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a. REPORT 14. ABSTRACT 16. SECURITY CLASSIFICATION OF:Unsteady flow separation during dynamic stall often leads to unacceptably large vibra-tory loads and acoustic noise, and limit forward flight speeds and maneuverability. To gain a quantitative understanding of the unsteady separation process, large-eddy simula-tion (LES) of turbulent flow over a pitching airfoil at realistic Reynolds and Mach numbers is performed. Numerical stability at high Reynolds number simulation is maintained us-ing an unstructured-grid LES technology, which obeys higher-order conservation principles and employs a globalcoefficient subgrid-scale turbulence model. A hybrid implicit-explicit time-integration scheme is employed to