Viscoelastic flow in a curved duct with rectangular cross section over a wide range of Dean number

2021 ◽  
Vol 33 (3) ◽  
pp. 033101
Author(s):  
Xuyang Sun ◽  
Shaowei Wang ◽  
Moli Zhao
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Viscoelastic Flow ◽  
Dean Number ◽  
Curved Duct ◽  
Wide Range

Flow Instability in a Curved Duct of Rectangular Cross Section

1992 ◽  
Vol 114 (4) ◽  
pp. 585-592 ◽  
Author(s):  
A. Belaidi ◽  
M. W. Johnson ◽  
J. A. C. Humphrey
Keyword(s):  
Cross Section ◽  
Flow Instability ◽  
Rectangular Cross Section ◽  
Symmetry Plane ◽  
Side Wall ◽  
Secondary Flows ◽  
Bend Angle ◽  
Dean Number ◽  
Curved Duct ◽  
Time Histories

An experimental investigation has been carried out in a curved duct of rectangular cross section in order to study the development of flow instability in such geometries. Hot wire anemometry was used to obtain detailed measurements of velocity on the symmetry plane of the duct for different curvature ratios. As the duct Dean number is increased, a centrifugal instability develops and the Dean vortices are seen to oscillate along the inner wall. To understand the contribution of these vortices to the laminar-turbulent transition, time histories and spectra of the flow were taken on the symmetry plane of the duct for different Reynolds numbers. These data reveal a time-periodic motion along the inner wall where the secondary flows originating from the side wall boundary layers collide. The bend angle where this instability develops depends on the Reynolds number while the frequency of the instability depends on the curvature ratio of the bend.

scholarly journals Flow Instability through a Curved Duct with Square Cross Section

1970 ◽  
Vol 29 ◽  
pp. 71-85
Author(s):  
Rabindra Nath Mondal ◽  
Md Saidul Islam ◽  
Shah Md Tarif Hossain
Keyword(s):  
Time Evolution ◽  
Cross Section ◽  
Flow Instability ◽  
Outer Wall ◽  
Dean Number ◽  
Square Duct ◽  
Curved Duct ◽  
Wide Range ◽  
Comprehensive Survey ◽  
Steady Solutions

Flow instability through a curved duct with square cross section is numerically studied by using the spectral method over a wide range of the Dean number 0≤Dn≤5000 for the curvature δ= 0.1. A temperature difference is applied between the vertical sidewalls for the Grashof number Gr=100, where the outer wall is heated and the inner wall is cooled. After a comprehensive survey over the parametric ranges, two branches of asymmetric steady solutions are obtained by the Newton-Raphson iteration method. Linear stability of the steady solutions is then investigated. It is found that only the first branch is linearly stable in a couple of interval of Dn while the other branch is linearly unstable. Steady values of the Nusselt numbers, Nu, are also calculated for two differentially heated vertical sidewalls. When there is no stable steady solution, time evolution of Nu is obtained and it is found in the unstable region the flow undergoes through various flow instabilities, if Dn is increased. Key words: Curved square duct; Steady solutions; Time evolution; Dean number; Nusselt number GANIT J. Bangladesh Math. Soc. (ISSN 1606-3694) 29 (2009) 71-85  DOI: http://dx.doi.org/10.3329/ganit.v29i0.8517

Moderate Reynolds Number Mixing in a T-Channel

2010 ◽  
Author(s):  
Susan Thomas ◽  
Tim Ameel
Keyword(s):  
Reynolds Number ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Large Body ◽  
Experimental Studies ◽  
Numerical Work ◽  
Moderate Reynolds Number ◽  
Wide Range ◽  
Particle Imaging ◽  
Experimental Trials

An experimental investigation of water flow in a T-shaped channel with rectangular cross section (20 × 20 mm inlet ID and 20 × 40 mm outlet ID) has been conducted for a Reynolds number Re range of 56 to 422, based on inlet diameter. Dynamical conditions and the T-channel geometry of the current study are applicable to the microscale. This study supports a large body of numerical work, and resolution and the interrogation region are extended beyond previous experimental studies. Laser induced fluorescence (LIF) and particle imaging velocimetry (PIV) are used to characterize flow behaviors over the broad range of Re where realistic T-channels operate. Scalar structures previously unresolved in the literature are presented. Special attention is paid to the unsteady flow regimes that develop at moderate Re, which significantly impact mixing but are not yet well characterized or understood. An unsteady symmetric topology, which develops at higher Re and negatively impacts mixing, is presented, and mechanisms behind the wide range of mixing qualities predicted for this regime are explained. An optimal Re operating range is identified based on multiple experimental trials.

