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104 votes
Accepted

Should water at the scale of a cell feel more like tar?

There is a beautiful article (a write-up of a talk, actually), by E.M. Purcell, Life at low Reynolds number, that explains how bacteria swim. Low Reynolds number is the technical way to phrase the sta …
Carlo Beenakker's user avatar
13 votes
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Riemann, fluid dynamics, and critical lines

Q: Does anyone know of a reference which discusses more thoroughly the critical line appearing in Riemann's hydrodynamics problem? A: A recent reference is Elliptical instability in hot Jupiter system …
Carlo Beenakker's user avatar
6 votes

Navier-Stokes fluid dynamics, Einstein gravity and holography

The first point to make is that the fluid/gravity correspondence relates the general theory of relativity to relativistic fluid dynamics. I don't see how the usual non-relativistic Navier-Stokes equat …
Carlo Beenakker's user avatar
5 votes

Why are solenoidal fields called solenoidal?

[To expand on Wojowu's comment.] Q: "Why the description of a divergence-free field as solenoidal? I expect that this name had historical origins but its unlikely that it was so named without some lin …
Carlo Beenakker's user avatar
5 votes

Textbook suggestions for rigorous fluid dynamics

An older, classic text is Mathematical Theory of Compressible Fluid Flow by Richard von Mises. More recent text books include Introduction to Mathematical Fluid Dynamics by R.E. Meyer. An Introductio …
Carlo Beenakker's user avatar
5 votes

Explanation for why an ideal fluid doesn't have increasing entropy?

Q: Explanation for why an ideal fluid doesn't have increasing entropy? A: The entropy will in fact increase for the most probable initial conditions. The question in the OP refers to the socalled irr …
Carlo Beenakker's user avatar
4 votes

References on thin film equation: derivation and properties

$\bullet$ Physical model: There is no physical model that gives this equation for arbitrary $m$; the values $m=1,2,3$ appear in viscous flow, as summarized in "Viscous Thin Films": For the no-slip bou …
Carlo Beenakker's user avatar
4 votes
Accepted

Incompressible Navier-Stokes equation with heat conduction

There is an extensive literature, this could be helpful entry point: Solving Navier-Stokes equations coupled with a heat transfer equation (2015) In this paper, the dynamics of an incompressible …
Carlo Beenakker's user avatar
3 votes
Accepted

Derivation of Bessel functions

I'll make an attempt at providing the steps you are seeking to go "from Euler equation to Bessel function". You start from the Euler equation, describing conservation of momentum, $$\rho\frac{\parti …
Carlo Beenakker's user avatar
3 votes
Accepted

Fluid dynamics textbook discussing Hele-Shaw flow

A mathematics-oriented text book is Conformal and Potential Analysis in Hele-Shaw Cells, by Gustafsson and Vasil'ev (2006). This monograph aims at giving a presentation of recent and new ideas that a …
Carlo Beenakker's user avatar
2 votes

Definition of the nonlinear part of the drift in a (stochastic) Navier-Stokes equation

For $d=2$ the existence and uniqueness of strong solutions for the stochastic Navier–Stokes equation, including the nonlinear drift term, has been proven by Menaldi and Sritharan, Stochastic 2-D Navie …
Carlo Beenakker's user avatar
2 votes

The derivation of Reynolds-averaged Navier-Stokes equations

The equation in the OP is not correct, it should read $$\overline{u_iu_j} = \overline{(\bar{u_i}+u_i')(\bar{u_j} + u_j')} = \overline{\bar{u_i}\bar{u_j}+\bar{u_i}u_j'+u_i'\bar{u_j}+u_i'u_j'} = \bar{u_ …
Carlo Beenakker's user avatar
2 votes

What is kth vortex formula?

Use that the velocity field is incompressible, $\nabla\cdot u=0$, to rewrite $$(u\cdot\nabla)u_j=\sum_{i} \nabla_i (u_iu_j).$$ You seek the curl of the curl of this expression, use that $$[\operatorna …
Carlo Beenakker's user avatar
1 vote

A question about intuition of fluid limit in queuing system

in the fluid (or continuum) limit, you should allow $k$ to vary continuously and consider instead of $\pi_k$ (the probability of a queue of exactly length $k$) the probability $\pi(k)dk$ that a queue …
Carlo Beenakker's user avatar
1 vote

Reynolds operator from the potential theoretic point of view

for what it's worth, here is one rather recent & pessimistic assessment: Gian-Carlo Rota wrote that "The Reynolds operators are the potentials, in the language of probabilistic potential theory, …
Carlo Beenakker's user avatar

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