Numerical Study of Bio-Inspired Corrugated Airfoil Geometry in a

Forward Flight at a Low Reynolds Number

YAGYA DUTTA DWIVEDI1, SUDHIR SASTRY Y. B.2, BDY SUNIL1,

CH. V. K. N. S. N. MOORTHY3, K. VISWANATH ALLAMRAJU1

Hyderabad, Telangana, 500043, INDIA

Management, Jain Deemed to be

forces and moments and compare them with a non-corrugated profile having similar geometry without

corrugations. Three different airfoils were chosen, the first triangular peaked corrugated is inspired from the

mid-section of a dragonfly wing, the second modified simplified corrugated is a different form of the dragonfly

wing section, which was modified to match the maximum thickness of the first airfoil, and the third is a non-

corrugated Hybrid airfoil obtained by joining the peaks of the second airfoil. These three models were

fabricated using an additive manufacturing process to undertake the experimental work in a low subsonic wind

tunnel to find aerodynamic characteristics. ANSYS FLUENT solver was applied to unravel the steady, laminar,

incompressible, two-dimensional, RANS equations. The tests were performed for 4 to +20 degrees angle of

attack at a Reynolds number of 80,000. The result revealed that the Hybrid airfoil is suitable only for up to a 4-

degree angle of attack. The modified simple corrugated airfoil produced significant aerodynamic performance

Received: May 29, 2021. Revised: April 18, 2022. Accepted: May 15, 2022. Published: July 12, 2022.

Over millions of years, Nature has evolved all

avians and insects to have definite wings. By

flapping, avians can create sufficient lift and thrust

force to make them highly maneuverable, fly easily,

and sustained endurance. Due to these qualities,

researchers have taken a lot of interest to understand

the said field of the flapping wing over the past few

Re regime [1], [2] during the 1970s and 1990s. The

dragonfly (Aeshna cyanea) forewing mid- cross-

section is characterized by well-defined

corrugations with varying dimensions over the span

from root to tip. The corrugated wing of the

dragonfly demonstrates sufficient hovering

kinetic energy than laminar flow so it will overcome

the negative pressure gradient. This phenomenon

reduces the flow separation and delays the stall of

the airfoil [8].Another important numerical study

[10] has demonstrated that there exists a strong

negative pressure between the leading edge (LE)

and the first corrugation. The next corrugations also

generate depression with lesser intensity than the

first corrugation. The most severe suction zone that

exists between the LE and the first corrugation, is

reattaching the backward part of the airfoil and

reducing flow separation.

Even though most of the above studies have focused

to understand the flow pattern and aerodynamic

efficiency of bio-inspired corrugated airfoils and

most of them have compared results with a flat

plate. The flat plate does not have any camber and

also maximum thickness of the flat plate cannot be

compared with the bio-inspired corrugated

airfoil.Therefore, the comparison with flat plate and

material, so the corrugations are removed and the

geometrical parameters are identical to the bio-

inspired airfoil called hybrid airfoil and then

compared the aerodynamic characteristics

computationally. Another airfoil which is also bio-

inspired corrugated has identical geometry except

the maximum thickness location is shifted towards

the trailing edge by 0.1c from the previous bio-

inspired airfoil. The primary objective of this work

is to assess the efficacy of bio-inspired corrugation

on the aerodynamic performance at Reynold number

corrugation on the flow structure and efficiency of

the airfoil. The three CAD models of airfoils were

prepared using commercial software and flow was

simulated by using ANSYS Fluent software. The

models were also fabricated by using a three-

dimensional (3D) printing machine and

times the chord length above and below the airfoil

(figure 2).

In these equations the ρ is the fluid density, ui and uj

are the velocity components in the x-direction, p is

pressure, xi and xj are the horizontal distance, CL,

2.3.1 Wind Tunnel

The wind tunnel isseparated into some different

parts: the convergent section, test section, and

divergent section. The motor rotates the fans and the

required wind velocity is developed inside the test

section. Turbulence intensity is kept within the limit

in the test section using honeycomb and two layers

of stainless steel wire screens (figure 6). The size of

the test section is 0.6x0.6x2 m. The flow velocity is

bridge principle. The accuracy of velocity

measurement is ± 0.5 m/s, force measurement ±0.5

N, and maximum turbulence is 1%. Six component

balance is calibrated before starting the present test

(figure 6). The Triangular peak corrugated airfoilis

fixed inside the wind tunnel as shown in figure 7.

The other wing models are also fixed similarly.

There are three main sources of errors[14] during

measurements of the forces and moments: accuracy

Fig. 8: 3D printed models of (a) Triangular peak

corrugated airfoil, (b) Modified simple corrugated

airfoil, and (c) Hybrid airfoil.

The second model hereafter Modified Simple

Corrugated (MSC) airfoil, was obtained from the

work of [13]. However, the airfoil was modified by

increasing the height of the second peak and also

increasing the maximum thickness to match the

triangular peak airfoil (figure 8b).

The third model hereafter Hybrid airfoil is a non-

corrugated airfoil created by joining the peaks of the

and walls to avoid flow interference with the wall

and wing. The height and width of the test section

are 600 mm and 600 mm respectively, the blockage

ratio was < 1%. A substantial gap with the wind

tunnel walls is maintained to avoid the wall effects

(a)

(b)

airfoils produced a negative lift at -4 degree AOA

(figure. 9 a)

It is noticed from figure 9(b), that the CD produced

byboth corrugated airfoils were almost similar up to

12 degrees AOA in that the Hybrid airfoil showed

the least drag coefficient. However, above 120

AOA, the CD produced by the Hybrid airfoil

increased sharply and after 160 AOA the hybrid

airfoil showed the highest increase in CD. This

shows that the drag produced by Hybrid airfoils

MSC airfoil can provide better aerodynamic

efficiency than the TPC airfoil.

Coefficient of the moment (CM)Vs AOA at Re

80000.

maneuverability and agility of the dragonfly as the

stability and maneuverability are just the opposite of

the activities.

3.2 Streamlines

Streamlines were obtained at 0-degree AOA for

each profile. Figure 11(a) and 11 (b) depict the

circulation of flow in the clockwise direction in the

valleys of the corrugated profiles. The flow

direction inside the valley is opposite to the

direction of the flow in the free stream. This

in a golf ball as it moves through the air. This results

in a reduction in the net drag produced by the

corrugated airfoil. However, these trapped vortices

weren't seen in the Hybrid airfoil (figure 11c) due to

the absence of peaks and valleys in this

configuration.

(a) (b) (c)

Fig. 11: Streamlines at 0 degrees AOA: (a)

3.3.1 Velocity Distribution

shown in figure 12. These contours are obtained by

ANSYS CFD_POST for the AOA of 8, 16, and 20

degrees and Reynolds number 80,000. At 8 degrees

AOA, all the corrugated airfoils showed nearly

similar flow characteristics. That’s why the CL, CD

and CL/CD at this 8 degrees AOA for both

corrugated airfoils are similar (figure 9, 10). At 16

degrees AOA, the velocity contours of the TPC

airfoil had discontinuity on the upper side and the

MSC airfoil was not observed. However, the Hybrid

works were done in past on this airfoil and

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