Week 1 - Fluids Flashcards
What does barotropic mean?
That the density is a function of pressure only.
What are the moment equations and how are they used to find quantities that are conserved in collisions?
The moment equations are the integrals over velocity space of the collisional part of the time derivative of f times some quantity Q. Where these are zeros we find the continuity equation, the momentum equation and the total energy equation.
How can we define a fluid?
As a collisional system where components move within the system.
What is the equation for mean free path for neutral particles?
l ~ 1/n*sigma, where sigma is the cross section
How is the fluid derivative defined?
With the extra term u*nabla
Describe the equation of fluid motion
It is the time derivative of the density of the quantity plus the divergence of the flux of the quantity equals sources minus sinks.
We can view fluids as collections of particles or continua. In which of these can we find the Euler equations and the Navier-Stokes equations?
In viewing fluids as collections of particles.
What is Boltzmann’s equation?
the time evolution of f (distribution function in phase space) as the sum of a force, diffusion and collision term
Why do we use the Chapman-Enskog procedure?
We solve Boltzmann’s equation in terms of l/L because there are too many unknowns to solve exactly. With this procedure the Euler equations and the Navier-Stokes equations are found as the zeroth and first order solution respectively.
What is the Mach number?
The ratio of the velocity of the object and the sound speed. M=1 means sonic speed
