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SUMMARY:Vortical dynamo in turbulent multiphase flows - Petrosyan\, A (Spa
 ce Research Institute\, Russian Academy of Sciences)
DTSTART:20120724T143500Z
DTEND:20120724T145500Z
UID:TALK39030@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Magnetic disturbances are known to be amplified by helical tur
 bulence. The possibility of amplification of large-scale hydrodynamic fiel
 ds by small-scale helical turbulence is considered. The important differen
 ce between hydrodynamic and magnetic theories is that the latter describe 
 the evolution of magnetic field on the background of a given hydrodynamic 
 flow (kinematic dynamo)\, whereas in hydrodynamics such a situation is mor
 e complex. The hydrodynamic problem is self-consistent and non-linear. A g
 eneration of large-scale helical vortices resulting from the instability o
 f small-scale helical turbulence with respect to two-scale disturbance is 
 considered. In order to investigate such instability\, we consider two cas
 es: (1) an incompressible fluid containing rigid particles\; (2) an incomp
 ressible fluid containing gas babbles. An equation describing the evolutio
 n of mean disturbances is derived and the instability increment is obtaine
 d. The analysis revealed that helical turbulence in an incompressible flui
 d with rigid particles and in incompressible fluid with gas babbles is uns
 table against vortical disturbances. The generation terms formally coincid
 ing with those in the theory of hydromagnetic dynamo are contained in Reyn
 olds averaged equations derived at the scale of mean motions. It should be
  noted that only helicity is enough for the process of generation in magne
 tohydrodynamics. In hydrodynamic theory\, because of the mentioned differe
 nces\, it is also necessary to take into account additional factors. In th
 is paper two such additional factors are the presence of rigid particles o
 r gas babbles whose motions provide the existence of divergence at a turbu
 lent scale and thus provide a non-zero value of the Reynolds stresses in t
 he averaged equations.\n
LOCATION:Seminar Room 1\, Newton Institute
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