated radiating fluid subject to an anisotropic thermal flux conducted strictly along its frozen-in magnetic field in the low- β limit. In a weakly resistive fluid the thinning of current sheets by these general incompatibilities inevitably results in sheet dissipation, resistive heating and topological changes in the field notwithstanding the small resistivity. Strong Faraday induction drives but also macroscopically limits this mode of energy dissipation, trapping or storing free energy in self-organized ideal-MHD structures. This property of MHD turbulence captured by the Taylor hypothesis is reviewed in relation to the Sun's corona, calling for a basic quantitative description of the breakdown of flux conservation in the low-resistivity limit

19. Visco-elastic effects with simultaneous thermal and mass diffusion in MHD free convection flow near an oscillating plate in the slip flow regime

Das, Bandita; Choudhury, Rita

2016-06-01

The present study analyzes the influence of visco-elastic flow of fluid through a porous medium bounded by an oscillating porous plate with heat source in the slip flow regime. Effects of heat transfer, mass transfer and chemical reaction are also taken into account. The porous plate is subjected to a transverse suction velocity. The dimensionless governing equations of the problem are solved by regular perturbation technique. The analytical expressions for the velocity, temperature, concentration, and Shearing stress have been obtained and illustrated graphically for different values of physical parameters involved in the problem. The investigation reveals that the visco-elastic fluid has significant effects on the considered flow field in comparison with Newtonian fluid flow phenomenon.

20. MHD simulations of Earth's bow shock at low Mach numbers: Standoff distances

Cairns, Iver H.; Lyon, J. G.

1995-09-01

Global, three-dimensional, ideal MHD simulations of Earth's bow shock are reported for low Alfven Mach numbers MA and quasi-perpendicular magnetic field orientations. The simulations use a hard, infinitely conducting magnetopause obstacle, with axisymmetric three-dimensional location given by a scaled standard model, to directly address previous gasdynamic (GD) and field-aligned MHD (FA-MHD) work. Tests of the simulated shocks' density jumps X for 1.4<~MA<~10 and the high MA shock location, and reproduction of the GD relation between magnetosheath thickness and X for quasi-gasdynamic MHD runs with MA>>MS, confirm that the MHD code is working correctly. The MHD simulations show the standoff distance as increasing monotonically with decreasing MA. Significantly larger as are found at low MA than predicted by GD and phenomenological MHD models and FA-MHD simulations, as required qualitatively by observations. The GD and FA-MHD predictions err qualitatively, predicting either constant or decreasing as with decreasing MA. This qualitative difference between quasiperpendicular MHD and FA-MHD simulations is direct evidence for as depending on the magnetic field orientation θ. The enhancement factor over the phenomenological MHD predictions at MA~2.4 agrees quantitatively with one observational estimate. A linear relationship is found between the magnetosheath thickness and X, modified both quantitatively and intrinsically by MHD effects from the GD result. The MHD and GD results agree in the high MA limit. An MHD theory is developed for as, restricted to sufficiently perpendicular θ and high sonic Mach numbers MS. It explains the simulation results with excellent accuracy. Observational and further simulation testing of this MHD theory, and of its predicted MA, θ, and MS effects, is desirable.

1. Numerical analysis of plasma flows in an MPC duct with diverter

NASA Technical Reports Server (NTRS)

1983-01-01

The two-dimensional MHD-flow of the ideal plasma in a channel of the magnetoplasma compressor (MPC) with an axial hole in the central electrode (divertor) is numerically simulated. The steady-state regime of the flow is obtained. The influence of finite and periodical density perturbation at the entry of the channel on the compressional flow properties is investigated. It is shown that the flow is stable under such perturbations.

2. An MHD simulation study of the poloidal mode field line resonance in the Earth's dipole magnetosphere

NASA Technical Reports Server (NTRS)

Ding, D. Q.; Denton, . E.; Hudson, M. K.; Lysak, R. L.

1995-01-01

The poloidal mode field line resonance in the Earth's dipole magnetic field is investigated using cold plasma ideal MHD simulations in dipole geometry. In order to excite the poloidal mode resonance, we use either an initial or a continuous velocity perturbation to drive the system. The perturbation is localized at magnetic shell L = 7 with plasma flow in the radial direction (electric field component in the azimuthal direction). It is found that with the initial perturbation alone, no polodial mode resonance can be obtained and the initially localized perturbation spreads out across all magnetic L shells. With the continuous perturbation, oscillating near the poloidal resonance frequency, a global-scale poloidal cavity mode can be obtained. For the first time, a localized guided poloidal mode resonance is obtained when a radial component of electric field is added to the initial perturbation such that the curl of the electric field is everywhere perpendicular to the background dipole magnetic field. During the localized poloidal resonance, plasma vortices parallel/antiparallel to the background dipole magnetic field B(sub 0). This circular flow, elongated radially, results in twisting of magnetic field flux tubes, which, in turn, leads to the slowdown of the circular plasma flow and reversal of the plasma vortices. The energy associated with the localized poloidal resonance is conserved as it shifts back and forth between the oscillating plasma vortices and the alternately twisted magnetic flux tubes. In the simulations the eigenfunctions associated with the localized poloidal resonance are grid-scale singular functions. This result indicates that ideal MHD is inadequate to describe the underlying problem and nonideal MHD effects are needed for mode broadening.

3. MHD Ballooning Instability in the Plasma Sheet

SciTech Connect

C.Z. Cheng; S. Zaharia

2003-10-20

Based on the ideal-MHD model the stability of ballooning modes is investigated by employing realistic 3D magnetospheric equilibria, in particular for the substorm growth phase. Previous MHD ballooning stability calculations making use of approximations on the plasma compressibility can give rise to erroneous conclusions. Our results show that without making approximations on the plasma compressibility the MHD ballooning modes are unstable for the entire plasma sheet where beta (sub)eq is greater than or equal to 1, and the most unstable modes are located in the strong cross-tail current sheet region in the near-Earth plasma sheet, which maps to the initial brightening location of the breakup arc in the ionosphere. However, the MHD beq threshold is too low in comparison with observations by AMPTE/CCE at X = -(8 - 9)R(sub)E, which show that a low-frequency instability is excited only when beq increases over 50. The difficulty is mitigated by considering the kinetic effects of ion gyrorad ii and trapped electron dynamics, which can greatly increase the stabilizing effects of field line tension and thus enhance the beta(sub)eq threshold [Cheng and Lui, 1998]. The consequence is to reduce the equatorial region of the unstable ballooning modes to the strong cross-tail current sheet region where the free energy associated with the plasma pressure gradient and magnetic field curvature is maximum.

4. Broken Ergodicity in MHD Turbulence in a Spherical Domain

NASA Technical Reports Server (NTRS)

Shebalin, John V.; wang, Yifan

2011-01-01

Broken ergodicity (BE) occurs in Fourier method numerical simulations of ideal, homogeneous, incompressible magnetohydrodynamic (MHD) turbulence. Although naive statistical theory predicts that Fourier coefficients of fluid velocity and magnetic field are zero-mean random variables, numerical simulations clearly show that low-wave-number coefficients have non-zero mean values that can be very large compared to the associated standard deviation. In other words, large-scale coherent structure (i.e., broken ergodicity) in homogeneous MHD turbulence can spontaneously grow out of random initial conditions. Eigenanalysis of the modal covariance matrices in the probability density functions of ideal statistical theory leads to a theoretical explanation of observed BE in homogeneous MHD turbulence. Since dissipation is minimal at the largest scales, BE is also relevant for resistive magnetofluids, as evidenced in numerical simulations. Here, we move beyond model magnetofluids confined by periodic boxes to examine BE in rotating magnetofluids in spherical domains using spherical harmonic expansions along with suitable boundary conditions. We present theoretical results for 3-D and 2-D spherical models and also present computational results from dynamical simulations of 2-D MHD turbulence on a rotating spherical surface. MHD turbulence on a 2-D sphere is affected by Coriolus forces, while MHD turbulence on a 2-D plane is not, so that 2-D spherical models are a useful (and simpler) intermediate stage on the path to understanding the much more complex 3-D spherical case.

5. The role of the electron convection term for the parallel electric field and electron acceleration in MHD simulations

SciTech Connect

Matsuda, K.; Terada, N.; Katoh, Y.; Misawa, H.

2011-08-15

There has been a great concern about the origin of the parallel electric field in the frame of fluid equations in the auroral acceleration region. This paper proposes a new method to simulate magnetohydrodynamic (MHD) equations that include the electron convection term and shows its efficiency with simulation results in one dimension. We apply a third-order semi-discrete central scheme to investigate the characteristics of the electron convection term including its nonlinearity. At a steady state discontinuity, the sum of the ion and electron convection terms balances with the ion pressure gradient. We find that the electron convection term works like the gradient of the negative pressure and reduces the ion sound speed or amplifies the sound mode when parallel current flows. The electron convection term enables us to describe a situation in which a parallel electric field and parallel electron acceleration coexist, which is impossible for ideal or resistive MHD.

