# Setting Outlets with gravity..

 Register Blogs Members List Search Today's Posts Mark Forums Read January 17, 2001, 10:15 Setting Outlets with gravity.. #1 Javier Larrondo Guest   Posts: n/a Hi, I have been doing the mathematical background when gravity is present. And need some confirmation and explanation in some terms of the equation. I'm using the reduced pressure formulation or density_difference model to simulate gravity, this will introduce in the momentum equation a reference pressure p_ref, which satisfies the hydrostatic-equilibrium equation: grad p_ref + rho_ref * G = 0 and if we define G = - grad(f) (**), where f is the gravitational potential, then you have grad ( p_ref + rho_ref*f ) = 0 grad(p_ref) + grad(rho_ref*f) = 0 the momentum equation rho_ref*DU/Dt = - grad(p) + h*grad^2(U) + F (*) where F is the bouyancy-source term, which is defined like: F = rho*G defining delta_rho = rho-rho_ref, then F = (rho_ref + delta_rho )*G using (**) F = delta_rho*G - grad(rho_ref*f) using this in the momentum equation rho_ref*DU/Dt = - grad(p) + h*grad^2(U) + delta_rho*G - grad(rho_ref*f) adding cero to the equation rho_ref*DU/Dt = - grad(p) + h*grad^2(U) + delta_rho*G - grad(rho_ref*f) + grad(p_ref)+grad(rho_ref*f) reordering and reducing terms, we have rho_ref*DU/Dt = grad(p-p_ref) + h*grad^2(U) + (rho-rho_ref)*G So, the question is : How do I set the value of the pressure in an outlet if I know that his hydrostatic value p is -100 Pa? Do I have to set in the outlet now (p-p_ref)? The pressure ploted in VR-Viewer is p or (p-p_ref)? Now is this calculation correct? if gravity in the -Z direccion (G=-g*k) then the equation of p_ref, reduces to d(p_ref)/dz +rho_ref*g =0, so p_ref=rho_ref*g*z which value of z have to use? z=0 or z= height of the domain? is it constant? or depends on z? that means that I have know a new field p_ref? thanks, for any comments Javier Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post giogio FLUENT 1 March 22, 2008 17:48 KK CFX 3 March 3, 2008 16:44 Shankar FLUENT 0 May 31, 2006 04:30 Floydian Phoenics 3 January 22, 2005 03:48 cfxbeginer CFX 2 November 29, 2001 23:39