Comparative Study of Control Techniques for Two-Dimensional Low-Speed Turbulent Flow Separation

Abstract

Relative performance of several passive and active methods for controlling two-dimensional turbulent separated flow associated with a curved backward-facing ramp were investigated at low speeds. Surface static pressure measurement and oil flow visualization results indicate that transverse grooves, longitudinal grooves, submerged vortex generators (with h/δ ~ O(0.1–0.2)), vortex generator jets (with β ≃ 90°, α ≃ 15°), elongated arches at +α, and huge-eddy breakup devices (LEBU’s) at +a placed near the baseline separation location reduce flow separation and increase pressure recovery. Spanwise cylinders reduce flow separation but decrease pressure recovery downstream. Arches and LEBU’s with α ≤ 0° examined so far have no significant effect in reducing separation. Wall cooling computation indicates that separation delay on a partially cooled ramp is nearly the same as on a fully-cooled ramp while minimizing the frictional drag increase associated with the wall cooling process.