Pattern selection and heat transfer in the Rayleigh-Benard convection near the vicinity of the convection onset with viscoelastic fluids

The effect of viscoelasticity on the flow and heat transport in the Rayleigh-Benard convection (RBC), a frequently encountered phenomenon in nature and industry, in a rectangular enclosure with horizontal periodic boundary is investigated via direct numerical simulation. The working fluid is described by a finitely extensible nonlinear elastic-Peterlin constitutive model almost all important features of viscoelastic fluid flow. Numerical simulations are conducted at a low concentration beta = 0.9, where beta = mu s / mu 0, mu(s) is the solvent viscosity, and mu 0 = mu s + mu p is the sum of mu(s) and the polymer viscosity mu(p). A parametric analysis is performed to understand the influence of the Weissenberg number Wi, the viscosity ratio beta, and the extension length L on the oscillating mode of the viscoelastic RBC. The results indicate that both Wi and beta weakly inhibit the convection onset and the transition from steady to oscillatory convection. The amplitude and frequency of the oscillations in the oscillatory flow regime are both suppressed. However, the strongly elastic nonlinearity makes the flow transition irregular and even brings about the relaminarization or lead to the convection cells traveling in the horizontal direction. The increasing extension length L induces multiple pairs of roll flow patterns at a specific setting of (Ra, Wi). Heat transport is reduced (up to 8.5%) by elasticity but still obeys the power law with Ra if the flow pattern has one pair of rolls. However, heat transfer enhancement occurs if multiple pairs of rolls are induced.

Automated summary

This study investigates the effect of viscoelasticity on flow and heat transport in rectangular Rayleigh-Benard convection using direct numerical simulation. The results show that viscoelasticity weakly inhibits convection onset and transition from steady to oscillatory convection. Amplitude and frequency of oscillations in the flow regime are suppressed. Elastic nonlinearity creates irregular flow transitions and can cause convection cells to travel horizontally. Multiple pairs of roll flow patterns enhance heat transfer.