
Regular flow reversals in RayleighBenard convection in a horizontal magnetic fieldRegular flow reversals in RayleighBenard convection in a horizontal magnetic field 
"/Tasaka, Yuji(1000000419946)/"Tasaka, Yuji ,
"/Igaki, Kazuto/"Igaki, Kazuto ,
"/Yanagisawa, Takatoshi/"Yanagisawa, Takatoshi ,
"/Vogt, Tobias/"Vogt, Tobias ,
"/Zuerner, Till/"Zuerner, Till ,
"/Eckert, Sven/"Eckert, Sven
93
(
4
)
, p.043109 , 20160408 , American Physical Society (APS)
ISSN:24700045
Description
Magnetohydrodynamic RayleighBenard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasitwodimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q. We explored convection regimes in a parameter range, at 2 x 10(3) < Q < 10(4) and 5 x 10(3) < Ra < 3 x 10(5), thus extending the regime diagram provided by Yanagisawa et al. [T. Yanagisawa et al., Phys. Rev. E 88, 063020 (2013)]. Three regimes were identified, of which the regime of regular flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra/Q = 10, where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a fourroll state in a dominant fiveroll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach.
FullText
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