CFD analysis of unsteady and anisotropic turbulent flow in a circular-sectioned 90° bend pipe with and without ribs: A comparative computational study

2021 ◽  
Vol 15 (2) ◽  
pp. 7964-7982
Author(s):  
Rachid Chiremsel ◽  
Ali Fourar ◽  
Fawaz Massouh ◽  
Zakarya Chiremsel
Keyword(s):  
Turbulent Flow ◽  
Axial Velocity ◽  
Computational Study ◽  
Circular Cross Section ◽  
Maximum Velocity ◽  
Curvature Radius ◽  
Reynolds Stresses ◽  
Dean Number ◽  
Number Range ◽  
Bend Pipe

The Reynolds–averaged Navier–Stokes (RANS) equations were solved along with Reynolds stress model (RSM), to study the fully-developed unsteady and anisotropic single-phase turbulent flow in 90° bend pipe with circular cross-section. Two flow configurations are considered the first is without ribs and the second is with ribs attached to solid walls. The number of ribs is 14 ribs regularly placed along the straight pipe. The pitch ratios is 40 and the rib height e (mm) is 10% of the pipe diameter. Both bends have a curvature radius ratio, of 2.0. The solutions of these flows were obtained using the commercial CFD software Fluent at a Dean number range from 5000 to 40000. In order to validate the turbulence model, numerical simulations were compared with the existing experimental data. The results are found in good agreement with the literature data. After validation of the numerical strategy, the axial velocity distribution and the anisotropy of the Reynolds stresses at several downstream longitudinal locations were obtained in order to investigate the hydrodynamic developments of the analyzed flow. The results show that in the ribbed bend pipe, the maximum velocity value is approximately 47% higher than the corresponding upstream value but it is 9% higher in the case of the bend pipe without ribs. It was also found for both cases that the distribution of the mean axial velocity depends faintly on the Dean number. Finally, it can be seen that the analyzed flow in the bend pipe without ribs appears more anisotropic than in bend pipe with ribs.

Experimental Observations of Flow Instability in a Helical Coil (Data Bank Contribution)

1993 ◽  
Vol 115 (3) ◽  
pp. 436-443 ◽  
Author(s):  
D. R. Webster ◽  
J. A. C. Humphrey
Keyword(s):  
Cross Section ◽  
Flow Instability ◽  
Time Integration ◽  
Circular Cross Section ◽  
Frequency Doubling ◽  
Outer Wall ◽  
Data Bank ◽  
Curvature Radius ◽  
Number Range ◽  
Pipe Cross Section

Experimental observations were made for the nominally fully developed flow through a helically coiled pipe of circular cross-section with a curvature radius to pipe radius ratio Rc/a = 18.2. Laser-Doppler measurements of the instantaneous streamwise velocity, uθ, and the cross-stream circumferential velocity, uφ, components were obtained along the midplane of the pipe cross-section. The Reynolds number range explored was 3800 < Re < 10500 (890 < De < 2460) and spans the laminar and turbulent flow regimes. Time integration of the velocity records has yielded previously unavailable mean and rms velocity profiles. In the range 5060 < Re < 6330, the time records of the velocity components reveal periodic flow oscillations with St ≈ 0.25 in the inner half of the pipe cross-section while the flow near the outer wall remains steady. A frequency doubling (St ≈ 0.5) is also observed at some midplane locations. This low frequency unsteadiness is distinct from the shear-induced turbulent fluctuations produced with increasing Re first at the outer wall and later at the inner wall of the coiled pipe. Simple considerations suggest that the midplane jet in the recirculating cross-stream flow is the source of instability.

Laser anemometer study of flow development in curved circular pipes

1978 ◽  
Vol 85 (3) ◽  
pp. 497-518 ◽  
Author(s):  
Y. Agrawal ◽  
L. Talbot ◽  
K. Gong
Keyword(s):  
Axial Velocity ◽  
Three Dimensional ◽  
Quantitative Agreement ◽  
Upstream Region ◽  
Uniform Motion ◽  
Dean Number ◽  
Number Range ◽  
Curved Pipe ◽  
Laser Anemometry ◽  
Pipe Radius

