The influence of non-Oberbeck-Boussinesq effects on rotating turbulent Rayleigh-Bénard convection

Abstract

The influence of non-Oberbeck-Boussinesq (NOB) effects on rotating turbulent Rayleigh-Bénard convection is investigated by means of three-dimensional direct numerical simulations (DNS). For this purpose the impact of temperature dependent material properties of water with a Prandtl number of Pr = 4.38 is considered at a Rayleigh number of Ra = 108. Simulations with and without superimposed rotation were performed within a Rossby number range of 0.3 ≤ Ro ≤ 3.0 and Ro = ∞. The generated flow fields are analysed with respect to deviations from the Oberbeck-Boussinesq (OB) cases.We obtain a breakdown of the top-bottom symmetry, that is, different boundary layer thicknesses, modified mean temperature profiles including an increase of the centre temperature and asymmetric velocity flow patterns in the non-rotating case. When the Rayleigh-Bénard cell is rotated, NOB effects decrease with increasing rotation rate, but are still significant. In particular they lead to a smaller temperature gradient within the bulk. The Nusselt number Nu in the non-rotating NOB cases slightly decreases, while it slightly increases in the rotating ones. However, the change in Nu remains within a few percent for all cases.