6. MHD-to-PIC transition for modeling of conduction and opening in a plasma opening switch

Schumer, J. W.

2001-06-01

The plasma opening switch (POS) is a critical element of some inductive-energy-storage pulsed-power generators. Detailed understanding of plasma redistribution and thinning during the POS conduction phase can be gained through magnetohydrodynamic fluid (MHD) simulations. As space-charge separation and kinetic effects become important late in the conduction phase (beginning of the opening phase), MHD methods become invalid and particle-in-cell (PIC) methods should be used. In this article, the applicability of MHD techniques is extended into PIC-like regimes by including non-ideal MHD phenomena such as the Hall effect and resistivity. The feasibility of the PIC technique is likewise extended into high-density, low-temperature MHD-like regimes by using a novel numerical cooling algorithm. At an appropriate time, an MHD-to-PIC transition must be accomplished in order to accurately simulate the POS opening phase. The mechanics for converting MHD (MACH2) output into PIC (MAGIC2d) input are introduced, as are the transition criteria determining when to perform this conversion. To establish these transition criteria, side-by-side MHD and PIC simulations are presented and compared. These separate simulations are then complemented by a proof-of-principle MHD-to-PIC transition, thereby demonstrating this MHD-to-PIC technique as a potentially viable tool for the simulation of POS plasmas. Practical limitations of the MHD-to-PIC transition method and applicability of the transition criteria to hybrid fluid-kinetic simulations are discussed.

7. Performance of Combustion Disk MHD Generators.

Jenkins, Marion Karl

Results of an experimental and analytical study of radial flow disk magnetohydrodynamic generators are presented. The overall goal of the study was to investigate disk generators for application to baseload power generation. The experimental work consisted of a series of combustion-driven steady state experiments with a hot-wall channel operated in a superconducting magnet. Channel operating characteristics were examined under a variety of plasma temperatures, velocities, and magnetic field strengths. The channel was operated continuously in tests lasting several hours, with plasma temperatures ranging up to 2800(DEGREES)K and magnetic fields up to 5.5 Tesla. Voltage -current characteristics showed the expected linear behavior, and the expected dependence on channel operating conditions such as magnetic field strength and velocity was observed. Plasma conditions were inferred from the electrical conductivity, which was measured parallel to the applied magnetic field in the channel inlet nozzle. Steady voltage and current distributions on the segmented ring cathode were fairly uniform, with the largest deviations occurring as expected near open and short circuit conditions. Statistical analysis of fluctuating voltage signals showed strong positive correlations between probes mounted at different locations within the channel, indicating the absence of spoke-type plasma nonuniformities that have been observed in shock tube-driven disk experiments. Measured values of voltages and currents were less than expected, indicating the presence of substantial loss mechanisms in the channel. These losses were postulated to be caused by insulator wall current leakage and electrode voltage drop. Radial voltage profiles and open circuit voltage measurements verified the presence of these effects. An ideal homogeneous plasma model was developed to account for the losses, and values obtained for the loss terms are in agreement with relevant linear generator results. Limiting values

8. Flow-induced vibratory response of idealized versus magnetic resonance imaging-based synthetic vocal fold models

PubMed Central

Pickup, Brian A.; Thomson, Scott L.

2010-01-01

Recent vocal fold vibration studies have used models defined using idealized geometry. Although these models exhibit important similarities with human vocal fold vibration, some aspects of their motion are less than realistic. In this report it is demonstrated that more realistic motion may be obtained when using geometry derived from magnetic resonance imaging (MRI) data. The dynamic response of both idealized and MRI-based synthetic vocal fold models are presented. MRI-based model improvements include evidence of mucosal wave-like motion and less vertical movement. Limitations of the MRI-based model are discussed and suggestions for further synthetic model development are offered. PMID:20815428

9. Thermal-diffusion and MHD for Soret and Dufour’s effects on Hiemenz flow and mass transfer of fluid flow through porous medium onto a stretching surface

Abdel-Rahman, Gamal M.

2010-06-01

In this paper, the thermal-diffusion and magnetic field effects on a stagnation point flowing over a flat stretching surface have been obtained and studied numerically with the variation of the viscosity under the Soret and Dufour's effects. The governing continuity, momentum, energy and concentration equations are converted into a system of non-linear ordinary differential equations by means of similarity transformation. The resulting system of coupled non-linear ordinary differential equations is solved numerically. Numerical results were presented for velocity, temperature and concentration profiles for different parameters of the problem as radiation parameter, magnetic field parameter, porous medium parameter, endothermic chemical reaction, heat source parameter, stretching parameter, the Soret and Dufour number and other. Also the effects of the pertinent parameters on the skin friction, the rate of heat and mass transfer are obtained and discussed numerically and illustrated graphically.

10. Similarity solution for the flow behind a shock wave in a non-ideal gas with heat conduction and radiation heat-flux in magnetogasdynamics

Nath, G.; Vishwakarma, J. P.

2014-05-01

The propagation of a spherical (or cylindrical) shock wave in a non-ideal gas with heat conduction and radiation heat-flux, in the presence of a spacially decreasing azimuthal magnetic field, driven out by a moving piston is investigated. The heat conduction is expressed in terms of Fourier's law and the radiation is considered to be of the diffusion type for an optically thick grey gas model. The thermal conductivity K and the absorption coefficient αR are assumed to vary with temperature and density. The gas is assumed to have infinite electrical conductivity and to obey a simplified van der Waals equation of state. The shock wave moves with variable velocity and the total energy of the wave is non-constant. Similarity solutions are obtained for the flow-field behind the shock and the effects of variation of the heat transfer parameters, the parameter of the non-idealness of the gas, both, decreases the compressibility of the gas and hence there is a decrease in the shock strength. Further, it is investigated that with an increase in the parameters of radiative and conductive heat transfer the tendency of formation of maxima in the distributions of heat flux, density and isothermal speed of sound decreases. The pressure and density vanish at the inner surface (piston) and hence a vacuum is form at the center of symmetry. The shock waves in conducting non-ideal gas with conductive and radiative heat fluxes can be important for description of shocks in supernova explosions, in the study of central part of star burst galaxies, nuclear explosion, chemical detonation, rupture of a pressurized vessels, in the analysis of data from exploding wire experiments, and cylindrically symmetric hypersonic flow problems associated with meteors or reentry vehicles, etc. The findings of the present works provided a clear picture of whether and how the non-idealness parameter, conductive and radiative heat transfer parameters and the magnetic field affect the flow behind the shock

11. Coherent Eigenmodes in Homogeneous MHD Turbulence

NASA Technical Reports Server (NTRS)

Shebalin, John V.

2010-01-01

The statistical mechanics of Fourier models of ideal, homogeneous, incompressible magnetohydrodynamic (MHD) turbulence is discussed, along with their relevance for dissipative magnetofluids. Although statistical theory predicts that Fourier coefficients of fluid velocity and magnetic field are zero-mean random variables, numerical simulations clearly show that certain coefficients have a non-zero mean value that can be very large compared to the associated standard deviation, i.e., we have coherent structure. We use eigenanalysis of the modal covariance matrices in the probability density function to explain this phenomena in terms of `broken ergodicity', which is defined to occur when dynamical behavior does not match ensemble predictions on very long time-scales. We provide examples from 2-D and 3-D magnetohydrodynamic simulations of homogeneous turbulence, and show new results from long-time simulations of MHD turbulence with and without a mean magnetic field

12. MHD generator electrode development

Retallick, F. D.; Dietrick, D. L.; Lloyd, I.; Rossing, B. R.; Smith, R.

1981-08-01

Metallurgical and engineering understanding of cold metallic electrode alternatives to the continued use of platinum as an anode clad material is discussed. The results of evaluating materials for MHD electrodes through use of a laboratory electrochemical and arc test are presented. Results for standard available materials as well as for some specially fabricated ones are presented. The development of a high temperature (11000 C to 14000 C) electrochemical test is outlined. Initial operation of the Westinghouse Electrode Systems Test Facility (WESTF), since major modification to include a magnet, is reported for a test section designed to operate as a small scale MHD generator and for test sections designed for the purpose of materials test evaluation in the operating MHD plasma environment.

