We report a numerical study of Rayleigh-Benard convection through random porous media using pore-scale modelling, focusing on the Lagrangian dynamics of fluid particles and heat transfer for varied porosities . Due to the interaction between the porous medium and the coherent flow structures, the flow is found to be highly heterogeneous, consisting of convection channels with strong flow strength and stagnant regions with low velocities. The modifications of flow field due to porous structure have a significant influence on the dynamics of fluid particles. Evaluation of the particle displacement along the trajectory reveals the emergence of anomalous transport for long times as is decreased, which is associated with the long-time correlation of Lagrangian velocity of the fluid. As porosity is decreased, the cross-correlation between the vertical velocity and temperature fluctuation is enhanced, which reveals a mechanism to enhance the heat transfer in porous-media convection.

In this numerical study on Rayleigh-Benard convection, we seek to improve the heat transfer by passive means. To this end we introduce a single tilted conductive barrier centered in an aspect ratio one cell, breaking the symmetry of the geometry and to channel the ascending hot and descending cold plumes. We study the global and local heat transfer and the flow organization for Rayleigh numbers 10(5) <= Ra <= 10(9) for a fixed Prandtl number of Pr = 4.3. We find that the global heat transfer can be enhanced up to 18%, and locally around 800%. The averaged Reynolds number is always decreased when a barrier is introduced, even for those cases where the global heat transfer is increased. We map the entire parameter space spanned by the orientation and the size of a single barrier for Ra = 10(8).

This paper presents a numerical study of the Rayleigh-Benard convection (RBC) in two-dimensional cells with asymmetric (ratchet) roughness distributed on the top and bottom surfaces. We consider two aspect ratios of roughness gamma = 1, 2 and the range of the Rayleigh number 1.0 x 10(6) <= Ra <= 2.0 x 10(10) with the Prandtl number Pr = 4. The influences of the roughness on the heat transfer and the flow structure are found to be strongly dependent on both Ra and the roughness geometry. We find that the roughness can have a significant influence on the organization of the secondary corner rolls, and the corner rolls are evidently suppressed by the roughness for intermediate values of Ra. In the presence of the roughness, a sharp jump of the Nu values is identified as the Ra value is slightly increased, accompanied with the dramatic changes of the large-scale flow structure and the plume dynamics. The influences of the ratchet orientation on the heat transfer and the flow structure are discussed and analyzed.