  For the purpose of Uncertainty Quantification (UQ) of Reynolds-Averaged
Navier-Stokes closures, we introduce a framework in which perturbations in the
eigenvalues of the anisotropy tensor are made in order to bound a
Quantity-of-Interest based on limiting states of turbulence. To make the
perturbations representative of local flow features, we introduce two
additional transport equations for linear combinations of these aforementioned
eigenvalues. The location, magnitude and direction of the eigenvalue
perturbations are now governed by the model transport equations. The general
behavior of our discrepancy model is determined by two coefficients, resulting
in a low-dimensional UQ problem. We will furthermore show that the behavior of
the model is intuitive and rooted in the physical interpretation of
misalignment between the mean strain and Reynolds stresses.
