CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > Siemens > STAR-CCM+

Helicopter Rotor Analysis with Periodic Domain

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 25, 2020, 08:04
Default Helicopter Rotor Analysis with Periodic Domain
  #1
New Member
 
David Lehnardt
Join Date: Apr 2018
Posts: 4
Rep Power: 5
D. Lehnardt is on a distinguished road
Hello everyone,

I am using Star CCM+ to model a helicopter rotor in hover flight conditions using a periodic domain of just one blade.

My boundary conditions are illustrated in the first image.

I have assigned rigid body motion to the entire domain since it is axisymmetric.

The problem I am encountering (second image) is that the free stream boundary is generating a non-zero velocity which increases in magnitude with increasing iterations and eventually messes up the flow field around the rotor.

I have tried increasing the domain size, increasing the mesh density at the boundary (problem is particularly bad with coarser surface mesh), I have tried a no-slip wall but nothing so far has worked.

The greatest velocity gradient is located at the corners where the free stream boundary meets the periodic boundary.

When I run this model as a steady state problem using MRF the problem was remedied by increasing the mesh density at the outer wall (free stream), but this is unfortunately not the case for when I run it as an unsteady problem using rigid body motion.

I am still an amateur in the CFD world and I am running out of ideas, and especially time..

Any help is greatly appreciated.

Regards,

D. Lehnardt
Attached Images
File Type: png Boundary conditions.png (17.6 KB, 21 views)
File Type: png Velocity at free stream boundary.png (82.8 KB, 20 views)
File Type: png Velocity scalar scene.png (121.0 KB, 17 views)
File Type: png Mesh.png (125.6 KB, 17 views)
D. Lehnardt is offline   Reply With Quote

Old   July 31, 2020, 02:38
Default
  #2
Senior Member
 
Ping
Join Date: Mar 2009
Posts: 553
Rep Power: 17
ping is on a distinguished road
i worry about the free stream bc use in this situation and suggest instead to use a pressure but you need to be careful due the height of your domain if gravity is enabled and then need to account for this which is well covered in a steve support article
ping is offline   Reply With Quote

Old   April 1, 2021, 01:58
Smile
  #3
New Member
 
Rinia
Join Date: Jan 2018
Posts: 25
Rep Power: 5
Rinia is on a distinguished road
Quote:
Originally Posted by D. Lehnardt View Post
Hello everyone,

I am using Star CCM+ to model a helicopter rotor in hover flight conditions using a periodic domain of just one blade.

My boundary conditions are illustrated in the first image.

I have assigned rigid body motion to the entire domain since it is axisymmetric.

The problem I am encountering (second image) is that the free stream boundary is generating a non-zero velocity which increases in magnitude with increasing iterations and eventually messes up the flow field around the rotor.

I have tried increasing the domain size, increasing the mesh density at the boundary (problem is particularly bad with coarser surface mesh), I have tried a no-slip wall but nothing so far has worked.

The greatest velocity gradient is located at the corners where the free stream boundary meets the periodic boundary.

When I run this model as a steady state problem using MRF the problem was remedied by increasing the mesh density at the outer wall (free stream), but this is unfortunately not the case for when I run it as an unsteady problem using rigid body motion.

I am still an amateur in the CFD world and I am running out of ideas, and especially time..

Any help is greatly appreciated.

Regards,

D. Lehnardt

Dear Lehnardt,

hope you have solved the problem.

I am making a similar simulation with yours about the wind turbine on the star ccm+.

Could you give me some advice about how to use the periodic domain to perform the one blade simulation? Just set the interface to periodic?


Regrads
Rinia is offline   Reply With Quote

Old   April 12, 2021, 09:50
Default
  #4
New Member
 
Join Date: Mar 2011
Posts: 17
Rep Power: 13
SESP is on a distinguished road
Hi David,

I would not build the case in that way.

Your approach seems fine for a steady-state analysis. It could be easier if you add stationary domain, but from your description it sounds like you got the steady case to a stable and converged state with refinement.

For the unsteady analysis with rigid body motion (or overset, which is also worth a try), I would model it as a 360 deg case. I think I never tried it, but to me the combination of rigid body motion with periodic boundary conditions does not seem like a good idea. Also here, think of adding a stationary domain around it. Personally, i would model a bigger fluid volume around the blade and then use overset on the 360 rotor. That will work without any problems, it just takes a bit of time get familiar with the setup and the relevant parameters.

Good luck,
Sebastian
SESP is offline   Reply With Quote

Old   April 12, 2021, 22:46
Default
  #5
New Member
 
Rinia
Join Date: Jan 2018
Posts: 25
Rep Power: 5
Rinia is on a distinguished road
Quote:
Originally Posted by SESP View Post
Hi David,

I would not build the case in that way.

Your approach seems fine for a steady-state analysis. It could be easier if you add stationary domain, but from your description it sounds like you got the steady case to a stable and converged state with refinement.

For the unsteady analysis with rigid body motion (or overset, which is also worth a try), I would model it as a 360 deg case. I think I never tried it, but to me the combination of rigid body motion with periodic boundary conditions does not seem like a good idea. Also here, think of adding a stationary domain around it. Personally, i would model a bigger fluid volume around the blade and then use overset on the 360 rotor. That will work without any problems, it just takes a bit of time get familiar with the setup and the relevant parameters.

Good luck,
Sebastian
Hi, Sebastian, thanks for your reply in CFDonlien.

The UserGuide of STAR CCM+2020 provides a illustration of the use of periodic boundary in turbomachinery. I performed the simulation according to guide and found that the lift has a sudden change when the blade returns to the starting position. This may be associated to the discontinuity when the rotating region returns to the starting position. I haven't solved this problem.

I intend to study the tip vortex flow of a six-blade propeller, so only one blade is simulated to reduce the compuitational time. Do you have any better method to deal with this simulation?
Rinia is offline   Reply With Quote

Old   April 13, 2021, 07:25
Default
  #6
New Member
 
Join Date: Mar 2011
Posts: 17
Rep Power: 13
SESP is on a distinguished road
Hi Rinia,

no, I have never tested a periodic interface with mesh motion where the mesh snaps back to its original position... In that case, the order of the interfaces (or more precisely, their index) is of importance, the interface moving must be declared first. But you probably know that already... Personally, i prefer full 360 degree when working with mesh motion for rotating components. Unfortunately, its more expensive...

Sebastian
SESP is offline   Reply With Quote

Reply

Tags
boundary condition, helicopter rotor, periodic, rigid body motion

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Domain Imbalance HMR CFX 5 October 10, 2016 05:57
Pressure distribution on a wall darazsbence CFX 17 October 6, 2015 10:38
[GAMBIT] periodic boundary condition for a rectangular duct domain Das ANSYS Meshing & Geometry 26 June 5, 2013 07:48
Ansys meshing of two-phase periodic domain kcsmith ANSYS Meshing & Geometry 11 March 9, 2011 21:08
CFX Solver Memory Error mike CFX 1 March 19, 2008 07:22


All times are GMT -4. The time now is 13:29.