CFD Online Discussion Forums - fv3 term in Spalart Allmaras model

Hello,
could anyone please explain to me what the fv3 term in the Spalart-Allmaras turbulence model does? I can't find any paper that suggests such a term, apart from this page http://turbmodels.larc.nasa.gov/spalart.html. There they say the term shouldn't be used, as it leads to "unusual transition behavior at low Reynolds numbers". The OpenFOAM realisation of this additional term is slightly different from the version proposed there:

Code:

    

    volScalarField chiByCv2 = (1/Cv2_)*chi;



    return

        (scalar(1) + chi*fv1)

       *(1/Cv2_)

       *(3*(scalar(1) + chiByCv2) + sqr(chiByCv2))

       /pow3(scalar(1) + chiByCv2);

Does anyone know, what it's for or could anyone point me to a paper that justifies it's existence?

cheers,
bjoern