Response of a Streamwise Vortex-Wall Interaction to Unsteady Forcing

摘要

Streamwise vortices exist in a number of engineering flows in both external and internal aerodynamics, often with undesirable effects. An experimental investigation of a streamwise vortex-wall interaction is performed through the use of a vortex generating wing section and a suspended splitter plate. The unsteady development of the interaction is documented through the use of surface pressure taps and stereo particle image velocimetry. A synthetic jet actuator is implemented below the vortex and the response of the vortex to unsteady forcing is evaluated with a focus on spatial amplification through convective instabilities. At low forcing frequencies large displacement of the vortex is recorded, but with almost no spatial amplification. This behavior is expected to be linked to transient growth mechanisms. Within a specific frequency range it is shown that spatial amplification of the vortex displacement occurs. This mechanism is related to the Crow instability and has recently been investigated using computational linear stability theory. The results here are in qualitative agreement with those studies. The vortex-wall interaction generates a secondary vortex structure which rolls-up from the boundary layer. This feature is involved in the dynamics of the instability and its behavior is described.