Numerical investigation of the aerodynamic performance of dragonfly-like flapping foil in take-off flight

Abstract

In this study, the aerodynamic performance of a dragonfly-like flapping foil is investigated in take-off flight using two-dimensional numerical simulations. Two parameters, foil spacing L * ( L/c) and the phase shift between forefoil and hindfoil ψ, which characterize the flow in the tandem configuration, are varied to explore their impact on the resulting aerodynamic performance. Both the vertical and thrust forces generated in one cycle are found to be strongly dependent on ψ and relatively weakly dependent on L *. The tandem configuration is beneficial for the vertical force generation in the range of 0° ≤ ψ ≤ 30°, and further, it aids the thrust force generation for 40° ≤ ψ ≤ 110°. The flow interactions between the forefoil and hindfoil can increase the vertical force generated in a cycle by a maximum of ∼1.2 times when ψ is close to 0° relative to the no foil–foil interaction case (additive effect of two single foils). These interactions can also increase the thrust force generated in a cycle by a maximum of ∼2.8 times when ψ is close to 80°. The vortex structures reveal that the enhancement in thrust force mainly depends on the timing of interactions and how the hindfoil utilizes the vortex detached from the forefoil to benefit from it. Further, we find that dragonflies use in-phase stroking pattern ( ψ = 0 °) with a large downstroke angle of attack, α D ( α D = 86 °), in the initial phase of take-off as it aids in generating additional vertical force. Our findings can significantly contribute to the design of micro aerial vehicles.

Numerical investigation on the effect of stroke plane inclination on the aerodynamic performance of dragonfly take-off flight

“…The pitch center is located at a half-chord distance from the leading edge of the airfoil. During in-phase oscillation of the foils, the foil spacing of 1.3𝑐𝑐 generates the maximum lift [8,9]. Therefore, the distance between the stroke plane of both airfoils, denoted by 𝐿𝐿, is 1.3𝑐𝑐.…”

“…Where 𝑢𝑢 and 𝑝𝑝 represent fluid velocity and pressure, respectively. Equations [7] and [8] are solved using a pressure-based solver in ANSYS Fluent 17.2 software. Pressure-velocity coupling is achieved by using a second-order PISO scheme.…”

“…The results also showed that the stroke plane angle of forewing and hindwing varied considerably during the take-off procedure. Also, Shanmugam and Sohn [8] found that in-phase stroking with a large angle of attack during downstroke helps generate a higher vertical force coefficient, which is beneficial during take-off flight.…”

A modified unsteady-nonlinear aeroelastic model for flapping wings

“…1 Due to importance and inherent complexities associated with FAVs, there are some researches focused on its aerodynamic aspects. [2][3][4][5][6][7][8][9][10][11][12] On the other hand, flexibility is another significant issue with FAVs that can [13][14][15][16][17][18] potentially affect their aerodynamic loadings for sustained flights.…”