13. Featured Image: Tests of an MHD Code

Kohler, Susanna

2016-09-01

Creating the codes that are used to numerically model astrophysical systems takes a lot of work and a lot of testing! A new, publicly available moving-mesh magnetohydrodynamics (MHD) code, DISCO, is designed to model 2D and 3D orbital fluid motion, such as that of astrophysical disks. In a recent article, DISCO creator Paul Duffell (University of California, Berkeley) presents the code and the outcomes from a series of standard tests of DISCOs stability, accuracy, and scalability.From left to right and top to bottom, the test outputs shown above are: a cylindrical Kelvin-Helmholtz flow (showing off DISCOs numerical grid in 2D), a passive scalar in a smooth vortex (can DISCO maintain contact discontinuities?), a global look at the cylindrical Kelvin-Helmholtz flow, a Jupiter-mass planet opening a gap in a viscous disk, an MHD flywheel (a test of DISCOs stability), an MHD explosion revealing shock structures, an MHD rotor (a more challenging version of the explosion), a Flock 3D MRI test (can DISCO study linear growth of the magnetorotational instability in disks?), and a nonlinear 3D MRI test.Check out the gif below for a closer look at each of these images, or follow the link to the original article to see even more!CitationPaul C. Duffell 2016 ApJS 226 2. doi:10.3847/0067-0049/226/1/2

14. Magnetohydrodynamics (MHD) program evaluation

SciTech Connect

Not Available

1983-05-01

Conclusions and Recommendations: (1) Progress has been made in performance testing of virtually every critical MHD component and subsystem, except for seed regeneration. (2) No insurmountable technical barriers have been identified; however, the component tests have for the most part been of short duration and, in most instances, were conducted under simulated coal-fired conditions. Long duration, coal-fired integrated tests of the MHD power train and of the HRSR subsystem are required to demonstrate system operability and durability. (3) It would appear most appropriate that the first series of complete power train and HRSR tests be conducted at the 50 MW/sub t/ level. The major objectives of these tests should be to verify predicted performance and to show system operability and durability for a period of at least 2000 hours. (4) Assuming successful 50 MW/sub t/ duration tests, a 150 MW/sub t/ completely integrated (topping and bottoming cycles) utility demonstration test is then suggested (3:1 scale-up). (5) The final development step would involve the fabrication of a commercial size plant at a power level of 500 MW/sub t/ or greater. (6) The ultimate adoption of MHD as a means for electric power generation will not be solely determined by its technical performance; the economic climate and projections at the time the technology is mature will strongly influence utility decisions. (7) Estimated capital costs of early commercial MHD plants seem to range from 10% to 30% greater than those for PCF plants with scrubbers. However, because of the higher inherent efficiency of MHD relative to PCF plants (50% vs 35%), the cost of electric power (COE) from an MHD system can nevertheless be competitive for an appropriately broad range of economic scenarios. (8) Finally, it is recognized that a major investment will be necessary to bring the technology to a state of commercial readiness.

15. MHD simulation of transition process from the magneto-rotational instability to magnetic turbulence by using a high-order MHD simulation scheme

Hirai, K.; Katoh, Y.; Terada, N.; Kawai, S.

2016-12-01

In accretion disks, magneto-rotational instability (MRI; Balbus & Hawley, 1991) makes the disk gas in the magnetic turbulent state and drives efficient mass accretion into a central star. MRI drives turbulence through the evolution of the parasitic instability (PI; Goodman & Xu, 1994), which is related to both Kelvin-Helmholtz (K-H) instability and magnetic reconnection. The wave number vector of PI is strongly affected by both magnetic diffusivity and fluid viscosity (Pessah, 2010). This fact makes MHD simulation of MRI difficult, because we need to employ the numerical diffusivity for treating discontinuities in compressible MHD simulation schemes. Therefore, it is necessary to use an MHD scheme that has both high-order accuracy so as to resolve MRI driven turbulence and small numerical diffusivity enough to treat discontinuities. We have originally developed an MHD code by employing the scheme proposed by Kawai (2013). This scheme focuses on resolving turbulence accurately by using a high-order compact difference scheme (Lele, 1992), and meanwhile, the scheme treats discontinuities by using the localized artificial diffusivity method (Kawai, 2013). Our code also employs the pipeline algorithm (Matsuura & Kato, 2007) for MPI parallelization without diminishing the accuracy of the compact difference scheme. We carry out a 3-dimensional ideal MHD simulation with a net vertical magnetic field in the local shearing box disk model. We use 256x256x128 grids. Simulation results show that the spatially averaged turbulent stress induced by MRI linearly grows until around 2.8 orbital periods, and decreases after the saturation. We confirm the strong enhancement of the K-H mode PI at a timing just before the saturation, identified by the enhancement of its anisotropic wavenumber spectra in the 2-dimensional wavenumber space. The wave number of the maximum growth of PI reproduced in the simulation result is larger than the linear analysis. This discrepancy is explained by

16. Validation of the linear ideal magnetohydrodynamic model of three-dimensional tokamak equilibria

SciTech Connect

Lanctot, M. J.; Reimerdes, H.; Garofalo, A. M.; Chu, M. S.; Strait, E. J.; Jackson, G. L.; La Haye, R. J.; Osborne, T. H.; Schaffer, M. J.; Liu, Y. Q.

2010-03-15

The first quantitative comparison of linear ideal magnetohydrodynamic (MHD) theory with external magnetic measurements of the nonaxisymmetric plasma perturbation driven by external long-wavelength magnetic fields in high-temperature tokamak plasmas is presented. The comparison yields good (within 20%) agreement for plasma pressures up to approx75% of the ideal stability limit calculated without a conducting wall. For higher plasma pressures, the ideal MHD model tends to overestimate the perturbed field indicating the increasing importance of stabilizing nonideal effects.

17. Disk MHD generator study

NASA Technical Reports Server (NTRS)

Retallick, F. D.

1980-01-01

Directly-fired, separately-fired, and oxygen-augmented MHD power plants incorporating a disk geometry for the MHD generator were studied. The base parameters defined for four near-optimum-performance MHD steam power systems of various types are presented. The finally selected systems consisted of (1) two directly fired cases, one at 1920 K (2996F) preheat and the other at 1650 K (2500 F) preheat, (2) a separately-fired case where the air is preheated to the same level as the higher temperature directly-fired cases, and (3) an oxygen augmented case with the same generator inlet temperature of 2839 (4650F) as the high temperature directly-fired and separately-fired cases. Supersonic Mach numbers at the generator inlet, gas inlet swirl, and constant Hall field operation were specified based on disk generator optimization. System pressures were based on optimization of MHD net power. Supercritical reheat stream plants were used in all cases. Open and closed cycle component costs are summarized and compared.

18. Application of rank-ordered multifractal analysis (ROMA) to intermittent fluctuations in 3D turbulent flows, 2D MHD simulation and solar wind data

Wu, C.; Chang, T.

2010-12-01

A new method in describing the multifractal characteristics of intermittent events was introduced by Cheng and Wu [Chang T. and Wu C.C., Physical Rev, E77, 045401(R), 2008]. The procedure provides a natural connection between the rank-ordered spectrum and the idea of one-parameter scaling for monofractals. This technique has been demonstrated using results obtained from a 2D MHD simulation. It has also been successfully applied to in-situ solar wind observations [Chang T., Wu, C.C. and Podesta, J., AIP Conf Proc. 1039, 75, 2008], and the broadband electric field oscillations from the auroral zone [Tam, S.W.Y. et al., Physical Rev, E81, 036414, 2010]. We take the next step in this procedure. By using the ROMA spectra and the scaled probability distribution functions (PDFs), raw PDFs can be calculated, which can be compared directly with PDFs from observations or simulation results. In addition to 2D MHD simulation results and in-situ solar wind observation, we show clearly using the ROMA analysis the multifractal character of the 3D fluid simulation data obtained from the JHU turbulence database cluster at http://turbulence.pha.jhu.edu. In particular, we show the scaling of the non-symmetrical PDF for the parallel-velocity fluctuations of this 3D fluid data.

19. Large eddy simulation of the unsteady flow-field in an idealized human mouth-throat configuration.

PubMed

Cui, X G; Gutheil, E

2011-11-10

The present study concerns the simulation and analysis of the flow field in the upper human respiratory system in order to gain an improved understanding of the complex flow field with respect to the process affecting drug delivery for medical treatment of the human air system. For this purpose, large eddy simulation (LES) is chosen because of its powerful performance in the transitional range of laminar and turbulent flow fields. The average gas velocity in a constricted tube is compared with experimental data (Ahmed and Giddens, 1983) and numerical data from Reynolds-averaged Navier-Stokes (RANS) equations coupled with low Reynolds number (LRN) κ-ω model (Zhang and Kleinstreuer, 2003) and LRN shear-stress transport κ-ω model (Jayaraju et al., 2007), for model validation. The present study emphasizes on the instantaneous flow field, where the simulations capture different scales of secondary vortices in different flow zones including recirculation zones, the laryngeal jet zone, the mixing zone, and the wall shear layer. It is observed that the laryngeal jet tail breaks up, and the unsteady motion of laryngeal jet is coupled with the unsteady distribution of secondary vortices in the jet boundary. The present results show that it is essential to study the unsteady flow field since it strongly affects the particle flow in the human upper respiratory system associated with drug delivery for medical treatment.

