Unsteady aerodynamic forces of a flapping wing

Area of Science:

• Fluid dynamics
• Aerodynamics
• Bio-inspired engineering

Background:

• Fruit fly flapping flight relies on complex unsteady aerodynamic forces.
• Understanding these forces is crucial for bio-mimetic flight technologies.

Purpose of the Study:

• To numerically investigate unsteady aerodynamic forces on a model fruit fly wing during flapping motion.
• To identify key non-dimensional parameters governing these forces and their impact on flight.

Main Methods:

• Solving Navier-Stokes equations for flapping wing motion (translation and rotation).
• Analyzing aerodynamic force coefficients based on Reynolds number (Re), stroke amplitude (Phi), angle of attack (alpha(m)), rotation duration (Delta tau(r)), and rotation timing.
• Comparing simulation results with existing hovering flight data.

Main Results:

• Aerodynamic forces are primarily dependent on five non-dimensional parameters.
• Above Re ≈ 100, lift and drag coefficients are high and stable, mainly due to delayed stall.
• Below Re ≈ 100, lift decreases and drag increases significantly, with a weaker leading-edge vortex.
• Lift generation is sufficient for hovering flight above Re ≈ 100.
• Force coefficients show minimal variation with Re, Phi, and Delta tau(r) above Re ≈ 100, suggesting force is proportional to Phi²n².

Conclusions:

• Reynolds number significantly impacts aerodynamic forces, with a critical threshold around 100.
• Stroke amplitude and wingbeat frequency are key factors for controlling flight force magnitude.
• The simple harmonic function for wing motion yields different force time courses compared to trapezoidal functions, but similar mean values.