High-Rayleigh-number convection in porous–fluid layers

We present a numerical study of convection in horizontal layer comprising fluid-saturated porous bed overlain by an unconfined fluid layer. Convection is driven vertical, destabilising temperature difference applied across the whole system, as canonical Rayleigh-B\'enard problem. Numerical simulations are carried out using single-domain formulation two-layer problem based on Darcy-Brinkman equations. explore dynamics and heat flux through system limit large Rayleigh number, but small Darcy such that flow exhibits vigorous both regions, while still remains strongly confined governed Darcy's law. demonstrate average thermal structure can be predicted previous results individual or layers. revisit controversy about role subcritical "penetrative convection" medium, confirm induced does not contribute to system. Lastly, we briefly temporal coupling between two layers find turbulent above acts low-pass filter longer-timescale variability