My feeling is that the time-scale constant CL ≈ 0.15 is an approximation of CL = Cmu^(3/4), where Cmu = 0.09 for the standard k-epsilon model [1]. In OpenFOAM the DRW model uses CL = 0.16431 instead.

For the RSM model I'm not sure why they use CL ≈ 0.30, but I believe that the rationale behind it may be similar to the one of the standard k-epsilon model. They might have used some constant of the RSM model instead.



[1] Gosman, A. D., and E. Loannides. "Aspects of computer simulation of liquid-fueled combustors." Journal of energy 7.6 (1983): 482-490.