Vorticity Generation by Rough Walls in 2D Decaying Turbulence

Abstract

In this work we present Lattice Boltzmann simulations of a decaying vortex array in a 2D rectangular domain, which is bounded by a random rough wall from one side. In order to separate the effects of the collisions with the rough wall, the opposite (smooth) rigid wall is placed at a larger distance from the center of the vortex array. Periodic boundary condition is imposed in the perpendicular direction. Well defined random roughness is generated by the widely studied Wolf-Villain surface growth algorithm. The main finding is that collisions with a rough wall generate excess vorticity compared with a smooth boundary, while the kinetic energy decreases monotonously. A proper measure is the integrated excess enstrophy, which exhibits an apparent maximum at an "optimal" roughness range. Numerical values of the excess enstrophy are very sensitive to a particular configuration (wall shape and vortex lattice randomization), however the "optimal" roughness exhibits surface features of similar characteristic sizes than that of the decaying vortices.

Direct numerical simulation of turbulence over anisotropic porous media

“…Due to the simplicity of the wall treatment and high computer efficiency, the LBM has become a popular tool for complex porous medium flow simulations (e.g., Hatiboglu & Babadagli 2008;Beugre et al 2010;Parmigiani et al 2011;Chukwudozie & Tyagi 2013). Furthermore, since the LBM is suitable for parallel computing using the Message Passing Interface and Graphics Processing Units as reported by Li et al (2013); Huang et al (2015) and has been validated for turbulent flow DNS (e.g., Lammers et al 2006;Chikatamarla et al 2010;Bespalko et al 2012;Suga et al 2015), it has often been applied to various complex turbulent flow problems such as flows in porous media (e.g., Hasert et al 2011;Krafczyk et al 2015;Kuwata & Suga 2015b) or over rough walls (e.g., Jin et al 2015;Tóth & Jánosi 2015;Kuwata & Suga 2016b,c). Because of the above distinctive computational features, this study employs the LBM for simulating the time-dependent turbulent flow fields over porous walls.…”

Single super-vortex as a proxy for ocean surface flow fields

“…Here, η 0 and R are the height and size parameters for the vortex, respectively, g is the gravitational acceleration, and f = 2 sin(ϕ) is the local Coriolis parameter at latitude ϕ with = 7.292 × 10 −5 s −1 for the Earth. The label "shielded" in the title of this section refers to the core of such a vortex being surrounded by a ring of opposite vorticity (Tóth and Jánosi, 2015); see Fig. 2c.…”

“…The vast majority of the ME studies is based on some automatic algorithm that identifies and tracks the eddies from gridded maps of sea level anomaly (SLA). Various Eulerian methods were developed and deployed in practice, such as detecting closed contours of SLA Mason et al, 2014;Li et al, 2016;Schütte et al, 2016;Pessini et al, 2018), evaluating the geometry of the velocity vectors (Nencioli et al, 2010), determining contours of the Okubo-Weiss parameter (Chelton et al, 2007;Kurian et al, 2011;Ubelmann and Fu, 2011;Schütte et al, 2016;Pessini et al, 2018) or using wavelet analysis to identify coherent eddylike structures (Rubio et al, 2009;Pnyushkov et al, 2018). Critical comparisons show that none of the Eulerian methods are superior to the others (Souza et al, 2011;Escudier et al, 2016).…”

Lattice Boltzmann direct numerical simulation of interface turbulence over porous and rough walls

“…Furthermore, since the LBM is suitable for parallel computing using the MPI and GPUs as reported by Huang et al (2015) ; Li et al (2013) and has been validated for turbulent flow DNS (e.g., Lammers et al, 2006;Chikatamarla et al, 2010;Bespalko et al, 2012;Suga et al, 2015 ), it has been often applied to various complex turbulent flow problems such as flows in porous media (e.g., Hasert et al, 2011;Krafczyk et al, 2015;Kuwata and Suga, 2015b ) or over rough walls (e.g., Jin et al, 2015;Tóth and Jánosi, 2015 ). Because of the above distinctive computational features, this study employs the LBM for simulating the time-dependent turbulent flow fields over porous and rough walls.…”