constitutive or closure relations
 

What exactly are constitutive or closure relations ?

I've read this term all over an CFD article I read, and I don't know the exact meaning of it.

Would you mind helping me?

hey eric,
would is meant by that term is usually the "closure" for any unknowns in your solution. Let's say for the Navier-Stokes equations, you have 5 equations: momentum in 3 directions, mass and energy conservations. Your equations however contain 6 unknown (u,v,q,p,rho,T), so you need a sixth equation to close the system: the equation of state relating rho, p and T!