Quantcast
  • Register
PhysicsOverflow is a next-generation academic platform for physicists and astronomers, including a community peer review system and a postgraduate-level discussion forum analogous to MathOverflow.

Welcome to PhysicsOverflow! PhysicsOverflow is an open platform for community peer review and graduate-level Physics discussion.

Please help promote PhysicsOverflow ads elsewhere if you like it.

News

PO is now at the Physics Department of Bielefeld University!

New printer friendly PO pages!

Migration to Bielefeld University was successful!

Please vote for this year's PhysicsOverflow ads!

Please do help out in categorising submissions. Submit a paper to PhysicsOverflow!

... see more

Tools for paper authors

Submit paper
Claim Paper Authorship

Tools for SE users

Search User
Reclaim SE Account
Request Account Merger
Nativise imported posts
Claim post (deleted users)
Import SE post

Users whose questions have been imported from Physics Stack Exchange, Theoretical Physics Stack Exchange, or any other Stack Exchange site are kindly requested to reclaim their account and not to register as a new user.

Public \(\beta\) tools

Report a bug with a feature
Request a new functionality
404 page design
Send feedback

Attributions

(propose a free ad)

Site Statistics

206 submissions , 164 unreviewed
5,103 questions , 2,249 unanswered
5,355 answers , 22,794 comments
1,470 users with positive rep
820 active unimported users
More ...

  Could Navier-Stokes equation be derived directly from Boltzmann equation?

+ 8 like - 0 dislike
3082 views

I know how to derive Navier-Stokes equations from Boltzmann equation in case where bulk and viscosity coefficients are set to zero. I need only multiply it on momentum and to integrate it over velocities.

But when I've tried to derive NS equations with viscosity and bulk coefficients, I've failed. Most textbooks contains following words: "for taking into the account interchange of particles between fluid layers we need to modify momentum flux density tensor". So they state that NS equations with viscosity cannot be derived from Boltzmann equation, can they?

The target equation is $$ \partial_{t}\left( \frac{\rho v^{2}}{2} + \rho \epsilon \right) = -\partial_{x_{i}}\left(\rho v_{i}\left(\frac{v^{2}}{2} + w\right) - \sigma_{ij}v_{j} - \kappa \partial_{x_{i}}T \right), $$ where $$ \sigma_{ij} = \eta \left( \partial_{x_{[i}}v_{j]} - \frac{2}{3}\delta_{ij}\partial_{x_{i}}v_{i}\right) + \varepsilon \delta_{ij}\partial_{x_{i}}v_{i}, $$ $w = \mu - Ts$ corresponds to heat function, $\epsilon$ refers to internal energy.

Edit. It seems that I've got this equation. After multiplying Boltzmann equation on $\frac{m(\mathbf v - \mathbf u)^{2}}{2}$ and integrating it over $v$ I've got transport equation which contains objects $$ \Pi_{ij} = \rho\langle (v - u)_{i}(v - u)_{j} \rangle, \quad q_{i} = \rho \langle (\mathbf v - \mathbf u)^{2}(v - u)_{i}\rangle $$ To calculate it I need to know an expression for distribution function. For simplicity I've used tau approximation; in the end I've got expression $f = f_{0} + g$. An expressions for $\Pi_{ij}, q_{i}$ then are represented by $$ \Pi_{ij} = \delta_{ij}P - \mu \left(\partial_{[i}u_{j]} - \frac{2}{3}\delta_{ij}\partial_{i}u_{i}\right) - \epsilon \delta_{ij}\partial_{i}u_{i}, $$ $$ q_{i} = -\kappa \partial_{i} T, $$ so I've got the wanted result.


This post imported from StackExchange Physics at 2016-02-10 14:08 (UTC), posted by SE-user Name YYY

asked Apr 17, 2015 in Theoretical Physics by NAME_XXX (1,060 points) [ revision history ]
edited Feb 10, 2016 by Dilaton
It seems to be done in Landau and Lifshitz 10, Chapter 1.

This post imported from StackExchange Physics at 2016-02-10 14:08 (UTC), posted by SE-user Robin Ekman
@RobinEkman : do you mean "Kinetics"?

This post imported from StackExchange Physics at 2016-02-10 14:08 (UTC), posted by SE-user Name YYY
Yes, that is correct.

This post imported from StackExchange Physics at 2016-02-10 14:08 (UTC), posted by SE-user Robin Ekman
Look up the Chapman Enskog equations.

This post imported from StackExchange Physics at 2016-02-10 14:08 (UTC), posted by SE-user tpg2114
@RobinEkman, not surprising... everything is in Landau and Lifshitz. I especially enjoy their recipe for banana bread.

This post imported from StackExchange Physics at 2016-02-10 14:08 (UTC), posted by SE-user hft
@RobinEkman : But I don't see the derivation there. There is only derivation of Boltzmann equation with tension tensor. Should it be multiplied on $\frac{mv^2}{2}$ and integrated over $ v $for getting hydrodynamics equation with viscosity?

This post imported from StackExchange Physics at 2016-02-10 14:08 (UTC), posted by SE-user Name YYY
@NameYYY - All the fluid equations are effectively moments of the Boltzmann equation. The Navier-Stokes equations are just the combined effects of the zeroth to the second or third moment equations, depending on the problem. So I guess I am a little confused. Viscosity is just another way of saying off-diagonal terms in a pressure tensor or that there is j-momentum transported through the i-th plane.

This post imported from StackExchange Physics at 2016-02-10 14:08 (UTC), posted by SE-user honeste_vivere
Since this question has been answered it showld be updated.

This post imported from StackExchange Physics at 2016-02-10 14:08 (UTC), posted by SE-user falematte

To the Chapman-Enskog method I would also like to add my personal favorite: Grad's method of moments: Grad, H. (1949) "On the kinetic theory of rarefied gases". Israel-Müller-Stewart theory is just a relativistic extension of Grad's ideas.

1 Answer

+ 1 like - 0 dislike

The book by Müller and Ruggeri  Rational extended thermodynamics, Springer 2013, contains a derivation of a relativistic version of the Navier-Stokes equations from the Boltzmann equation. From the relativistic equations one gets the Navier-Stokes equations by taking the limit $c\to\infty$.

answered Aug 3, 2017 by Arnold Neumaier (15,787 points) [ no revision ]

Your answer

Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead.
To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL.
Please consult the FAQ for as to how to format your post.
This is the answer box; if you want to write a comment instead, please use the 'add comment' button.
Live preview (may slow down editor)   Preview
Your name to display (optional):
Privacy: Your email address will only be used for sending these notifications.
Anti-spam verification:
If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:
p$\hbar$y$\varnothing$icsOverflow
Then drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds).
Please complete the anti-spam verification




user contributions licensed under cc by-sa 3.0 with attribution required

Your rights
...