Experiments in nonlinear saturation of stationary crossflow vortices in a swept-wing boundary layer
Conference Paper
Overview
Overview
abstract
1996, American Institute of Aeronautics and Astronautics, Inc. All Rights Reserved. Stability experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45 swept airfoil. The pressure gradient is designed to provide purely crossflow-dominated transition; that is, the boundary layer is subcritical to Tollmien- Schlichting (T-S) disturbances. The airfoil surface is hand polished to a 0.25 m rms finish. Under these conditions, stationary crossflow disturbances grow to nonuniform amplitude due to sub-micron surface irregularities near the leading edge. Uniform stationary crossflow waves are produced by controlling the initial conditions with spanwise arrays of micronsized roughness elements near the attachment line. Roughness spacing and Reynolds number are varied to investigate the growth of all amplified wavelengths. Spectral decompositions isolate single-mode growth rates for the fundamental and harmonic disturbances. The measurements show early nonlinear growth causing amplitude saturation well before transition. Comparisons with nonlinear PSE calculations show excellent agreement in both the amplitude saturation and the disturbance mode shape.
