A5052030443- Fluid Dynamics and Turbulent Flows
- Solar and Space Plasma Dynamics
- Heat Transfer Mechanisms
- Fluid Dynamics and Vibration Analysis
- Plant Water Relations and Carbon Dynamics
- Geomagnetism and Paleomagnetism Studies
- Metallurgical Processes and Thermodynamics
- Nanofluid Flow and Heat Transfer
- Particle Dynamics in Fluid Flows
- Magnetic confinement fusion research
- Characterization and Applications of Magnetic Nanoparticles
- Ionosphere and magnetosphere dynamics
- Wind and Air Flow Studies
- Fusion materials and technologies
- Aerodynamics and Acoustics in Jet Flows
- Combustion and flame dynamics
- Rheology and Fluid Dynamics Studies
- Nuclear reactor physics and engineering
- Power Transformer Diagnostics and Insulation
- Meteorological Phenomena and Simulations
- Solidification and crystal growth phenomena
- Nuclear Engineering Thermal-Hydraulics
- Aerodynamics and Fluid Dynamics Research
- Fluid Dynamics and Heat Transfer
- Magnetic Properties and Applications
Technische Universität Ilmenau
2015-2024
Dalian University of Technology
2018
Northeastern University
2012-2018
A magnetic field imposed on a flow of an electrically conducting fluid can profoundly change behavior. We consider this effect for the situation laminar-turbulent transition in magnetohydrodynamic duct, pipe, and channel flows with homogeneous insulating walls. Experimental recent computational results obtained pipes, ducts channels are reviewed.
Significance Since the time Kolmogorov postulated universality of small-scale turbulence, an important research topic has been to experimentally establish it beyond doubt. The likelihood increases with increasing distance (say, in wave number space) from nonuniversal large scales. This as some power flow Reynolds number, and so a great deal emphasis put on creating quantifying very high flows under controlled conditions. present paper shows that universal properties inertial range turbulence...
Abstract High-resolution direct numerical simulations are conducted to analyse turbulent states of the flow an electrically conducting fluid in a duct square cross-section with insulating walls and imposed transverse magnetic field. The Reynolds number is $1{0}^{5} $ Hartmann varies from $0$ $400$ . It found that there broad range numbers which neither laminar nor fully turbulent, but has core, boundary layers zones near parallel Analysis fluctuations shows each zone consists two layers:...
Direct numerical simulation is applied to investigate instability and transition turbulence in the flow of an electrically conducting incompressible fluid between two parallel unbounded insulating walls affected by a wall-normal magnetic field (the Hartmann flow). The linear stability analysis this provided unrealistically high critical Reynolds numbers, about orders magnitude higher than those observed experiments. We propose explanation based on streak growth breakdown mechanism described...
Mesoscale convection covers an intermediate scale range between small-scale turbulence and the global organization of flow. It is often characterized by order patterns despite very high Rayleigh numbers strong turbulent fluctuations. In this review, we discuss several aspects mesoscale convection, which have been investigated three-dimensional direct numerical simulations. The studies are performed in a characteristic configuration plane layer that heated from below cooled above or subject...
The effect of a uniform spanwise magnetic field on turbulent channel flow is investigated for the case low Reynolds number. Direct numerical simulation (DNS) and large eddy (LES) computations are performed two values hydrodynamic number (104 2×104) with Hartmann varying in wide range. It shown that main suppression velocity fluctuations momentum transfer wall-normal direction. This leads to drag reduction transformation mean profile. centerline grows, gradients near wall decrease, typical...
Mean flow properties of turbulent magnetohydrodynamic channel with electrically insulating walls are studied using high-resolution direct numerical simulations. The Lorentz force due to the homogeneous wall-normal magnetic field is computed in quasi-static approximation. For strong fields, mean velocity profile shows a clear three-layer structure consisting viscous region near each wall and plateau middle connected by logarithmic layers. This reflects significance viscous, turbulent,...
We analyse the long-time evolution of three-dimensional flow in a closed cubic turbulent Rayleigh–Bénard convection cell via Koopman eigenfunction analysis. A data-driven basis derived from diffusion kernels known machine learning is employed here to represent regularized generator unitary group sense Galerkin approximation. The resulting eigenfunctions can be grouped into subsets accordance with discrete symmetries box. In particular, projection velocity field onto first reveals four stable...
Instability and transition to turbulence in a magnetohydrodynamic channel flow are studied numerically for the case of uniform magnetic field imposed along spanwise direction. Optimal perturbations their maximum amplifications over finite time intervals computed framework linear problem using an iterative scheme based on direct adjoint governing equations. It is shown that, at sufficiently strong field, amplification no longer provided by classical streamwise rolls, but rather rolls oriented...
