Learning Forum

[Nathaniel]

Hi Yall,

I am studying dynamic stability derivates of aerospace vehicles. I am trying to set up an analysis that has the following steps:

1. Steady initial conditions with the local frame not moving relative to the global frame (this works fine)
2. I then need to run a transient study where I pitch, roll, and translate my vehicle.

I have successfully achieved my results using dynamic meshing or using a sliding mesh approach for the rotations. 

However, I am trying to increase my computational efficiency as I need to run many such cases. I am trying to run my case using a single moving reference frame for the entire domain, as sketched below in 2d. Doing so, however, produces very weird results. I have sizeable static pressure variations across my domain in the far field. 

I am currently using the pressure far field for my entire boundary condition, with a constant Mach and constant direction. Additionally, I activated the frame motion for my entire domain and set a constant rotation and a constant translation.

 Am I approaching this correctly? Should I instead define things as moving meshes? If possible, I'd like to avoid the need to use dynamic or sliding meshes.

Additionally, I've attached a picture of a constant rotation-only vector and pressure field. In this case, the frame rotates counterclockwise. Thank you for your time!

[Federico]

Hello Nathaniel, 

the moving reference frame (MRF) approach is not meant for unsteady analyses 10. Modeling Flows with Moving Reference Frames

For transient studies, I would recommend you stick to Dynamic Mesh or Sliding mesh models.