A5034746585- Fluid Dynamics and Turbulent Flows
- Metallurgical Processes and Thermodynamics
- Fluid Dynamics and Thin Films
- Plant Water Relations and Carbon Dynamics
- Solidification and crystal growth phenomena
- Combustion and flame dynamics
- Wind and Air Flow Studies
- Flow Measurement and Analysis
- Solar and Space Plasma Dynamics
- Characterization and Applications of Magnetic Nanoparticles
- Nonlinear Dynamics and Pattern Formation
- Geomagnetism and Paleomagnetism Studies
- Theoretical and Computational Physics
- Nanofluid Flow and Heat Transfer
- Physics and Engineering Research Articles
- Heat Transfer Mechanisms
- Fluid Dynamics and Vibration Analysis
- Electrical and Bioimpedance Tomography
- Advanced Thermodynamics and Statistical Mechanics
- Particle Dynamics in Fluid Flows
- Non-Destructive Testing Techniques
- Spacecraft and Cryogenic Technologies
- Adsorption and Cooling Systems
- Scientific Measurement and Uncertainty Evaluation
- Meteorological Phenomena and Simulations
University of Stuttgart
1995-2023
Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)
2014-2023
Technische Universität Ilmenau
2005-2014
Technische Universität Dresden
1995-2000
Helmholtz-Zentrum Dresden-Rossendorf
1992-1995
Princeton University
1994-1995
École Normale Supérieure de Lyon
1994
We describe a noncontact technique for velocity measurement in electrically conducting fluids. The technique, which we term Lorentz force velocimetry (LFV), is based on exposing the fluid to magnetic field and measuring drag acting upon lines. Two series of measurements are reported, one determined through angular rotary magnet system fixed measured directly. Both experiments confirm that signal linear function flow velocity. then derive scaling law relates localized distribution magnetized...
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.
Pumped heat electricity storage (PHES) has been recently suggested as a potential solution to the large-scale energy problem. PHES requires neither underground caverns compressed air (CAES) nor kilometer-sized water reservoirs like pumped hydrostorage and can therefore be constructed anywhere in world. However, since no large system exists yet, theoretical predictions are scarce, efficiency of such systems is unknown. Here we formulate simple thermodynamic model that predicts function...
The transformation of initially isotropic turbulent flow electrically conducting incompressible viscous fluid under the influence an imposed homogeneous magnetic field is investigated using direct numerical simulation. Under assumption large kinetic and small Reynolds numbers (magnetic Prandtl number P m [Lt ]1) quasi-static approximation applied for computation fluctuations. assumed to be contained in a three-dimensional cubic box with periodic boundary conditions. Large-scale forcing...
A Lorentz force flowmeter is a device for the contactless measurement of flow rates in electrically conducting fluids. It based on magnet system that acts upon flow. We formulate theory which connects measured to unknown rate. first apply three specific cases, namely (i) pipe exposed longitudinal magnetic field, (ii) under influence transverse field and (iii) interaction localized distribution material with uniformly moving sheet metal. These examples provide key scaling laws method...
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...
The convective flow in a thin liquid layer with free surface heated from below is studied using combination of accurate experiments silicone oil ( v =0.1 cm 2 s −1 ) and high-resolution direct numerical simulations the time-dependent governing equations. It demonstrated that above certain value ε threshold primary instability, ε=0, square convection cells rather than seemingly all-embracing hexagons are persistent dominant features Bénard convection. transition hexagonal to sets via...
We report high-resolution local-temperature measurements in the upper boundary layer of turbulent Rayleigh–Bénard (RB) convection with variable Rayleigh number Ra and aspect ratio Γ. The primary purpose work is to create a comprehensive data set temperature profiles against which various phenomenological theories numerical simulations can be tested. performed two series for air ( Pr = 0.7) cylindrical container, cover range from ≈10 9 12 Γ≈1 Γ≈10. In first Γ was varied while difference kept...
The linear stability of the parallel flow ψ0=sin(y) (Kolmogorov flow) is considered, taking into account viscosity, friction, and confinement (lateral walls). computations provide neutral curves in parameter space, wave numbers, speeds, as well spatial structure first unstable modes. Evidence presented that parameters depend nonuniformly on confinement. It shown already weak transverse significantly decreases longitudinal wavelength perturbations at instability onset. Strong changes...
