[Daniel4]

hi

im doing a simulation for flow around airfoil NACA 4412. but the residual seem not going to be stable.it keeps going up and down. the residual for angle of attack -5,0 and 5 is stable.but for the -10,10 and 15 is like the pic given.

is anyone can help me with this?

[me3840]

While your residuals in magnitude seem high (this is probably related to the grid), the oscillations you see are probably the result of a transient phenomenon. Are you running steady-state? If so, residuals like this for a high angle of attack may be expected. Can you post images of your grid and give some information on the physics regime?

[Daniel4]

Originally Posted by me3840

While your residuals in magnitude seem high (this is probably related to the grid), the oscillations you see are probably the result of a transient phenomenon. Are you running steady-state? If so, residuals like this for a high angle of attack may be expected. Can you post images of your grid and give some information on the physics regime?

physics model
-gradients
-2D
-segregated flow
-steady
-ideal gas
-inviscid

do you mean grid as the mesh?if so,here it is..

[me3840]

You're running the physics inviscid but it looks like you have a nice boundary layer mesh? Why is that?

What mach number is this at?

[dai549592484]

First of all, are the results good enough? say Cd,CL.
If the results are good than have a look at the absolute residuals value.
If the absolute residuals value is small enough then don't pay too much attention to the residuals.

[Daniel4]

Originally Posted by me3840

You're running the physics inviscid but it looks like you have a nice boundary layer mesh? Why is that?

What mach number is this at?

im not sure why..thats why im here asking for opinions.

it was running with 3,000,000 reynolds number and that makes it as 43.81m/s as the velocity..

any suggestion?maybe i should do something else in physics or something..

[Daniel4]

Originally Posted by dai549592484

First of all, are the results good enough? say Cd,CL.
If the results are good than have a look at the absolute residuals value.
If the absolute residuals value is small enough then don't pay too much attention to the residuals.

the results are not good enough apart from angle of attack -5,0 and 5.others than those are not.

[dai549592484]

reduce your URF and see what happens.

BTW, did you use the same mesh for different AOA?
Judging by your mesh, I suppose that you used the same mesh and changed the direction of incident wind, right?

There is a tutorial in ccm+ help file which tells you how to use overset mesh to test the effect of AOA. (You do have to use overset mesh, however, you will have a brief idea about where you need more meshes.)

Since you can get good result for some AOA, I would say it is caused by mesh most probably.

[Daniel4]

Originally Posted by dai549592484

reduce your URF and see what happens.

BTW, did you use the same mesh for different AOA?
Judging by your mesh, I suppose that you used the same mesh and changed the direction of incident wind, right?

There is a tutorial in ccm+ help file which tells you how to use overset mesh to test the effect of AOA. (You do have to use overset mesh, however, you will have a brief idea about where you need more meshes.)

Since you can get good result for some AOA, I would say it is caused by mesh most probably.

what is URF?

yes i am using the same mesh for different aoa.is it something wrong with it?

where i can find the help file?if i may ask that

[mosef]

URF = Under Relaxation Factor

[Daniel4]

i got the lift coefficient right, but why the drag coefficient seem wrong and quite different from the theoretical?

i used the direction in the report as (1,0,0) or should i change to another value?