Drag reduction by a linear viscosity profile.
Drag reduction by polymers in turbulent flows raises an apparent contradiction: the stretching of the polymers must increase the viscosity, so why is the drag reduced? A recent theory proposed that drag reduction, in agreement with experiments, is consistent with the effective viscosity growing linearly with the distance from the wall. With this self-consistent solution the reduction in the Reynolds stress overwhelms the increase in viscous drag. In this Rapid Communication we show, using direct numerical simulations, that a linear viscosity profile indeed reduces the drag in agreement with the theory and in close correspondence with direct simulations of the FENE-P model at the same flow conditions.
De Angelis
Elisabetta
E
Dipartimento di Meccarica e Aeronautica, Università di Roma La Sapienza, Via Eudossiana 18, 00184, Roma, Italy.
Casciola
Carlo M
CM
L'vov
Victor S
VS
Pomyalov
Anna
A
Procaccia
Itamar
I
Tiberkevich
Vasil
V