"Secondary flow patterns and mixing in laminar pulsating flow through a" by Mojtaba Jarrahi, Cathy Castelain et al.
 

Civil and Environmental Engineering Publications

Secondary flow patterns and mixing in laminar pulsating flow through a curved pipe

Document Type

Article

Publication Date

2011

Journal

EXPERIMENTS IN FLUIDS

Volume

50

Issue

6

First Page

1539

URL with Digital Object Identifier

https://doi.org/10.1007/s00348-010-1012-z

Last Page

1558

Abstract

Mixing by secondary flow is studied by particle image velocimetry (PIV) in a developing laminar pulsating flow through a circular curved pipe. The pipe curvature ratio is eta = r (0)/r (c) = 0.09, and the curvature angle is 90A degrees. Different secondary flow patterns are formed during an oscillation period due to competition among the centrifugal, inertial, and viscous forces. These different secondary-flow structures lead to different transverse-mixing schemes in the flow. Here, transverse mixing enhancement is investigated by imposing different pulsating conditions (Dean number, velocity ratio, and frequency parameter); favorable pulsating conditions for mixing are introduced. To obviate light-refraction effects during PIV measurements, a T-shaped structure is installed downstream of the curved pipe. Experiments are carried out for the Reynolds numbers range 420 a parts per thousand currency sign Re-st a parts per thousand currency sign 1,000 (Dean numbers 126.6 a parts per thousand currency sign Dn a parts per thousand currency sign 301.5) corresponding to non-oscillating flow, velocity component ratios 1 a parts per thousand currency sign (beta = U (max,osc)/U (m,st)) a parts per thousand currency sign 4 (the ratio of velocity amplitude of oscillations to the mean velocity without oscillations), and frequency parameters 8.37 < (alpha = r (0)(omega/nu)(0.5)) < 24.5, where alpha(2) is the ratio of viscous diffusion time over the pipe radius to the characteristic oscillation time. The variations in cross-sectional average values of absolute axial vorticity (|zeta|) and transverse strain rate (|epsilon|) are analyzed in order to quantify mixing. The effects of each parameter (Re-st, beta, and alpha) on transverse mixing are discussed by comparing the dimensionless vorticities (|zeta (P) |/|zeta (S) |) and dimensionless transverse strain rates (|epsilon (P) |/|epsilon (S) |) during a complete oscillation period.

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