Instability of a Curved Pipe Flow With a Sudden Expansion

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Michael Shusser ◽  
Artyom Ramus ◽  
Oleg Gendelman
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Oscillatory Flow ◽  
Outer Wall ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Straight Pipe ◽  
Periodic Oscillations ◽  
Curved Pipe ◽  
Flow Variables

Numerical calculations of laminar flow of an incompressible fluid through an axisymmetric sudden expansion followed by a curved pipe recently done by the authors discovered an early instability of this flow for a certain expansion ratio, as it becomes unsteady with periodic oscillations of the flow variables at a Reynolds number when both curved pipe flow and flow in a straight pipe with an axisymmetric sudden expansion remain stable. This study describes in detail the created oscillatory flow and suggests that the early instability of the ratio 3 flow could be caused by the higher velocity gradient near the outer wall of the bend.

Flow in a Curved Pipe With a Sudden Expansion

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Michael Shusser ◽  
Artyom Ramus ◽  
Oleg Gendelman
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Vortex Pair ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Straight Pipe ◽  
Curved Pipe ◽  
Recirculation Flow ◽  
Recirculating Flow ◽  
Steady Laminar

This study considers a combination of two well studied flows: the flow in a curved pipe and the flow in a straight pipe with a sudden expansion. Steady laminar flow of an incompressible fluid through an axisymmetric sudden expansion followed by a curved pipe was investigated numerically. The influence of the expansion ratio and the Reynolds number on the vortex pair in the bend and on the recirculating flow caused by the sudden expansion was studied. A correlation for the length of the recirculation flow was obtained.

Bifurcation Characteristics of Flows in Rectangular Sudden Expansion Channels

2005 ◽  
Author(s):  
Francine Battaglia ◽  
George Papadopoulos
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Critical Reynolds Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Two Dimensional ◽  
Effective Expansion ◽  
Three Dimensional Simulations

The effect of three-dimensionality on low Reynolds number flows past a symmetric sudden expansion in a channel was investigated. The geometric expansion ratio of in the current study was 2:1 and the aspect ratio was 6:1. Both experimental velocity measurements and two- and three-dimensional simulations for the flow along the centerplane of the rectangular duct are presented for Reynolds numbers in the range of 150 to 600. Comparison of the two-dimensional simulations with the experiments revealed that the simulations fail to capture completely the total expansion effect on the flow, which couples both geometric and hydrodynamic effects. To properly do so requires the definition of an effective expansion ratio, which is the ratio of the downstream and upstream hydraulic diameters and is therefore a function of both the expansion and aspect ratios. When the two-dimensional geometry was consistent with the effective expansion ratio, the new results agreed well with the three-dimensional simulations and the experiments. Furthermore, in the range of Reynolds numbers investigated, the laminar flow through the expansion underwent a symmetry-breaking bifurcation. The critical Reynolds number evaluated from the experiments and the simulations was compared to other values reported in the literature. Overall, side-wall proximity was found to enhance flow stability, helping to sustain laminar flow symmetry to higher Reynolds numbers in comparison to nominally two-dimensional double-expansion geometries. Lastly, and most importantly, when the logarithm of the critical Reynolds number from all these studies was plotted against the reciprocal of the effective expansion ratio, a linear trend emerged that uniquely captured the bifurcation dynamics of all symmetric double-sided planar expansions.

Analysis of the Fluid Flow in 3D Symmetric Enlarged Channel

2015 ◽  
Vol 813-814 ◽  
pp. 652-657
Author(s):  
Seranthian Ramanathan ◽  
M.R. Thansekhar ◽  
P. Rajesh Kanna ◽  
S. Shankara Narayanan
Keyword(s):  
Reynolds Number ◽  
Fluid Flow ◽  
Software Package ◽  
Critical Reynolds Number ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
3 Dimensional ◽  
Ansys Workbench

