Motion: Turbulence Quantities appear to ‘dip’ during Motion Analyses
When multiple inner iterations per time step are used for Motion analyses, the Convergence Monitor sometimes shows a "dip" in the Turbulent Kinetic Energy (TKE) quantity for each time step.
The TKE quantity appears to dip because of the local redefinition of turbulence in the vicinity of the new position of the moving part. This occurs only when the part reaches its new position at the beginning of a new time step.
In a Motion simulation, the part is moved at the beginning of each time step (at the first inner iteration). When this happens, the local TKE distribution around the outer surface of the moving part is recalculated due to the local influence of the moving walls. Additionally, a wall shear multiplier that accounts for the turbulence effects is used to provide a correct shear stress value. This is critical to accurately predicting drag forces.
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