Velocity measurements in axisymmetric jets of dilute polymer solutions

Abstract

Experiments are described in which the velocity profiles of axisymmetric jets are measured in water and in dilute solutions of water-soluble polymers. The ambient fluid and that entering through the nozzle were homogeneous. The similarity characteristics of velocity profiles including a linear variation of centre-line velocity with the inverse of the distance from the nozzle were unaltered by these substances. On adding large polyethylene oxide molecules to the system the jet spread at an increased angle, possibly due to the entrainment rate being enhanced by an increase in turbulent elasticity for polyethylene oxide solutions. It is also postulated that additives which had no effect on the velocity were not large enough to influence the small microscale eddies in which the energy to activate an entrainment cycle is stored.