[ldb83]

Hello~ I am a beginner for FLUENT.
Now I am simulating the oscillation airfoil in infinite water depth.
I used pressure-based and UDF for the motion of oscillation.
also standard k-e model is used for the model.
water flow from left boundary with 2.0 m/sec^2 and the frequency of body oscillation is 5Hz.

Question

1. I give no slip condition to the upper and lower wall to consider infinite water depth. I am not sure it is enough or not? Should I give additional consideration to the boundary?

2. I am wondering standard k-e model is suitable for this kind of simulation.

Have a nice day all of you~

[stefanos]

for infinite boundaries, and more specifically, for solutions that require the viscous fluid not to reflect on the boundary, i think that the "pressure farfield" condition is a more suitable option, however it's setting up is a bit more complex than the other BCs. I haven't worked on it so i can't tell you more. You can check out the manual on that.

[stefanos]

Originally Posted by stefanos

for infinite boundaries, and more specifically, for solutions that require the viscous fluid not to reflect on the boundary, i think that the "pressure farfield" condition is a more suitable option, however it's setting up is a bit more complex than the other BCs. I haven't worked on it so i can't tell you more. You can check out the manual on that.

however, as long as the oscillation amplitude of your airfoil is not extreme, for your domain i don't think that you'll have any problem retaining the no-slip BCs

[Aeronautics El. K.]

1. m/s^2 are units for acceleration, not for velocity, right?
2. There are 2 papers titled "Evaluation of turbulence models for unsteady flows of an oscillating airfoil" by Srinivasan, Ekaterinaris and McCroskey and "computation of separated and unsteady flows with one- and two- equation models by Ekaterinaris and Menter, which could answer your questions about the turbulence model.

[ldb83]

Thank you for your kind reply. It will be very useful for my simulation~

1. It's my mistake. I have used m/s for velocity.
2. I will review the papers mentioned by you.

[ldb83]

Originally Posted by Aeronautics El. K.

1. m/s^2 are units for acceleration, not for velocity, right?
2. There are 2 papers titled "Evaluation of turbulence models for unsteady flows of an oscillating airfoil" by Srinivasan, Ekaterinaris and McCroskey and "computation of separated and unsteady flows with one- and two- equation models by Ekaterinaris and Menter, which could answer your questions about the turbulence model.

Thank you for your kind reply. It will be very useful for my simulation~

1. It's my mistake. I have used m/s for velocity.
2. I will review the papers mentioned by you.

[ldb83]

Originally Posted by stefanos

for infinite boundaries, and more specifically, for solutions that require the viscous fluid not to reflect on the boundary, i think that the "pressure farfield" condition is a more suitable option, however it's setting up is a bit more complex than the other BCs. I haven't worked on it so i can't tell you more. You can check out the manual on that.

Thank you for your kind reply. Can I add one more questions?
I have seen some simulation using pressure-outlet to consider infinite depth.
Do you think that pressure-outlet condition is more suitable than no-slip condition??

[Aeronautics El. K.]

May I ask what exactly do you mean by "infinite water depth"?

I believe there's not such thing. Water depth is finite and max depth is somewhere in the Pacific and counts about 11km.

The no-slip condition doesn't define the depth. Neither does so the pressure outlet.
I think that the depth should be defined via the operating pressure.

[ldb83]

Originally Posted by Aeronautics El. K.

May I ask what exactly do you mean by "infinite water depth"?

I believe there's not such thing. Water depth is finite and max depth is somewhere in the Pacific and counts about 11km.

The no-slip condition doesn't define the depth. Neither does so the pressure outlet.
I think that the depth should be defined via the operating pressure.

It means that any boundary condition is not considered in my simulation.
so I would like to consider only the effect from oscillating airfoil.

If the airfoil is oscillated in shallow water depth, there is some wave reflection from bottom boundary. however In my simulation, I don't want to consider that kind of effect.

so now I am little bit confusing should I define the upper and lower wall as pressure-out.

I am not sure my interpretation is enough or not.

[Aeronautics El. K.]

Hello Lee!

I just noticed at the pictures you uploaded that the inlet and outlet boundaries are only 12m apart while your airfoil's chord is 1m. It is quite probable then, that the boundaries will influence the solution that's why you should increase this distance.

I guess that by "upper and lower wall" you mean, actually, the upper and lower boundaries of your domain. In this case, I think you should do what Stefanos suggested and define them as pressure far-field.

[ldb83]

Originally Posted by Aeronautics El. K.

Hello Lee!

I just noticed at the pictures you uploaded that the inlet and outlet boundaries are only 12m apart while your airfoil's chord is 1m. It is quite probable then, that the boundaries will influence the solution that's why you should increase this distance.

I guess that by "upper and lower wall" you mean, actually, the upper and lower boundaries of your domain. In this case, I think you should do what Stefanos suggested and define them as pressure far-field.

Mr. Lefteris~
Thank you so much your recommendation.
I was thinking the distance is too short compared to chord length.
so I am planing to increase the domain length as 40 times of chord length.
also the upper and lower boundary is changed to pressure-outlet.
I think that It could be also reasonable boundary condition compared to pressure far field.
anyway Many thanks~

[Aeronautics El. K.]

You're right. A little revision in fluent's user's guide helps.
Pressure outlet is the general condition... Pressure far field is recommended for compressible flow. I was wrong on that, sorry.

[ldb83]

Originally Posted by Aeronautics El. K.

You're right. A little revision in fluent's user's guide helps.
Pressure outlet is the general condition... Pressure far field is recommended for compressible flow. I was wrong on that, sorry.

Thank you so much for you comment.
Your comment was very valuable for my simulation.
Have a nice day~

[mhmmad_ibraham]

Hello sir...
please send me your udf of oscillation motion as fast as you can...
my E_mail is m70hm@yahoo.com

[nitman118]

hi,
can you share your udf with me....it will be really helpful,thanks.....
id: nitman118@gmail.com