Thickness Effect on the Thrust Generation of Heaving Elliptic Airfoils

Reynolds number, thickness and camber effects on flapping airfoil propulsion

“…However, at very low Reynolds number (Re= 200) where viscous forces dominate and there is no net thrust production from the plunging oscillations, drag is successively increased as the thickness increases. This latter behaviour is in agreement with previously reported results in the studies of Wang (2000), Vandenberghe et al (2006) and An et al (2009). The failure of the UPM code in predicting an optimum thickness, in agreement with the previous study of Cebeci et al (2004), is due to the inviscid code's inability to capture the leading edge vortices produced (see discussion in Section 3.1).…”

“…In summary, the results in Rozhdestvensky and Ryzhov (2003), Lentink and Gerritsma (2003) and An et al (2009) indicate that thick airfoils can improve plunging airfoil performance, whereas Vandenberghe et al (2006) and Wang (2000) suggest that thin airfoils perform better, and the inviscid analysis of Cebeci et al (2004) concludes no influence of airfoil thickness on plunging airfoil propulsion. Also according to the literature (Mueller and Batill, 1982;Kunz and Kroo, 2001) for static (nonflapping) airfoils at low Reynolds number flows, thin and sharp airfoils perform better than the thick and blunt airfoils.…”

“…They reported that increasing the thickness (from 8.4% to 16.8%) decreased the resultant rotational speed of the wing, and further thickness increase (to 25.2%) produced no rotational motion, indicating no net thrust. More recently, An et al (2009) used the lattice Boltzmann method to study plunging bodies of varying thickness from 5% (thin ellipse), 10% and then in steps of 10-100% thick (circular cylinder) at very low Reynolds number of (Re=50, 100 and 185) and Strouhal number of (St=0.2 and 0.4). Based on the wake vortex pattern and velocity profiles behind the plunging body, they identified that the thickness distribution of the airfoil is a crucial design parameter for thrust generation.…”

High fidelity numerical simulation of airfoil thickness and kinematics effects on flapping airfoil propulsion

“…Based on the inviscid simulation from an unsteady panel code, Cebeci et al (2004) found that thickness had a negligible effect on the propulsive efficiency. An et al (2009) found that thickness ratio was a crucial parameter for thrust production and their results indicated that propulsive efficiency, 〈C T 〉=〈C pow 〉 θ 0 , θ pitch amplitude and pitch angle of airfoil, deg ϕ phase lag between pitching and plunging motions, deg there existed an optimal thickness ratio for the thrust generation at Reynolds number 185. Ashraf et al (2011) systematically studied the thickness effects on the propulsive performances of flapping airfoils at different Reynolds numbers ranging from 200 to 2 Â 10 6 .…”

Propulsion for Biological Inspired Micro-Air Vehicles (MAVs)

“…At the same time, the effect of airfoil configuration has been considered far less and the published work is not always in agreement. For example, the results [12]- [14] show that thick airfoils can improve plunging airfoil performance, whereas [15]- [17] suggest than thin airfoils perform better, and the inviscid analysis [16] concludes no influence of airfoil thickness on plunging airfoil propulsion. Some authors attribute the superior efficiency of natural systems of thrust generation and propulsive efficiency to wing flexibility and focused their research on flexible wings with chord and span flexibilities [18] [19].…”