spray droplet distortion parameter
 

Can somebody explain me why the droplet distortion parameter 'y' is limited to positive values in the TAB oscillation equation?
This is done in the lagrangianSpray (2.2.x) [1] and dieselSpray (2.0.x) [2] library.

To my understanding y=0 corresponds to spherical droplet, a positive deformation flattens the droplet perpendicular to the flight directions (y>0) and a negative deformation elongates the droplet (y<0) in flight direction.

I do understand the implications concerning the distorted sphere model due to Liu (1993), i.e. 0<y<1, but this doesn't explain why the distortion parameters y and yDot are set to 0.0 as soon as y is negative.

I would be happy about any comment/explanation on this issue.

-Armin



Here the links to the source code
[1] https://github.com/OpenFOAM/OpenFOAM...yParcel.C#L419
[2] https://github.com/OpenFOAM/OpenFOAM...upModel.C#L121

References:
Liu, A.B.; Mather, D.; Reitz, R.D., "Effects of Drop Drag and Breakup on Fuel Sprays," SAE Paper 930072, SAE Transactions, Vol. 102, Section 3, Journal of Engines, pp. 63-95, 1993

I reported a bug on this issue:
http://www.openfoam.org/mantisbt/view.php?id=1018

If somebody would still have a comment/explanation, please also write it to the bug tracker.