INVESTIGATIONS ON TRANSITION TO TURBULENCE IN PIPE FLOW OF NEWTONIAN AND VISCOELASTIC FLUIDS

The linear stability analysis of fully developed pipe flow of a second order and a “contravariant” Maxwell-type fluid predicts stability against twodimensional infinitesimal disturbances of rotational symmetry.

A sinuous perturbation, superposed on the pipe flow of aqueous polymer solutions, produces distinct regions of instability, dependent on disturbance amplitude and frequency.

A broad region of Reynolds numbers is found for natural transition to turbulence with laminarization effect of polymer additions in two extremely different cases of inlet conditions.