LOW-SPEED STREAKS IN DRAG-REDUCED TURBULENT-FLOW

The effect of a surfactant drag-reducing additive (530 ppm Habon G sol ution) on the structure of wall turbulence, both in a flume and in pip e flow, was investigated experimentally. Real-time infrared thermograp hy was used for how visualization and measurements of the spanwise spa cing between the thermal streaks. The experiments were carried out ove r a broad range of friction velocities, i.e., u(p)=0.51-3.27 cm/s. Wi th wall shear velocities 1.54 less than or equal to u(p)less than or equal to 3.27 cm/s drag reduction of 82%-85% was achieved in a tube fl ow, well below the predictions of the Virk maximum drag reduction asym ptote proposed for high polymers. The results of spanwise streak spaci ng indicate that wall shear velocity may be an appropriate parameter f or describing nondimensional streak spacing behavior in drag reducing hows. A hypothesis, based on the average spanwise streak spacing lambd a(+) can be applied to describe the mean velocity profiles of Habon G solutions. The ratio (lambda(p)(+)-100)/100 was applied to describe me an velocity profiles with 530 ppm Habon G solution. (C) 1997 American Institute of Physics.