Aerodynamic force and flow structures of two airfoils in flapping motions
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Aerodynamic force and flow structures of two airfoils in a tandem configuration in flapping motions are studied, by solving the Navier-Stokes equations in moving overset grids. Three typical phase differences between the fore- and aftairfoil flapping cycles are considered. It is shown that: (1) in the case of no interaction (single airfoil), the time average of the vertical force coefficient over the downstroke is 2.74, which is about 3 times as large as the maximum steady-state lift coefficient of a dragonfly wing; the time average of the horizontal force coefficient is 1.97, which is also large. The reasons for the large force coefficients are the acceleration at the beginning of a stroke, the delayed stall and the “pitching-up” motion near the end of the stroke. (2) In the cases of two-airfoils, the time-variations of the force and moment coefficients on each airfoil are broadly similar to that of the single airfoil in that the vertical force is mainly produced in downstroke and the horizontal force in upstroke, but very large differences exist due to the interaction. (3) For in-phase stroking, the major differences caused by the interaction are that the vertical force on FA in downstroke is increased and the horizontal force on FA in upstroke decreased. As a result, the magnitude of the resultant force is almost unchanged but it inclines less forward. (4) For counter stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased. As a result, the magnitude of the resultant force is decreased by about 20 percent but its direction is almost unchanged. (5) For 90°-phase-difference stroking, the major differences are that the vertical force on AA in downstroke and the horizontal force on FA in upstroke are decreased greatly and the horizontal force on AA in upstroke increased. As a result, the magnitude of the resultant force is decreased by about 28% and it inclines more forward. (6) Among the three cases of phase angles, inphase flapping produces the largest vertical force (also the largest resultant force); the 90°-phase-difference flapping results in the largest horizontal force, but the smallest resultant force.
Key Wordsdragonfly flight two airfoils flapping motion Navier-Stokes simulation
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- 1.Alexander DE. Unusual phase relationships between the forewings and hindwings in flying dragonflies.J Exp Biol, 1984, 109: 379–383Google Scholar
- 2.Norberg RA. Hovering flight of the dragonfly Aeschna juncea L., kinematics and aerodynamics. In Swimming and Flying in Nature Wu TY, Brokaw CJ, Brennen C, eds. New York: Plenum Press, 1975. 763–781Google Scholar
- 3.Wakenling JM, Ellington CP. Dragonfly flight, II. velocities, accelerations and kinematics of flapping flight.J Exp Biol, 1997, 200: 557–582Google Scholar
- 4.Weis-Fogh T. Quick estimates of flight fitness in hovering animals, including novel mechanisms for lift production.J Exp Biol, 1973, 59: 169–230Google Scholar
- 5.Somps C, Luttges M. Dragonfly flight: novel uses of unsteady separation flows.Science, 1985, 28: 1326–1328Google Scholar
- 6.Saharon D, Luttges M. Dragonfly unsteady aerodynamics: the role of the wing phase relations in controlling the produced flows. AIAA Paper 89-0832, 1989Google Scholar
- 7.Saharon D, Luttges M. Visualization of unsteady separated flow produced by mechanically driven dragonfly wing kinematics model. AIAA Paper 88-0569, 1988Google Scholar
- 10.Meakin R. Moving body overset grid methods for complete aircraft tiltrotor simulations. AIAA Paper 93-3350, 1993Google Scholar
- 11.Hilgenstock A. A fast method for the elliptic generation of three dimensional grids with full boundary control. In: Num Grid Generation in CFM'88. Pineridge Press Ld, 1988. 137–146Google Scholar
- 13.Wekeling JM, Ellington CP. Dragonfly flight, I. Gliding flight and steady-state aerodynamic forces.J Exp Biol, 1997, 200: 543–556Google Scholar