Enhanced Heat Transfer in Rayleigh-Bénard Flows at Transcritical Conditions

Rayleigh-Bénard (RB) flows arise from a horizontal fluid layer subject to a downwards gravitational force coupled with heating from the underside and cooling from above. Despite extensive computational, theoretical, and experimental research of this canonical configuration, the behavior at supercritical pressures is poorly understood. At these conditions, strong gradients and fluctuations in thermodynamic properties lead to significant deviations from classical theory in the Oberbeck-Boussinesq (OB) regime. We present a series of highly-resolved RB simulations at transcritical and supercritical conditions, at Rayleigh numbers of up to 10⁹. Heat transfer values, as characterized by the Nusselt number, are enhanced by up to O(100%) compared to OB values at the same Rayleigh number. In characterizing this intensified heat transfer behavior, we present statistics and flow structures, highlighting differences not only among each region of the domain but also with OB simulations.