Rotating Fluid Zones

Discovery generally solves the equations of fluid flow and heat transfer in a stationary (or inertial) reference frame. However, there are many problems where the equations might need to be solved in a moving (or non-inertial) reference frame. For example, fans and mixing tanks with their rotating blades, impellers, and similar objects (comprising a cylindrical body and blades) cause the fluid around those parts to flow with some rotation. In most cases, the moving parts render the problem unsteady when viewed from the stationary frame. However, the flow around the moving part can (with certain restrictions) be modeled as a steady-state problem with respect to the moving frame.

For simulations involving moving parts, Discovery uses the moving reference frame model with a steady speed and modifies the equations of motion to incorporate the additional acceleration terms that occur due to the transformation from the stationary to the moving reference frame. By solving these equations in a steady-state manner, the flow around the moving parts can be modeled.

Guidelines and Best Practices

  • The location of the rotating fluid zone must be a revolved body with cylindrical or conical outer faces.
  • A rotating fluid zone and porous zone cannot be specified on the same body.
  • A rotating fluid zone cannot share a fluid-fluid interface with another rotating fluid zone.
  • Only Wall condition options Rotating with the fluid zone or Stationary are allowed. The default wall behavior for a rotating fluid zone is Rotating with the fluid zone.
    • User specified moving walls are not permitted on a rotating fluid zone.
  • Rotating fluid zones are not supported in compressible flow simulations.
  • Rotating fluid zones are not supported in time-dependent fluid flow simulations.
  • For some simulations involving solid-body rotation, there could be some discrepancies between solutions in Explore and Refine.
  • Results Variables for rotating fluids zones are shown in the absolute reference frame.
  • For closed domain cases, you might run into convergence discrepancies.
  • In Refine, it might be necessary to reduce the target residual and increase the maximum number of iterations. Monitor plots should be used to help assess convergence.
  • In a fluid-solid heat transfer simulation, the effect of rotation of a solid thermal region on the fluid will be included only where a face of that region is in contact with a rotating fluid zone.
  • Fluid flow conditions cannot be created on faces representing the rotating device or outer cylindrical/conical faces of a rotating fluid zone.
  • Non-coaxial bodies cannot be created in a single rotating fluid zone.
  • If a face on the solid thermal region is in contact with faces on both a rotating and a stationary fluid zone, you must imprint the face to obtain heat transfer between the solid thermal region and both fluid zones.
  • Rotating geometry consisting of thin blades may be difficult to resolve in Explore, which in turn leads to poor results. Use a higher fidelity setting for better results.
  • In Explore, all flow conditions located on a rotating fluid zone are defined relative to the absolute frame.
    • For example, if a rotating fluid zone includes a swirl inlet, the rotational velocity is to be entered in absolute frame and not with respect to the rotating fluid zone.
  • In Refine, all flow conditions located on a rotating fluid zone are defined relative to the absolute frame except for a mass flow outlet. Flow through a mass flow outlet takes the direction of the upstream flow.