Is FASTRAN sensitive to the grid?

june_zhazha · November 13, 2011, 07:58

I use FASTRAN to calculate the AGARD-B model in the wind tunnel, so i don't change the inlet conditions . I ratate the model to get the angle of attack ,such as 2°,4°,6°,but when the angle of attack was 6°, the process running by first order form converged ，but the process running by second order form was suddenly divergent.

Is the FASTRAN so sensitive to the grid?

cfdnewbie · November 13, 2011, 08:50

I havent used fastran, but what you are describing sounds like you changed the discretization from first to second, right? then it's no wonder higher AOA will give you more vortices, and thus unsteadiness...

june_zhazha · November 16, 2011, 09:28

Quote:

Originally Posted by cfdnewbie

I havent used fastran, but what you are describing sounds like you changed the discretization from first to second, right? then it's no wonder higher AOA will give you more vortices, and thus unsteadiness...

Then how can i improve the calculation?

cfdnewbie · November 16, 2011, 13:11

If the problem itself is unsteady due to high AOA, then that's the real physics, and your first order is way too dissipative!
Refine the grid, use higher order (4,6,8,....) schemes....

November 13, 2011, 07:58	Is FASTRAN sensitive to the grid?	#1
june_zhazha New Member Join Date: Aug 2009 Posts: 5 Rep Power: 16	I use FASTRAN to calculate the AGARD-B model in the wind tunnel, so i don't change the inlet conditions . I ratate the model to get the angle of attack ,such as 2°,4°,6°,but when the angle of attack was 6°, the process running by first order form converged ，but the process running by second order form was suddenly divergent. Is the FASTRAN so sensitive to the grid?

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November 13, 2011, 08:50		#2
cfdnewbie Senior Member cfdnewbie Join Date: Mar 2010 Posts: 557 Rep Power: 20	I havent used fastran, but what you are describing sounds like you changed the discretization from first to second, right? then it's no wonder higher AOA will give you more vortices, and thus unsteadiness...

November 16, 2011, 13:11		#4
cfdnewbie Senior Member cfdnewbie Join Date: Mar 2010 Posts: 557 Rep Power: 20	If the problem itself is unsteady due to high AOA, then that's the real physics, and your first order is way too dissipative! Refine the grid, use higher order (4,6,8,....) schemes....