Initial acceleration effects on the flow field development around rapidly pitching airfoils

Numerical simulation of dynamic-stall suppression by tangential blowing

“…Researchers (Koochesfahani and SmiUanovski, 1993;Gendrich, et al, 1993) have experimentally and computationally shown that for high enough pitch rates in conjunction with acceleration periods that end well ahead of the leading-edge separation point (i.e, for separation t+ > 1.25 times period of acceleration), the dynamic-stall phenomenon is essentially insensitive to the acceleration profile. The lack of sensitivity is attributed 4-3 to the domination of motion-history effects over initial-acceleration effects (Koochesfahani and Smiljanovski, 1993).…”

“…The lack of sensitivity is attributed 4-3 to the domination of motion-history effects over initial-acceleration effects (Koochesfahani and Smiljanovski, 1993). Gendrich et al (1993) published results for a NACA 0012 airfoil being pitched at W+ = 0.2 about the quarter chord in a Re, = 1.6 x 10i, M.. = 0.1 flow (acceleration period ending at a = 1.2% 4.5% 18.00 -leading-edge separation occurring in the range 16* < a < 200). Based on integrated-loads, surface-pressure, and surface-pressure-gradient data, they conclude that the initial-acceleration history has little influence on the subsequent dynamic-stall flow field.…”

The effects of leading-edge tubercles on dynamic stall

“…Extensive work was also done to show that the flow was highly repeatable and thus a candidate for phase averaging to airfoil pitch angle. Gendrich (1999) detailed specific formation angles and a highly resolved vortex structure, but did not measure the flow downstream of the DSV formation region.…”

“…Gendrich (1999) found that at low incidence angles the boundary layer remained attached to the airfoil surface but with increasing boundary layer thickness as a function of the AoA. A thin region of vorticity, with sign opposite to that of the boundary layer, formed underneath the primary vorticity along the airfoil surface in the recirculating region.…”

“…A thin region of vorticity, with sign opposite to that of the boundary layer, formed underneath the primary vorticity along the airfoil surface in the recirculating region. Gendrich (1999) defined this flow condition as detached but not separated, where detached flow was defined as when ‘a thin region of opposite-sign vorticity is present under the primary shear layer’. Separated flow was defined as when the flow no longer followed the contours of the airfoil shape.…”