Heat Transfer for Laminar Flow in Spiral Ducts of Rectangular Cross Section

2005 ◽  
Vol 127 (3) ◽  
pp. 352-356 ◽  
Author(s):  
Michael W. Egner ◽  
Louis C. Burmeister
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Radius Of Curvature ◽  
Dean Number ◽  
Aspect Ratios ◽  
Small Pitch

Laminar flow and heat transfer in three-dimensional spiral ducts of rectangular cross section with aspect ratios of 1, 4, and 8 were determined by making use of the FLUENT computational fluid dynamics program. The peripherally averaged Nusselt number is presented as a function of distance from the inlet and of the Dean number. Fully developed values of the Nusselt number for a constant-radius-of-curvature duct, either toroidal or helical with small pitch, can be used to predict those quantities for the spiral duct in postentry regions. These results are applicable to spiral-plate heat exchangers.

scholarly journals Flow through a helical pipe with rectangular cross-section

1970 ◽  
Vol 4 (2) ◽  
pp. 99-110
Author(s):  
Md Mahmud Alam ◽  
Delowara Begum ◽  
K Yamamoto
Keyword(s):  
Aspect Ratio ◽  
Iterative Method ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Main Tool ◽  
Numerical Approach ◽  
Dean Number ◽  
Helical Pipe ◽  
Flow Through ◽  
Marine Engineering

The effects of torsion, aspect ratio and curvature on the flow in a helical pipe of rectangular cross- section are studied by introducing a non-orthogonal helical coordinate system. Spectral method is applied as main tool for numerical approach where Chebyshev polynomial is used. The numerical calculations are obtained by the iterative method. The calculations are carried out for 0≤ δ ≤0.02, 1≤ λ ≤ 2.85, 1≤ γ ≤2.4, at Dn = 50 & 100 respectively, where d is the non-dimensional curvature, l the torsion parameter, g the aspect ratio and  Dn the pressure driven parameter (Dean number).DOI: http://dx.doi.org/10.3329/jname.v4i2.991 Journal of Naval Architecture and Marine Engineering Vol.4(2) 2007 p.99-110

A Numerical Study of Dean Instability in Non-Newtonian Fluids

2005 ◽  
Vol 128 (1) ◽  
pp. 34-41 ◽  
Author(s):  
H. Fellouah ◽  
C. Castelain ◽  
A. Ould El Moctar ◽  
H. Peerhossaini
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Power Law ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Newtonian Fluids ◽  
Dean Number ◽  
Bingham Number ◽  
Curved Channels ◽  
Power Law Index

We present a numerical study of Dean instability for non-Newtonian fluids in a laminar 180deg curved-channel flow of rectangular cross section. A methodology based on the Papanastasiou model (Papanastasiou, T. C., 1987, J. Rheol., 31(5), pp. 385–404) was developed to take into account the Bingham-type rheological behavior. After validation of the numerical methodology, simulations were carried out (using FLUENT CFD code) for Newtonian and non-Newtonian fluids in curved channels of square or rectangular cross section and for a large aspect and curvature ratios. A criterion based on the axial velocity gradient was defined to detect the instability threshold. This criterion was used to optimize the grid geometry. The effects of curvature and aspect ratio on the Dean instability are studied for all fluids, Newtonian and non-Newtonian. In particular, we show that the critical value of the Dean number decreases with increasing curvature ratio. The variation of the critical Dean number with aspect ratio is less regular. The results are compared to those for Newtonian fluids to emphasize the effect of the power-law index and the Bingham number. The onset of Dean instability is delayed with increasing power-law index. The same delay is observed in Bingham fluids when the Bingham number is increased.

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