[cfd seeker]

I am trying to simulate flapping motion of the wing using Dynamic Mesh. I have setup the case in Fluent but I have some doubts and questions regarding it. I am uploading the pictures which will show the dynamic mesh setup. Kindly tell me is it correct? The problem consist of a domain around the wing, symmetry plane, wing and fluid zones. Few questions......

1. I have declared domain(farfield) as "Stationary" zone as shown in pic1. Is it correct? how to set value of "Cell Height"(shown by a question mark in pic1)?

2. Fluid is set as "Deforming" as shown in pic2. Is it correct? values of the "Zone Parameters" will be taken from "Zone Scale Info" as shown in pic2? right?

3. S1020 is the name of wing which will be given motion using a DEFINE_GRID_MOTION udf and S1020 is set as "User Defined" as shown in pic3 is it correct? how to set value of "Cell Height"(shown by a question mark in pic3)?

4. Symmetry plane is set as "Stationary" as shown in pic4 is it correct? how to set value of "Cell Height"(shown by a question mark in pic4)?

Also after the finalization of UDF I will use full structured hexa mesh for this problem. For this purpose in Dynamic mesh I will only use "Smoothing" and "Layering" for mesh update? am I right kindly comment? I cannot use "Remeshing" as it only works for unstructured meshes? right?

[nimbus1947]

What i am about to you tell you works for unstructured tetrahedral mesh.

1. Cell Height is the ideal height based on which Fluent calculates whether to split or collapse cells.
Ref:https://www.sharcnet.ca/Software/Flu...ug/node396.htm
2. Use DEFINE_CG_MOTION for the motion of wall.
Ref:https://www.sharcnet.ca/Software/Flu.../udf/fludf.pdf
3. Symmetry plane should be set as deforming.
4. Farfield -> Stationary ? -- Not required
fluid -> Deforming? -- not required

[aerosjc]

1. Farfield not necessary to be stationary. I never set a certain value for the cell height. I just keep the original value. It's ok for my case.
2. Fluid not necessary to be deforming. So, do not need to worry the zone parameters.
Leave them alone.
3. You should refer to the UDF manual for more infomation about DEFIEN_GRID_MOTION and DEFINE_CG_MOTION. In fact, you should use DEFINE_CG_MOTION to define the motion of your wing. And, you should set "Rigid Body" for your wing.
4. I think the symmetry plane may be better to be set as deforming.
5. I don't know whether you want to rotate the wing a big angle, say 45 degrees, or not. Smoothing is available for small degrees. I hold an opinion that layering is not suitable for your flapping case. Remeshing is designed for big degrees or big displacement movement. Actually, I do not know how to move the structural mesh for a big displacement. If you make it, please tell me how.

[cfd seeker]

Originally Posted by aerosjc

1. Farfield not necessary to be stationary. I never set a certain value for the cell height. I just keep the original value. It's ok for my case.
2. Fluid not necessary to be deforming. So, do not need to worry the zone parameters.
Leave them alone.
3. You should refer to the UDF manual for more infomation about DEFIEN_GRID_MOTION and DEFINE_CG_MOTION. In fact, you should use DEFINE_CG_MOTION to define the motion of your wing. And, you should set "Rigid Body" for your wing.
4. I think the symmetry plane may be better to be set as deforming.
5. I don't know whether you want to rotate the wing a big angle, say 45 degrees, or not. Smoothing is available for small degrees. I hold an opinion that layering is not suitable for your flapping case. Remeshing is designed for big degrees or big displacement movement. Actually, I do not know how to move the structural mesh for a big displacement. If you make it, please tell me how.

2. Fluid not necessary to be deforming. So, do not need to worry the zone parameters.
Leave them alone.

Are you sure about this ...I guess fluid region will get deform once wing will flap, we check on Smoothing, Layering and Remeshing in order to smooth, layer and remesh "Deformed" portion of the mesh in the FLUID zone, isn't it? your comments

[cfd seeker]

4. I think the symmetry plane may be better to be set as deforming.

I am not sure about this? any body else can clarify it please....

3. You should refer to the UDF manual for more infomation about DEFIEN_GRID_MOTION and DEFINE_CG_MOTION. In fact, you should use DEFINE_CG_MOTION to define the motion of your wing. And, you should set "Rigid Body" for your wing.

We can use both Macros but ifact Define_Grid_Motion is more better than Define_CG_Motion

[aerosjc]

I agree with you on the idea that the fluid region will deform once the wing will flap. But I think that the setting of smoothing, layering and remeshing is doing this job, so we do not need to set the " deforming " option. This is my opinion.

[aerosjc]

I remember the macro DEFINE_GRID_MOTION is for your mesh motion, instead of your wing motion. my opinion.

