THESIS
2019
vi, 41 pages : color illustrations ; 30 cm
Abstract
As micro aerial vehicles (MAVs) find more applications in industry, their unsteady aerodynamic
behavior becomes increasingly important. In the literature, stationary airfoils in ground effect
have been studied over a wide range of Reynolds numbers (Re), but plunging airfoils in ground
effect have been studied mostly at high Re, which may not be directly relevant to small MAVs.
In this study, we perform two-dimensional numerical simulations of the flow around a plunging
NACA 0012 airfoil in ground effect at a low Reynolds number (Re = 1000) and a moderate angle
of attack (α = 10°) in order to better understand the unsteady aerodynamics of MAVs during
take-off and landing. We use (i) a non-dimensional ground clearance of 0.2 ≤ H ≡ h/c ≤ ꝏ,
where c is the chord length; (ii) a reduc...[
Read more ]
As micro aerial vehicles (MAVs) find more applications in industry, their unsteady aerodynamic
behavior becomes increasingly important. In the literature, stationary airfoils in ground effect
have been studied over a wide range of Reynolds numbers (Re), but plunging airfoils in ground
effect have been studied mostly at high Re, which may not be directly relevant to small MAVs.
In this study, we perform two-dimensional numerical simulations of the flow around a plunging
NACA 0012 airfoil in ground effect at a low Reynolds number (Re = 1000) and a moderate angle
of attack (α = 10°) in order to better understand the unsteady aerodynamics of MAVs during
take-off and landing. We use (i) a non-dimensional ground clearance of 0.2 ≤ H ≡ h/c ≤ ꝏ,
where c is the chord length; (ii) a reduced plunging frequency of 0 ≤ K ≡ 2πƒ
pc/U
ꝏ ≤ 7, where U
ꝏ is the free-stream velocity; and (iii) a non-dimensional plunging amplitude of A ≡ a/c = 0.001. Our results show the coexistence of two distinct modes of vortex shedding: (i) a forced
mode due to the plunging motion, which occurs at frequency K, and (ii) a natural mode due to
vortex shedding, which arises from global hydrodynamic instability. We find that within a certain
range of K, lock-in can occur between the forced and natural modes, producing synchronized
motion in the airfoil wake. We examine this lock-in behavior and the routes to lock-in using
nonlinear time-series analysis. Knowledge of the critical plunging conditions required for lock-in
is important for understanding and optimizing the design of MAVs.
Keywords: low Reynolds number, plunging airfoil, ground effect
Post a Comment