# Volume Output

# Output format

  • tecplot: exports *.szplt files
  • paraview: exports *.vtu files

# Primitive Variables

These primitive flow variables (rho, u, v, w, p) will be output from Flow360 solver. Note that values are non-dimensional.

# Vorticity

Outputs non-dimensional vorticity. Non-dimensionalised by

# Cp

Coefficient of pressure defined by .

# Mach

Outputs Mach number.

# Q criterion

This is one of several mathematical criteria that are used to identify vortices and vortical flow structures associated with them. The quantity of Q is the second invariant of velocity gradient tensor.

The Q criterion was originally proposed by Hunt et al. (1988). It identifies the vortices as flow regions with positive Q values. An additional condition is that the pressure in the eddy region should be lower than the ambient pressure. Chakraborty et al. (2005) explained that in an incompressible flow, Q is a local measure of the excess rotation rate relative to the strain rate. In practical terms, a vortex is detected in the case of Q>0.

As a rule of thumb, to visualize vortical structures in a flow field for an aeronautical application, plot iso-surfaces of a finite small positive threshold on Q values. For example, a threshold roughly equals to , where is freestream Mach number, and is non-dimensional reference length.

Reference: https://doi.org/10.1016/j.softx.2020.100604 (opens new window) for more details.

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