A 50%-chord trailing edge flap was fitted to a NACA 0006 airfoil spanning the test section of a water tunnel, equipped with a suite of electric linear motors to produce a range of flap deflection frequencies and amplitudes. The fore element of the wing was kept at constant incidence, either at 0 or 20 deg, corresponding to “attached” or “separated” flow cases, respectively. The aim is to ascertain whether lift-coefficient response to flap actuation in separated flow evinces lag from the flap motion, and second, to quantify lift and pitching moment transients beyond quasi-steady conditions, as possible routes toward enabling aggressive maneuvers or mitigation of gust response. Taking advantage of the favorable temporal scaling in water, the flap was deflected at rates of as high as 0.25 convective times. Forces and moments were measured separately at the main airfoil element and at the flap, by respective load cells. The time history of the lift coefficient shows a rise or “spike” proportional to flap pitch rate and no lag in lift response after initiation of actuation, whether the flow is attached or separated and whether the flap begins from zero deflection position or a highly deflected position. Positive or negative lift increment is attainable in an attached or fully separated flow, depending on the direction of flap deflection. Transients in lift are modeled reasonably well by direct superposition of classical analytical models for pitch-rate effects, added mass, and unsteady airfoil theory; pitch rate in particular dominates for the highest-rate flap deflections. The analytical model is, however, unable to account for viscous separation before or after the flap deflection occurs.
Revisiting Conventional Flaps at High Deflection Rate
AIAA Journal ; 55 , 8 ; 2676-2685
2017-05-15
10 pages
Article (Journal)
Electronic Resource
English
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