F. C. G. A Nicolleau | Searcharxiv

arXiv2019

Lattice Boltzmann Method simulations of high Reynolds number flows past porous obstacles

Lattice Boltzmann Method (LBM) simulations for turbulent flows over a fractal and non-fractal obstacles are presented. The wake hydrodynamics are compared and discussed in terms of flow relaxation, Strouhal numbers and wake length for different Reynolds numbers. Three obstacle topologies are studied, Solid (SS), Porous Regular (PR) and Porous Fractal (FR). In particular we observe that the oscillation present in the case of the solid square can be annihilated or only pushed downstream depending on the topology ot the porous obstacle. The Lattice Boltzmann Method (LBM) is implemented over a range of four Reynolds numbers from 12352 to 49410. The suitability of LBM for these high Reynolds number cases is studied. Its results are compared to available experimental data and published literature. Compelling agreements between all three tested obstacles show a significant validation of LBM as a tool to investigate high Reynolds number flows in complex geometries. This is particularly important as the LBM method is much less time consuming than a classical Navier-Stokes equation based computing method and high Reynolds numbers need to be achieved with enough details (i.e. resolution) to predict for example canopy flows.

physics.flu-dyn↗

arXiv2017

Passage of a shock wave through inhomogeneous media and its impact on a gas bubble deformation

The paper investigates shock-induced vortical flows within inhomogeneous media of nonuniform thermodynamic properties. Numerical simulations are performed using an Eularian type mathematical model for compressible multi-component flow problems. The model, which accounts for pressure non-equilibrium and applies different equations of state for individual flow components, shows excellent capabilities for the resolution of interfaces separating compressible fluids as well as for capturing the baroclinic source of vorticity generation. The developed finite volume Godunov type computational approach is equipped with an approximate Riemann solver for calculating fluxes and handles numerically diffused zones at flow component interfaces. The computations are performed for various initial conditions and are compared with available experimental data. The initial conditions promoting a shock-bubble interaction process include: weak to high planar shock waves with a Mach number ranging from $1.2$ to $3$ and isolated cylindrical bubble inhomogeneities of helium, argon, nitrogen, krypton and sulphur hexafluoride. The numerical results reveal the characteristic features of the evolving flow topology. The impulsively generated flow perturbations are dominated by the reflection and refraction of the shock, the compression and acceleration as well as the vorticity generation within the medium. The study is further extended to investigate the influence of the ratio of the heat capacities on the interface deformation.

physics.flu-dyn↗