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In this study, the effects of the computational spanwise domain length on the flowfield with massive separation and on the flowfield with dynamic stall are investigated by largeeddy simulation. The objective airfoil is NACA0012 and the chord-based Reynolds number is of 2.56× 10. The objective flowfields are that around a fixed angle of attack of 10 and 25 degrees, and that around a pitching airfoil between AoA of 5 degrees and 25 degrees. The spanwise length effect become significant after the stall, as observed as the attenuation of the large vortices. Observations of the flowfield clarified that the undulation of two large vortices from the leading edge and the trailing edge is one of the mechanisms for the spanwise length effects. The qualitative analysis for this mechanism is performed to address the sufficient spanwise length, and the spanwise length have to be at least 1.0c for the flowfield with large vortex structures so as to resolve its spanwise distribution.

A dielectric barrier discharge plasma actuator (PA) was applied to reduce trailing edge noise and vortices emitted from a NACA0012 airfoil model. The PA in length of 1 m was installed at 60 % of the chord length on the pressure side of the model. The velocity field around the trailing edge of the model was measured via 2D-PIV at the uniform flow velocity of 15, 30, and 40 m/s. The Reynolds numbers based on the code length of the model for the three cases were 2.0x10 5 , 4.0x10 5 , and 5.4x10 5 , respectively. When the PA was off, the measured velocity and the result of the proper orthogonal decomposition showed that the strong vortices were periodically emitted from the trailing edge of the model at the uniform flow velocity of 15 m/s. These trailing vortices were dramatically reduced by the PA. As the uniform flow velocity increased, the trailing edge vortices decreased. As the result, the effect of the PA was decreased as the uniform flow velocity increased.