Transient linear growth in laminar magnetohydrodynamic duct flow is analysed. The straight with rectangular cross-section and electrically insulating walls. applied uniform magnetic field oriented perpendicular to the mean direction parallel one of Optimal perturbations their maximum amplifications over finite time intervals are computed. optimal increasingly damped by field, localized boundary layers irrespective aspect ratio. Typically, have non-vanishing streamwise wavenumber as found...
We present results of a numerical analysis Hartmann's historical experiments on flows mercury in pipes and ducts under the influence magnetic fields. The computed critical parameters for laminar-turbulent transition as well friction coefficients are excellent agreement with data. simulations provide first detailed view flow structures that experimentally inaccessible. Novel regimes localized turbulent spots near sidewalls parallel to field otherwise laminar discovered. finally suggest how...
Three-dimensional turbulent magnetoconvection at a Rayleigh number of $Ra=10^7$ in liquid gallium Prandtl $Pr=0.025$ is studied closed square cell for very strong external vertical magnetic fields $B_0$ direct numerical simulations which apply the quasistatic approximation. As or equivalently Hartmann $Ha$ are increased, convection flow that highly absence crosses Chandrasekhar linear stability limit thermal ceased an infinitely extended layer and can be assigned with critical $Ha_{\rm c}$....
Direct numerical simulations are carried out to study flow structure and transport properties in turbulent Rayleigh-B\'{e}nard convection a cylindrical cell of aspect ratio one with an imposed axial magnetic field. Flows at the Prandtl number 0.025 Rayleigh Hartmann numbers up $10^9$ 1400 considered. The results consistent those earlier experimental data. As anticipated, heat transfer rate kinetic energy suppressed by strong At same time, their growth is found be faster flows high numbers....
Horizontally extended turbulent convection, termed mesoscale convection in natural systems, remains a challenge to investigate both experiments and simulations. This is particularly so for very low molecular Prandtl numbers, such as occur stellar the Earth's outer core. The present study reports three-dimensional direct numerical simulations of Rayleigh–Bénard square boxes side length $L$ height $H$ with aspect ratio $\varGamma =L/H$ 25, numbers that span almost 4 orders magnitude,...
We employ a linear stability analysis and direct numerical simulations to study the characteristics of wall modes in thermal convection rectangular box under strong inclined magnetic fields. The walls cell are electrically insulated. assumes periodicity spanwise direction perpendicular plane homogeneous field. Our shows that for fixed vertical field, imposition horizontal fields results an increase critical Rayleigh number along with decrease wavelength modes. become tilted resulting...
Abstract Local dissipation-scale distributions and high-order statistics of the energy dissipation rate are examined in turbulent channel flow using very high-resolution direct numerical simulations at Reynolds numbers ${\mathit{Re}}_{\tau } = 180$ , $381$ $590$ . For sufficiently large $ moments bulk agree with those homogeneous isotropic turbulence, including only a weak Reynolds-number dependence both finest largest scales. Systematic, but -independent, variations arise as wall is...
Instability of a flow an electrically conducting fluid in annular channel is analyzed. Strong constant magnetic field imposed the axial direction. Similarly to toroidal duct experiments, driven by azimuthal Lorentz force resulting from interaction between and radial electric currents created difference potential cylinders. The instability base flow, while clearly centrifugal nature, significantly different Dean detected earlier hydrodynamic systems similar MHD at low moderate fields. Growing...
The scaling theory of Grossmann and Lohse [J. Fluid Mech. 407, 27 (2000)] for turbulent heat momentum transfer is extended to the magnetoconvection case in presence a (strong) vertical magnetic field. A comparison with existing laboratory experiments direct numerical simulations quasistatic limit allows us restrict parameter space very low Prandtl numbers thus reduce number unknown parameters model. Also included Chandrasekhar limit, which outer induction field $\mathbit{B}$ large enough...
We predict a novel flow regime in liquid metals under the influence of magnetic field. It is characterized by long periods nearly steady, two-dimensional interrupted violent three-dimensional bursts. Our prediction has been obtained from direct numerical simulations channel geometry at low Reynolds number and translates into physical parameters which are amenable to experimental verification laboratory conditions. The new occurs wide range may have implications for metallurgical applications.
Decay of honeycomb-generated turbulence in a duct with static transverse magnetic field is studied via direct numerical simulations. The simulations follow the revealing experimental study Sukoriansky et al. (1986), particular paradoxical observation high-amplitude velocity fluctuations, which exist downstream portion flow when strong imposed entire including honeycomb exit, but not other configurations. It shown that fluctuations are caused by large-scale quasi-two-dimensional structures...
The electromagnetic drag force and torque acting on a magnetic dipole due to the translatory motion of an electrically conducting bar with square cross section infinite length is computed by numerical analysis for different orientations locations dipole. study motivated novel techniques termed Lorentz velocimetry eddy current testing noncontact measurements velocity liquid detection defects in interior solid bodies, respectively. present, simplified configuration provides explains important...