Advanced turbulence modelling of separated flow in a diffuser

The paper describes an investigation into the predictive performance of lin ear and non-linear eddy-viscosity models and differential stress-transport closures for separated flow in a nominally two-dimensional, asymmetric diff user. The test case forms part of a broader collaborative exercise between academic and industrial partners. It is demonstrated that advanced turbulen ce models using strain-dependent coefficients and anisotropy-resolving clos ure offer tangible advantages in predictive capability, although the qualit y of their performance can vary significantly, depending on the details of closure approximations adopted. Certain features of the flow defy resolutio n by any of the closures investigated. In particular, no model resolves cor rectly the flow near the diffuser's inclined wall immediately downstream of the inlet corner, which may reflect the presence of a "flapping" motion as sociated with a highly-localised process of unsteady separation and reattac hment.