20. Dynamo action in dissipative, forced, rotating MHD turbulence

Shebalin, John V.

2016-06-01

Magnetohydrodynamic (MHD) turbulence is an inherent feature of large-scale, energetic astrophysical and geophysical magnetofluids. In general, these are rotating and are energized through buoyancy and shear, while viscosity and resistivity provide a means of dissipation of kinetic and magnetic energy. Studies of unforced, rotating, ideal (i.e., non-dissipative) MHD turbulence have produced interesting results, but it is important to determine how these results are affected by dissipation and forcing. Here, we extend our previous work and examine dissipative, forced, and rotating MHD turbulence. Incompressibility is assumed, and finite Fourier series represent turbulent velocity and magnetic field on a 643 grid. Forcing occurs at an intermediate wave number by a method that keeps total energy relatively constant and allows for injection of kinetic and magnetic helicity. We find that 3-D energy spectra are asymmetric when forcing is present. We also find that dynamo action occurs when forcing has either kinetic or magnetic helicity, with magnetic helicity injection being more important. In forced, dissipative MHD turbulence, the dynamo manifests itself as a large-scale coherent structure that is similar to that seen in the ideal case. These results imply that MHD turbulence, per se, may play a fundamental role in the creation and maintenance of large-scale (i.e., dipolar) stellar and planetary magnetic fields.

1. Dynamo action in dissipative, forced, rotating MHD turbulence

SciTech Connect

Shebalin, John V.

2016-06-15

Magnetohydrodynamic (MHD) turbulence is an inherent feature of large-scale, energetic astrophysical and geophysical magnetofluids. In general, these are rotating and are energized through buoyancy and shear, while viscosity and resistivity provide a means of dissipation of kinetic and magnetic energy. Studies of unforced, rotating, ideal (i.e., non-dissipative) MHD turbulence have produced interesting results, but it is important to determine how these results are affected by dissipation and forcing. Here, we extend our previous work and examine dissipative, forced, and rotating MHD turbulence. Incompressibility is assumed, and finite Fourier series represent turbulent velocity and magnetic field on a 64{sup 3} grid. Forcing occurs at an intermediate wave number by a method that keeps total energy relatively constant and allows for injection of kinetic and magnetic helicity. We find that 3-D energy spectra are asymmetric when forcing is present. We also find that dynamo action occurs when forcing has either kinetic or magnetic helicity, with magnetic helicity injection being more important. In forced, dissipative MHD turbulence, the dynamo manifests itself as a large-scale coherent structure that is similar to that seen in the ideal case. These results imply that MHD turbulence, per se, may play a fundamental role in the creation and maintenance of large-scale (i.e., dipolar) stellar and planetary magnetic fields.

2. Finite-Difference Solution for Laminar or Turbulent Boundary Layer Flow over Axisymmetric Bodies with Ideal Gas, CF4, or Equilibrium Air Chemistry

NASA Technical Reports Server (NTRS)

Hamilton, H. Harris, II; Millman, Daniel R.; Greendyke, Robert B.

1992-01-01

A computer code was developed that uses an implicit finite-difference technique to solve nonsimilar, axisymmetric boundary layer equations for both laminar and turbulent flow. The code can treat ideal gases, air in chemical equilibrium, and carbon tetrafluoride (CF4), which is a useful gas for hypersonic blunt-body simulations. This is the only known boundary layer code that can treat CF4. Comparisons with experimental data have demonstrated that accurate solutions are obtained. The method should prove useful as an analysis tool for comparing calculations with wind tunnel experiments and for making calculations about flight vehicles where equilibrium air chemistry assumptions are valid.

3. Ideal ballooning modes in axisymmetric mirror machines

SciTech Connect

Baldwin, D.E.; McNamara, B.; Willmann, P.

1980-12-15

A simple code is described that finds marginally stable (..omega../sup 2/ = 0) ballooning-type MHD modes, localized about a field line in an axisymmetric, open-ended, plasma confinement device. The equations are based on a lower bound for the perturbed energy delta W, derived by W. Newcomb from the ideal MHD energy principle, and are cast in the form of a Ricatti equation for the first derivative of the eigenfunction, with the open boundary conditions that this derivative vanish at the plasma boundary down each field line. The input to the code is the two-dimensional shape of a field line, the field strength B(s), and parameters to define pressure profiles throughout the system. The objective is to find the highest plasma pressures for which the given line is MHD-stable.

4. Analytical estimates of turbulent MHD transport coefficients

NASA Technical Reports Server (NTRS)

Montgomery, D.; Hatori, T.

1984-01-01

Turbulent transfer rates from small-scale MHD excitations to large-scale Fourier modes are calculated algebraically, using the method of Biskamp and Welter. Three cases are considered: two-dimensional Navier-Stokes flows, two-dimensional incompressible MHD, and the weakly three-dimensional Strauss equations. In all cases, an initially large spectral gap between the small-scale and large-scale excitations is assumed, and attention focusses on the initial values of the back-transfer rates. The sign of the transfer is determined by the sign of an analytically calculable eddy viscosity and/or anomalous resistivity. We are able to confirm the results of Biskamp and Welter for the case of two-dimensional MHD, but find some differences for the case of the Strauss equations. It is argued that the Strauss equations may not exhibit an inverse cascade phenomenon for the spatially periodic case unless their initial spectra are such that the behavior is essentially that of two-dimensional MHD.

5. Time-dependent solution for axisymmetric flow over a blunt body with ideal gas, CF4, or equilibrium air chemistry

NASA Technical Reports Server (NTRS)

Hamilton, H. H., II; Spall, J. R.

1986-01-01

A time-asymptotic method has been used to obtain steady-flow solutions for axisymmetric inviscid flow over several blunt bodies including spheres, paraboloids, ellipsoids, and spherically blunted cones. Comparisons with experimental data and results of other computational methods have demonstrated that accurate solutions can be obtained using this approach. The method should prove useful as an analysis tool for comparing with experimental data and for making engineering calculations for blunt reentry vehicles.

6. Local conservative regularizations of compressible magnetohydrodynamic and neutral flows

Krishnaswami, Govind S.; Sachdev, Sonakshi; Thyagaraja, A.

2016-02-01

Ideal systems like magnetohydrodynamics (MHD) and Euler flow may develop singularities in vorticity ( w =∇×v ). Viscosity and resistivity provide dissipative regularizations of the singularities. In this paper, we propose a minimal, local, conservative, nonlinear, dispersive regularization of compressible flow and ideal MHD, in analogy with the KdV regularization of the 1D kinematic wave equation. This work extends and significantly generalizes earlier work on incompressible Euler and ideal MHD. It involves a micro-scale cutoff length λ which is a function of density, unlike in the incompressible case. In MHD, it can be taken to be of order the electron collisionless skin depth c/ωpe. Our regularization preserves the symmetries of the original systems and, with appropriate boundary conditions, leads to associated conservation laws. Energy and enstrophy are subject to a priori bounds determined by initial data in contrast to the unregularized systems. A Hamiltonian and Poisson bracket formulation is developed and applied to generalize the constitutive relation to bound higher moments of vorticity. A "swirl" velocity field is identified, and shown to transport w/ρ and B/ρ, generalizing the Kelvin-Helmholtz and Alfvén theorems. The steady regularized equations are used to model a rotating vortex, MHD pinch, and a plane vortex sheet. The proposed regularization could facilitate numerical simulations of fluid/MHD equations and provide a consistent statistical mechanics of vortices/current filaments in 3D, without blowup of enstrophy. Implications for detailed analyses of fluid and plasma dynamic systems arising from our work are briefly discussed.

7. MHD Integrated Topping Cycle Project

SciTech Connect

Not Available

1992-07-01

This seventeenth quarterly technical progress report of the MHD Integrated Topping Cycle Project presents the accomplishments during the period August 1, 1991 to October 31, 1991. Manufacturing of the prototypical combustor pressure shell has been completed including leak, proof, and assembly fit checking. Manufacturing of forty-five cooling panels was also completed including leak, proof, and flow testing. All precombustor internal components (combustion can baffle and swirl box) were received and checked, and integration of the components was initiated. A decision was made regarding the primary and backup designs for the 1A4 channel. The assembly of the channel related prototypical hardware continued. The cathode wall electrical wiring is now complete. The mechanical design of the diffuser has been completed.

