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Abstract

The effect of turbulence damping polymer additive on the fluid flow structure near the wall region of a circular pipe was made visible using real-time laser holographic interferometry. The interference fringes were recorded by high-speed motion photography. The gross flow behaviour of dilute solutions of Polyox WSR 301 in distilled water was studied in a 2.63 cm pipe. It was observed that (i) The onset of drag reduction occurred at a critical value of wall shear stress and Reynolds number. (ii) The fluid property parameter, δ, which governs the drag reduction capacity of the solution, had a power-law dependence on polymer concentration given by [23] [ Formula omitted ] Motion pictures of real-time holographic fringe displays for pure solvent and polymer solution were appraised qualitatively. Under similar flow conditions turbulent eddies in drag-reducing flow were observed (i) to show less small scale structure than those in the pure solvent, and (ii) to burst from the wall region into the bulk flow with a lower frequency.