  It is well known that Boussinesq turbulent-viscosity hypothesis can introduce
uncertainty in predictions for complex flow features such as separation,
reattachment, and laminar-turbulent transition. This study adopts a recent
physics-based uncertainty quantification (UQ) approach to address such model
form uncertainty in Reynolds-averaged Naiver- Stokes (RANS) simulations. Thus
far, almost all UQ studies have focused on quantifying the model form
uncertainty in turbulent flow scenarios. The focus of the study is to advance
our understanding of the performance of the UQ approach on two different
transitional flow scenarios: a flat plate and a SD7003 airfoil, to close this
gap. For the T3A (flat-plate flow) flow, most of the model form uncertainty is
concentrated in the laminar-turbulent transition region. For the SD7003 airfoil
flow, the eigenvalue perturbations reveal a decrease as well as an increase in
the length of the separation bubble. As a consequence, the uncertainty bounds
successfully encompass the reattachment point. Likewise, the region of reverse
flow that appear in the separation bubble is either suppressed or bolstered by
the eigenvalue perturbations. In this context, the UQ methodology is applied to
transition and show great results. This is the first successful RANS UQ study
for transitional flows.
