C-Grid Boundary Conditions

Draksis314 · June 2, 2011, 19:44

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.

Draksis314 · June 6, 2011, 22:18

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?

Martin Hegedus · June 6, 2011, 23:59

I'm not familiar with Cradle's SC/Tetra. If the code is compressible, you should use a characteristic (Riemann) boundary condition.

Draksis314 · June 7, 2011, 15:58

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?

Draksis314 · June 7, 2011, 18:21

I'm not sure what you mean. My question is basically: "What BCs should I use for this?"

Martin Hegedus · June 10, 2011, 16:58

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?

Draksis314 · June 10, 2011, 17:49

Yes, my simulation is incompressible. Natural inflow outflow is a BC in which the air can freely move out and into the domain.

June 2, 2011, 19:44	C-Grid Boundary Conditions	#1
Draksis314 New Member Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 14	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.

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June 6, 2011, 22:18		#2
Draksis314 New Member Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 14	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
Martin Hegedus Senior Member Martin Hegedus Join Date: Feb 2011 Posts: 500 Rep Power: 19	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
Draksis314 New Member Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 14	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
Draksis314 New Member Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 14	I'm not sure what you mean. My question is basically: "What BCs should I use for this?"

June 10, 2011, 17:49		#7
Draksis314 New Member Anonymous Join Date: Jun 2011 Posts: 5 Rep Power: 14	Yes, my simulation is incompressible. Natural inflow outflow is a BC in which the air can freely move out and into the domain.