12.13.6 Swirl Modification

Once you chose the RNG model, the swirl modification takes effect, by default, for all three-dimensional flows and axisymmetric flows with swirl. The default swirl constant ( $\alpha_s$ in this equation in the separate Theory Guide) is set to 0.07, which works well for weakly to moderately swirling flows. However, for strongly swirling flows, you may need to use a larger swirl constant.

To change the value of the swirl constant, you must first enable the Swirl Dominated Flow option under RNG Options in the Viscous Model dialog box.

This option will not appear unless you have activated the RNG $k$- $\epsilon$ model.