[cfd seeker]

Originally Posted by aerosjc

I agree with you on the idea that the fluid region will deform once the wing will flap. But I think that the setting of smoothing, layering and remeshing is doing this job, so we do not need to set the " deforming " option. This is my opinion.

I confirmed it from a very experienced user that for this problem zones will be defined as fallows....
1. Farfield to set as "Stationary"
2. Symmetry also as "Stationary"
3. Fluid to define as "Deforming"
4. Wing to set as "Rigid Body" once you use DEFINE_CG_MOTION macro

[aerosjc]

ok, but I also made a success without your 1, 2, 3.

[cfd seeker]

Originally Posted by aerosjc

ok, but I also made a success without your 1, 2, 3.

Strange because I also confirmed it from the posts in other forums. Have you compared your results with any benchmark case?

[aerosjc]

Could you give me some cases for confirmation? Many thanks!

[cfd seeker]

Originally Posted by aerosjc

Could you give me some cases for confirmation? Many thanks!

you mean Papers or my case and data files?

[cfd seeker]

Originally Posted by aerosjc

Could you give me some cases for confirmation? Many thanks!

http://www.cfd-online.com/Forums/flu...volume-3d.html
Read this thread

[Vidit Sharma]

Hi All..

Sir,
I am trying to rotate a 2D box or a 2D cup structure in Fluent using smoothing and remeshing. I am using tri mesh and as mentioned in Fluent Manual I am using smoothing and remeshing and also set the remeshing parameters from mesh info tab given in the remeshing menu. But the problem is that when i start simulation and it goes to first time step Fluent display "Updating mesh at time level N..." and here it stops and it happened alot of time and even waiting after a whole day it didnt worked. I also tried time step size from 0.01 to 0.000001 but it still show this problem.

Can you plz help in this case?

Thank u in advance

[akshaymanikjade]

you pls check your dynamic mesh parameter properly.....if have proper idea to set or no then let me know so will help in this regard..

[srvsahay]

Hi everyone,
I am new to dynamic mesh and trying to model my right wall as moving wall based on force balance.

My udf looks like this(same udf as provided in user manual):

#include "udf.h"
static real v_prev=0.0;
DEFINE_CG_MOTION(pstn, dt, vel, omega, time, dtime)
{

Thread *t;
face_t f;
real NV_VEC (A);
real force, dv;
/* reset velocities */
NV_S (vel, =, 0.0);
NV_S (omega, =, 0.0);
if (!Data_Valid_P ())
return;
/* get the thread pointer for which this motion is defined */
t = DT_THREAD (dt);
/* compute pressure force on body by looping through all faces */
force = 0.0;
begin_f_loop (f, t)
{
F_AREA (A, f, t);
force += F_P (f, t) * NV_MAG (A);
}
end_f_loop (f, t)
/* compute change in velocity, i.e., dv = F * dt / mass
velocity update using explicit Euler formula */
if(force>0)
dv = dtime * force / 50.0;
else
dv=0;
v_prev += dv;
Message ("time = %f, x_vel = %f, force = %f\n", time, v_prev, force);
Message ("yo");
/* set x-component of velocity */
vel[0] = v_prev;
}

However the shape of my right wall gets deformed. I want the shape to be intact. Please suggest what should be the settings in dynamic mesh. Which method should i use?

[r7carvalho]

Hi, the forces are different, so you have a shear deformation. The solution would be to declare a global scope variable and comput it average in the face. After, you aply the same velocity in the whole thread (face, boundary, cells, etc).

Originally Posted by srvsahay

Hi everyone,
I am new to dynamic mesh and trying to model my right wall as moving wall based on force balance.

My udf looks like this(same udf as provided in user manual):

#include "udf.h"
static real v_prev=0.0;
DEFINE_CG_MOTION(pstn, dt, vel, omega, time, dtime)
{

Thread *t;
face_t f;
real NV_VEC (A);
real force, dv;
/* reset velocities */
NV_S (vel, =, 0.0);
NV_S (omega, =, 0.0);
if (!Data_Valid_P ())
return;
/* get the thread pointer for which this motion is defined */
t = DT_THREAD (dt);
/* compute pressure force on body by looping through all faces */
force = 0.0;
begin_f_loop (f, t)
{
F_AREA (A, f, t);
force += F_P (f, t) * NV_MAG (A);
}
end_f_loop (f, t)
/* compute change in velocity, i.e., dv = F * dt / mass
velocity update using explicit Euler formula */
if(force>0)
dv = dtime * force / 50.0;
else
dv=0;
v_prev += dv;
Message ("time = %f, x_vel = %f, force = %f\n", time, v_prev, force);
Message ("yo");
/* set x-component of velocity */
vel[0] = v_prev;
}

However the shape of my right wall gets deformed. I want the shape to be intact. Please suggest what should be the settings in dynamic mesh. Which method should i use?