Direct numerical simulations of homogeneous turbulence in density-stratified fluids

1981 ◽  
Author(s):  
James J. Riley ◽  
Ralph W. Metcalfe ◽  
Michael A. Weissman
Keyword(s):  
Numerical Simulations ◽  
Direct Numerical Simulations ◽  
Homogeneous Turbulence ◽  
Stratified Fluids

The analysis and modelling of dilatational terms in compressible turbulence

1991 ◽  
Vol 227 ◽  
pp. 473-493 ◽  
Author(s):  
S. Sarkar ◽  
G. Erlebacher ◽  
M. Y. Hussaini ◽  
H. O. Kreiss
Keyword(s):  
Asymptotic Analysis ◽  
Numerical Simulations ◽  
Isotropic Turbulence ◽  
Stokes Equations ◽  
Mixing Layer ◽  
Direct Numerical Simulations ◽  
Homogeneous Turbulence ◽  
Compressible Turbulence ◽  
Quasi Equilibrium ◽  
Compressible Mixing Layer

It is shown that the dilatational terms that need to be modelled in compressible turbulence include not only the pressure-dilatation term but also another term - the compressible dissipation. The nature of the compressible velocity field, which generates these dilatational terms, is explored by asymptotic analysis of the compressible Navier-Stokes equations in the case of homogeneous turbulence. The lowest-order equations for the compressible field are solved and explicit expressions for some of the associated one-point moments are obtained. For low Mach numbers, the compressible mode has a fast timescale relative to the incompressible mode. Therefore, it is proposed that, in moderate Mach number homogeneous turbulence, the compressible component of the turbulence is in quasi-equilibrium with respect to the incompressible turbulence. A non-dimensional parameter which characterizes this equilibrium structure of the compressible mode is identified. Direct numerical simulations (DNS) of isotropic, compressible turbulence are performed, and their results are found to be in agreement with the theoretical analysis. A model for the compressible dissipation is proposed; the model is based on the asymptotic analysis and the direct numerical simulations. This model is calibrated with reference to the DNS results regarding the influence of compressibility on the decay rate of isotropic turbulence. An application of the proposed model to the compressible mixing layer has shown that the model is able to predict the dramatically reduced growth rate of the compressible mixing layer.

Settling velocity and concentration distribution of heavy particles in homogeneous isotropic turbulence

1993 ◽  
Vol 256 ◽  
pp. 27-68 ◽  
Author(s):  
Lian-Ping Wang ◽  
Martin R. Maxey
Keyword(s):  
Numerical Simulations ◽  
Drag Force ◽  
Settling Velocity ◽  
Isotropic Turbulence ◽  
Concentration Field ◽  
Terminal Velocity ◽  
Direct Numerical Simulations ◽  
Flow Dynamics ◽  
Homogeneous Turbulence ◽  
Heavy Particles

The average settling velocity in homogeneous turbulence of a small rigid spherical particle, subject to a Stokes drag force, has been shown to differ from that in still fluid owing to a bias from the particle inertia (Maxey 1987). Previous numerical results for particles in a random flow field, where the flow dynamics were not considered, showed an increase in the average settling velocity. Direct numerical simulations of the motion of heavy particles in isotropic homogeneous turbulence have been performed where the flow dynamics are included. These show that a significant increase in the average settling velocity can occur for particles with inertial response time and still-fluid terminal velocity comparable to the Kolmogorov scales of the turbulence. This increase may be as much as 50% of the terminal velocity, which is much larger than was previously found. The concentration field of the heavy particles, obtained from direct numerical simulations, shows the importance of the inertial bias with particles tending to collect in elongated sheets on the peripheries of local vortical structures. This is coupled then to a preferential sweeping of the particles in downward moving fluid. Again the importance of Kolmogorov scaling to these processes is demonstrated. Finally, some consideration is given to larger particles that are subject to a nonlinear drag force where it is found that the nonlinearity reduces the net increase in settling velocity.

Instability of strained vortex layers and vortex tube formation in homogeneous turbulence

1995 ◽  
Vol 282 ◽  
pp. 313-338 ◽  
Author(s):  
T. Passot ◽  
H. Politano ◽  
P.L. Sulem ◽  
J.R. Angilella ◽  
M. Meneguzzi
Keyword(s):  
Numerical Simulations ◽  
Vortex Tube ◽  
Three Dimensional ◽  
Quantitative Agreement ◽  
Finite Amplitude ◽  
Tube Formation ◽  
Direct Numerical Simulations ◽  
Homogeneous Turbulence ◽  
Tubular Structures ◽  
Vortex Tubes

A modulational perturbation analysis is presented which shows that when a strained vortex layer becomes unstable, vorticity concentrates into steady tubular structures with finite amplitude, in quantitative agreement with the numerical simulations of Lin & Corcos (1984). Elaborated three-dimensional visualizations suggest that this process, due to a combination of compression and self-induced rotation of the layer, is at the origin of intense and long-lived vortex tubes observed in direct numerical simulations of homogeneous turbulence.

Direct numerical simulations of wake vortices in intense homogeneous turbulence

AIAA Journal ◽  
1997 ◽  
Vol 35 ◽  
pp. 1030-1040
Author(s):  
Frederic Risso ◽  
Alexandre Corjon ◽  
Alain Stoessel
Keyword(s):  
Numerical Simulations ◽  
Direct Numerical Simulations ◽  
Homogeneous Turbulence ◽  
Wake Vortices
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