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chris12345 November 7, 2012 06:13

Overset Grid on a helicopter main-rotor
Hello fellow CFD,

This past few weeks ive been working on a project on CFD analysis on the flow field of the downwash generated by the main-rotor.

My setup at the moment is:

Surface/Volume Mesh:
  • Advance layer meshing:
  • Prism layers at the rotors, 15 layers, thickness: 5mm, first layer: 0.1 mm, stretching mode: Wall thickness
Physics model:
  • Ideal Gas
  • SSK - Menter K-Omega Turbulence
  • turbulence supression
  • Segregated Flow
  • Implicit Unsteady
Volumetric Control:
I have a volumetric control where the rotor blades are moving that matches the size of the cells in the bakground mesh.

Run Setup:

I have divided the regions into two parts: The background region which contains all stationary parts such as, the freestream boundary, Fuselage, landing gear etc. The overset part contains the hub, and the two rotor blades, these blade have a constant collective pitch to reduce the complexity of the model. The tip velocity is around 191 m/s and I have given a timestep that matches 0.5 degree change for every time step and the number of inner iterations is 25.

The results are insufficient since I have a Lift force error of about 20 %.

I checked my resudials and noticed that my continuity and energy plots doesnt converge anymore (for each time step). It doesnt diverge but doesnt converge either. The other problem is my diffusion rate plot, it goes through the roof at each inner iterations. I tried this setup again but without the inclusion of the fuselage and I got less spikes on the diffusion rate.

To my question now, how can I make my continuity and energy plots converge better? I tried to reduce my cell size, I get better convergence at the beginning but after a while these plots keep coming back to a constant state.

Any thips=

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