error in Setup and Results

cuteapathy · June 19, 2012, 01:42

Dear all,

I am trying to simulate the wind turbine case in Fluent. The whole mesh is made by one bigger outside cylinder and one propeller in the smaller inside cylinder.

For the settings of propeller and smaller inside cylinder, I use the moving wall and set the rotational speed to be 20 rad/s.

For the settings of outside cylinder, I use the stationary wall.

For the settings of inlet, I use the velocity-inlet and set the velocity magnitude to be 20 m/s.

For the settings of outlet, I use outflow.

For the settings of solution initialization, I set gauge pressure to be 0, X velocity to be 10 m/s, and Y, Z velocity to be 0 m/s.

For the settings of run calculation, I set number of time steps to be 10, the remaining is the default value.

When I calculated the case, it worked. I got green checks on four parts of Fluent on workbench. While I wanted to see some animation and tried to open the result window. I got the error message on the Setup window. I have attached the error message here. The other error message showed in workbench is, "An error occurred in FLUENT during save". The result window showed up finally, but there were no numerical results there. I have no idea why this happened.

Could anyone kindly give me some advice how to fix this? Any help would be greatly welcome since I am new to Fluent and stuck here for a long time. I would really need some experienced help.

Thank you very much.
Michelle

chris85 · June 19, 2012, 04:13

For initialisation would you not use 20 m/s, dont see the need for 10 m/s in this case. Also the outer boundary layer you are modelling with a stationary wall, maybe put this as a moving wall with velocity of 20m/s in the X direction and a no slip condition attached to it.

The case may take a while to solve to steady state so setup a monitor of lift on the blade surface to monitor when steady state has been reached. Convergence will come earlier than this.

cuteapathy · June 19, 2012, 08:45

Dear Chris,

Thank you for your advice. I appreciate your help. For this case, I set time to be the transient case and number of time steps to be 10. Do you think it will be better if I could change it to the steady case?

chris85 · June 19, 2012, 09:32

What time step are you using? 10 time steps is fairly small though. You first need to determine the correct time step to use.

Then you need to run the transient solution until it is stable, by this I mean monitor a quantity such as lift/drag on a surface and run until value is steady.

Convergence alone will not give a complete solution.

I would not change to a steady case as there will be change in flow properties with respect to time and thus a transient solution needed.

cuteapathy · June 19, 2012, 10:26

Dear Chris,

When I give the positive velocity here, I get the message about reversed flow. i am thinking whether I need to change all velocity values to be negative.

Where could I monitor a quantity such as lift/drag?

If I tried time steps 10, I am wondering how I could see the animation for my simulation. I mean I would like to see the rotating propeller.

cuteapathy · June 19, 2012, 10:28

Dear Chris,

I forgot to ask whether I need to set the settings for the cell zone conditions? Thank you.

chris85 · June 19, 2012, 10:31

Cell zone conditions should be representative of the fluid being examined. In this case air.

How is the mesh quality actually? What sort of mesh you got? Bit early to get an animation going. You need a good solution before going into a detailed post processing.

cuteapathy · June 19, 2012, 10:46

Dear Chris,

Do I need to set the velocity for cell zone conditions?

So the message about the reversed flow is fine?

I got the mesh converted from OpenFOAM. How could I check my mesh quality in Fluent?

How could I see the animation for this case?

Thank you very much.

chris85 · June 19, 2012, 11:39

Quote:

Originally Posted by cuteapathy

Dear Chris,

Do I need to set the velocity for cell zone conditions?

So the message about the reversed flow is fine?

I got the mesh converted from OpenFOAM. How could I check my mesh quality in Fluent?

How could I see the animation for this case?

Thank you very much.

Ok the velocity in the cells is got at the start from the initialisation, this initialises the cells with the values put in here. You should have 20 m/s here.

Mesh quality is big area you need to do some reading on this. Main things are cell skewness and orthogonal quality. Also must consider if refined enough and be careful of the mesh in near wall regions. this becomes complex and differs depending on the solver used.

Too early for an animation, need to get a good solution before you start doing detailed post processing.

cuteapathy · June 19, 2012, 12:16

Dear Chris,

When I tried to save the project, the error message which I attached in the first article keeps showing. Did I do something wrong about my settings?

I tried to open the result and the same error message showed up. The system keeps telling me "An error occurred in FLUENT during save". I could not save my work and need to start from the beginning every time. What can I do for this one?

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June 19, 2012, 04:13		#2
chris85 New Member Chris Join Date: Nov 2011 Posts: 16 Rep Power: 14	For initialisation would you not use 20 m/s, dont see the need for 10 m/s in this case. Also the outer boundary layer you are modelling with a stationary wall, maybe put this as a moving wall with velocity of 20m/s in the X direction and a no slip condition attached to it. The case may take a while to solve to steady state so setup a monitor of lift on the blade surface to monitor when steady state has been reached. Convergence will come earlier than this.

June 19, 2012, 08:45		#3
cuteapathy Member Join Date: Jan 2012 Posts: 36 Rep Power: 14	Dear Chris, Thank you for your advice. I appreciate your help. For this case, I set time to be the transient case and number of time steps to be 10. Do you think it will be better if I could change it to the steady case?

June 19, 2012, 09:32		#4
chris85 New Member Chris Join Date: Nov 2011 Posts: 16 Rep Power: 14	What time step are you using? 10 time steps is fairly small though. You first need to determine the correct time step to use. Then you need to run the transient solution until it is stable, by this I mean monitor a quantity such as lift/drag on a surface and run until value is steady. Convergence alone will not give a complete solution. I would not change to a steady case as there will be change in flow properties with respect to time and thus a transient solution needed.

June 19, 2012, 10:26		#5
cuteapathy Member Join Date: Jan 2012 Posts: 36 Rep Power: 14	Dear Chris, When I give the positive velocity here, I get the message about reversed flow. i am thinking whether I need to change all velocity values to be negative. Where could I monitor a quantity such as lift/drag? If I tried time steps 10, I am wondering how I could see the animation for my simulation. I mean I would like to see the rotating propeller.

June 19, 2012, 10:28		#6
cuteapathy Member Join Date: Jan 2012 Posts: 36 Rep Power: 14	Dear Chris, I forgot to ask whether I need to set the settings for the cell zone conditions? Thank you.

June 19, 2012, 10:31		#7
chris85 New Member Chris Join Date: Nov 2011 Posts: 16 Rep Power: 14	Cell zone conditions should be representative of the fluid being examined. In this case air. How is the mesh quality actually? What sort of mesh you got? Bit early to get an animation going. You need a good solution before going into a detailed post processing.

June 19, 2012, 10:46		#8
cuteapathy Member Join Date: Jan 2012 Posts: 36 Rep Power: 14	Dear Chris, Do I need to set the velocity for cell zone conditions? So the message about the reversed flow is fine? I got the mesh converted from OpenFOAM. How could I check my mesh quality in Fluent? How could I see the animation for this case? Thank you very much.

June 19, 2012, 12:16		#10
cuteapathy Member Join Date: Jan 2012 Posts: 36 Rep Power: 14	Dear Chris, When I tried to save the project, the error message which I attached in the first article keeps showing. Did I do something wrong about my settings? I tried to open the result and the same error message showed up. The system keeps telling me "An error occurred in FLUENT during save". I could not save my work and need to start from the beginning every time. What can I do for this one?