8. Shock Waves in Hall-MHD

Hagstrom, George; Hameiri, Eliezer

2012-03-01

Hall-MHD is a partial differential equation of degenerate parabolic type that describes the dynamics of an ideal two fluid plasma with massless electrons. We study shock waves and discontinuities in this system. We characterize planar travelling wave solutions and find solutions with discontinuities in the hydrodynamic variables. These solutions, which correspond to the ion-acoustic wave, arise due to the presence of hydrodynamic real characteristics in Hall-MHD. We demonstrate finite-time discontinuity formation for certain types of initial data with discontinuous derivatives and study the shock structure under different regularizations. We also explore the possible existence of solutions with discontinuous magnetic field. A non-algebraic, non-local set of jump conditions is derived under the assumption of [B]!=0. These conditions are used to study the contact discontinuity and it is shown that massless electrons crossing the surface of discontinuity may enter and leave at different locations. These conditions suggest the possible existence of mathematically novel shocks in Hall-MHD.

9. Advances in Simulation of Wave Interaction with Extended MHD Phenomena

SciTech Connect

Batchelor, Donald B; Abla, Gheni; D'Azevedo, Ed F; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, Joshua; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Foley, S.; Fu, GuoYong; Harvey, R. W.; Jaeger, Erwin Frederick; Jardin, S. C.; Jenkins, T; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; Lynch, Vickie E; McCune, Douglas; Ramos, J.; Schissel, D.; Schnack,; Wright, J.

2009-01-01

The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: 1) recent improvements to the IPS, 2) application of the IPS for very high resolution simulations of ITER scenarios, 3) studies of resistive and ideal MHD stability in tokamk discharges using IPS facilities, and 4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.

10. Advances in Simulation of Wave Interactions with Extended MHD Phenomena

SciTech Connect

Batchelor, Donald B; D'Azevedo, Eduardo; Bateman, Glenn; Bernholdt, David E; Bonoli, P.; Bramley, Randall B; Breslau, Joshua; Elwasif, Wael R; Foley, S.; Jaeger, Erwin Frederick; Jardin, S. C.; Klasky, Scott A; Kruger, Scott E; Ku, Long-Poe; McCune, Douglas; Ramos, J.; Schissel, David P; Schnack, Dalton D

2009-01-01

The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: (1) recent improvements to the IPS, (2) application of the IPS for very high resolution simulations of ITER scenarios, (3) studies of resistive and ideal MHD stability in tokamak discharges using IPS facilities, and (4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.

11. Magnetohydrodynamic (MHD) modelling of solar active phenomena via numerical methods

NASA Technical Reports Server (NTRS)

Wu, S. T.

1988-01-01

Numerical ideal MHD models for the study of solar active phenomena are summarized. Particular attention is given to the following physical phenomena: (1) local heating of a coronal loop in an isothermal and stratified atmosphere, and (2) the coronal dynamic responses due to magnetic field movement. The results suggest that local heating of a magnetic loop will lead to the enhancement of the density of the neighboring loops through MHD wave compression. It is noted that field lines can be pinched off and may form a self-contained magnetized plasma blob that may move outward into interplanetary space.

12. MHD thrust vectoring of a rocket engine

Labaune, Julien; Packan, Denis; Tholin, Fabien; Chemartin, Laurent; Stillace, Thierry; Masson, Frederic

2016-09-01

In this work, the possibility to use MagnetoHydroDynamics (MHD) to vectorize the thrust of a solid propellant rocket engine exhaust is investigated. Using a magnetic field for vectoring offers a mass gain and a reusability advantage compared to standard gimbaled, elastomer-joint systems. Analytical and numerical models were used to evaluate the flow deviation with a 1 Tesla magnetic field inside the nozzle. The fluid flow in the resistive MHD approximation is calculated using the KRONOS code from ONERA, coupling the hypersonic CFD platform CEDRE and the electrical code SATURNE from EDF. A critical parameter of these simulations is the electrical conductivity, which was evaluated using a set of equilibrium calculations with 25 species. Two models were used: local thermodynamic equilibrium and frozen flow. In both cases, chlorine captures a large fraction of free electrons, limiting the electrical conductivity to a value inadequate for thrust vectoring applications. However, when using chlorine-free propergols with 1% in mass of alkali, an MHD thrust vectoring of several degrees was obtained.

13. Noncanonical Hamiltonian density formulation of hydrodynamics and ideal MHD

SciTech Connect

Morrison, P.J.; Greene, J.M.

1980-04-01

A new Hamiltonian density formulation of a perfect fluid with or without a magnetic field is presented. Contrary to previous work the dynamical variables are the physical variables, rho, v, B, and s, which form a noncanonical set. A Poisson bracket which satisfies the Jacobi identity is defined. This formulation is transformed to a Hamiltonian system where the dynamical variables are the spatial Fourier coefficients of the fluid variables.

14. ANALYTICAL APPROXIMATION OF THE BIODEGRADATION RATE FOR IN SITU BIOREMEDIATION OF GROUNDWATER UNDER IDEAL RADIAL FLOW CONDITIONS. (R824785)

EPA Science Inventory

We derive the long-term biodegradation rate of an organic contaminant (substrate) for an in situ bioremediation model with axisymmetric flow conditions. The model presumes that a nonsorbing electron acceptor is injected into a saturated homogeneous porous medium which initially c...

15. ANALYTICAL APPROXIMATION OF THE BIODEGRADATION RATE FOR IN SITU BIOREMEDIATION OF GROUNDWATER UNDER IDEAL RADIAL FLOW CONDITIONS. (R824785)

EPA Science Inventory

We derive the long-term biodegradation rate of an organic contaminant (substrate) for an in situ bioremediation model with axisymmetric flow conditions. The model presumes that a nonsorbing electron acceptor is injected into a saturated homogeneous porous medium which initially c...

16. Design Study: Rocket Based MHD Generator

NASA Technical Reports Server (NTRS)

1997-01-01

This report addresses the technical feasibility and design of a rocket based MHD generator using a sub-scale LOx/RP rocket motor. The design study was constrained by assuming the generator must function within the performance and structural limits of an existing magnet and by assuming realistic limits on (1) the axial electric field, (2) the Hall parameter, (3) current density, and (4) heat flux (given the criteria of heat sink operation). The major results of the work are summarized as follows: (1) A Faraday type of generator with rectangular cross section is designed to operate with a combustor pressure of 300 psi. Based on a magnetic field strength of 1.5 Tesla, the electrical power output from this generator is estimated to be 54.2 KW with potassium seed (weight fraction 3.74%) and 92 KW with cesium seed (weight fraction 9.66%). The former corresponds to a enthalpy extraction ratio of 2.36% while that for the latter is 4.16%; (2) A conceptual design of the Faraday MHD channel is proposed, based on a maximum operating time of 10 to 15 seconds. This concept utilizes a phenolic back wall for inserting the electrodes and inter-electrode insulators. Copper electrode and aluminum oxide insulator are suggested for this channel; and (3) A testing configuration for the sub-scale rocket based MHD system is proposed. An estimate of performance of an ideal rocket based MHD accelerator is performed. With a current density constraint of 5 Amps/cm(exp 2) and a conductivity of 30 Siemens/m, the push power density can be 250, 431, and 750 MW/m(sup 3) when the induced voltage uB have values of 5, 10, and 15 KV/m, respectively.

17. Nuclear MHD Converter

DTIC Science & Technology

2007-11-02

model the Power Conversion Unit (gas reactor + nozzle and MHD channel), and the cross sections derived from Task 1.. The configuration extends ...8 1.1 Project Objectives 8 1.2 Report Organization 9 Tables and Figures 10 2 PROJECT DESCRIPTION 11 3 REFLECTOR MODELING 13 3.1 Symbols...outlet. This conclusion remains true even if the effect of dissociation and attachment are included in the numerical model . Furthermore, a

18. Understanding Accretion Disks through Three Dimensional Radiation MHD Simulations

Jiang, Yan-Fei

19. Comparison of LES of steady transitional flow in an idealized stenosed axisymmetric artery model with a RANS transitional model.

PubMed

Tan, F P P; Wood, N B; Tabor, G; Xu, X Y

2011-05-01

In this study, two different turbulence methodologies are investigated to predict transitional flow in a 75% stenosed axisymmetric experimental arterial model and in a slightly modified version of the model with an eccentric stenosis. Large eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) methods were applied; in the LES simulations eddy viscosity subgrid-scale models were employed (basic and dynamic Smagorinsky) while the RANS method involved the correlation-based transitional version of the hybrid k-ε/k-ω flow model. The RANS simulations used 410,000 and 820,000 element meshes for the axisymmetric and eccentric stenoses, respectively, with y(+) less than 2 viscous wall units for the boundary elements, while the LES used 1,200,000 elements with y(+) less than 1. Implicit filtering was used for LES, giving an overlap between the resolved and modeled eddies, ensuring accurate treatment of near wall turbulence structures. Flow analysis was carried out in terms of vorticity and eddy viscosity magnitudes, velocity, and turbulence intensity profiles and the results were compared both with established experimental data and with available direct numerical simulations (DNSs) from the literature. The simulation results demonstrated that the dynamic Smagorinsky LES and RANS transitional model predicted fairly comparable velocity and turbulence intensity profiles with the experimental data, although the dynamic Smagorinsky model gave the best overall agreement. The present study demonstrated the power of LES methods, although they were computationally more costly, and added further evidence of the promise of the RANS transition model used here, previously tested in pulsatile flow on a similar model. Both dynamic Smagorinsky LES and the RANS model captured the complex transition phenomena under physiological Reynolds numbers in steady flow, including separation and reattachment. In this respect, LES with dynamic Smagorinsky appeared more successful than DNS

20. A nonlinear structural subgrid-scale closure for compressible MHD. I. Derivation and energy dissipation properties

SciTech Connect

Vlaykov, Dimitar G.; Grete, Philipp; Schmidt, Wolfram; Schleicher, Dominik R. G.

