Electromagnetic flow control in poorly conducting fluids

Flow control has a wide range of possible applications, e.g., to reduce the drag of vehicles or to achieve certain effects, such as to increase the lift of landing or starting airplanes. If the fluids in question have a certain, albeit low, electrical conductivity - such as seawater and ionized air, for example - it is possible to control the flow in a contactless manner by using electromagnetic forces. The image to the left demonstrates the suppression of flow separation on an inclined profile, which is simply represented here by a plate. This plate is equipped with permanent magnets and electrodes. As soon as current flows from the electrodes into the liquid, a wall parallel Lorentz force is created by the cross product of current density and magnetic field. The Lorentz force acts mainly in the direct vicinity of the plate and in streamwise direction and completely suppresses flow separation. This increases the - here downwards directed - lift of the plate and drastically reduces its drag.

The kind of separation suppression described above is very energy-intensive, as the entire momentum required to re-attach the separated flow must be generated by the Lorentz force alone. A more energetically favorable variant is the application of periodic Lorentz forces only at the leading edge of the profile, which excites the shear layer at the edge of the separated region and generates large vortices. These vortices transport momentum from the free stream into the separated region. While the lift is oscillating under these conditions, its mean value is drastically increased compared to the separated case and reaches values similar to those under the action of stationary Lorentz forces. However, much less energy is required to obtain the desired effect.

An attractive field for electromagnetic flow control are electrochemical processes. They are already working with electric currents to achieve the desired electrode reactions. Beneficial Lorentz forces can thus be easily generated by simply adding permanent magnets at the right places.

Easily intelligibible introductions (in German) to the topic of flow control by electromagnetic forces were given as part of the Dresden Long Nights of Science, the Open Lab Days as well as in frame of the yearly training for teachers. A fairly up-to-date summary is provided by the recording (Youtube-link) of a talk at the EuMHD Summer School 2022.

Publications

G. Mutschke: Magnetic Control of Flow and Mass Transfer in Weakly Conducting Fluids; In: B. Doudin et al. (eds.) Magnetic Microhydrodynamics, Topics in Applied Physics 120 (2024) 23-31. 10.1007/978-3-031-58376-6_3

B. Monnier, D. R. Williams, T. Weier, T. Albrecht: Comparison of a Separated Flow Response to Localized and Global-type Disturbances, Experiments in Fluids 57 (2016), 114. 10.1007/s00348-016-2199-4

T. Albrecht, T. Weier, G. Gerbeth, D. R. Williams: Separated flow response to single pulse actuation, AIAA Journal 53(1) (2015), 190-199. 10.2514/1.J053026

T. Weier, S. Landgraf, C. Cierpka: Über die Lorentzkraft-getriebene dreidimensionale Strömung um eine magnetische Kugel in einem elektrischen Feld, In: Czarske, J., Büttner, L., Fischer, A., Ruck, B., Leder, A., Dopheide, D. (Hrsg.) Proceedings der 23. GALA-Fachtagung "Lasermethoden in der Strömungsmesstechnik", 978-3-9816764-1-9, 18-1-18-8 18

T. Albrecht, J. Stiller, H. Metzkes, T. Weier, G. Gerbeth: Electromagnetic flow control in poor conductors, European Physical Journal - Special Topics 220 (2013), 275-285. 10.1140/epjst/e2013-01813-4

T. Albrecht, V. Del Campo, T. Weier, H. Metzkes, J. Stiller: Deriving forces from 2D velocity field measurements, European Physical Journal - Special Topics 220 (2013), 91-100. 10.1140/epjst/e2013-01799-9

J. König, M. Neumann, S. Mühlenhoff, K. Tschulik, T. Albrecht, K. Eckert, M. Uhlemann, T. Weier, L. Büttner, J. Czarske: Optical velocity measurements of electrolytic boundary layer flows influenced by magnetic fields, European Physical Journal - Special Topics 220 (2013), 79-89. 10.1140/epjst/e2013-01798-x

T. Albrecht, T. Weier, G. Gerbeth, H. Metzkes, J. Stiller: A method to estimate the planar, instantaneous body force distribution from velocity field measurements, Physics of Fluids 23(2) (2011), 021702. 10.1063/1.3552110

T. Weier, T. Albrecht, G. Gerbeth, H. Metzkes, J. Stiller: The electromagnetically forced flow over a backward-facing step, 7^th International Symposium On Turbulence and Shear Flow Phenomena (TSFP-7), 28.-31.07.2011, Ottawa, Canada. P31P

