Numerical investigation on the aerodynamic efficiency of bio-inspired corrugated and cambered airfoils in ground effect

Abstract

This research numerically investigates the flapping motion effect on the flow around two subsonic airfoils near a ground wall. Thus far, the aerodynamic efficiency of the dragonfly-inspired flapping airfoil has not been challenged by an asymmetric cambered airfoil considering the ground effect phenomenon, especially in the MAV flight range. The analysis is carried out on the basis of an unsteady Reynolds-averaged Navier-stokes (URANS) simulation, whereby the Transition SST turbulence model simulates the flow characteristics. Dragonfly-inspired and NACA4412 airfoils are selected in this research to assess the geometry effect on aerodynamic efficiency. Moreover, the impacts of Reynolds number (Re), Strouhal number (St), and average ground clearance of the flapping airfoil are investigated. The results indicate a direct relationship between the airfoil’s aerodynamic performance (C_l/C_d) and the ground effect. The C_l/C_d increases by reducing the airfoil and ground distance, especially at h_{0}=c. At Re=5times 10^4, by increasing the St from 0.2 to 0.6, the values of C_l/C_d decrease from 10.34 to 2.1 and 3.22 to 1.8 for NACA4412 and dragonfly airfoils, respectively. As a result, the C_l/C_d of the NACA4412 airfoil is better than that of the dragonfly airfoil, especially at low oscillation frequency. The efficiency difference between the two airfoils at St=0.6 is approximately 14%, indicating that the C_l/C_d difference decreases substantially with increasing frequency. For Re=5times 10^3, the results show the dragonfly airfoil to have better C_l/C_d in all frequencies than the NACA4412 airfoil.