2016-06-15

Compressible magnetohydrodynamic (MHD) turbulence is ubiquitous in astrophysical phenomena ranging from the intergalactic to the stellar scales. In studying them, numerical simulations are nearly inescapable, due to the large degree of nonlinearity involved. However, the dynamical ranges of these phenomena are much larger than what is computationally accessible. In large eddy simulations (LESs), the resulting limited resolution effects are addressed explicitly by introducing to the equations of motion additional terms associated with the unresolved, subgrid-scale dynamics. This renders the system unclosed. We derive a set of nonlinear structural closures for the ideal MHD LES equations with particular emphasis on the effects of compressibility. The closures are based on a gradient expansion of the finite-resolution operator [W. K. Yeo (CUP, 1993)] and require no assumptions about the nature of the flow or magnetic field. Thus, the scope of their applicability ranges from the sub- to the hyper-sonic and -Alfvénic regimes. The closures support spectral energy cascades both up and down-scale, as well as direct transfer between kinetic and magnetic resolved and unresolved energy budgets. They implicitly take into account the local geometry, and in particular, the anisotropy of the flow. Their properties are a priori validated in Paper II [P. Grete et al., Phys. Plasmas 23, 062317 (2016)] against alternative closures available in the literature with respect to a wide range of simulation data of homogeneous and isotropic turbulence.

1. A nonlinear structural subgrid-scale closure for compressible MHD. I. Derivation and energy dissipation properties

Vlaykov, Dimitar G.; Grete, Philipp; Schmidt, Wolfram; Schleicher, Dominik R. G.

2016-06-01

Compressible magnetohydrodynamic (MHD) turbulence is ubiquitous in astrophysical phenomena ranging from the intergalactic to the stellar scales. In studying them, numerical simulations are nearly inescapable, due to the large degree of nonlinearity involved. However, the dynamical ranges of these phenomena are much larger than what is computationally accessible. In large eddy simulations (LESs), the resulting limited resolution effects are addressed explicitly by introducing to the equations of motion additional terms associated with the unresolved, subgrid-scale dynamics. This renders the system unclosed. We derive a set of nonlinear structural closures for the ideal MHD LES equations with particular emphasis on the effects of compressibility. The closures are based on a gradient expansion of the finite-resolution operator [W. K. Yeo (CUP, 1993)] and require no assumptions about the nature of the flow or magnetic field. Thus, the scope of their applicability ranges from the sub- to the hyper-sonic and -Alfvénic regimes. The closures support spectral energy cascades both up and down-scale, as well as direct transfer between kinetic and magnetic resolved and unresolved energy budgets. They implicitly take into account the local geometry, and in particular, the anisotropy of the flow. Their properties are a priori validated in Paper II [P. Grete et al., Phys. Plasmas 23, 062317 (2016)] against alternative closures available in the literature with respect to a wide range of simulation data of homogeneous and isotropic turbulence.

2. Implicit and Multigrid Method for Ideal Multigrid Convergence: Direct Numerical Simulation of Separated Flow Around NACA 0012 Airfoil

NASA Technical Reports Server (NTRS)

Liu, Chao-Qun; Shan, H.; Jiang, L.

1999-01-01

Numerical investigation of flow separation over a NACA 0012 airfoil at large angles of attack has been carried out. The numerical calculation is performed by solving the full Navier-Stokes equations in generalized curvilinear coordinates. The second-order LU-SGS implicit scheme is applied for time integration. This scheme requires no tridiagonal inversion and is capable of being completely vectorized, provided the corresponding Jacobian matrices are properly selected. A fourth-order centered compact scheme is used for spatial derivatives. In order to reduce numerical oscillation, a sixth-order implicit filter is employed. Non-reflecting boundary conditions are imposed at the far-field and outlet boundaries to avoid possible non-physical wave reflection. Complex flow separation and vortex shedding phenomenon have been observed and discussed.

3. Two-Phase Viscous Flow Modeling of Interior Ballistics, Algorithm, and Numerical Predictions for an Idealized Lagrange gun

DTIC Science & Technology

1983-01-01

Covolume 1.08 xO 10 m/kg Ratio of Specific Heats 1.271 Initial Gas Pressure 300 MPa nIitial Gas Temperature 3000 K The axial iomain is uniformly divided...Cycle. (Adaptation from Ref. 1) ................................. 7 2 Pressure Histories at the Breech (-)-) and at Projectile Base (---) and Their...gas-particle flow from the igniter. As the flame spreads throughout the propellant bed, gases are generated, pressure waves evolve, fluidization of

4. MHD equilibria with diamagnetic effects

Tessarotto, M.; Zorat, R.; Johnson, J. L.; White, R. B.

1997-11-01

An outstanding issue in magnetic confinement is the establishment of MHD equilibria with enhanced flow shear profiles for which turbulence (and transport) may be locally effectively suppressed or at least substantially reduced with respect to standard weak turbulence models. Strong flows develop in the presence of equilibrium E× B-drifts produced by a strong radial electric field, as well as due to diamagnetic contributions produced by steep equilibrium radial profiles of number density, temperature and the flow velocity itself. In the framework of a kinetic description, this generally requires the construction of guiding-center variables correct to second order in the relevant expansion parameter. For this purpose, the Lagrangian approach developed recently by Tessarotto et al. [1] is adopted. In this paper the conditions of existence of such equilibria are analyzed and their basic physical properties are investigated in detail. 1 - M. Pozzo, M. Tessarotto and R. Zorat, in Theory of fusion Plasmas, E.Sindoni et al. eds. (Societá Italiana di Fisica, Editrice Compositori, Bologna, 1996), p.295.

5. Magnetic reconnection in Hall-MHD including electron inertia

Gomez, D. O.; Andres, N.; Martin, L. N.; Dmitruk, P.

2013-12-01

Magnetic reconnection is an important energy conversion process in highly conducting plasmas, such as those present in the solar corona or in planetary magnetospheres. Within the framework of resistive one-fluid MHD, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which might significantly increase the reconnection rates. Within the more general framework of two-fluid MHD for a fully ionized hydrogen plasma, we retain the effects of the Hall current and electron inertia. We performed 2.5D Hall MHD simulations including electron inertia using a pseudo-spectral code which yields exact conservation (to round-off errors) of all the ideal invariants. We obtain finite reconnection rates even in the case of zero resistivity, thus showing the important influence of the electron inertia.

6. The impact of non-ideal magnetohydrodynamics on binary star formation

Wurster, James; Price, Daniel J.; Bate, Matthew R.

2017-04-01

We investigate the effect of non-ideal magnetohydrodynamics (MHD) on the formation of binary stars using a suite of three-dimensional smoothed particle magnetohydrodynamics simulations of the gravitational collapse of 1 M⊙, rotating, perturbed molecular-cloud cores. Alongside the role of Ohmic resistivity, ambipolar diffusion and the Hall effect, we also examine the effects of magnetic field strength, orientation and amplitude of the density perturbation. When modelling sub-critical cores, ideal MHD models do not collapse whereas non-ideal MHD models collapse to form single protostars. In supercritical ideal MHD models, increasing the magnetic field strength or decreasing the initial-density perturbation amplitude decreases the initial binary separation. Strong magnetic fields initially perpendicular to the rotation axis suppress the formation of binaries and yield discs with magnetic fields ∼10 times stronger than if the magnetic field was initially aligned with the rotation axis. When non-ideal MHD is included, the resulting discs are larger and more massive, and the binary forms on a wider orbit. Small differences in the supercritical cores caused by non-ideal MHD effects are amplified by the binary interaction near periastron. Overall, the non-ideal effects have only a small impact on binary formation and early evolution, with the initial conditions playing the dominant role.

7. Large Eddy Simulation of Transitional Flow in an Idealized Stenotic Blood Vessel: Evaluation of Subgrid Scale Models

PubMed Central

Pal, Abhro; Anupindi, Kameswararao; Delorme, Yann; Ghaisas, Niranjan; Shetty, Dinesh A.; Frankel, Steven H.

