Pulsating Flow for Mixing Intensification in a Twisted Curved Pipe

2007 ◽  
Author(s):  
Brahim Timite ◽  
Cathy Castelain ◽  
Hassan Peerhossaini
Keyword(s):  
Secondary Flow ◽  
Pipe Flow ◽  
Numerical Study ◽  
Pulsating Flow ◽  
Experimental Results ◽  
Chaotic Advection ◽  
Mean Deviation ◽  
Mixing Enhancement ◽  
Curved Pipe ◽  
Deceleration Phase

This work concerns the manipulation of a twisted curved pipe flow for mixing enhancement. Previous work [1,2,3] has shown that geometrical perturbations to a curved pipe flow can increase mixing and heat transfer by chaotic advection. In this work the flow entering the twisted pipe undergoes a pulsatile motion. The flow was studied experimentally and numerically. The numerical study is carried out 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 twisted curved pipe. 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 bends during the pulsation phase. These measurements were made for a range of steady Reynolds number (300 ≤ Rest ≤ 1200), frequency parameter (1 ≤ α = r0.(ω/υ)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. Experimental results also show that pulsating flow through a twisted curved pipe increases mixing over the steady twisted curved pipe. This mixing enhancement increases with β.

Pulsating Flow for Mixing Intensification in a Twisted Curved Pipe

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
B. Timité ◽  
M. Jarrahi ◽  
C. Castelain ◽  
H. Peerhossaini
Keyword(s):  
Secondary Flow ◽  
Pipe Flow ◽  
Numerical Study ◽  
Pulsating Flow ◽  
Experimental Results ◽  
Chaotic Advection ◽  
Mean Deviation ◽  
Mixing Enhancement ◽  
Curved Pipe ◽  
Deceleration Phase

This work concerns the manipulation of a twisted curved-pipe flow for mixing enhancement. Previous works have shown that geometrical perturbations to a curved-pipe flow can increase mixing and heat transfer by chaotic advection. In this work the flow entering the twisted pipe undergoes a pulsatile motion. The flow is studied experimentally and numerically. The numerical study is carried out by a computational fluid dynamics (CFD) code (FLUENT 6) in which a pulsatile velocity field is imposed as an inlet condition. The experimental setup involves principally a “Scotch-yoke” pulsatile generator and a twisted curved pipe. Laser Doppler velocimetry 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 and velocity measurements, coupled with the numerical results, have permitted analysis of the evolution of the swirling secondary flow structures that develop along the bends during the pulsation phase. These measurements were made for a range of steady Reynolds number (300≤Rest≤1200), frequency parameter (1≤α=r0⋅(ω/υ)1/2<20), and two velocity component 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. Experimental results also show that pulsating flow through a twisted curved pipe increases mixing over the steady twisted curved pipe. This mixing enhancement increases with β.

Numerical Study of Turbulent Helical Pipe Flow With Comparison to the Experimental Results

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Anup Kumer Datta ◽  
Yasutaka Hayamizu ◽  
Toshinori Kouchi ◽  
Yasunori Nagata ◽  
Kyoji Yamamoto ◽  
...  
Keyword(s):  
Experimental Data ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Pipe Flow ◽  
Numerical Study ◽  
Circular Cross Section ◽  
Turbulence Models ◽  
Experimental Results ◽  
Helical Pipe ◽  
Wide Range

Turbulent flow through helical pipes with circular cross section is numerically investigated comparing with the experimental results obtained by our team. Numerical calculations are carried out for two helical circular pipes having different pitches and the same nondimensional curvature δ (=0.1) over a wide range of the Reynolds number from 3000 to 21,000 for torsion parameter β (=torsion /2δ  = 0.02 and 0.45). We numerically obtained the secondary flow, the axial flow and the intensity of the turbulent kinetic energy by use of three turbulence models incorporated in OpenFOAM. We found that the change to fully developed turbulence is identified by comparing experimental data with the results of numerical simulations using turbulence models. We also found that renormalization group (RNG) k−ε turbulence model can predict excellently the fully developed turbulent flow with comparison to the experimental data. It is found that the momentum transfer due to turbulence dominates the secondary flow pattern of the turbulent helical pipe flow. It is interesting that torsion effect is more remarkable for turbulent flows than laminar flows.

