RESUMO
We provide the first demonstration that molecular-level methods based on gas kinetic theory and molecular chaos can simulate turbulence and its decay. The direct simulation Monte Carlo (DSMC) method, a molecular-level technique for simulating gas flows that resolves phenomena from molecular to hydrodynamic (continuum) length scales, is applied to simulate the Taylor-Green vortex flow. The DSMC simulations reproduce the Kolmogorov -5/3 law and agree well with the turbulent kinetic energy and energy dissipation rate obtained from direct numerical simulation of the Navier-Stokes equations using a spectral method. This agreement provides strong evidence that molecular-level methods for gases can be used to investigate turbulent flows quantitatively.
RESUMO
Nanoparticles suspended in ambient air within microscale geometries form a Knudsen layer when diffusing in a Brownian fashion toward a solid wall. More specifically, the particle number density adjacent to the wall approaches a nonzero value proportional to the flux. An approximate theory for the coefficient of proportionality as a function of the particle sticking fraction at the wall and the drift velocity normal to the wall is compared to Langevin particle simulations. The resulting boundary condition enables accurate advection-diffusion simulations of nanoparticle-aerosol transport.
RESUMO
Bird's direct simulation Monte Carlo method is used to compute the molecular velocity distribution of a gas with heat flow. At continuum nonequilibrium conditions (small heat flux), Chapman-Enskog behavior is obtained for inverse-power-law molecules (hard-sphere through Maxwell): the Sonine-polynomial coefficients away from walls (i.e., the normal solution) agree with theory. At noncontinuum nonequilibrium conditions (large heat flux), these coefficients differ systematically from their continuum values as the local Knudsen number (nondimensional heat flux) is increased.