Viscoelastic thermally-driven flows in normal and microgravity conditions : laminar and turbulent states

Lappa, Marcello and Boaro, Alessio and Ferialdi, Hermes; Oliveira, Monica S. N. and Zografos, Konstantinos and Poole, Robert J. and Ellero, Marco and Anderson, Patrick D., eds. (2023) Viscoelastic thermally-driven flows in normal and microgravity conditions : laminar and turbulent states. In: 21st International Workshop on Numerical Methods for Non-Newtonian Flows. University of Strathclyde, Glasgow, p. 41. ISBN 9781914241420

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A survey is provided of recent numerical results concerning the dynamics of thermal convection in visco-elastic fluids subjected to thermal stimuli of various kinds (heating from below or from the side) and driving forces. The considered flows encompass canonical realizations of thermo-gravitational and surface-tension driven flows such as those obtained when the considered fluid is heated from below (namely, Rayleigh-Bénard and Marangoni-Bénard convection, respectively), and more exotic variants, such as those induced in microgravity conditions by the application of time-varying accelerations with a zero mean value (thermovibrational convection). The goal is to illustrate recent developments about the behaviour of all these forms of convection in the respective non-linear (finite-amplitude) states for the cases where the so-called concept of overstability is applicable. These problem are tackled through numerical solution of the three-dimensional Navier-Stokes and energy equations, properly cast in the framework of the Oldroyd-B or FENE-CR paradigms. An attempt is made to distillate some common ground by highlighting analogies and differences and interpreting the observed phenomena in the context of existing theories related to spatially localised oscillatory structures in fluid flow (the so-called oscillons), competing multiple solutions (i.e. states which exhibit SIC), strange attractors and elastic vs Kolmogorov turbulence.