Effects of aspect ratio on Rayleigh-Benard convection under non-Oberbeck-Boussinesq effects in glycerol

This study investigates the non-Oberbeck-Boussinesq (NOB) Rayleigh-Benard convection inside a two-dimensional rectangular cavity for a fluid with a high Prandtl number (Pr = 2547.0). The parametric study focuses on the aspect ratio (Gamma, 0.3 <= Gamma <= 8) dependence of heat transfer and fluid flows on the Rayleigh number (Ra) ranging from 5 x 10(3) to 10(8) and an NOB assumption with a temperature difference (Delta(theta) over tilde) of up to 50 K. We numerically find that the critical Ra (Ra-c) for convection onset decreases as Delta(theta) over tilde. increases for small Gamma, while it increases as Delta(theta) over tilde increases for large Gamma. Four flow regimes are classified based on kinetic and thermal energy dissipation rates in the Gamma-Ra plane. The aspect ratio dependency of the Nusselt number (Nu), Reynolds number (Re), and top and bottom thermal boundary layer (BL) thicknesses ((lambda) over bar (theta)(h, c)) is also investigated under both OB and NOB conditions. It is found that the Gamma effect on Re (up to 61%) is more serious than that on Nu (up to 4.5%), while Gamma does not obviously affect the generality of the classical NOB effects on scaling exponents of Nu, Re, and (lambda) over bar (theta)(h, c) for fully chaotic regimes. Top-bottom (lambda) over bar (theta)(h, c) asymmetry is confirmed, where the top BL is always thicker than the bottom one, and their ratio is up to 1.8 for Delta(theta) over tilde = 50 K at Ra = 10(8). Although (lambda) over bar (theta)(h) + (lambda) over bar (theta)(c) increases with an NOB effect enhancement for all aspect ratios, the compensation between (lambda) over bar (theta)(h) and (lambda) over bar (theta)(c) leads to small deviation (up to 7.0%) of (lambda) over bar (theta)(h) + (lambda) over bar (theta)(c) from unity. This contributes to the robustness of Nu because it is confirmed that the NOB effects on Nu are dominated by the change in (lambda) over bar (theta)(h) + (lambda) over bar (theta)(c).