Non-Oberbeck-Boussinesq effects in two-dimensional Rayleigh-Benard convection of different fluids

Non-Oberbeck-Boussinesq (NOB) effects in three representative fluids are quantitatively investigated in two-dimensional Rayleigh-Benard convection. Numerical simulations are conducted in air, water, and glycerol with Prandtl numbers of Pr = 0:71; 4:4, and 2547, respectively. We consider Rayleigh number Ra is an element of[106, 109] involving temperature difference (Delta(theta) over bar) of up to 60K. The velocity and temperature profiles are found to be top-bottom antisymmetric under NOB conditions. As Pr increases, the time-averaged temperature of the cavity center (t) increases under NOB conditions and the value of (t) is only weakly influenced by Ra for all fluids. For Pr = 4.4 and 2547, with the enhancement of NOB effects, (t) linearly increases and the maximum theta(rms) decreases/increases, and its location shifts toward/away from the wall near the bottom/top wall. Dispersed (t) points and opposite phenomenon are observed in Pr = 0.71. The Nusselt number (Nu) and thermal boundary layer thickness at hot and cold walls ((lambda) over bar (theta)(h,c)) of the three fluids are comparable, and the Reynolds number (Re) significantly decreases as Pr increases. Under the NOB conditions with Pr = 4.4 and 2547, Nu decreases, Re increases, and (lambda) over bar (theta)(h) ((lambda) over bar (theta)(c)) thins (thickens) in an approximately linear fashion. Furthermore, the NOB effects on Nu, Re, and lambda(theta)(h,c) are relatively small for Pr = 0.71 and 4.4, whereas the modifications caused by NOB effects at Pr = 2547 are more significant. The power-law scaling factors of Nu, Re, and (lambda) over bar (theta)(h,c) are demonstrated to be robust to Pr, as well as NOB effects.

Automated summary

In this study, the non-Oberbeck-Boussinesq (NOB) effects in three representative fluids in two-dimensional Rayleigh-Benard convection were quantitatively investigated. It was found that the temperature and velocity profiles were top-bottom antisymmetric under NOB conditions. The time-averaged temperature of the cavity center increased with increasing Prandtl number, and its value was weakly influenced by the Rayleigh number for all fluids. Furthermore, the NOB effects on various parameters such as the Nusselt number and thermal boundary layer thickness were relatively small for Pr = 0.71 and 4.4, but significant for Pr = 2547.