Laminar-turbulent transition in polymer solutions

Abstract

WHETHER transition from laminar to turbulent flow is delayed in dilute drag-reducing polymer solutions, unchanged, or occurs at an earlier Reynold's number has been a vexing question since research began in this area. Using the classic Reynold's dye-streak technique, Giles and Pettit¹ showed that pipe-flow turbulence was delayed by a factor of 2 or more by small additions of polymer. Similarly, Castro and Squire² and White and McEligot³ found transition delay in small pipes from measurements of pressure fluctuations and actual drag-reduction performance. But more refined pipe-flow studies by Little et al.⁴ show convincing evidence for polymer solution transition earlier than for the pure solvent and this has been confirmed by laser–Doppler annemometry⁵. Here we show that polymer solutions in a boundary-layer flow exhibit a transition to turbulence at a lower Reynold's number than the pure water solvent.