Stability studies in pipe flows unsing water and dilute polymer solutions

Abstract

AbstractThe response of water and 20 ppm. solutions of Separan AP‐30 and Polyox WSR 301 to the periodic motion of a thin sleeve was measured using a laser Doppler velocimeter. The sleeeve was moved in an axial direction by an external coupling at frequencies from 1/4 to 1.O Hz and at amplitudes of 1/2 to 2 in. The flow filed downstream of the distrbance was found to consist of three regions: 1. a near field with a separation wake from the sleeve moving toward the piep centerline; 2. an intermediate field in which alternate laminar and turbulent slugs passed a point; and 3. a far field with decaying turbulent lfow. Defferences in the behavior of water flows and polymer flows appeared in each region. In the near field, wakes spread faster in water flows. In the intermediate field, the laminar slugs disappeared into turbulence more rapidly in water flows. And in the far field, the turbulence was not as developed in the polymer flows.Detailed statistical evaluations were made on the signals in each region for a Reynolds number of 2000. The response of the dilte polymer polymer solutions appeared to be governed by the initial interaction with the sleeve. Fewer high frequencies were generated than in the pure solvent so the periodic disturbance persisted downstream. In pure water the eddies from the separation wake interacted strongly with the periodic distrurbance leading to rapid decay of the periodic portion. Shear rates were not high enough to attribute the dilute polymer differences to viscoelastic effects.