Large-Eddy BreakUp Devices - a 40 Years Perspective from a Stockholm Horizon

Area of Science:

• Fluid dynamics
• Aerodynamics
• Turbulence research

Background:

• Large Eddy BreakUp (LEBU) devices, including thin plates and airfoils, were introduced in the 1980s.
• LEBUs are mounted in the outer regions of turbulent boundary layers.
• Initial studies suggested LEBUs could modify turbulence and reduce skin friction drag.

Purpose of the Study:

• To investigate the net effect of LEBU devices on drag.
• To reconcile conflicting results between wind tunnel studies and other experimental/simulation data.
• To explore the reasons behind discrepancies in reported drag reduction.

Main Methods:

• Review of wind-tunnel studies claiming drag reduction.
• Analysis of towing-tank experiments with flat plates and axisymmetric bodies.
• Evaluation of recent large-eddy simulations of LEBU effects.

Main Results:

• Towing-tank experiments and large-eddy simulations indicate no net drag reduction with LEBUs.
• These studies consistently show an increase in total drag.
• Wind tunnel experiments reported positive net drag reduction, contrasting with other findings.

Conclusions:

• LEBU devices alter boundary layer characteristics but do not provide net drag reduction based on towing-tank and simulation data.
• Discrepancies between wind tunnel results and other methods require further investigation.
• Despite lack of net drag reduction, LEBUs' effect on boundary layer manipulation warrants continued interest.