Structural analysis of turbulent transport in a heated drag-reducing channel flow with surfactant additives

Turbulence transport features in a heated drag-reducing surfactant solution (CTAC, 30 wppm) channel flow was investigated by simultaneously measuring velocity and temperature fluctuations in the thermal boundary layer. Measurement was made at inlet fluid temperature of 304 K and at three Reynolds numbers (based on channel height, bulk velocity and solvent viscosity): 3.5 × 104, 2.5 × 104 and 1.5 × 104. Structural analysis showed that the drag-reducing additives inhibited the motions associated with ejections of low-momentum fluid away from the wall and sweeps of high-momentum fluid toward the wall (the second and fourth quadrant motion respectively) but had no obvious effect on the outward motion of high-momentum fluid and wall-ward motion of low-momentum fluid (the first and third quadrant motion respectively). The depression of wall-normal turbulent heat flux was due to the decreased contributions of the second and fourth quadrant motions.