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Competing Lagrangians for incompressible and compressible viscous flow.

Marner, F. and Scholle, M. and Herrmann, D. and Gaskell, P. H. (2019) 'Competing Lagrangians for incompressible and compressible viscous flow.', Royal Society open science., 6 (1). p. 181595.


A recently proposed variational principle with a discontinuous Lagrangian for viscous flow is reinterpreted against the background of stochastic variational descriptions of dissipative systems, underpinning its physical basis from a different viewpoint. It is shown that additional non-classical contributions to the friction force occurring in the momentum balance vanish by time averaging. Accordingly, the discontinuous Lagrangian can alternatively be understood from the standpoint of an analogous deterministic model for irreversible processes of stochastic character. A comparison is made with established stochastic variational descriptions and an alternative deterministic approach based on a first integral of Navier–Stokes equations is undertaken. The applicability of the discontinuous Lagrangian approach for different Reynolds number regimes is discussed considering the Kolmogorov time scale. A generalization for compressible flow is elaborated and its use demonstrated for damped sound waves.

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Publisher statement:© 2019 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License, which permits unrestricted use, provided the original author and source are credited.
Date accepted:07 December 2018
Date deposited:16 January 2019
Date of first online publication:16 January 2019
Date first made open access:16 January 2019

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