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-   -   Mrf-turbine blade with mrf (http://www.cfd-online.com/Forums/fluent/115101-mrf-turbine-blade-mrf.html)

battersai March 23, 2013 21:40

Mrf-turbine blade with mrf
 
I am a Master's students in solid mechanics, conducting FSI on turbine blade.I am new to FLUENT.

I know the pressure at inlet (607428.1 pa) and pressure at outlet (249970.4 pa).The temperature at inlet is 1010K.

1)I used an arbitrary static pressure to initialise the solution.It was slightly lower that the total pressure. Is it ok?

2)I have used pressure inlet and outlet, periodic boundary zones, coupled the fluid and solid zones with a shadow wall to enable conjugate heat transfer, used ideal gas equations for air and got results for a stationary blade.I have also set proper interfaces between inlet passage and rotor, rotor and outlet passage.

The blade is rotating at 8000rpm. Can such high velocities be simulated, assuming I gradually increase the speed?

I am guessing that I should set the cellzone velocity in absolute +830rpm,wall shadow ( which has fluid as adjacent zone) as moving wall with a relative zero velocity and axis as rotation as +X. I guess I neednt care about the solid turbine zone at all in rotation.

3)Also, the flow suddenly accelerates to high velocities new outlet, I just need the pressure distribution and velocities near the turbine wall.So doesnt really matter.But if I am to avoid it, how ?

Kindly let me know if I am correct, attached are few pictures.

Thanks a ton in advance

http://s24.postimg.org/eabeh4wwl/image.jpg

http://s23.postimg.org/q7yq6ffkb/image.jpg

http://s24.postimg.org/lwod60tqt/image.jpg

http://s12.postimg.org/ask9knxb1/image.jpg

Gowrav March 25, 2013 06:08

Reply to Sai
 
Hi,
i will try to answer few.. Mayn't correct too.
asked 8000 rpm high or not.. Numerical Values doesn't make diff in simltn.. It may be high when considern yur design.
Since yu ve mentioned FSI- i hope yur talking about 1 way FSI, you are taking pressure and temperature on blades for the evaluation of stresses along with centrifugal.
If thats the case i feel solid body is not required in fluent.. (Just reduce no of elements). Also coupled wall BC is also not required. Yu can directly take temp/pressure on wall(blade) - to import into structural one.
Since its transient hope yur using sliding mesh, if steady state MRF,MPM will do..
Along with cell zones.. Motion to the mesh/reference need to be mentioned.
There s compressor example given in tutorial much relevant with yur case .. Have a look
Regards
Gowrav

Far March 25, 2013 08:29

Use 0 static pressure at oulet and see what happens? what is the operating pressure? I know there is option of average static pressure in newer version, use that option.

stumpy March 25, 2013 14:28

Need to know more about the FSI before suggestion a solution approach. 1-way? 2-way using System Coupling? Steady or transient? Thermal coupling or force/displacement coupling?
Are you planning on a sliding mesh approach in Fluent (do you care about transient interactions between the blade and stators) or is a mixing plane or frozen rotor approach suitable.

battersai March 25, 2013 17:37

Quote:

Originally Posted by Gowrav (Post 416163)
Hi,
i will try to answer few.. Mayn't correct too.
asked 8000 rpm high or not.. Numerical Values doesn't make diff in simltn.. It may be high when considern yur design.
Since yu ve mentioned FSI- i hope yur talking about 1 way FSI, you are taking pressure and temperature on blades for the evaluation of stresses along with centrifugal.
If thats the case i feel solid body is not required in fluent.. (Just reduce no of elements). Also coupled wall BC is also not required. Yu can directly take temp/pressure on wall(blade) - to import into structural one.
Since its transient hope yur using sliding mesh, if steady state MRF,MPM will do..
Along with cell zones.. Motion to the mesh/reference need to be mentioned.
There s compressor example given in tutorial much relevant with yur case .. Have a look
Regards
Gowrav

Thank you for your reply Gowrav.
8000rpm is the design speed of the JT8D jet engine, I took the geometry of the blade from JT8D, so took their operating conditions too.
The solid body is required since ANSYS does not allow surface temperature import, only volume temperature import is allowed, so am forced to simulate conjugate heat transfer. Yes, it is 1 way FSI
Its a steady state simulation, not taking transience into account.
I am just concerned about the rotation direction of the fluid. If +x is the axis, is -837 rpm the speed of moving fluid cell zone?

battersai March 25, 2013 17:38

Quote:

Originally Posted by Far (Post 416206)
Use 0 static pressure at oulet and see what happens? what is the operating pressure? I know there is option of average static pressure in newer version, use that option.

Thanks far, for your reply.
Am using 0 operating pressure ( as in the tutorial) so I assume I should try 101325pa at the outlet?

battersai March 25, 2013 17:41

Quote:

Originally Posted by stumpy (Post 416309)
Need to know more about the FSI before suggestion a solution approach. 1-way? 2-way using System Coupling? Steady or transient? Thermal coupling or force/displacement coupling?
Are you planning on a sliding mesh approach in Fluent (do you care about transient interactions between the blade and stators) or is a mixing plane or frozen rotor approach suitable.

Its a steady state, one way FSI, just need the temperature and pressure data for structural simulations. I am not worried about the stator-rotor interactions. I have aligned the inlet to give the flow a tangential velocity to avoid the presence of a stator. hope it is ok.

I am using force and thermal coupling. I am not using a sliding mesh, just MRF. If mixing planes are the interfaces which are created between stator and rotor, yes, I have created them as said in the tutorial.

Thanks for your reply,stumpy.

Far March 26, 2013 02:10

Use zero pressure at outlet and start with lower rpm. The procedure would be :

1. use 0 static pressure at outlet and 2000 RPM

2. Iterate few hundred iterations and increase RPM = 4000

3. Repeat step 4 and increase RPM to 6000 and finally 8000

4. Calculate outlet total pressure if it is lower then increase outlet static pressure.

PS: Use average static pressure if outlet boundary is placed less than 1.5 C downstream

battersai March 26, 2013 17:52

Quote:

Originally Posted by Far (Post 416386)
Use zero pressure at outlet and start with lower rpm. The procedure would be :

1. use 0 static pressure at outlet and 2000 RPM

2. Iterate few hundred iterations and increase RPM = 4000

3. Repeat step 4 and increase RPM to 6000 and finally 8000

4. Calculate outlet total pressure if it is lower then increase outlet static pressure.

PS: Use average static pressure if outlet boundary is placed less than 1.5 C downstream

Thanks far.
I completed that part already. Could you please tell me which is the sign of rotation I should give( positive or negative). The axis is +X and blade is rotating in the anti-clockwise direction in front view.
Also , in fluent tutorial for fan, the top wall has been specified as non-moving wall, do you know why ?


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