A 3-Dimensional fluid flow over the sudden expansion region of a horizontal duct for various Reynolds numbers have been studied by using the CFD Software package ANSYS Workbench Fluent v 13.0. The expansion ratio and aspect ratio for the sudden expansion are taken as 2.5 and 4 respectively. This work deals with the finding of critical Reynolds number for a fluid and also the length of re-attachments on stepped walls at various Reynolds numbers for the same fluid. The simulation is carried out in sudden expansion for Reynolds number ranging from 200 to 4000. The variations of local Nusselt number along the stepped walls of the sudden expansion are presented with the heat flux of 35 W/m2 on the stepped walls. Also, the plots of pressure coefficient (Cp) along the stepped walls for different Reynolds numbers are presented in this work.

scholarly journals Augmented of turbulent heat transfer in an annular pipe with abrupt expansion

2016 ◽  
Vol 20 (5) ◽  
pp. 1621-1632 ◽  
Author(s):  
Hussein Togun ◽  
Tuqa Abdulrazzaq ◽  
Salim Kazi ◽  
Ahmad Badarudin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Surface Temperature ◽  
Local Nusselt Number ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Inner Diameter ◽  
Annular Pipe

This paper presents a study of heat transfer to turbulent air flow in the abrupt axisymmetric expansion of an annular pipe. The experimental investigations were performed in the Reynolds number range from 5000 to 30000, the heat flux varied from 1000 to 4000 W/m2, and the expansion ratio was maintained at D/d=1, 1.25, 1.67 and 2. The sudden expansion was created by changing the inner diameter of the entrance pipe to an annular passage. The outer diameter of the inner pipe and the inner diameter of the outer pipe are 2.5 and 10 cm, respectively, where both of the pipes are subjected to uniform heat flux. The distribution of the surface temperature of the test pipe and the local Nusselt number are presented in this investigation. Due to sudden expansion in the cross section of the annular pipe, a separation flow was created, which enhanced the heat transfer. The reduction of the surface temperature on the outer and inner pipes increased with the increase of the expansion ratio and the Reynolds number, and increased with the decrease of the heat flux to the annular pipe. The peak of the local Nusselt number was between 1.64 and 1.7 of the outer and inner pipes for Reynolds numbers varied from 5000 to 30000, and the increase of the local Nusselt number represented the augmentation of the heat transfer rate in the sudden expansion of the annular pipe. This research also showed a maximum heat transfer enhancement of 63-78% for the outer and inner pipes at an expansion ratio of D/d=2 at a Re=30000 and a heat flux of 4000W/m2.

A Numerical Investigation for Curved Pipe Flow at High Reynolds Number

1983 ◽  
Vol 50 (2) ◽  
pp. 239-243 ◽  
Author(s):  
M. Holt ◽  
W.-S. Yeung
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
High Reynolds Number ◽  
Mixed Boundary ◽  
Three Dimensional ◽  
Mixed Boundary Conditions ◽  
Curved Pipe ◽  
Efficient Scheme ◽  
High Reynolds ◽  
Considerable Detail

A numerical scheme for solving the curved pipe flow at high Reynolds number is presented in considerable detail. This paper complements an earlier paper presenting mainly numerical results. An efficient scheme based on the conventional Telenin method is developed to solve the general three-dimensional Laplace equation subject to Dirichlet, Neumann, or mixed boundary conditions.

The effect of expansion ratio on the critical Reynolds number in single fracture flow with sudden expansion

2015 ◽  
Vol 30 (11) ◽  
pp. 1718-1726 ◽  
Author(s):  
Jiazhong Qian ◽  
Lei Ma ◽  
Hongbin Zhan ◽  
Qiankun Luo ◽  
Xiao Wang ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Single Fracture ◽  
Fracture Flow

scholarly journals The criterion for turbulence in curved pipes

1929 ◽  
Vol 124 (794) ◽  
pp. 243-249 ◽  
Keyword(s):  
Reynolds Number ◽  
Cross Section ◽  
Small Hole ◽  
Stream Line ◽  
Straight Pipe ◽  
Curved Pipe ◽  
Curved Pipes ◽  
The Cross

Summary .—Experiments are described in which coloured fluid is introduced through a small hole in the side of a glass helix through which water is running. The conclusion reached by Mr. C. M. White, as a result of resistance measurements, that a higher speed of flow is necessary to maintain turbulence in a curved pipe than in a straight one, is verified directly. In a pipe bent into a helix the diameter of which was 18 times that of the cross-section, steady stream-line motion persisted up to a Reynolds number, 5830, i. e ., 2·8 times Reynolds' criterion for a straight pipe. This occurred in spite of the fact that the flow was highly turbulent on entering the helix.

