arXiv subjects

Nicola de Divitiis

Publications and source records attributed to Nicola de Divitiis.

23 records · Page 2Linked to original sources

arXiv2009

Self-Similarity in Fully Developed Homogeneous Isotropic Turbulence Using the Lyapunov Analysis

In this work, we calculate the self-similar longitudinal velocity correlation function and the statistical properties of velocity difference using the results of the Lyapunov analysis of the fully developed isotropic homogeneous turbulence just presented by the author in a previous work (arXiv:0911.1463). There, a closure of the von Karman-Howarth equation is proposed and the statistics of velocity difference is determined through a specific analysis of the Fourier-transformed Navier-Stokes equations. The correlation functions correspond to steady-state solutions of the von Karman-Howarth equation under the self-similarity hypothesis introduced by von Karman. These solutions are numerically determined with the statistics of velocity difference. The obtained results adequately describe the several properties of the fully developed isotropic turbulence.

physics.flu-dyn↗

arXiv2009

Lyapunov Analysis of Homogeneous Isotropic Turbulence

The present work studies the isotropic and homogeneous turbulence for incompressible fluids through a specific Lyapunov analysis, assuming that the turbulence is due to the bifurcations associated to the velocity field. The analysis consists in the study of the mechanism of the energy cascade from large to small scales through the Lyapunov analysis of the relative motion between two particles and in the calculation of the velocity fluctuation through the Lyapunov analysis of the local deformation and the Navier-Stokes equations. The analysis provides an explanation for the mechanism of the energy cascade, leads to the closure of the von Kármán-Howarth equation, and describes the statistics of the velocity difference. Several tests and numerical results are presented.

physics.flu-dyn↗

arXiv2009

Self-Similar Solutions in the Homogeneous Isotropic Turbulence

We calculate the self-similar longitudinal velocity correlation function, the energy spectrum and the corresponding other properties using a theory on the isotropic homogeneous turbulence just presented by the author in a previous work. The correlation functions correspond to steady-state solutions of the evolution equation under the self-similarity hypothesis introduced by von Kármán. These solutions are numerically calculated and the results adequately describe several properties of the isotropic turbulence.

physics.flu-dyn↗

arXiv2009

A Statistical Theory of Homogeneous Isotropic Turbulence

The present work proposes a theory of isotropic and homogeneous turbulence for incompressible fluids, which assumes that the turbulence is due to the bifurcations associated to the velocity field. The theory is formulated using a representation of the fluid motion which is more general than the classical Navier-Stokes equations, where the fluid state variables are expressed in terms of the referential coordinates. The theory is developed according to the following four items: 1) Study of the route toward the turbulence through the bifurcations analysis of the kinematic equations. 2) Referential description of the motion and calculation of the velocity fluctuation using the Lyapunov analysis of the local deformation. 3) Study of the mechanism of the energy cascade from large to small scales through the Lyapunov analysis of the relative kinematics equations of motion. 4) Determination of the statistics of the velocity difference with the Fourier analysis. Each item contributes to the formulation of the theory. The theory gives the connection between number of bifurcations, scales and Reynolds number at the onset of the turbulence and supplies an explanation for the mechanism of the energy cascade which leads to the closure of the von Kármán-Howarth equation. The theory also gives the statistics of the velocity difference fluctuation and permits the calculation of its PDF. The presented results show that the proposed theory describes quite well the properties of the isotropic turbulence.

physics.flu-dyn↗

arXiv2009

Impact of floats on water

The impact of a wedge-shaped body on the free surface of a weightless inviscid incompressible liquid is considered. Both symmetrical and unsymmetrical entries at constant velocity are dealt with. The differential problem corresponds to the physico-mathematical model of a distribution of potential singularities and, in particular, the flow singularities at the ends of the wetted regions are represented by sinks. A conformal transformation of the flow field is adopted and the unknown intensities of the discontinuities are found by an optimization procedure, together with the solution of the nonlinear free-surface problem. The flow separation at a sideslip is also considered.

physics.flu-dyn↗