Gábor Tóth

57201571059

Publications - 4

Regional statistics in confined two-dimensional decaying turbulence

Gábor Tóth Gábor Házi

Publication Name: Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences

Publication Date: 2011-06-28

Volume: 369

Issue: 1945

Page Range: 2555-2564

Description:

Two-dimensional decaying turbulence in a square container has been simulated using the lattice Boltzmann method. The probability density function (PDF) of the vorticity and the particle distribution functions have been determined at various regions of the domain. It is shown that, after the initial stage of decay, the regional area averaged enstrophy fluctuates strongly around a mean value in time. The ratio of the regional mean and the overall enstrophies increases monotonously with increasing distance from the wall. This function shows a similar shape to the axial mean velocity profile of turbulent channel flows. The PDF of the vorticity peaks at zero and is nearly symmetric considering the statistics in the overall domain. Approaching the wall, the PDFs become skewed owing to the boundary layer. © 2011 The Royal Society.

Open Access: Yes

DOI: 10.1098/rsta.2011.0070

Lattice BGK simulation of multipolar vortex: Formation

Gábor Tóth Gábor Házi

Publication Name: Advances in Applied Mathematics and Mechanics

Publication Date: 2010-12-01

Volume: 2

Issue: 5

Page Range: 533-544

Description:

Analytical and numerical studies have shown that multipolar vortices can emerge in two-dimensional flow due to azimuthal normal mode perturbations of shielded vortices. It has been found that mode 2 and 3 perturbations can lead to the formation of stable tripoles and quadrapoles, respectively, while higher order modes result in more complex unstable compound vortices. We have used the lattice Boltzmann method to simulate the effect of azimuthal perturbations on shielded vortices at moderate Reynolds numbers. We have found that azimuthal normal mode perturbations result in the formation of multipoles, which decay due to viscous dissipation. We could also observe that the outcome of such simulations is very sensitive to the displacement of perturbations above wavenumber-3 excitations, in spite of the significant viscosity we used. © 2010 Global Science Press.

Open Access: Yes

DOI: 10.4208/aamm.10-10S01

Lattice boltzmann simulation of two-dimensional wall bounded turbulent flow

Gábor Tóth Gábor Házi

Publication Name: International Journal of Modern Physics C

Publication Date: 2010-05-01

Volume: 21

Issue: 5

Page Range: 669-680

Description:

This paper reports on a numerical study of two-dimensional decaying turbulence in a square domain with no-slip walls. The generation of strong small-scale vortices near the no-slip walls have been observed in the lattice Boltzmann simulations just like in earlier pseudospectral calculations. Due to these vortices the enstrophy is not a monotone decaying function of time. Considering a number of simulations and taking their ensemble average, we have found that the decay of enstrophy and that of the kinetic energy can be described well by power-laws. The exponents of these laws depend on the Reynolds number in a similar manner than was observed before in pseudospectral simulations. Considering the ensemble averaged 1D Fourier energy spectra calculated along the walls, we could not find a simple power-law, which fits well to the simulation data. These spectra change in time and reveal an exponent close to -3 in the intermediate and an exponent -5/3 at low wavenumbers. On the other hand, the two-dimensional energy spectra, which remain almost steady in the intermediate decay stage, show clear power-law behavior with exponent larger than -3 depending on the initial Reynolds number. © 2010 World Scientific Publishing Company.

Open Access: Yes

DOI: 10.1142/S0129183110015403

Merging of shielded Gaussian vortices and formation of a tripole at low Reynolds numbers

Gábor Tóth Gábor Házi

Publication Name: Physics of Fluids

Publication Date: 2010-01-01

Volume: 22

Issue: 5

Page Range: 1-7

Description:

The interaction between two corotating shielded Gaussian vortices is studied by two-dimensional numerical simulations at low Reynolds numbers. It is shown that the outcome of the interactions can be a shielded monopole, a tripole, or dipolar breaking depending on the initial separation distance and Reynolds number. A flow regime map is given in the parameter space of initial separation distance and Reynolds number. Using formal decomposition for vorticity, we show that the tripole formation is due the same physical mechanism than merging of unshielded vortices, while in dipolar breaking both the symmetric and antisymmetric vorticity contributions play important role. © 2010 American Institute of Physics.

Open Access: Yes

DOI: 10.1063/1.3428539