BUFFETING OF A FIN - STREAMWISE EVOLUTION OF FLOW STRUCTURE

The encounter of a broken-down vortex with a fin is characterized usin g high-image-density particle image velocimetry, which provides instan taneous and averaged representations of the distorted now structure, A veraged patterns of sectional streamlines and streamwise vorticity sho w well-defined, large-scale vortical motions having vorticity of the s ame orientation as, and counter to, the incident vortex, The countervo rtex, generated at the inclined leading edge of the fin, exhibits subs tantial values of vorticity and circulation, Corresponding instantaneo us images show pronounced concentrations of streamwise vorticity, whic h can have peak vorticity levels and values of circulation that exceed the averaged values by factors of three to five, The location and for m of these vorticity concentrations vary randomly with time.