(354i) Scaleout of Pipeline Drag Reduction By Wall-Injected Polyox U310 Solutions to Marine Boundary Layers

Turbulent drag reduction by wall-injected Polyox U310 solutions was studied by simultaneous axial pressure profile and flow visualization measurements at Reynolds numbers from 40000 to 102000 in a transparent test pipe of ID 15.8 mm and L/D 430. Friction factors for solvent, deionized water, adhered to the Prandtl-Karman law for Newtonian fully-developed turbulent flow in smooth pipes, 1/â??f = 4.0 log Reâ??f - 0.4, to within 0.5 units of 1/â??f. The U310 Polyox, of MW ~ 10x10⁶, was injected as a concentrated solution C_inj = 100 wppm through 6 equi-spaced 2.3 mm ID circumferential ports at friction-normalized injection velocities V_inj⁺ ~ 1 << pipeline mean velocity V⁺ ~ 25. Downstream polymer concentrations C_line varied from 0.05 to 2 wppm, exhibiting eventual fractional drag reductions DR_line from ~ 0.03 to nearly the asymptotic maximum drag reduction DR_MDR ~ 0.75 possible at the present Re. Polymer dissolution into the flow was assessed from the initial increase in fractional drag reduction towards the eventual downstream DR_line, which provided a characteristic development distance (L/D)_dr ~ 60, and also from flash photography which provided a characteristic distance (L/D)_pv ~ 100 where red-dyed strands of the injected solution disappeared. Finally, an attempt was made to â??scale-outâ? the pipeline drag reduction observations to a flat plate boundary layer by treating the latter as an equivalent pipe flow with U_CL = U_o, the free-stream velocity, R⁺ = du_Ï?/ν , with d thickness, u_Ï? friction velocity and v kinematic viscosity at the boundary layer trailing edge L. Drag reduction from the present pipe flow results, measured by flow enhancement or slip Sâ??_line = (1/â??f_p â?? 1/â??f_n)_Reâ??f, was translated to the classical HMS Highburton Polyox W301 ejection trials of Canham et. al (1971). This scale-out suggested that the present Polyox U310 might have provided their reported drag reductions at roughly 1/50 th their polymer expenditure rate per unit of hull wetted area.