Petiolate wings: effects on the leading-edge vortex in flapping flight

Area of Science:

• Fluid dynamics
• Aerodynamics
• Biomechanics

Background:

• Many insect wings are petiolate, featuring a stalk between the hinge and wing surface.
• The aerodynamic effects of petiolation, especially on leading-edge vortex (LEV) formation, are not well understood.
• The LEV is crucial for lift enhancement in flying insects, birds, and bats.

Purpose of the Study:

• To investigate the aerodynamic implications of wing petiolation on leading-edge vortex (LEV) formation and strength.
• To quantify the impact of varying degrees of petiolation on lift coefficients.
• To understand how petiolation influences the dynamics and structure of the LEV during flapping flight.

Main Methods:

• Particle image velocimetry (PIV) was used to measure flow fields around rectangular wings.
• Wings with aspect ratio 3 and petiolation values (P) from 1 to 3 were tested.
• A mechanical device ('Flapperatus') generated insect-like flapping kinematics at a Reynolds number of 1400 and dimensionless stroke amplitude of 6.5.

Main Results:

• Increased petiolation resulted in larger, stronger LEVs with greater surface area coverage, particularly inboard.
• The LEV's structure evolved from arch-like to continuous with the tip vortex.
• LEV detachment occurred earlier in the stroke for more petiolate wings (e.g., 50% span for P=3).

Conclusions:

• Wing petiolation significantly enhances leading-edge vortex formation and strength.
• Petiolation increases lift coefficients in the first half of the flapping stroke.
• Time-averaged lift coefficients generally increase with the degree of petiolation within the tested range.