Bifurcation Characteristics of Flows in Rectangular Sudden Expansion Channels

2005 ◽  
Vol 128 (4) ◽  
pp. 671-679 ◽  
Author(s):  
Francine Battaglia ◽  
George Papadopoulos
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Critical Reynolds Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Two Dimensional ◽  
Effective Expansion ◽  
Three Dimensional Simulations

The effect of three dimensionality on low Reynolds number flows past a symmetric sudden expansion in a channel was investigated. The geometric expansion ratio in the current study was 2:1 and the aspect ratio was 6:1. Both experimental velocity measurements and two- and three-dimensional simulations for the flow along the centerplane of the rectangular duct are presented for Reynolds numbers in the range of 150 to 600. Comparison of the two-dimensional simulations with the experiments revealed that the simulations failed to capture completely the total expansion effect on the flow, which is influenced by both geometric and hydrodynamic effects. To properly do so requires the definition of an effective expansion ratio, which is the ratio of the downstream and upstream hydraulic diameters and is therefore a function of both the expansion and aspect ratios. When two-dimensional simulations were performed using the effective expansion ratio, the new results agreed well with the three-dimensional simulations and the experiments. Furthermore, in the range of Reynolds numbers investigated, the laminar flow through the expansion underwent a symmetry-breaking bifurcation. The critical Reynolds number evaluated from the experiments and the simulations were compared to other values reported in the literature. Overall, side-wall proximity was found to enhance flow stability, thus sustaining laminar flow symmetry to higher Reynolds numbers. Last, and most important, when the logarithm of the critical Reynolds number was plotted against the reciprocal of the effective expansion ratio, a linear trend emerged that uniquely captured the bifurcation dynamics of all symmetric double-sided planar expansions.

Maximum Air Suction Into a Louvered Funnel Through Optimum Design

2012 ◽  
Vol 56 (01) ◽  
pp. 1-11 ◽  
Author(s):  
Dipti P. Mishra ◽  
Sukanta K. Dash
Keyword(s):  
Reynolds Number ◽  
Pipe Flow ◽  
Numerical Experiments ◽  
Simple Relation ◽  
Maximum Amount ◽  
Fluid Temperature ◽  
Entrance Length ◽  
A Value ◽  
Suction Rate ◽  
Flow Case

The rate of air suction into a louvered cylindrical funnel with lateral openings has been computed numerically by solving the equations of conservation of mass, momentum, and energy along with the two k-z turbulence closure equations. It was found that the air suction rate into a louvered funnel can be maximum for an optimum nozzle protrusion length into the funnel irrespective of the nozzle fluid temperature. There also exists an optimum funnel diameter (irrespective of the nozzle fluid temperature) and funnel height for which the air suction rate can be the maximum. Keeping the volume of the funnel constant, the shape of the funnel was changed to a frustum. It was found that an inverted frustum with a value of r1/r2 = 0.8 could suck the maximum amount of air compared to a cylindrical funnel of the same volume. The cylindrical sucking funnel has interestingly a much shorter entrance length compared to a simple pipe flow case with the same entrance Reynolds number. The entrance length for the sucking funnel is also a function of the nozzle fluid temperature, and a simple relation for the entrance length as a function of Ren and Tn/T∞ could also be developed for a sucking funnel. Numerical experiments were done for an inclined funnel to compute the mass suction into it. It was found that for Gr/Re2 ≤ 0.4 (where Gr is the Grashof number and Re is the Reynolds number) given by the funnel inclination had no effect on the rate of mass suction while for 0.4 < Gr/Re2 < 1 the funnel inclination had marginal influence. As the value of Gr/Re2 increased beyond 1 the influence of the funnel inclination on rate of mass suction was found to be significant.

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