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SUMMARY:Plumes and turbulent transport - Nobumitsu Yokoi (University of To
 kyo)
DTSTART:20240118T160000Z
DTEND:20240118T170000Z
UID:TALK208516@talks.cam.ac.uk
DESCRIPTION:Plumes\, thermals and jets are ubiquitously observed in convec
 tion in nature\, and play an important role in effectively mixing the mass
 \, momentum\, and heat there. Plumes are similar to streamers in fusion pl
 asmas in that they are basically generated in the direction parallel to th
 e gradient of large-scale structure in turbulence. In the framework of mul
 tiple-scale renormalised perturbation expansion theory\, where the respons
 e-function formalism is adopted as well as the multiple-scale analysis\, n
 on-equilibrium properties of turbulence are naturally incorporated into th
 e expression of turbulence correlations. Utilising theses analytical resul
 ts\, deviations of the timescale and length scale from the expressions bas
 ed on the local equilibrium turbulence can be argued. Examples of such non
 -equilibrium effects on turbulent transport are presented in the talk. To 
 apply this non-equilibrium effect to the transport associated with multipl
 e plumes\, the double filtering approach in the time and space domains is 
 introduced. In this formulation\, any fluctuation in the space domain is d
 ivided into the coherent/dispersion and the incoherent/random ones. Energy
  transfer mechanism between the coherent and incoherent fluctuation energi
 es is also discussed on the basis of transport equations of them. Regardin
 g plume motions as coherent/dispersion fluctuations\, a turbulence model f
 or the convection with multiple plumes is proposed. Application to stellar
  convections with the aid of numerical simulations shows that the turbulen
 t heat flux in the convection driven by surface cooling\, which could not 
 be reproduced by the standard gradient diffusion with the mixing-length mo
 del at all\, can be properly reproduced by the present non-equilibrium tra
 nsport model. Possible suggestions towards studies on plume formation mech
 anism will be made.
LOCATION:Seminar Room 1\, Newton Institute
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