2014-01-01

In the present study, we performed large eddy simulation (LES) of axisymmetric, and 75% stenosed, eccentric arterial models with steady inflow conditions at a Reynolds number of 1000. The results obtained are compared with the direct numerical simulation (DNS) data (Varghese et al., 2007, “Direct Numerical Simulation of Stenotic Flows. Part 1. Steady Flow,” J. Fluid Mech., 582, pp. 253–280). An inhouse code (WenoHemo) employing high-order numerical methods for spatial and temporal terms, along with a 2nd order accurate ghost point immersed boundary method (IBM) (Mark, and Vanwachem, 2008, “Derivation and Validation of a Novel Implicit Second-Order Accurate Immersed Boundary Method,” J. Comput. Phys., 227(13), pp. 6660–6680) for enforcing boundary conditions on curved geometries is used for simulations. Three subgrid scale (SGS) models, namely, the classical Smagorinsky model (Smagorinsky, 1963, “General Circulation Experiments With the Primitive Equations,” Mon. Weather Rev., 91(10), pp. 99–164), recently developed Vreman model (Vreman, 2004, “An Eddy-Viscosity Subgrid-Scale Model for Turbulent Shear Flow: Algebraic Theory and Applications,” Phys. Fluids, 16(10), pp. 3670–3681), and the Sigma model (Nicoud et al., 2011, “Using Singular Values to Build a Subgrid-Scale Model for Large Eddy Simulations,” Phys. Fluids, 23(8), 085106) are evaluated in the present study. Evaluation of SGS models suggests that the classical constant coefficient Smagorinsky model gives best agreement with the DNS data, whereas the Vreman and Sigma models predict an early transition to turbulence in the poststenotic region. Supplementary simulations are performed using Open source field operation and manipulation (OpenFOAM) (“OpenFOAM,” http://www.openfoam.org/) solver and the results are inline with those obtained with WenoHemo. PMID:24801556

8. Large eddy simulation of transitional flow in an idealized stenotic blood vessel: evaluation of subgrid scale models.

PubMed

Pal, Abhro; Anupindi, Kameswararao; Delorme, Yann; Ghaisas, Niranjan; Shetty, Dinesh A; Frankel, Steven H

2014-07-01

In the present study, we performed large eddy simulation (LES) of axisymmetric, and 75% stenosed, eccentric arterial models with steady inflow conditions at a Reynolds number of 1000. The results obtained are compared with the direct numerical simulation (DNS) data (Varghese et al., 2007, "Direct Numerical Simulation of Stenotic Flows. Part 1. Steady Flow," J. Fluid Mech., 582, pp. 253-280). An inhouse code (WenoHemo) employing high-order numerical methods for spatial and temporal terms, along with a 2nd order accurate ghost point immersed boundary method (IBM) (Mark, and Vanwachem, 2008, "Derivation and Validation of a Novel Implicit Second-Order Accurate Immersed Boundary Method," J. Comput. Phys., 227(13), pp. 6660-6680) for enforcing boundary conditions on curved geometries is used for simulations. Three subgrid scale (SGS) models, namely, the classical Smagorinsky model (Smagorinsky, 1963, "General Circulation Experiments With the Primitive Equations," Mon. Weather Rev., 91(10), pp. 99-164), recently developed Vreman model (Vreman, 2004, "An Eddy-Viscosity Subgrid-Scale Model for Turbulent Shear Flow: Algebraic Theory and Applications," Phys. Fluids, 16(10), pp. 3670-3681), and the Sigma model (Nicoud et al., 2011, "Using Singular Values to Build a Subgrid-Scale Model for Large Eddy Simulations," Phys. Fluids, 23(8), 085106) are evaluated in the present study. Evaluation of SGS models suggests that the classical constant coefficient Smagorinsky model gives best agreement with the DNS data, whereas the Vreman and Sigma models predict an early transition to turbulence in the poststenotic region. Supplementary simulations are performed using Open source field operation and manipulation (OpenFOAM) ("OpenFOAM," http://www.openfoam.org/) solver and the results are inline with those obtained with WenoHemo.

9. Laboratory-produced MHD plasma jets

Bellan, Paul

2008-04-01

Because space plasmas are neither confined by vacuum chamber walls nor have magnetic fields produced by physical coils, space plasmas have shapes that are much less determinate than lab plasmas. An experimental program underway at Caltech produces plasmas where the shape is neither fixed by a vacuum chamber wall nor imposed by an external coil set, but rather is allowed to be determined by self-organizing MHD processes subject to the constraint of imposed boundary conditions analogous to the boundary conditions of space plasmas. These self-organizing processes are believed to be fundamental to astrophysical jets, solar coronal loops, and MHD turbulence (e.g. Taylor relaxation). The experimental dynamics are sufficiently reproducible to allow detailed study despite the morphology being complex and dynamic. A surprising result has been the observation that instead of the plasma uniformly filling up the available volume, the plasma is spatially localized in a highly collimated, small diameter magnetic flux tube, the length and axis of which change in time in response to MHD forces. A model shows that the collimation results from stagnation of linked magnetic flux frozen into a MHD-driven jet that accelerates plasma from the wall into the flux tube, filling the flux tube with plasma. Jet flow has been imaged with a high-speed multi-frame camera, diagnosed via Doppler spectroscopy, and most recently (i) the collision between two opposing, color-coded jets flowing from opposite ends of a flux tube has been observed, and (ii) the collision of a jet with a target cloud has been observed.

10. Can a numerically stable subgrid-scale model for turbulent flow computation be ideally accurate?: a preliminary theoretical study for the Gaussian filtered Navier-Stokes equations.

PubMed

2003-09-01

This paper introduces a candidate for the origin of the numerical instabilities in large eddy simulation repeatedly observed in academic and practical industrial flow computations. Without resorting to any subgrid-scale modeling, but based on a simple assumption regarding the streamwise component of flow velocity, it is shown theoretically that in a channel-flow computation, the application of the Gaussian filtering to the incompressible Navier-Stokes equations yields a numerically unstable term, a cross-derivative term, which is similar to one appearing in the Gaussian filtered Vlasov equation derived by Klimas [J. Comput. Phys. 68, 202 (1987)] and also to one derived recently by Kobayashi and Shimomura [Phys. Fluids 15, L29 (2003)] from the tensor-diffusivity subgrid-scale term in a dynamic mixed model. The present result predicts that not only the numerical methods and the subgrid-scale models employed but also only the applied filtering process can be a seed of this numerical instability. An investigation concerning the relationship between the turbulent energy scattering and the unstable term shows that the instability of the term does not necessarily represent the backscatter of kinetic energy which has been considered a possible origin of numerical instabilities in large eddy simulation. The present findings raise the question whether a numerically stable subgrid-scale model can be ideally accurate.

11. Three-dimensional analysis of MHD generators and diffusers

SciTech Connect

Vanka, S P; Ahluwalia, R K; Doss, E D

1982-03-01

The three-dimensional flow and heat transfer phenomena in MHD channels and diffusers are analyzed by solving the governing partial differential equations for flow and electrical fields. The equation set consists of the mass continuity equation, the three momentum equations, the equations for enthalpy, turbulence kinetic energy and its dissipation rate, and the Maxwell equations. This set of coupled equations is solved by the use of a finite-difference calculation procedure. The turbulence is represented by a two-equation model of turbulence in which partial differential equations are solved for the turbulence kinetic energy and its dissipation rate. Calculations have been performed for Faraday and diagonally-connected channels. Specifically, the AEDC (Faraday) and the UTSI (diagonal) channels have been analyzed, and the results are compared with experimental data. The agreement is fairly good for all the measured quantities. The effects of channel loading on the three-dimensional flow characteristics of Faraday and diagonally-connected generators have been also analyzed. A simple argument is presented to show qualitatively the role of MHD body forces in generating axial vorticity and hence secondary flows in the cross-stream. Calculations have also been made to study the flow evolution in MHD diffusers. The calculations show that the velocity overshoots and secondary flows decay along the diffusers length. Plots of velocity, skin friction and pressure recovery are presented to illustrate the flow development in MHD diffusers.

