Comparative experimental study of local mixing of active and passive scalars in turbulent thermal convection

Abstract

We investigate experimentally the statistical properties of active and passive scalar fields in turbulent Rayleigh-Bénard convection in water, at $Ra\sim 10^{10}$. Both the local concentration of fluorescence dye and the local temperature are measured near the sidewall of a rectangular cell. It is found that, although they are advected by the same turbulent flow, the two scalars distribute differently. This difference is twofold, i.e. both the quantities themselves and their small-scale increments have different distributions. Our results show that there is a certain buoyant scale based on time domain, i.e. the Bolgiano time scale $t_B$, above which buoyancy effects are significant. Above $t_B$, temperature is active and is found to be more intermittent than concentration, which is passive. This suggests that the active scalar possesses a higher level of intermittency in turbulent thermal convection. It is further found that the mixing of both scalar fields are isotropic for scales larger than $t_B$ even though buoyancy acts on the fluid in the vertical direction. Below $t_B$, temperature is passive and is found to be more anisotropic than concentration. But this higher degree of anisotropy is attributed to the higher diffusivity of temperature over that of concentration. From the simultaneous measurements of temperature and concentration, it is shown that two scalars have similar autocorrelation functions and there is a strong and positive correlation between them.

13 pages and 12 figures

References in corpus (12)

• Particles and fields in fluid turbulence
• Scaling in thermal convection: A unifying theory
• Orientation changes of the large-scale circulation in turbulent Rayleigh-Benard convection
• Heat transport by turbulent Rayleigh-Benard Convection in cylindrical samples with aspect ratio one and larger
• Lagrangian temperature, velocity and local heat flux measurement in Rayleigh-Benard convection
• Passive scalar intermittency in low temperature helium flows
• Scaling and universality in turbulent convection
• Geometric features of the mixing of passive scalars at high Schmidt numbers
• Active vs passive scalar turbulence
• Measured oscillations of the velocity and temperature fields in turbulent Rayleigh-Bénard convection in a rectangular cell
• Active and Passive Fields in Turbulent Transport: the Role of Statistically Preserved Structures
• Statistics of active vs. passive advections in magnetohydrodynamic turbulence

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• Disentangle plume-induced anisotropy in the velocity field in buoyancy-driven turbulence
• Scaling of maximum probability density functions of velocity and temperature increments in turbulent systems
• A five-dimensional Lorenz-type model near the temperature of maximum density
• Effects of shock topology on temperature field in compressible turbulence