Measured oscillations of the velocity and temperature fields in turbulent Rayleigh-Bénard convection in a rectangular cell

Abstract

Temperature and velocity oscillations have been found in a rectangular Rayleigh-Bénard convection cell, in which one large-scale convection roll exists. At Rayleigh number Ra=8.9x10(11) and Prandtl number Pr=4, temperature oscillations can be observed in most parts of the system and the oscillation period remains almost constant, tT=74+/-2 s. Velocity oscillation can only be found in its horizontal component vy (perpendicular to the large-scale circulation plane) near the cell sidewall, its oscillation period is also constant, tv=65+/-2 s, at these positions. Temperature and velocity oscillations have different Ra dependences, which are, respectively, indicated by the Péclect number PeT=0.55Ra0.47 and Pev=0.28Ra0.50. In comparison to the case of a cylindrical cell, we find that velocity oscillations are affected by the system geometry.

The effect of cell tilting on turbulent thermal convection in a rectangular cell

“…On the other hand, the oscillation is weakest in the cell centre (at position C1). Therefore, the oscillation distributions near the sidewall and in the centre are consistent with the previous observations in the level case (Zhou et al 2007). As shown in figure 5, the intensity of oscillation is the strongest, and is almost the same at the positions B1 (Bv1) and T3 (Tv3) in temperature (velocity) signals.…”

“…A prominent feature in RBC is the emergence of a well-defined low-frequency oscillation of the local temperature and velocity, which has been observed in many experiments (Castaing et al 1989;Sano et al 1989;Niemela et al 2001;Funfschilling & Ahlers 2004;Qiu et al 2004;Zhou, Sun & Xia 2007;Xi et al 2009). In earlier studies, it was suspected that the oscillation is caused by the thermal boundary layer instability that is periodically triggered by the incoming plumes coupled with the LSC, and it was found that the oscillation period is more or less the same as the turnover time of the LSC (Castaing et al 1989;Sano et al 1989).…”

“…The working fluid is water, with Pr 6.3. The experimental apparatus and set-up are similar to those described by Xia et al (2003) and Zhou et al (2007), except that the cell size is smaller here. The top and bottom plates are made of copper, and the sidewall is made of Plexiglas.…”

“…In this section, the Reynolds number, which is defined as Re = LV/ν, is discussed using several characteristic speeds for V. In RBC, the oscillation period is comparable to the complete turnover time of the single LSC, for aspect ratios close to one Zhou et al 2007;Weiss & Ahlers 2013). Thus, the Reynolds number Re o , based on the oscillation period (τ o ), can be defined as…”

Thermal instability of the fluid column in a borehole: application to the Yaxcopoil hole (Mexico)

“…Both numerical and laboratory experiments confirm that the temperature oscillation is a general and universal phenomenon in thermal convection. These experiments revealed an erratic growth and decay of the convection amplitude in the states when the threshold of the stable convection is exceeded (Alonso et al 2005;He 2007;Zhou et al 2007). See also comprehensive reviews by Cross and Hohenberg (1993), Erenburg et al (2003) and Govorukhin and Shevchenko (2005).…”