Numerical and Experimental Studies on Electromagnetic Stirring
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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: [email protected] SFB 609. Supported by DFG. Motivation and Objectives.

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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: [email protected]

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


Motivation and objectives
Motivation and Objectives Stirring

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


Previous work
Previous work Stirring …

Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004

Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth

Numerical and Experimental Studies on Electromagnetic Stirring


Previous work1
Previous work Stirring …

Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004

Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth

Numerical and Experimental Studies on Electromagnetic Stirring


Previous work2
Previous work Stirring …

Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004

Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth

Numerical and Experimental Studies on Electromagnetic Stirring


Achievements
StirringAchievements

Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004

Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth

Numerical and Experimental Studies on Electromagnetic Stirring


Achievements1
… Achievements Stirring

Sino-German Workshop on EPM, Shanghai, Oct. 11-12, 2004

Stiller, Frana, Grundmann, Cramer, Varshney, Gerbeth

Numerical and Experimental Studies on Electromagnetic Stirring


Numeric s i
Numeric Stirrings 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


Numeric s ii
Numeric Stirrings 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


Multimag facility at fzr
MULTIMAG Facility at FZR Stirring

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


Measurement techniques
Measurement Techniques Stirring

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


Results rmf i
Results Stirring: 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


Results rmf ii
Results Stirring: 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


Results rmf iii
Results Stirring: 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


Results rmf iii1
Results Stirring: 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


Results rmf iii2
Results Stirring: 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


Results rmf iii3
Results Stirring: 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


Results pmf
Results: PMF Stirring

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


Summary
Summary Stirring

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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