Abstract
The Boltzmann description of the preceding paper for tagged particle fluctuations in a nonequilibrium gas is further analyzed in the limit of small mass ratio between the gas and the tagged particles. For a large class of nonequilibrium states the Boltzmann-Lorentz collision operator for the tagged particle distribution is expanded to leading order in the mass ratio, resulting in a Fokker-Planck operator. The drift vector and diffusion tensor are calculated exactly for Maxwell molecules. The Fokker-Planck operator depends on the nonequilibrium state only through the hydrodynamic variables for the fluid. The diffusion tensor is a measure of the “noise” amplitude and is not simply determined from the nonequilibrium temperature; instead, it depends on the fluid stress tensor components as well. For the special case of uniform shear flow, the Fokker-Planck equation is of the linear type and may be solved exactly. The associated set of Langevin equations is also identified and used to describe spatial diffusion in the Lagrangian coordinates of the fluid. The effect of viscous heating on diffusion is discussed and the dependence of the diffusion coefficient on the shear rate is calculated.
Similar content being viewed by others
References
M. C. Marchetti and J. W. Dufty,J. Stat. Phys. 32:xxx (this issue).
S. Chandrasekhar,Rev. Mod. Phys. 15, 1 (1943) reprinted inNoise and Stochastic Processes, N. Wax, ed. (Dover, New York, 1954).
M. San Miguel and J. Sancho,Physica 99A:357 (1979).
J. Fernandez de la Mora and J. Mercer,Phys. Rev. A26:2178 (1982).
A.-M. Tremblay, M. Arai, and E. Siggia,Phys. Rev. A23:1451 (1981); D. Ronis, I. Procaccia, and J. Machta,Phys. Rev. A22:714 (1980).
A.-M. Tremblay, B. Patton, P. Marton, and P. Maldague,Phys. Rev. A19:1721 (1979).
N. G. van Kampen,Stochastic Processes in Physics and Chemistry (North-Holland, Amsterdam, 1981).
R. Zwanzig, inSystems Far From Equilibrium, L. Garrido, ed. (Springer-Verlag, Berlin, 1980).
H. Grabert and W. Weidlich,Phys. Rev. A21:2147 (1980).
W. Schlup,Physica 19:485 (1973).
J. Moyal,J. R. Stat. Soc. (B) 11:150 (1949).
Author information
Authors and Affiliations
Additional information
Research supported by National Science Foundation grant CHE 8207263.
Rights and permissions
About this article
Cite this article
Rodríguez, R.F., Salinas-Rodríguez, E. & Dufty, J.W. Fokker-Planck and Langevin descriptions of fluctuations in uniform shear flow. J Stat Phys 32, 279–298 (1983). https://doi.org/10.1007/BF01012711
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF01012711