Dynamic stall due to a ramp-type pitching motion is investigated on the NACA 0012 airfoil at chord Reynolds number of $Re_{c}=1.0\times 10^{6}$ through the use of wall-resolved large-eddy simulation. Emphasis is placed on the unsteady boundary-layer interactions that develop as the airfoil approaches stall. At this Reynolds number it is shown that turbulent separation moves upstream across much of the airfoil suction surface. When turbulent separation reaches the leading-edge separation bubble, a bursting event is initiated leading to a strong coherent leading-edge vortex structure. This vortex wraps up the turbulent shear layer to form a large dynamic stall vortex. The use of large-eddy simulation elucidates the roll of the laminar separation bubble in defining the onset of the dynamic stall process. Comparisons are made to identical simulations at lower Reynolds numbers of $Re_{c}=0.2\times 10^{6}$ and $0.5\times 10^{6}$. This comparison demonstrates trends in the boundary-layer mechanics that explain the sensitivity of the dynamic stall process to Reynolds number.

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The effects of inlet endwall boundary layer thickness and up-stream unsteady wakes are investigated experimentally in a low-speed linear cascade. The examined airfoil is the front-loaded L2F, a high-lift low-pressure turbine profile with high resistance to separation even in the low Reynolds number regime. Cases are documented with and without incoming wakes for two inlet endwall boundary layers of different thickness at a Reynolds number of Re = 30,000. Periodic incoming wakes are simulated with moving bars upstream of the cascade. The inlet endwall boundary layer is conditioned with a two-part splitter plate, one part downstream and one part upstream of the wake generator. By the documentation of pressure distributions on the blades, velocity profiles in the cascade inlet as well as total pressure loss and phase-locked velocity data in the outlet, this work attempts to show that varying the inlet endwall boundary layer thickness combined with the effect of incoming wakes has significant influence on the performance of blades with relatively low aspect ratio in cascade experiments. Depending on boundary layer thickness, wakes are shown to have either a stronger impact on midspan or on endwall performance. Time-resolved velocity and vorticity plots additionally show the motion of the vortex and loss core at the blade trailing edge during the event of wake passing.

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