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

Abstract

The influence of rotation on turbulent Rayleigh-Bénard convection in combination with non-Oberbeck-Boussinesq (NOB) effects is investigated by means of three-dimensional direct numerical simulations (DNS). For this purpose the impact of temperature dependent material properties is studied in glycerol with a Prandtl number of Pr = 2547.9 within a range of Rayleigh numbers of 10^5 ≤ Ra ≤ 10^8, and in water with Pr = 4.38 at Ra = 10^8, both under no rotation and superimposed with rotation within a Rossby number range of 0.3 ≤ Ro ≤ 3.0. The generated flow fields are analysed with respect to deviations from the Oberbeck-Boussinesq (OB) case. 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 for glycerol as well as for water 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 gradient of the temperature 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.