Pulsatile viscous flow in a curved pipe: Effects of pulsation on the development of secondary flow

This work presents an experimental and numerical study of pulsated Dean flow, three-dimensional pulsatile flow in a curved pipe. The numerical study is performed by CFD code (Fluent 6) in which a pulsated velocity field is imposed as an inlet condition. The experimental setup involves principally a “Scotch-yoke” pulsatile generator and a 90° bend. Laser Doppler Velocimetry (LDV) measurements have shown that the Scotch-yoke generator produces pure sinusoidal instantaneous mean velocities with a mean deviation of 3%. Visualizations by laser-induced fluorescence (LIF) and velocity measurements, coupled with the numerical results, have permitted analysis of the evolution of the swirling secondary flow structures that develop along the bend during the pulsation phase. These measurements were made for a range of stationary Reynolds number (300⩽Rest⩽1200), frequency parameter (1⩽α=r0(ω/ν)1/2<20), and two velocity components ratios (β=Umax,osc/Ust). We observe satisfactory agreement between the numerical and experimental results. For high β, the secondary flow structure is modified by a Lyne instability and a siphon effect during the deceleration phase. The intensity of the secondary flow decreases as the parameter α increases during the acceleration phase. During the deceleration phase, under the effect of reverse flow, the secondary flow intensity increases with the appearance of Lyne flow.