The large scale “wind of turbulence” thermally driven flow is analyzed for very Rayleigh numbers between 4∙1011 and 7∙1011 Prandtl number 0.71 (air at 40°C) aspect ratios order one. wind direction near the upper plate found to horizontally oscillate with a typical time similar eddy turnover time. temporal autocorrelation reveals an extremely long memory system direction. We then apply extend dynamical model Gledzer, Dolzhansky, Obukhov flow, which based on Boussinesq equations in bulk can be...
We report an investigation of temperature profiles in turbulent Rayleigh–Bénard convection water based on direct numerical simulations (DNS) for a cylindrical cell with unit aspect ratio the same Prandtl number Pr and similar Rayleigh numbers Ra as used recent high-precision measurements by Funfschilling et al . ( J. Fluid Mech ., vol. 536, 2005, p. 145). The Nusselt Nu computed = 4.38 10 8 , 3 × 5 9 are found to be excellent agreement experimental data corrected finite thermal conductivity...
This article aims to demonstrate that molten metal flow at a high temperature can be measured effectively in contactless manner by using external direct current magnetic fields. The device applied the present work is termed Lorentz force flowmeter (LFF) and based on exposing magnet system measuring drag acting it. Two series of measurements are reported. In first series, we perform model experiment laboratory eutectic alloy GaInSn, which liquid room temperature. second devoted two plant...
We report highly resolved temperature measurements in turbulent Rayleigh–Bénard convection air at a fixed Prandtl number Pr = 0.7. Extending our previous work (du Puits et al 2007 J. Fluid Mech. 572 231–54), we carried out various aspect ratios while keeping the Rayleigh constant. demonstrate that field inside convective boundary layers of both horizontal plates is virtually independent on global flow pattern accompanying variation ratio. Thanks to technical upgrades experimental facility as...
The Future Fuels project combines research in several institutes of the German Aerospace Center (DLR) on production and use synthetic fuels for space, energy, transportation, aviation. This article gives an overview questions considered results achieved so far also provides insight into multidimensional interdisciplinary approach. Various methods models were used which are embedded context based established approaches. prospects large-scale fuel using renewable electricity solar radiation...
Surface-tension-driven convection in a planar fluid layer is studied by numerical simulation of the three-dimensional time-dependent governing equations limit infinite Prandtl number. Emphasis placed on spatial scale weakly supercritical flows and generation small-scale structures strongly flows. The decrease size hexagonal cells that we find agreement with experimental results. In case high Marangoni number, discontinuities temperature gradient are formed between cells, producing universal...
We report a theoretical investigation of the robustness two-dimensional inviscid magnetohydrodynamic (MHD) flows at low magnetic Reynolds numbers with respect to three-dimensional perturbations. use combination linear stability analysis and direct numerical simulations analyse three problems, namely flow in interior triaxial ellipsoid, two unbounded flows: vortex elliptical streamlines sheet parallel field. The ellipsoid is found present an exact analytical model which demonstrates both...
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...
The long-wavelength instability for thermocapillary-driven convection in two dimensions is studied numerically. system under consideration consists of a horizontal periodical liquid layer bounded from below by rigid wall and above deformable free surface. heated the bottom cooled above. problem can be approximated Stokes equation has dimensionless parameters. One parameter dynamic Bond number which ratio between gravity thermocapillary force. other static number, describes surface tension....
We report experiments on turbulent Rayleigh-B\'enard convection of air in a cylindrical large-scale facility with diameter $7\phantom{\rule{0.3em}{0ex}}\text{meters}$ and Rayleigh numbers up to $\mathrm{Ra}\ensuremath{\approx}{10}^{12}$. The is used explore the structure circulation for continuously varying aspect ratios between $\ensuremath{\Gamma}\ensuremath{\approx}1$ $\ensuremath{\Gamma}\ensuremath{\approx}10$. Using autocorrelation functions derived from high-resolution time series...
We present an experimental study of a liquid metal flow in rectangular channel under the influence inhomogeneous magnetic field. This is fundamental problem magnetohydrodynamics that relevant to technique electromagnetic braking process continuous casting steel as well for Lorentz force velocimetry. Based on local velocity and electric potential measurements we identify three distinct regions; namely (i) turbulence suppression region, (ii) vortical (iii) wall jet region. It shown region...
We use a combination of numerical simulations and experiments to elucidate the structure flow an electrically conducting fluid past localized magnetic field, called obstacle. demonstrate that stationary pattern is considerably more complex than in wake behind ordinary body. The steady shown undergo two bifurcations (rather one) involve up six just two) vortices. find first bifurcation leads formation pair vortices within region field we call inner vortices, whereas second gives rise attached...