Rayleigh-Bénard convection in liquids with temperature-dependent material properties

Abstract

The influence of non-Oberbeck-Boussinesq (NOB) effects on Rayleigh-Bénard convection in liquids is investigated by means of three-dimensional direct numerical simulations (DNS). For this purpose the impact of temperature dependent material properties is studied in water with a Prandtl number of Pr = 4.38 within a range of Rayleigh numbers of 10^7 ≤ Ra ≤ 10^9 and in glycerol with Pr = 2547.9 and within 10^5 ≤ Ra ≤ 10^9. The imposed temperature differences ∆ reach up to 70K in the case of water and up to 80K in the case of glycerol. 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, entailing an increase of the centre temperature, and asymmetric velocity flow patterns. Furthermore the influence on the scaling behaviour of the Reynolds number Re and the Nusselt number Nu is studied.