BUG: curvatureSeparation: incorrect modelling constant

The curvatureSeparation model of the finite-area framework is based on Owen & Ryley (1983), Eq. 11:

F_w = \frac{4}{3} \, \rho \, |\mathbf{u}|^2 \, \frac{R_1 - R_2}{R_1} 
- \frac{\rho |\mathbf{g}| cos(\theta +\beta) \left(R_1^2 - R_2^2 \right)}{2 R_1} 
+ \frac{\sigma}{R_2}

where F_w is the radial stress at the wall, and the rest of the variables are well-defined in the original-research paper.

The implementation of the Foam::curvatureSeparation::correct function (as of December 2024, SHA:e1d45ec26e) is as follows:

F_w = \frac{72}{60} \, \rho \, |\mathbf{u}|^2 \, \frac{R_1 - R_2}{R_1} 
- \frac{\rho |\mathbf{g}| cos(\theta +\beta) \left(R_1^2 - R_2^2 \right)}{2 R_1} 
+ \frac{\sigma}{R_2}

The original paper and implementation differ in terms of the leading coefficient of the inertial-force term, that is \frac{4}{3} vs \frac{72}{60}.