12. Experimental, Numerical and Analytical Studies of the MHD-driven plasma jet, instabilities and waves

Zhai, Xiang

This thesis describes a series of experimental, numerical, and analytical studies involving the Caltech magnetohydrodynamically (MHD)-driven plasma jet experiment. The plasma jet is created via a capacitor discharge that powers a magnetized coaxial planar electrodes system. The jet is collimated and accelerated by the MHD forces. We present three-dimensional ideal MHD finite-volume simulations of the plasma jet experiment using an astrophysical magnetic tower as the baseline model. A compact magnetic energy/helicity injection is exploited in the simulation analogous to both the experiment and to astrophysical situations. Detailed analysis provides a comprehensive description of the interplay of magnetic force, pressure, and flow effects. We delineate both the jet structure and the transition process that converts the injected magnetic energy to other forms. When the experimental jet is sufficiently long, it undergoes a global kink instability and then a secondary local Rayleigh-Taylor instability caused by lateral acceleration of the kink instability. We present an MHD theory of the Rayleigh-Taylor instability on the cylindrical surface of a plasma flux rope in the presence of a lateral external gravity. The Rayleigh-Taylor instability is found to couple to the classic current-driven instability, resulting in a new type of hybrid instability. The coupled instability, produced by combination of helical magnetic field, curvature of the cylindrical geometry, and lateral gravity, is fundamentally different from the classic magnetic Rayleigh-Taylor instability occurring at a two-dimensional planar interface. In the experiment, this instability cascade from macro-scale to micro-scale eventually leads to the failure of MHD. When the Rayleigh-Taylor instability becomes nonlinear, it compresses and pinches the plasma jet to a scale smaller than the ion skin depth and triggers a fast magnetic reconnection. We built a specially designed high-speed 3D magnetic probe and

13. Conceptual design of a coal-fired MHD retrofit of the J. E. Corette Plant: Design definition

SciTech Connect

Not Available

1988-02-01

The design, construction, and operation of a fully integrated coal burning MHD/steam-power system has been identified as a necessary step for commercialization of MHD power gerneation. The addition of an MHD power system to an existing utility's conventional steam power plant is presently considered an efficient and attractive method for realization of this, and the conceptual design of a coal-fired MHD power plant has been initiated as an important item of the National MHD development program. Current activities of the MHD development program comprise proof-of-concepts testing of MHD topping cycle components and bottoming cycle components at the Components Development and Integration Facility (CDIF) and the Coal Fired Flow Facility (CFFF), respectively, at subscale levels. The MHD plant will provide for operation and testing of a fully integrated MHD/steam power system in a utility environment at a larger size consistent with its objectives. Its main objectives are to verify the technical and economic feasibility of commercial MHD power genration including environmental aspects and to provide electric utilities and equipment manufacturers with the necessary information and confidence to proceed with commercialization of MHD. The coal-fired J.E. Corette steam plant unit of the Montana Power Company at Billings, Montana has been selected for this MHD conceptual design activity.

14. MHD Program Plan, FY 1992

1991-10-01

The current MHD program being implemented is a result of a consensus established in public meetings held by the Department of Energy in 1984. Essential elements of the current program include the following: (1) develop technical and environmental data for the integrated MHD topping cycle system through POC testing (1,000 hours); (2) develop technical and environmental data for the integrated MHD bottoming cycle sub system through POC testing (4,000 hours); (3) design, construct, and operate a seed regeneration POC facility (SRPF) capable of processing spent seed materials from the MHD bottoming cycle; (4) prepare conceptual designs for a site specific MHD retrofit plant; and (5) continue system studies and supporting research necessary for system testing. The current MHD program continues to be directed toward coal fired power plant applications, both stand-alone and retrofit. Development of a plant should enhance the attractiveness of MHD for applications other than electrical power. MHD may find application in electrical energy intensive industries and in the defense sector.

15. An experimental studies with disk MHD channels on argon plazma

SciTech Connect

Koneev, S.M.A.; Kovalev, L.K.; Larionoff, A.E.; Poltavets, V.N.

1994-12-31

The most interesting works carried out over the past few years in the field of MHD generating electric power are the ones studying disk MHD channels. The results published give a hope to overcome one of the MHD generator essential disadvantages - relatively low effectiveness of converting heat power into electric one. In some works performed by different authors and at different plants the coefficients of energy conversion achieving 20% have been obtained and there is a hint of the future possible increase of up to 40%. In the majority of experimental studies non-equilibrium ionized inertial gases (Ar, He) with alkali metal (Cs, K) were used as a working medium, the operating temperature being 1800-2000 K. The present paper is dedicated to an experimental test rig-with-a-disk-MHD-channel development for operating on thermally ionized Ar with the temperature of up to 9000 K and pressure 10 up to 10 Pa. For heating a working medium an electric arc in a special plazmotron is used. As the experiments on linear MHD channels have shown, along the whole working area the plasma is non-equilibrium with a substantial break off of an electron temperature providing conductivity of more then 100 Sm/m. The aim of creation this test rig is in simulating the processes of the working medium flow and electric energy generation in disk MHD channels. An important research element is calculation techniques debugging and acquiring experience of development and carrying out disk MHD generator studies for the following experimental full-scale MHD plants with a disk channel to be created.

16. Effect of Trapped Energetic Ions on MHD Activity in Spherical Tori

SciTech Connect

R.B. White; Ya.I. Kolesnichenko; V.V. Lutsenko; V.S. Marchenko

2002-05-30

It is shown that the increase of beta (the ratio of plasma pressure to the magnetic field pressure) may change the character of the influence of trapped energetic ions on MHD stability in spherical tori. Namely, the energetic ions, which stabilize MHD modes (such as the ideal-kink mode, collisionless tearing mode, and semi-collisional tearing mode) at low beta, have a destabilizing influence at high beta unless the radial distribution of the energetic ions is very peaked.

17. The iFlow modelling framework v2.4: a modular idealized process-based model for flow and transport in estuaries

Dijkstra, Yoeri M.; Brouwer, Ronald L.; Schuttelaars, Henk M.; Schramkowski, George P.

2017-07-01

The iFlow modelling framework is a width-averaged model for the systematic analysis of the water motion and sediment transport processes in estuaries and tidal rivers. The distinctive solution method, a mathematical perturbation method, used in the model allows for identification of the effect of individual physical processes on the water motion and sediment transport and study of the sensitivity of these processes to model parameters. This distinction between processes provides a unique tool for interpreting and explaining hydrodynamic interactions and sediment trapping. iFlow also includes a large number of options to configure the model geometry and multiple choices of turbulence and salinity models. Additionally, the model contains auxiliary components, including one that facilitates easy and fast sensitivity studies. iFlow has a modular structure, which makes it easy to include, exclude or change individual model components, called modules. Depending on the required functionality for the application at hand, modules can be selected to construct anything from very simple quasi-linear models to rather complex models involving multiple non-linear interactions. This way, the model complexity can be adjusted to the application. Once the modules containing the required functionality are selected, the underlying model structure automatically ensures modules are called in the correct order. The model inserts iteration loops over groups of modules that are mutually dependent. iFlow also ensures a smooth coupling of modules using analytical and numerical solution methods. This way the model combines the speed and accuracy of analytical solutions with the versatility of numerical solution methods. In this paper we present the modular structure, solution method and two examples of the use of iFlow. In the examples we present two case studies, of the Yangtze and Scheldt rivers, demonstrating how iFlow facilitates the analysis of model results, the understanding of the

18. Thermodynamic MHD Modeling of Coronal Mass Ejections

Linker, Jon A.; Lionello, R.; Mikic, Z.; Riley, P.; Titov, V.

2007-05-01

Coronal mass ejections (CMEs) disrupt the large-scale coronal magnetic field and propel plasma and magnetic flux outward into interplanetary space. The most energetic CMEs typically originate from active regions on the Sun. Accurately modeling active regions while also capturing the entire corona requires MHD models that include energy transport (radiative losses,anisotropic thermal conduction, and coronal heating) in the transition region and solar corona. We refer to this as the thermodynamic MHD model. The more accurate representation of energy flow in the thermodynamic MHD model allows us to to compute simulated EUV and X-ray emission as would be observed from spacecraft such as SOHO, STEREO, and Hinode. With this approach, theorists no longer get to argue what emission they think their favorite model's magnetic field evolution implies; we can actually go compute the emission and compare with observations. As an example, we show a simulation of the May 12, 1997 CME, and compare the simulated emission with observations from the actual event of dimming regions, postflare loops, and reformation of loops near the northern polar coronal hole. Work supported by NASA, NSF and the Center for Integrated Space Weather Modeling (an NSF Science and Technology Center).

19. Sex Education and Ideals

ERIC Educational Resources Information Center

de Ruyter, Doret J.; Spiecker, Ben

2008-01-01

This article argues that sex education should include sexual ideals. Sexual ideals are divided into sexual ideals in the strict sense and sexual ideals in the broad sense. It is argued that ideals that refer to the context that is deemed to be most ideal for the gratification of sexual ideals in the strict sense are rightfully called sexual…

20. Sex Education and Ideals

ERIC Educational Resources Information Center

de Ruyter, Doret J.; Spiecker, Ben

2008-01-01

This article argues that sex education should include sexual ideals. Sexual ideals are divided into sexual ideals in the strict sense and sexual ideals in the broad sense. It is argued that ideals that refer to the context that is deemed to be most ideal for the gratification of sexual ideals in the strict sense are rightfully called sexual…