Ponente: Dr. Hirdesh Pharasi
Institución: Instituto de Ciencias Físicas, UNAM
Hora de inicio: 17:30:00
Lugar: Auditorio ICF
Rotation plays an important role in the atmospheric, oceanic, geophysical and astrophysical flows. These flows are generally driven by buoyancy. As a model for these flows we consider an extension to the classical Rayleigh-B ́enard problem: a thin layer of fluid confined between two horizontal plates, heated from below and cooled from above, is rotated about a vertical axis. In this rotating Rayleigh-B ́enard system, we have investigated the effect of Coriolis force at the onset of convection as well as on the turbulent convective flows for a fluid of the Prandtl number Pr < 1. We have carried out direct numerical simulations of 3D flows in a periodic simulation box with thermally conducting and stress-free top and bottom boundaries. Different shapes of convective patterns  have been observed near oscillatory instability in a simulation box by varying its rotation rate and horizontal cross-section.
The investigations of the turbulent convection in a periodic rectangular simulation box
show interesting scaling behavior . The Nusselt number Nu shows two scaling regimes in presence of the Coriolis force. Nu scales with the Rayleigh number Ra as Ra2/7 for the ratio Rayleigh number and Tayler number Ra/Ta > 1. There exists a critical value of Nusselt number Nuc, below which the scaling of Nu with Ra is not universal and is dependent on Ta. This usually occurs for the ratio Ra/Ta . 1. The convective entropy spectrum EΦ(k)  also shows scaling behavior. The lower branch of EΦ(k), which corresponds to temperature modes with zero horizontal mean, scales with k approximately as k−γΦ with γ Φ = 1.40±0.15 for the reduced Rayleigh number r = Ra/Rac > 103 and with 1.8 < γΦ < 2.4 for r < 103.
The spectra of the convective heat flux H(k) , defined as Nu − 1 = H(k)dk, scales with the wave number k as k −δ with δ ∼ 2 for higher values of r(> 103). It is the same universal scaling range of the Rayleigh number, where Nu scales with Ra approximately as Ra2/7. The scaling results are independent of Ta and Pr. However, for smaller values of r(< 103) the exponent δ shows Ta and Pr dependence. The value varies in the range of 2.0 ≤ δ ≤ 2.8.