Theory 33/Transport & flow/Turbulent drag reduction
Drag Reduction Is a Time Ratio
The claim
Polymer drag reduction is set by the ratio of polymer relaxation time to eddy turnover time, so a polymer only reduces drag in the range where the two match.
01Mechanism
The polymer must stretch and damp turbulence before relaxing; the ratio determines whether it can.
02Prediction
Reduction should peak at an intermediate ratio.
03Refutation
Reduction increasing with concentration would remove the time match.