Intermittent fluctuations due to Lorentzian pulses in turbulent thermal convection

Abstract

Turbulent motions due to flux-driven thermal convection is investigated by numerical simulations and stochastic modelling. Tilting of convection cells leads to the formation of sheared flows and quasi-periodic relaxation oscillations for the energy integrals far from the threshold for linear instability. The probability density function for the temperature and radial velocity fluctuations in the fluid layer changes from a normal distribution at the onset of turbulence to a distribution with an exponential tail for large fluctuation amplitudes for strongly driven systems. The frequency power spectral density has an exponential shape, which is a signature of deterministic chaos. By use of a novel deconvolution method, this is shown to result from the presence of Lorentzian pulses in the underlying time series, demonstrating that exponential frequency spectra can persist in also in turbulent flow regimes.

21 pages (single column format), 14 figures

References in corpus (5)

• A Comparison of Turbulent Thermal Convection Between Conditions of Constant Temperature and Constant Flux
• Convergence of statistical moments of particle density time series in scrape-off layer plasmas
• Power law spectra and intermittent fluctuations due to uncorrelated Lorentzian pulses
• On the relevance of uncorrelated Lorentzian pulses for the interpretation of turbulence in the edge of magnetically confined toroidal plasmas
• Order and chaos in two-dimensional Rayleigh-Bénard convection