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Numerical and Experimental Studies on Electromagnetic Stirring

Numerical and Experimental Studies on Electromagnetic Stirring J. Stiller , K. Frana, R. Grundmann TU Dresden, Germany & A. Cramer, K. Varshney, G. Gerbeth FZ Rossendorf, Germany email: stiller@tfd.mw.tu-dresden.de. SFB 609. Supported by DFG. Motivation and Objectives.

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Numerical and Experimental Studies on Electromagnetic Stirring

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  1. Numerical and Experimental Studies on Electromagnetic Stirring J. Stiller, K. Frana, R. Grundmann TU Dresden, Germany & A. Cramer, K. Varshney, G. GerbethFZ Rossendorf, Germany email: stiller@tfd.mw.tu-dresden.de SFB 609 Supported by DFG Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  2. Motivation and Objectives Central topic: Stirring with alternating magnetic fields • Rotating (RMF) • Traveling (TMF) • Pulsating (PMF) Rotating Field • Aspect ratioH/D • Taylor number • Design of tailored superposition fields Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  3. Previous work … Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  4. Previous work … Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  5. Previous work … Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  6. … Achievements Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  7. … Achievements Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  8. Numerics I Direct Numerical Simulation Mathematical Model • Field frequency: ω<1/μσR2 • Flow velocity: u<ωR • Resolve all scales • No turbulence model < Maxwell equationsdecouple Methods and Codes • Low-induction / low frequency • approximation: • Navier-Stokes problem foru • Lorentz force: fj×B0 • Current density: jσ(t A0) • Electrical potential: 20 Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  9. Numerics II Finite Element Solver • PSPG, linear shape functions • AB2 time integration • 2nd order in space and time • 8…12 million elements • local grid refinement to resolve Bödewadt layers • linear stability threshold[Grants&Gerbeth 2002] reproduced within 0.2% Initial grid ~ 105tets, 32 partitions Convergence study: RMF driven flowin infinite cylinder Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  10. MULTIMAG Facility at FZR Example: measured Br distribution in TMF Iron-free coil system • Superposition of rotating, traveling, pulsating and DC fields • Electrical power supply: 500kW • Measurement volume: D = 365mm, H = 400mm Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  11. Measurement Techniques Calibration curves of the PD sensors „Standard“ vs. miniaturized PD sensors Ultrasonic Doppler Velocimetry Potential difference Sensors • Mini-sensor is only weakly invasive • Turbulence measurements possible • Expensive electronics required • Non-invasive • Measurement of velocity profiles • Less sensitive than PD Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  12. Results: RMF I DNS: Ta= 3·105 ≈ 7.5Tac Snapshot of instantaneous velocity • Key features • Large-scale azimuthal fluctuations • Taylor-Görtler vortices Q contours of fluctuation velocity Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  13. Results: RMF II TG vortices at various Taylor numbers 1.125Tac 2.5Tac 7.5Tac Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  14. Results: RMF III Turbulence spectra at 7.5Tac Comparison of frequency and wave spectra at r/R = ¾, assuming validity ofTaylor’s hypothesis Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  15. Results: RMF III Turbulence spectra at 7.5Tac Comparison of frequency and wave spectra at r/R = ¾, assuming validity ofTaylor’s hypothesis Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  16. Results: RMF III Turbulence spectra at 7.5Tac • DNS resolved Comparison of frequency and wave spectra at r/R = ¾, assuming validity ofTaylor’s hypothesis Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  17. Results: RMF III Turbulence spectra at 7.5Tac • DNS resolved • Slope k4 or steeper inshort-wave part of inertial subrange • No harmonics • Significantcontribution of frequencies1/2…1/10ωF Comparison of frequency and wave spectra at r/R = ¾, assuming validity ofTaylor’s hypothesis Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  18. Results: PMF Pulsating magnetic field: Experiment f Setup and expected flow • Observations • 90% of kinetic energy is „turbulent“ • Low-frequencyoscillations are dominant Vertical profile of axial velocity near rim (UDV, bottom left) Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

  19. Summary Conclusions • Excellent agreement between DNS and experimental results for RMF driven flow up to ~ 10Tac • Taylor-Görtler vortices and associated large-scale fluctuations provide an efficient mixing mechanism which is complemented by the mean secondary flow • Both, RMF and PMF driven flows, are dominated by long-lived structures which give rise to low-frequency oscillations and thus render RANS methods useless Perspectives • Continued investigation of magnetically driven flows based on DNS and experiments: TMF, PMF, combined fields, spin-up • Large-Eddy-Simulations at higher Reynolds numbers • Tailored fields for more efficient stirring and mixing • Non-isothermal flows • Electromagnetic flow control for CG model configuration (joint effort in SFB 609) Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004 Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth Numerical and Experimental Studies on Electromagnetic Stirring

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