C. Cierpka, T. Weier, G. Gerbeth: Synchronized force and particle image velocimetry measurements on a NACA 0015 in post stall under control of time periodic electromagnetic forcing, Physics of Fluids 22 (2010), 075109. 10.1063/1.3466662

T. Albrecht, H. Metzkes, R. Grundmann, G. Mutschke, G. Gerbeth: Tollmien-Schlichting wave damping by a streamwise oscillating Lorentz force, Magnetohydrodynamics 44(3) (2008), 205-222. 2008/3/MG.44.3.1.R

C. Cierpka, T. Weier, G. Gerbeth: Evolution of vortex structures in an electromagnetically excited separated flow, Experiments in Fluids 45 (2008), 943-953. 10.1007/s00348-008-0512-6

T. Weier, C. Cierpka, G. Gerbeth, Coherent structure eduction from PIV data of an electromagnetically forced separated flow, Journal of Fluids and Structure 24 (2008), 1339-1348. 10.1016/j.jfluidstructs.2008.06.005

T. Albrecht, H. Metzkes, G. Mutschke, R. Grundmann, G. Gerbeth: Tollmien-Schlichting wave cancellation using an oscillating Lorentz force, In: Palma, J., Lopes, A.S. (eds.) Advances in Turbulence XI, (2007), 218-220. 10.1007/978-3-540-72604-3_69

C. Cierpka, T. Weier, G. Gerbeth, Electromagnetic control of separated flows using periodic excitation with different wave forms, In: R. King (ed.) Active Flow Control, Notes on Numerical Fluid Mechanics and Multidisciplinary Design 95, (2007), 27-41. 10.1007/978-3-540-71439-2_2

T. Weier, V. Shatrov, G. Gerbeth, Flow control and propulsion in weak conductors, In: S. Molokov, R. Moreau, K. Moffatt (eds.) Magnetohydrodynamics - Historical Evolution and Trends, (2007), 295-312. 10.1007/978-1-4020-4833-3_18

T. Albrecht, G. Grundmann, G. Mutschke, G. Gerbeth: On the stability of the boundary layer subject to a wall-parallel Lorentz force, Physics of Fluids 18 (2006), 098103. 10.1063/1.2353401

G. Mutschke, G. Gerbeth, T. Albrecht, R. Grundmann: Separation Control at Hydrofoils using Lorentz forces, European Journal of Mechanics B 25(2) (2006), 137-152. 10.1016/j.euromechflu.2005.05.002

T. Weier, Elektromagnetische Strömungskontrolle mit wandparallelen Lorentzkräften in schwach leitfähigen Fluiden, Dissertation TU Dresden, (2006). WTB FZR-454 2006

T. Weier, G. Gerbeth, Experimental Results on the Effect of Wall-Parallel Lorentz Forces on Lift and Drag of Hydrofoils, 2^nd International Symposium on Seawater Drag Reduction, Busan, Korea, 23–26 May 2005, 267-281. pdf

T. Weier, G. Gerbeth, Control of Separated Flows by Time Periodic Lorentz Forces, European Journal of Mechanics B 23(6) (2004), 835-849. 10.1016/j.euromechflu.2004.04.004

T. Weier, G.; Gerbeth, G. Mutschke, O. Lielausis, G. Lammers, Control of flow separation using electromagnetic forces, Flow, Turbulence and Combustion, 71(1-4) (2003) 5-17. 10.1023/B:APPL.0000014922.98309.21

T. Weier, U. Fey, G. Gerbeth, G. Mutschke, O. Lielausis, E. Platacis, Boundary Layer Control by Means of Wall Parallel Lorentz Forces, Magnetohydrodynamics, 37(1/2) (2001), 177-186. 2001/1/MG.37.1.22.R

T. Weier, U. Fey, G. Gerbeth, G. Mutschke, V. Avilov, Boundary layer control by means of electromagnetic forces, ERCOFTAC bulletin, 44 (2000), 36-40. pdf

T. Weier, G. Gerbeth, G. Mutschke, U. Fey, O. Posdziech, O. Lielausis, E.Platacis, Some results on electromagnetic control of flow around bodies, Proc. of the International Symposium on Seatwater Drag Reduction, Newport, Rhode Island (USA), 22.-24. Juli 1998, 395-400. DTIC_ADA362573

T. Weier, G. Gerbeth, G. Mutschke, E. Platacis, O. Lielausis, Experiments on cylinder wake stabilization in an electrolyte solution by means of electromagnetic forces localized on the cylinder surface, Experimental Thermal and Fluid Science, 16, (1998), 84-91. 10.1016/S0894-1777(97)10008-5