On the transient process of flow reattachment by external excitation

A. Darabi, I. Wygnanski

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

The transient reattachment process of a turbulent flow to an inclined flat surface was investigated experimentally. The process was initiated by periodic excitation that was introduced in a step-wise fashion at the hinge of the flap where the flow normally separated. Reattachment of the separated flow is essentially a constant-rate process whose slope depends upon the frequency and amplitude of the excitation and the flap deflection. Exception to this is an adverse surge in the flap aerodynamic loading immediately following the onset of the excitation. The duration of the surge scales with the flight time of the first induced vortex over the entire flap and it is unrelated to the nature of the oscillations. Overall reattachment time attains a minimum at reduced frequencies around F+=1.5. This optimal frequency is independent of the amplitude. The entire process is dominated by large spanwise vortices that were initiated by the excitation and amplified by the shear layer. It was demonstrated that as the coherent structures grow they contribute to net transport of fluid directed away from the surface that causes favorable pressure difference across the reattaching flow.

Original languageEnglish
Title of host publication1st Flow Control Conference
PublisherAmerican Institute of Aeronautics and Astronautics Inc.
ISBN (Print)9781624101052
DOIs
StatePublished - 2002
Event1st Flow Control Conference 2002 - St. Louis, MO, United States
Duration: 24 Jun 200226 Jun 2002

Publication series

Name1st Flow Control Conference

Conference

Conference1st Flow Control Conference 2002
Country/TerritoryUnited States
CitySt. Louis, MO
Period24/06/0226/06/02

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