Interface evoluation between binary immiscible fluids under weak magnetic field. - In: 9th International Conference on Fundamental and Applied MHD, Thermo Acoustic and Space Technologies, (2014), S. 341-345
Laminar-turbulent transition in magnetohydrodynamic duct, pipe, and channel flows. - In: Applied mechanics reviews, ISSN 1088-8535, Bd. 66 (2014), 3, S. 030802, insges. 17 S.
A magnetic field imposed on a flow of an electrically conducting fluid can profoundly change flow behavior. We consider this effect for the situation of laminar-turbulent transition in magnetohydrodynamic duct, pipe, and channel flows with homogeneous magnetic field and electrically insulating walls. Experimental and recent computational results obtained for flows in pipes, ducts and channels are reviewed.
http://dx.doi.org/10.1115/1.4027198
Turbulent boundary layer in high Rayleigh number convection in air. - In: Physical review letters, ISSN 1079-7114, Bd. 112 (2014), 12, 124301, insges. 5 S.
Flow visualizations and particle image velocimetry measurements in the boundary layer of a Rayleigh-Bénard experiment are presented for the Rayleigh number Ra 1/4 1.4 × 1010. Our visualizations indicate that the appearance of the flow structures is similar to ordinary (isothermal) turbulent boundary layers. Our particle image velocimetry measurements show that vorticity with both positive and negative sign is generated and that the smallest flow structures are 1 order of magnitude smaller than the boundary layer thickness. Additional local measurements using laser Doppler velocimetry yield turbulence intensities up to I 1/4 0.4 as in turbulent atmospheric boundary layers. From our observations, we conclude that the convective boundary layer becomes turbulent locally and temporarily although its Reynolds number Re [approximately] 200 is considerably smaller than the value 420 underlying existing phenomenological theories. We think that, in turbulent Rayleigh-Bénard convection, the transition of the boundary layer towards turbulence depends on subtle details of the flow field and is therefore not universal.
https://doi.org/10.1103/PhysRevLett.112.124301
Spatial and temporal resolution of a local Lorentz force flowmeter. - In: Measurement science and technology, ISSN 1361-6501, Bd. 25 (2014), 5, S. 055302, insges. 7 S.
http://dx.doi.org/10.1088/0957-0233/25/5/055302
An experimental method for the investigation of indoor airflows in a reduced scale model room : development and application, 2014. - Online-Ressource (PDF-Datei: V, 97 Bl., 2,94 MB) : Ilmenau, Techn. Univ., Diss., 2013
Parallel als Druckausg. erschienen
In der vorliegenden Arbeit wurde ein Verfahren zur experimentellen Untersuchung nicht-isothermer Raumluftströmungen in einem stark verkleinerten Modellraum unter Berücksichtigung aller Ähnlichkeitskennzahlen entwickelt. Mit diesem Verfahren konnte erstmals eine sehr hohe Genauigkeit bezüglich der Ähnlichkeitskennzahlen Reynolds-Zahl Re, Rayleigh-Zahl Ra, Prandtl-Zahl Pr sowie der Archimedes-Zahl Ar erreicht werden. Die Anpassung der Randbedingungen an den Modellmaßstab erfolgt bei dieser Methode über die Anpassung der Materialeigenschaften eines beliebigen Arbeitsgases durch Erhöhen des Drucks p. Dieses Verfahren konnte in der weltweit einzigartigen Experimentieranlage SCALEX (SCALEX = scaled convective airflow laboratory experiment) umgesetzt und auf zwei Beispielproblemstellungen der Raumluftströmung (isotherme sowie gemischte Konvektion) erfolgreich angewendet werden. Dazu wurden die Geschwindigkeitsverteilungen der groß-skaligen Strömungsstrukturen in einem im Maßstab von 1:10 verkleinerten Modellraum hinreichend komplexer Geometrie für den Fall isothermer sowie gemischter Konvektion untersucht. Die Geschwindigkeitsmessungen wurden mit einem 2D-laser Doppler velocimetry System durchgeführt. Als Arbeitsgas wurde Schwefelhexafluorid (SF6) bei einem Druck von p = 4.517bar verwendet. Die Ergebnisse der vorliegenden Arbeit sowie die neu entstandene Anlage tragen zu einem umfangreichen Verständnis sowie einem vereinfachten experimentellen Zugang zum komplexen Themengebiet der Raumluftströmungen bei.
http://www.db-thueringen.de/servlets/DocumentServlet?id=23794
Flow rate measurement in aggressive conductive fluids. - In: The European physical journal, ISSN 2100-014X, Bd. 67 (2014), 02022, S. 02022-p.1-02022-p.5
https://doi.org/10.1051/epjconf/20146702022
Contact-free measurement of the flow field of a liquid metal inside a closed container. - In: The European physical journal, ISSN 2100-014X, Bd. 67 (2014), 02033, S. 03033-p.1-03033-p.4
https://doi.org/10.1051/epjconf/20146702033
Patterned turbulence in spatially evolving magnetohydrodynamic duct and pipe flows. - In: Theoretical and computational fluid dynamics, ISSN 1432-2250, Bd. 28 (2014), 3, S. 319-334
Laminar-turbulent transition in spatially evolving magnetohydrodynamic pipe and duct flows is investigated numerically. The results are in good agreement with the classical 1937 experiments of J. Hartmann and F. Lazarus. It is found that the recently discovered flow regimes with turbulent spots near sidewalls are realized in spatially developing flows and must be detectable in experiments.
http://dx.doi.org/10.1007/s00162-013-0317-y
Electromagnetic drag on a magnetic dipole caused by a translating and rotating conducting cylinder. - In: Journal of engineering mathematics, ISSN 1573-2703, Bd. 88 (2014), 1, S. 177-195
We report an analytical and numerical investigation of the forces and torques on a magnetic point dipole due to the presence of a moving electrically conducting cylinder. The kinematic induction problem is formulated in the quasistatic approximation that is appropriate for low magnetic Reynolds numbers. The motion of the cylinder is either a steady translation along its axis or a steady rotation about it. We find different power laws for the dependence of the force on the distance between dipole and cylinder when it is either small or large compared with the cylinder radius. The power laws for large distances are derived systematically by a long-wave expansion in the axial coordinate. For rotation, the case of a finite cylinder is studied by means of a dipole approximation.
http://dx.doi.org/10.1007/s10665-013-9683-0
A mixing-length model for side layers of magnetohydrodynamic channel and duct flows with insulating walls. - In: Physics of fluids, ISSN 1089-7666, Bd. 26 (2014), 2, 025106, insges. 11 S.
We propose a simple extension of Prandtls classical mixing-lengthmodel for channel flow in order to describe the effects of a uniform spanwise magnetic field. The mixing length is assumed to be constrained by an additional length scale called the Joule damping length. It is based on the friction velocity and the Joule damping time. The limitation of mixing length is implemented by using the harmonic mean of the wall distance and the Joule damping length. Near the wall, the model captures the combined linear-logarithmic dependence of velocity on the wall distance observed in direct numerical simulations. It also provides a satisfactory prediction for the overall velocity distribution for different Reynolds and Hartmann numbers. The velocity profile of turbulent side layers in magnetohydrodynamic duct flows in a strong field can also be computed with the help of the model provided that the Hartmann layers are already laminar.
https://doi.org/10.1063/1.4864660