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, 30wppm) 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.