An experimental study of the effects of pitch-pivot-point location on the propulsion performance of a pitching airfoil

Abstract

a b s t r a c tAn experimental investigation was conducted to characterize the evolution of the unsteady vortex structures in the wake of a pitching airfoil with the pitch-pivot-point moving from 0.16C to 0.52C (C is the chord length of the airfoil). The experimental study was conducted in a low-speed wind tunnel with a symmetric NACA0012 airfoil model in pitching motion under different pitching kinematics (i.e., reduced frequency k ¼3.8-13.2). A high-resolution particle image velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the characteristics of the wake flow and the resultant propulsion performance of the pitching airfoil. Besides conducting "free-run" PIV measurements to determine the ensemble-averaged velocity distributions in the wake flow, "phase-locked" PIV measurements were also performed to elucidate further details about the behavior of the unsteady vortex structures. Both the vorticity-moment theorem and the integral momentum theorem were used to evaluate the effects

Self-directed propulsion of an unconstrained flapping swimmer at low Reynolds number: hydrodynamic behaviour and scaling laws

“…Therefore, the flapping-wing system is often simplified as a flapping foil, which is fixed in the uniform oncoming flow (Triantafyllou, Techet & Hover 2004). It is revealed that the thrust generation of a flapping foil is related to the formation of reverse von Kármán vortex streets (Godoy-Diana et al 2009), which is determined by multiple parameters, including the flapping frequency, the flapping amplitude, the flapping profile, the pitch-pivot-point location and the phase angle between heave and pitch motions (Read, Hover & Triantafyllou 2003;Hover, Haugsdal & Triantafyllou 2004;Tuncer & Kaya 2005;Tian et al 2016;Mackowski & Williamson 2017;Dash et al 2018;. Based on parametric studies of a fixed flapping foil, some scaling laws have been proposed.…”

Experimental investigation on the leading-edge vortex formation and detachment mechanism of a pitching and plunging plate

“…Besides the three dimensionless parameters discussed above, LEV development has also been characterized using other dimensionless parameters (Anderson et al 1998;Read, Hover & Triantafyllou 2003;Yu, Wang & Hu 2013;Tian et al 2016). Furthermore, Dabiri (2009) introduced the optimal vortex formation time to predict the LEV detachment time.…”

“…1998; Read, Hover & Triantafyllou 2003; Yu, Wang & Hu 2013; Tian et al . 2016). Furthermore, Dabiri (2009) introduced the optimal vortex formation time to predict the LEV detachment time.…”

Unsteady aerodynamics of a pitching NACA 0012 airfoil at low Reynolds number

“…Recently, Tian et al 23 performed experiments in a closed-circuit low-speed wind tunnel with a symmetric NACA 0012 airfoil model undertaking a sinusoidal pitching motion with 5 pitching amplitude at zero mean angle of attack and at Re ¼ 3400. The pitchpivot-point location was changed from 0.16c to 0.52c with the reduced frequency of the pitching motion ranged from k ¼ 3.8 to 13.2.…”