scholarly journals Steady and unsteady flow of non-newtonian fluid in curved pipe with triangular

2006 ◽  
Vol 3 (3) ◽  
pp. 470-480
Author(s):  
Baghdad Science Journal
Keyword(s):  
Unsteady Flow ◽  
Pressure Gradient ◽  
Secondary Flow ◽  
Cross Section ◽  
Numerical Study ◽  
Equations Of Motion ◽  
Curved Pipe ◽  
First Case ◽  
Stable Flow ◽  
Flow Cross

This paper deals with numerical study of the flow of stable and fluid Allamstqr Aniotina in an area surrounded by a right-angled triangle has touched particularly valuable secondary flow cross section resulting from the pressure gradient In the first case was analyzed stable flow where he found that the equations of motion that describe the movement of the fluid

Mixing by Time-Dependent Orbits in Spatiotemporal Chaotic Advection

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Mohammad Karami ◽  
Ebrahim Shirani ◽  
Mojtaba Jarrahi ◽  
Hassan Peerhossaini
Keyword(s):  
Secondary Flow ◽  
Lyapunov Exponents ◽  
Amplitude Ratio ◽  
Flow Patterns ◽  
Chaotic Advection ◽  
Mixing Enhancement ◽  
Flow Pulsation ◽  
Mean Flow ◽  
Homoclinic Connections ◽  
Vorticity Vector

The simultaneous effects of flow pulsation and geometrical perturbation on laminar mixing in curved ducts have been numerically studied by three different metrics: analysis of the secondary flow patterns, Lyapunov exponents and vorticity vector analysis. The mixer that creates the flow pulsation and geometrical perturbations in these simulations is a twisted duct consisting of three bends; the angle between the curvature planes of successive bends is 90 deg. Both steady and pulsating flows are considered. In the steady case, analysis of secondary flow patterns showed that homoclinic connections appear and become prominent at large Reynolds numbers. In the pulsatile flow, homoclinic and heteroclinic connections appear by increasing β, the ratio of the peak oscillatory velocity component of the mean flow velocity. Moreover, sharp variations in the secondary flow structure are observed over an oscillation cycle for high values of β. These variations are reduced and the homoclinic connections disappear at high Womersley numbers. We show that small and moderate values of the Womersley number (6 ≤ α ≤ 10) and high values of velocity amplitude ratio (β ≥ 2) provide a better mixing than that in the steady flow. These results correlate closely with those obtained using two other metrics, analysis of the Lyapunov exponents and vorticity vector. It is shown that the increase in the Lyapunov exponents, and thus mixing enhancement, is due to the formation of homoclinic and heteroclinic connections.

Mixing Enhancement in a Chaotic Micromixer Using Pulsating Flow

2014 ◽  
Author(s):  
Mohammad Karami ◽  
Mojtaba Jarrahi ◽  
Ebrahim Shirani ◽  
Hassan Peerhossaini
Keyword(s):  
Reynolds Number ◽  
Lyapunov Exponent ◽  
Steady Flow ◽  
Concentration Distribution ◽  
Pulsating Flow ◽  
Chaotic Advection ◽  
Mixing Enhancement ◽  
Mean Flow ◽  
Number Range ◽  
Velocity Amplitude

This study determines the simultaneous effects of spatial disturbance and flow pulsation on micromixing by using three different metrics: concentration distribution, Lyapunov exponent and axial vorticity. Numerical simulations are performed for both steady and pulsating flows through a microchannel made up of C-curved repeating units. Moreover, a straight microchannel is analyzed to compare the effects of chaotic advection and molecular diffusion, the main mechanisms of transverse mixing in the chaotic and straight mixer respectively. Simulations are carried out in the steady flow for the Reynolds number range 1≤Re≤50 and in the pulsating flow for velocity amplitude ratios 1≤β≤2.5, and the ratio of the peak oscillatory velocity component to the mean flow velocity, Strouhal numbers 0.1≤St≤0.5. It was found that chaotic advection improves mixing without significant increase in pressure drop. The analysis of concentration distribution implied that full mixing occurs after Reynolds number 50 in the steady flow. When the flow is pulsatile, small and moderate values of the Strouhal number (0.1≤St≤0.3) and high values of velocity amplitude ratio (β ≥ 2) are favorable conditions for mixing enhancement. Moreover, mixing has an oscillating trend along the microchannel due to the coexistence of regular and chaotic zones in the fluid. These results correlate closely with those obtained using two other metrics, analysis of the Lyapunov exponent and axial vorticity.

