How are a transient simulations performed??

Luk

Hi all, Well, my problem is quite suprising even for myself: I am not new in CFD but I realised that I have completly no idea how are performed a transient (non - steady) simulations (in CFX for example). Can anyone give me answer for the following question: how is a transient term of NS equation advected in time in TRANSIENT simulations? I understand steady state with pseudo-timestep: in SIMPLE algorithm it is like: guess p, calculate u,v,w, solve the pressure correction, update u,v,w and do it till convergence. Ok, in the end you have STEADY STATE u,v,w,p etc. But what is with transient scheme? Is another scheme (Lax, MacCormack or other) used in CFX for this type of calculation? What does it mean coefficient loops when you set up the option for transient simulation? I was thinking that if You solve for u,v,w in one iteration (for example in Lax-Wendrrof scheme) You dont need to refresh or get some internal-convergence going to t+1 time and just put the values to the right side of the equation explicitely.

I would be very grateful for help because I realized to be extremely confused in this point, Regards, Luk