Effects of actuated boundaries on Tollmien-Schlichting waves and developed boundary layer turbulence

Abstract

The potential for hydrodynamic drag reduction using small-scale actuation to influence turbulent boundary layer flow is investigated. When coupled with lab data, numerical simulations allow for the most complete understanding of the effect of various parameters on boundary layer turbulence. Two computational fluid dynamics (CFD) model sets are created in COMSOL, a multiphysics software package, to compare to experimental data and inform future research in the flowSiTTE laminar-to-turbulent flow tank. Effects on boundary layer dynamics and turbulence are studied through the implementation of an actuated boundary along the tank lid, using a standing wave to counter shear stress streaks characteristic of fully developed boundary layer turbulence. Numerical velocity data from the tank lid model are consistent with laboratory data collected with Particle Image Velocimetry (PIV). Additionally, boundary layer actuation of transitional turbulence is studied by analyzing the formation and dampening of Tollmien-Schlichting (TS) waves on a NACA 0012 airfoil. Standing wave actuation with amplitudes of 10-100μm along the airfoil is shown to reduce hydrodynamic drag by up to 15% at a wide range of frequencies. Boundary actuation delays the formation of the separation layer along the airfoil’s trailing edge – the region of flow responsible for much of the airfoil’s drag – keeping the flow attached for nearly the entire chord length and significantly reducing pressure drag.