Secondary Flow Velocity Field in Laminar Pulsating Flow Through Curved Pipes: PIV Measurements

2009 ◽  
Author(s):  
Mojtaba Jarrahi ◽  
Cathy Castelain ◽  
Hassan Peerhossaini
Keyword(s):  
Secondary Flow ◽  
Oscillation Period ◽  
Pulsating Flow ◽  
Transverse Strain ◽  
Piv Measurements ◽  
Curved Pipe ◽  
Transverse Mixing ◽  
Curved Pipes ◽  
Flow Through ◽  
Transverse Strains

Effects of different parameters on the secondary flow pattern have been studied experimentally by particle image velocimetry (PIV) for a developing laminar pulsating flow through a circular curved pipe. The curvature ratio is η = rc/r0 = 11 and the curvature angle is 90°. As different secondary flow patterns formed by oscillation cause different transverse mixings, the enhancement of transverse mixing is investigated here. A T-shaped structure installed downstream of the curved pipe allowed PIV measurements obviating light diffraction effects. From knowledge of the velocity components of the secondary flow, the variation in axial vorticity (ξ) and transverse strain (ε) were calculated. The experiments were carried out for the range of stationary Reynolds numbers 420≤Rest≤1000 (corresponding to Dean numbers 126.6≤Dn≤301.51), velocity component ratios 1≤(β = Umax,osc/Um,st)≤4 and frequency parameters 8.37&lt;(α = r0(ω/v)0.5)&lt;24.5. To guarantee being in the laminar regime, the higher values of β (β = 3 and 4) were studied just for Rest = 420. The effects of each parameter ((Rest, β and α) on transverse mixing are discussed by comparing the dimensionless vorticities (|ζP|/|ζS|) and dimensionless transverse strains (|εP|/|εS|) during a complete oscillation period.

Calculations of a Curved-Pipe Flow Using Reynolds Stress Closure

1991 ◽  
Vol 205 (4) ◽  
pp. 231-244 ◽  
Author(s):  
Y G Lai ◽  
R M C So ◽  
M Anwer ◽  
B C Hwang
Keyword(s):  
Secondary Flow ◽  
Reynolds Stress ◽  
Pipe Flow ◽  
Wall Region ◽  
Sudden Increase ◽  
Normal Stresses ◽  
Mean Flow ◽  
Flow Measurements ◽  
Curved Pipe ◽  
Near Wall

It has been observed that as a fully developed turbulent flow enters a curved bend the anisotropy of the normal stresses near the outer bend (furthest from the centre of the bend curvature) increases. According to the arguments of vorticity generation, a sudden increase in the anisotropy of the normal stresses may lead to the formation of a secondary flow of the second kind. If this secondary motion is to be calculated, then a near-wall Reynolds stress closure that can mimic the anisotropic turbulence behaviour near a wall has to be used. This study presents the results of just such an attempt. In addition, two high Reynolds number closures assuming wall functions in the near-wall region are tested for their ability to replicate the behaviour of the normal stresses in a curved-pipe flow. These two closures differ in their modelling of the pressure-strain terms. Consequently, the effects of near-wall and pressure-strain modelling on curved-pipe flow calculations can be examined. Comparisons are also made with recent curved-pipe flow measurements. The results show that pressure-strain modelling alone is not sufficient to predict the rapid rise of the anisotropy of the normal stresses near the outer bend, and hence the formation of the secondary flow of the second kind. Overall, the near-wall Reynolds stress closure gives a more accurate prediction of the measured mean flow and turbulence statistics, and a realistic calculation of the secondary flow of the second kind near the outer bend.

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

2010 ◽  
Vol 50 (6) ◽  
pp. 1539-1558 ◽  
Author(s):  
Mojtaba Jarrahi ◽  
Cathy Castelain ◽  
Hassan Peerhossaini
Keyword(s):  
Secondary Flow ◽  
Flow Patterns ◽  
Pulsating Flow ◽  
Curved Pipe ◽  
Flow Through
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