  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 Letter 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.
