Disc brake simulation problem 14 vs 15

Roland R · November 16, 2015, 08:06

Dear All,

Last year, I complated a simulation including a solid discbrake, solid pad and the fluid domain (in CFX 14). The disc was defined as rotating solid domain. The pad was defined as a heat source. The simulation seemed to be very realistic; it was similar to this:

http://usercontent2.hubimg.com/4026495_f260.jpg

Now, I tried to complate this simulation again but it doesn't operate well. The settings are same to the previous model but the result show that the disc (solid) are not in rotating. The temperature of disc is very high near by pad but the "smear" of temperature doesn't occur along disc. It seems to me that the disc is a stationary domain, it is not in rotating. I try it in CFX 15, CFX 14 but the results are same...

What can be the reason?
Thanks;
Roland

ghorrocks · November 16, 2015, 16:07

Rotating solids is in V15, but not V14. So I would expect the V14 result to not include rotation. If you got the other way around then that is very strange.

Roland R · November 16, 2015, 18:34

Quote:

Originally Posted by ghorrocks

Rotating solids is in V15, but not V14. So I would expect the V14 result to not include rotation. If you got the other way around then that is very strange.

Thank you for your answer. My main problem that the result (temperature distribution at disc) is not ok in v15 at the moment.

ghorrocks · November 16, 2015, 18:47

Have you had a look at the documentation? Here's a quote from it:

A rotating solid can be modeled in two different ways:

Moving reference frame and solid motion off. If a stationary domain surrounds the solid, a frame change model is required to account for the reference frame changes. Best accuracy will be achieved with a Transient Rotor Stator interface, but this requires a transient simulation.

Stationary reference frame and solid motion on. This activates the term involving as mentioned above. If a stationary domain surrounds the solid, no frame change model is needed, so it is possible to use a steady state simulation.

Roland R · November 20, 2015, 05:06

Quote:

Originally Posted by ghorrocks

Have you had a look at the documentation? Here's a quote from it:

A rotating solid can be modeled in two different ways:

Moving reference frame and solid motion off. If a stationary domain surrounds the solid, a frame change model is required to account for the reference frame changes. Best accuracy will be achieved with a Transient Rotor Stator interface, but this requires a transient simulation.

Stationary reference frame and solid motion on. This activates the term involving as mentioned above. If a stationary domain surrounds the solid, no frame change model is needed, so it is possible to use a steady state simulation.

Hello,

thank you for your help. Based on your instructions, the simulation operates well.
Finally one question: In case of using of "solid motion", it is possible to apply the "boundary advection". What does it meann exactly? Based on CFD help, it was not clear for me.

Thanks;
Roland

ghorrocks · November 20, 2015, 05:19

It is not entirely clear, is it? To be honest, I am not sure.

I would just try the different options and see what they do.

Roland R · December 10, 2015, 12:15

Hello,

I complated some test cases to invastigate the solid motion option. Based on my results, I have found a new problem.

If I investigate a simple fully filled disc then the temperature distribution is OK at the disc.

BUT:
If I investigate a more complicated brake disc including holes, ribs, blades etc, then the calculations go into divergence in the second iteration. The temperature values are around 0 [K] in all nodes. I checked the BC's more times. I tried to use some tricks;
- gradual RPM increasing for disc
- initialization from a converged non rotational disc
- etc etc
But nothing result. It seems to me, that the solid motion option is very similar to the wall velocity option. If the wall velocity is parallel with the wall then the result is OK. But if the model includes velocity component which is perpendicular to the motion wall then it will result non realistic temperature values.

What do you think about this problem? Is it possible, that the solid motion option can be used for filled disc geometry only?

Thanks
Roland

ghorrocks · December 10, 2015, 15:58

Sounds possible.

Have you tried the other approach discussed in the documentation for modelling solid rotating bodies?

Roland R · December 10, 2015, 18:15

As far as I know, these options are available in CFX to investigate brakedisc:
- rotation domain in solid in steady =>> it doesn't operate
- solid motion in steady =>> it doesn't operate
- rotation domain in transient rotor stator =>> it operates well but it can not be applied in case of high mesh element number.

