94 research outputs found
Prediction of strong shock structure using the bimodal distribution function
A modified Mott-Smith method for predicting the one-dimensional shock wave
solution at very high Mach numbers is constructed by developing a system of
fluid dynamic equations. The predicted shock solutions in a gas of Maxwell
molecules, a hard sphere gas and in argon using the newly proposed formalism
are compared with the experimental data, direct-simulation Monte Carlo (DSMC)
solution and other solutions computed from some existing theories for Mach
numbers M<50. In the limit of an infinitely large Mach number, the predicted
shock profiles are also compared with the DSMC solution. The density,
temperature and heat flux profiles calculated at different Mach numbers have
been shown to have good agreement with the experimental and DSMC solutionsComment: 22 pages, 9 figures, Accepted for publication in Physical Review
Detailed plan for the COMET WP3 initial research activity - list of research projects and goals, participants and timing
Detailed plan for the COMET Work Package (WP) 3
The Moment Guided Monte Carlo method for the Boltzmann equation
In this work we propose a generalization of the Moment Guided Monte Carlo
method developed in [11]. This approach permits to reduce the variance of the
particle methods through a matching with a set of suitable macroscopic moment
equations. In order to guarantee that the moment equations provide the correct
solutions, they are coupled to the kinetic equation through a non equilibrium
term. Here, at the contrary to the previous work in which we considered the
simplified BGK operator, we deal with the full Boltzmann operator. Moreover, we
introduce an hybrid setting which permits to entirely remove the resolution of
the kinetic equation in the limit of infinite number of collisions and to
consider only the solution of the compressible Euler equation. This
modification additionally reduce the statistical error with respect to our
previous work and permits to perform simulations of non equilibrium gases using
only a few number of particles. We show at the end of the paper several
numerical tests which prove the efficiency and the low level of numerical noise
of the method.Comment: arXiv admin note: text overlap with arXiv:0908.026
The effect of groove texture patterns on piston-ring pack friction
A cylinder liner possesses fairly intricate surface requirements due to its complicated functions. It needs to provide adequate surface roughness to resist wear as well as to store and retain lubricants during high temperatures. The liner surface texture is anisotropic, produced by the honing process, with resultant deep visible scratches left on it [1]. The prominence of the honing grooves observed suggests that surface texture significantly affects ring-pack performance, although this effect is not clearly understood. In this paper, a numerical model was developed to investigate the effects of groove characteristics on the lubrication condition and friction at the interface between the piston ring and cylinder liner. This model aims to solve the average Reynolds equation, which depends on the real surface topographies of the cylinder liner, and describes the influence of surface irregularities on the lubricant flow under hydrodynamic lubrication conditions, considering lubricant film rupture and cavitations. Numerical results help to determine the optimum lateral groove characteristics to reduce friction and then noxious emissions
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