Jmj. Dentoonder et al., THE ROLE OF ELONGATIONAL VISCOSITY IN THE MECHANISM OF DRAG REDUCTIONBY POLYMER ADDITIVES, Applied scientific research, 54(2), 1995, pp. 95-123
The role of elongational viscosity in the mechanism of drag reduction
by polymer additives is investigated qualitatively by means of direct
numerical simulations of a turbulent pipe flow. For the polymer soluti
on, a generalised Newtonian constitutive model is utilised in which th
e viscosity depends on the second and third invariant of the rate-of-s
train tenser via an elongation parameter. This elongation parameter is
capable of identifying elongational type of regions within the flow.
The simulations show that complementary to stretching of the polymers,
also compression must be incorporated to have drag reduction, contrar
y to many suggestions done in the literature on the mechanism which as
sume that stretching of the polymers is most important.