# C-Grid Boundary Conditions

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 June 2, 2011, 19:44 C-Grid Boundary Conditions #1 New Member   Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 8 I am using a C-grid from here to analyze the NACA 0012 airfoil using Cradle's SC/Tetra. I am having some trouble setting the boundary conditions. What BCs should I use? For what I have already tried, some regions of the grid develop a very high pressure and others have a very low pressure. (This only happens when the angle of attack is non-zero, and in case it matters, I am simulating the angle of attack by varying the inflow direction). I hope somebody can help me! Thanks in advance. P.S. I'm obviously new to this forum and hope to become more active once my work gets more difficult.

 June 6, 2011, 22:18 #2 New Member   Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 8 So far, I have tried making the entire circular portion of the C-grid inflow and the rest a static pressure of 0, making the entire grid natural inflow/outflow and beginning with an initial condition which contained the velocity I wanted, and several other variations of the theme. Could somebody please help me?

 June 6, 2011, 23:59 #3 Senior Member   Martin Hegedus Join Date: Feb 2011 Posts: 486 Rep Power: 12 I'm not familiar with Cradle's SC/Tetra. If the code is compressible, you should use a characteristic (Riemann) boundary condition.

 June 7, 2011, 15:58 #4 New Member   Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 8 Is the Riemann BC the same as Natural Inflow/Outflow? This is what I believe, based on the small amount of literature that I actually understand. Also, where should the Riemann BC be applied? I presume I also need in inlet, and where should that be?

 June 7, 2011, 18:21 #5 New Member   Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 8 I'm not sure what you mean. My question is basically: "What BCs should I use for this?"

June 10, 2011, 16:58
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Martin Hegedus
Join Date: Feb 2011
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Quote:
 Originally Posted by Draksis314 Is the Riemann BC the same as Natural Inflow/Outflow? This is what I believe, based on the small amount of literature that I actually understand. Also, where should the Riemann BC be applied? I presume I also need in inlet, and where should that be?

http://turbmodels.larc.nasa.gov/naca0012_val.html

Not sure what a "Natural" Inflow/Outflow B.C. is. I'm totally guessing that the idea is the same, but meant for an incompressible solver. Is your solution methodology incompressible?

 June 10, 2011, 17:49 #7 New Member   Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 8 Yes, my simulation is incompressible. Natural inflow outflow is a BC in which the air can freely move out and into the domain.

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