Buoyancy- and thermocapillary-driven flows in differentially heated cavities for low-Prandtl-number fluids

Abstract

The influence of thermocapillary forces on buoyancy-driven convection is numerically simulated for shallow open cavities with differentially heated endwalls and filled with low-Prandtl-number fluid. Calculations are carried out by solving two-dimensional Navier-Stokes equations coupled to the energy equation, for three aspects ratios A = (length/height) = 4, 12.5 and 25, and several values of the Grashof number (up to 6 × 104) and Reynolds number (|Re| ≤ 1.67 × 104). Thermocapillarity can have a quite significant effect on the stability of a primarily buoyancy-driven flow. The result of the combination of the two basic mechanisms (thermo-capillarity) and buoyancy) depends on whether their effects are additive (positive Re) or opposing (negative Re); counter-acting mechanisms yield more complex flow patterns. The critical Grashof number Grc for the onset of the unsteady regime is found to decrease substantially within a small range of negative Re, and to increase for positive Re (and also for large negative Re). For Gr = 4 × 104, A = 4 and small negative Reynolds numbers, −2.4 × 103 ≤ Re < 0, mono-periodic and bi- or quasi-periodic regimes are shown to exist successively, followed by a reverse transition. The development of the instabilities from an initial steady-state regime has been investigated by varying Re for Gr = 1.5 × 104 (below Grc at Re = 0); the onset of buoyant instabilities is enhanced in a narrow range of Re only (-1200 < Re < -200). It is also noteworthy that for small enough Grashof numbers (e.g. Gr = 3 × 103), a steady-state solution prevails over the whole range of Reynolds numbers investigated. This means that a critical Grashof number exists below which the effect of the thermocapillary forces is no longer destabilizing.

Numerical study of buoyancy- and thermocapillary-driven flows in a cavity

“…It can be seen that the curve does not intersect the Gr = 0 line at any point. This is consistent with both the steady and unsteady results calculated by Mundrane & Zebib [7], Ben Hadid & Roux [11].…”

Combined Solutal and Thermal Buoyancy Thermocapillary Convection in a Square Open Cavity

“…The boundary layer scalings for buoyant and thermocapillary convection have been established well Carpenter and Homsy (1989). Then, Hadid and Roux (1992) analyzed a shallow cavity and showed that surface tension can have a quite significant effect on the stability of a primary buoyancy driven flow. Effects of a magnetic field on the combined convection were studied by Rudraiah et al (1995) and Hossain et al (2005).…”

Buoyant Marangoni convection of nanofluids in square cavity

“…Carpenter and Homsy [6] established the boundary layer scalings for the buoyant and thermocapillary convection. Hadid and Roux [7] analyzed a shallow cavity, and showed that the surface tension had a quite significant effect on the stability of a primary buoyancy driven flow. Rudraiah et al [8] and Hossain et al [9] studied the effects of a magnetic field on the combined convection.…”