Transverse Forcing by Acoustic Excitation
For friction drag reduction in a turbulent boundary layer
S.H. Schaafsma (TU Delft - Aerospace Engineering)
Woutijn J. Baars – Mentor (TU Delft - Aerodynamics)
Marios Marios – Graduation committee member (TU Delft - Aerodynamics)
B.W. van Oudheusden – Graduation committee member (TU Delft - Aerodynamics)
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Abstract
This research investigates the application of acoustic excitation as a novel method for transverse forcing to achieve friction drag reduction in a turbulent boundary layer. Traditional transverse wall motion, while effective in reducing drag, poses experimental challenges due to mechanical complexity and limitations at high Reynolds numbers. This study explores an alternative approach where transverse velocity gradients are induced through oscillatory acoustic fields rather than wall motion. An experimental setup was developed at the Delft University Boundary Layer Facility (DUBLF), incorporating a system of phase-synchronized speakers to generate controlled transverse acoustic forcing. Particle Image Velocimetry (PIV) was used to characterize the boundary layer and assess the effect of forcing across a range of Reynolds numbers. Results show measurable reductions in friction drag, with the optimal configuration achieving up to 6.02% drag reduction at Reτ = 1847. The study further reveals that the induced transverse velocity fields modulate near-wall turbulence structures, contributing to reduced turbulent kinetic energy and Reynolds stresses. This method provides a mechanically simpler and potentially scalable alternative for active flow control, with the potential to provide new insights into the mechanisms of transverse forcing in turbulent boundary layers.