RÉSUMÉ

Numerical simulations of a low-pressure turbine (LPT) cascade have been performed with both RANS solver and DNS solver. Transition models with RANS solver cannot reproduce the transition process well in separation bubbles because the transport equation for intermittency factor γ does not contain enough physical mechanisms. Therefore, DNS data is provided to examine the nature of instability mechanisms leading to separated-flow transition under low turbulent intensity. In DNS results, both K-H instability in the separated shear layer and viscous T-S instability in the near wall region are observed. Hyperbolic instability is found in transitionalprocess. The streamwise vortices form in the interaction region after secondary instability between a large-scale spanwisevortices and the inner boundary layer. Theinjection and sweeping process is observed. The power spectra of pressure indicating several frequency peaks associated with different flow structures is investigated.