  The modification of dominant coherent structures that extend through the
log-region of a drag reduced turbulent boundary layer is studied via
examination of two-point correlations from time-resolved
particle-image-velocimetry. Measurements were acquired in polymer oceans
(uniform concentration) at drag reduction levels corresponding to the low drag
reduction regime (< 40%), the high drag reduction (HDR) regime (>40%), and at
an intermediate level (46%). The mean velocity profiles and two-point
correlations were compared with that of water (Newtonian, DR = 0%). These
results show that with increasing drag reduction the inclination of these
dominant coherent structures decrease, their streamwise extent increases, and
the fluctuations in the correlations are suppressed (especially at HDR). These
observations are examined in comparison with the coherent structure literature
(Newtonian and polymeric).
