Far Field Boundary Conditions
Hi, I am looking forward to implement an open boundary (far field boundary condition) in an unstructured code which does not account for these situations. I am looking for some information )papers or simmilar) which could help me on this task.
Does anybody know any references concerning the subject??? 
Re: Far Field Boundary Conditions
Boundary conditions depend upon lots of things; please be specific so that any suggestion would be meaningful.
However, some of the papers ( I had posted a reference list sometime ago ) will give you far field boundary conditions for the solution of compressible inviscid/viscous flow problems on unstructured grids. Jawahar 
Re: Far Field Boundary Conditions
Sorry I didn't make myself clear. I am trying to implement an open boundary condition in an unstructured code. My aim is to study the air flow around a standard NACA airfoil and I want to do it, not in a wind tunnel, like a closed boundary will give me, but on an open air boundary. I am aiming to reduce considerably the size of my domain. At the moment, I need to simulate it under a domain of 50!!! times the chord of the arfoil so the closed boundary effect can be minimized. Any suggestion will be welcomed. Thankjs very much, Jawahar

Re: Far Field Boundary Conditions
I would use absorbing boundary conditions (Riemann based). The standard reference is a Jameson paper... I haven't got it available here but do a search on "Jameson" in this forum (or the forum archive) and I think you'll find it  I have a vague memory that this has been discussed here previously.
The extent of the computational domain should be at least 10 times the chord, preferably 20, even with this kind of boundary conditions. With an unstructured code this shouldn't be a problem though since you can expand the cells further away from the object. 
Re: Far Field Boundary Conditions
If your aim is to reduce the size of the computational domain the paper "Global farfield computational boundary conditions for C and O grid topologies" by A.Verhoff in AIAA Journal, Vol.36, No.2, pp. 148156, may be useful for you. Whether structured or unstructured the concepts are same.
Hope this helps. Uma 
Re: Far Field Boundary Conditions
Hi,
I did a serch with Jameson....and nothing other than a post from a discussion on Density time marching based methods vs pressure based methods......so it must have expired! Can you find any more details on this Jameson paper?? Thanks............................................ .Duane 
Re: Far Field Boundary Conditions
Try the following farfield boundary conditions. I find it very effective for both structured and unstructured grid computations. You may locate the outer boundary between 812 chords. Again, you can try a couple of numerical experiments to fix the outer boundary ! I've assumed you are using circle as the outer boundary !
Create an extra ring of cells beyond the last ring of cells. For freestream Mach number less than 1:  Prescribe asymptotic farfield solutions in those cells. i.e uniform flow on which is superimposed the circulatory flow caused by a point vortex at the midpoint of the airfoil's chord. The instantaneous circulation GAMMA at the airfoil decides the strength of the vortex. The flow induced by the vortex is then computed from small perturbation theory after including the compressibility effects (PrandtlGlauert transformation). (Also refer to " Foundations of Aerodynamics " by Kuethe & Chow) For supersonic freestream Mach numbers, just prescribe the freestream values in the outer ring cells. Everything I've stated applies to cellvertex methods also. You can prescribe these conditions at points lying on the outer circle. Good Luck ! Jawahar 
Re: Far Field Boundary Conditions
Thanks very much indeed for your kindness and interest. Your advices have been extremly useful. XAVI

Re: Far Field Boundary Conditions
To complement Jawahar's posting, I think you would find the following paper very useful :
J.L. Thomas and M.D. Salas "FarField Boundary Conditions for Transonic Lifting Solutions to the Euler Equations", AIAA Journal, July 1996, Vol. 24, No. 7, pp 10741080. 
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