It seems to me; there is not possible to solve this problem in steady state case...

ghorrocks · December 10, 2015, 18:36

I know ANSYS did work on this to make rotating solid domain models easier in V15. I am not sure whether that applied to transient runs only or steady state models as well.

You might need to ask ANSYS support for advice here.

Roland R · December 11, 2015, 12:03

I had a short consultation with our support. Based on this, at the moment, there is one method which calculate the disc rotation and the heat advection exactly: a transient simulation

The solid motion option can be used only for fully rotational symmetry part, etc. a filled disc, cylinder...

November 16, 2015, 08:06	Disc brake simulation problem 14 vs 15	#1
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	Dear All, Last year, I complated a simulation including a solid discbrake, solid pad and the fluid domain (in CFX 14). The disc was defined as rotating solid domain. The pad was defined as a heat source. The simulation seemed to be very realistic; it was similar to this: http://usercontent2.hubimg.com/4026495_f260.jpg Now, I tried to complate this simulation again but it doesn't operate well. The settings are same to the previous model but the result show that the disc (solid) are not in rotating. The temperature of disc is very high near by pad but the "smear" of temperature doesn't occur along disc. It seems to me that the disc is a stationary domain, it is not in rotating. I try it in CFX 15, CFX 14 but the results are same... What can be the reason? Thanks; Roland

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November 16, 2015, 16:07		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Rotating solids is in V15, but not V14. So I would expect the V14 result to not include rotation. If you got the other way around then that is very strange.

November 16, 2015, 18:47		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Have you had a look at the documentation? Here's a quote from it: A rotating solid can be modeled in two different ways: Moving reference frame and solid motion off. If a stationary domain surrounds the solid, a frame change model is required to account for the reference frame changes. Best accuracy will be achieved with a Transient Rotor Stator interface, but this requires a transient simulation. Stationary reference frame and solid motion on. This activates the term involving as mentioned above. If a stationary domain surrounds the solid, no frame change model is needed, so it is possible to use a steady state simulation.

November 20, 2015, 05:19		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	It is not entirely clear, is it? To be honest, I am not sure. I would just try the different options and see what they do.

December 10, 2015, 12:15		#7
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	Hello, I complated some test cases to invastigate the solid motion option. Based on my results, I have found a new problem. If I investigate a simple fully filled disc then the temperature distribution is OK at the disc. BUT: If I investigate a more complicated brake disc including holes, ribs, blades etc, then the calculations go into divergence in the second iteration. The temperature values are around 0 [K] in all nodes. I checked the BC's more times. I tried to use some tricks; - gradual RPM increasing for disc - initialization from a converged non rotational disc - etc etc But nothing result. It seems to me, that the solid motion option is very similar to the wall velocity option. If the wall velocity is parallel with the wall then the result is OK. But if the model includes velocity component which is perpendicular to the motion wall then it will result non realistic temperature values. What do you think about this problem? Is it possible, that the solid motion option can be used for filled disc geometry only? Thanks Roland

December 10, 2015, 15:58		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Sounds possible. Have you tried the other approach discussed in the documentation for modelling solid rotating bodies?

December 10, 2015, 18:15		#9
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	As far as I know, these options are available in CFX to investigate brakedisc: - rotation domain in solid in steady =>> it doesn't operate - solid motion in steady =>> it doesn't operate - rotation domain in transient rotor stator =>> it operates well but it can not be applied in case of high mesh element number. It seems to me; there is not possible to solve this problem in steady state case...

December 10, 2015, 18:36		#10
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	I know ANSYS did work on this to make rotating solid domain models easier in V15. I am not sure whether that applied to transient runs only or steady state models as well. You might need to ask ANSYS support for advice here.

December 11, 2015, 12:03		#11
Roland R Senior Member Roland Rakos Join Date: Mar 2009 Posts: 131 Rep Power: 17	I had a short consultation with our support. Based on this, at the moment, there is one method which calculate the disc rotation and the heat advection exactly: a transient simulation The solid motion option can be used only for fully rotational symmetry part, etc. a filled disc, cylinder...