Oscillations of the large-scale circulation in turbulent Rayleigh-Bénard convection: the off-center mode and its relationship with the torsional mode

Abstract

We report an experimental study of the large-scale circulation (LSC) in a turbulent Rayleigh-Bénard convection cell with aspect ratio unity. The temperature-extremum-extraction (TEE) method for obtaining the dynamic information of the LSC is presented. With this method, the azimuthal angular positions of the hot ascending and cold descending flows along the sidewall are identified from the measured instantaneous azimuthal temperature profile. The motion of the LSC is then decomposed into two different modes: the azimuthal mode and the translational or off-center mode. Comparing to the previous sinusoidal-fitting (SF) method, it is found that both methods give the same information about the azimuthal motion of the LSC, but the TEE method in addition can provide information about the off-center motion of the LSC, which is found to oscillate time-periodically around the cell's central vertical axis with an amplitude being nearly independent of the turbulent intensity. It is further found that the azimuthal angular positions of the hot ascending flow near the bottom plate and the cold descending flow near the top plate oscillate periodically out of phase by $\pi$, leading to the torsional mode of the LSC. These oscillations are then propagated vertically along the sidewall by the hot ascending and cold descending fluids. When they reach the mid-height plane, the azimuthal positions of the hottest and coldest fluids again oscillate out of phase by $\pi$. It is this out-of-phase horizontal positional oscillation of the hottest and coldest fluids at the same horizontal plane that produces the off-center oscillation of the LSC. A direct velocity measurement further confirms the existence of the bulk off-center mode of the flow field near cell center.

13 pages, 14 figures, the paper has been submitted to J. Fluid Mech

References in corpus (5)

• Rotations and cessations of the large-scale circulation in turbulent Rayleigh-Benard convection
• Orientation changes of the large-scale circulation in turbulent Rayleigh-Benard convection
• Plume motion and large-scale circulation in a cylindrical Rayleigh-Bénard cell
• Origin of the Temperature Oscillation in Turbulent Thermal Convection
• High Rayleigh number turbulent convection in a gas near the gas-liquid critical point

Cited by in corpus (17)

• The cause of oscillations of the large-scale circulation of turbulent Rayleigh-B{é}nard convection
• Prandtl-Blasius temperature and velocity boundary layer profiles in turbulent Rayleigh-Bénard convection
• Jump Rope Vortex in Liquid Metal Convection
• Combined measurement of velocity and temperature in liquid metal convection
• Koopman analysis of the long-term evolution in a turbulent convection cell
• Flow regimes of Rayleigh-Bénard convection in a vertical magnetic field
• Inclined turbulent thermal convection in liquid sodium
• Thermal boundary layer profiles in turbulent Rayleigh-Bénard convection in a cylindrical sample
• Experimental Investigation of Longitudinal Space-Time Correlations of the Velocity Field in Turbulent Rayleigh-Bénard Convection
• Effect of Plumes on Measuring the Large Scale Circulation in Turbulent Rayleigh-Bénard Convection
• Transition phenomena in unstably stratified turbulent flows
• Low-dimensional model of the large-scale circulation of turbulent Rayleigh-B{é}nard convection in a cubic container
• Local Lorentz force and ultrasound Doppler velocimetry in a vertical convection liquid metal flow
• Oscillatory large-scale circulation in liquid-metal thermal convection and its structural unit
• Effects of tilt on the orientation dynamics of the large-scale circulation in turbulent Rayleigh-B{é}nard convection
• Synchronizing the helicity of Rayleigh-Bénard convection by a tide-like electromagnetic forcing
• Thermoelectric Precession in Turbulent Magnetoconvection