Boundary layer transition modeling on leading edge inflatable kite airfoils

Area of Science:

• Fluid Dynamics
• Aerodynamics
• Renewable Energy

Background:

• Airborne wind energy systems utilize kite airfoils operating across a wide range of Reynolds numbers due to pumping cycles.
• Understanding boundary layer transition is crucial for optimizing airfoil performance in these dynamic conditions.

Purpose of the Study:

• To computationally analyze boundary layer transition on leading edge inflatable kite airfoils.
• To evaluate the impact of transition modeling on airfoil aerodynamics for airborne wind energy applications.

Main Methods:

• Utilized computational fluid dynamics (CFD) with a combination of the shear stress transport (SST) turbulence model and the $$ transition model.
• Implemented the models in OpenFOAM and validated the approach using sailwing airfoil experimental data.
• Applied the validated method to analyze leading edge inflatable kite airfoils.

Main Results:

• The transition model accurately predicted sailwing airfoil aerodynamics across various angles of attack at low Reynolds numbers.
• For kite airfoils, transition modeling showed mixed effects: laminar separation negatively impacted aerodynamics, but delayed thickening and separation were observed.
• Laminar boundary layer thickening was slower than turbulent boundary layer thickening, delaying separation.

Conclusions:

• Boundary layer transition significantly influences the aerodynamic performance of kite airfoils in airborne wind energy systems.
• Aerodynamic performance can be improved by strategically controlling boundary layer transition: delaying it during traction and promoting it during retraction.
• The findings provide insights for designing more efficient kite airfoils for airborne wind energy generation.