Summary: The stability and convergence of the interior penalty (IP) discontinuous Galerkin method are closely related to the penalty coefficient \(\sigma _{f}\). Using sharp trace inequalities adapted to the functional space, K. Shahbazi [J. Comput. Phys. 205, No. 2, 401–407 (2005; Zbl 1072.65149)] has derived optimal values of \(\sigma _{f}\) for constant diffusivity problems on triangular meshes. We propose a generalisation of his analysis to account for mesh anisotropy and different element types on the one hand, and strong variations of the diffusivity on the other, which characterise the Spalart-Allmaras RANS turbulence model. The adequacy of this new definition is illustrated by applications to benchmark 2D computations. Finally, a comparison with two state of the art finite volume solvers is presented for a 3D high-lift cascade flow.