An experimental investigation was carried out of the development of steady, laminar, incompressible flow of a Newtonian fluid in the entry region of a curved pipe for the entry condition of uniform motion. Two semicircular pipes of radius ratios 1/20 and 1/7 were investigated, covering a Dean number range from 138 to 679. The axial velocity and the component of secondary velocity parallel to the plane of curvature of the pipe were measured using laser anemometry. It was observed that, in the upstream region where the boundary layers are thin compared with the pipe radius, the axial velocity within the irrotational core first develops to form a vortex-like flow. In the downstream region, characterized by viscous layers of thickness comparable with the pipe radius, there appears to be three-dimensional separation at the inner wall. There is also an indication of an additional vortex structure embedded within the Dean-type secondary motion. The experimental axial velocity profiles are compared with those constructed from the theoretical analyses of Singh and Yao & Berger. The quantitative agreement between theory and experiment is found to be poor; however, some of the features observed in the experiment are in qualitative agreement with the theoretical solution of Yao & Berger.

Large Curvature Effect on Pulsatile Entrance Flow in a Curved Tube: Model Experiment Simulating Blood Flow in an Aortic Arch

1996 ◽  
Vol 118 (2) ◽  
pp. 180-186 ◽  
Author(s):  
T. Naruse ◽  
K. Tanishita
Keyword(s):  
Blood Flow ◽  
Aortic Arch ◽  
Maximum Velocity ◽  
Curvature Radius ◽  
Wall Region ◽  
Dean Number ◽  
Large Curvature ◽  
Curved Tube ◽  
Wall Shear ◽  
Entrance Flow

We measured the velocity profiles of pulsatile entrance flow in a strongly curved tube using a laser-Doppler anemometer in order to simulate blood flow in the aortic arch under various conditions, i.e., a ratio of tube to curvature radius of 1/3, Womersley parameters of 12 and 18, and peak Dean number up to 1200. Axial isovelocity contours of the cross-section showed the potential vortex to be near the entrance, and with the maximum velocity there being skewed towards the inner wall; thereafter shifting towards the outer wall. During the deceleration phase, reverse axial flow occurred near the inner wall, and a region of this flow extended downstream. The large curvature contributes to the enhancement of the secondary flow and flow reversal, which elevates the wall-shear stress oscillations. The location of elevated wall-shear oscillations corresponds to the vessel wall region where atherosclerotic formation frequently occurs; thereby indicating that both the large curvature and pulsatility play key roles in formation of localized atherosclerotic lesions.

Measurements and prediction of fully developed turbulent flow in an equilateral triangular duct

1978 ◽  
Vol 85 (1) ◽  
pp. 57-83 ◽  
Author(s):  
A. M. M. Aly ◽  
A. C. Trupp ◽  
A. D. Gerrard
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Pipe Flow ◽  
Axial Velocity ◽  
Reynolds Stresses ◽  
Cross Sectional ◽  
Number Range ◽  
Law Of The Wall ◽  
The Cross ◽  
Wall Shear

Fully developed air-flows through an equilateral triangular duct of 12·7 cm sides were investigated over a Reynolds number range of 53 000 to 107 000. Based on equivalent hydraulic diameter, friction factors were found to be about 6% lower than for pipe flow. Mean axial velocity distributions near the wall were describable by the inner law of the wall (when based on local wall shear stress) but the constants differ slightly from those for pipe flow. As expected, the secondary flow pattern was found to consist of six counter-rotating cells bounded by the corner bisectors. Maximum secondary velocities of about 1 ½% of the bulk velocity were observed. The effects of secondary currents were evident in the cross-sectional distributions of mean axial velocity, wall shear stress and Reynolds stresses, and very prominent in the turbulent kinetic energy distribution. For the flow prediction, the vorticity production terms were expressed by modelling the Reynolds stresses in the plane of the cross-section in terms of gradients in the mean axial velocity and a geometrically calculated turbulence length scale. The experimental and predicted characteristics of the flow are shown to be in good agreement.

Turbulent flow in smooth concentric annuli with small radius ratios

1974 ◽  
Vol 64 (2) ◽  
pp. 263-288 ◽  
Author(s):  
K. Rehme
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Turbulent Flow ◽  
Strong Influence ◽  
Maximum Velocity ◽  
Small Radius ◽  
Stress Distributions ◽  
Number Range ◽  
Fully Developed Turbulent Flow ◽  
Flow Through

Fully developed turbulent flow through three concentric annuli was investigated experimentally for a Reynolds-number rangeRe= 2 × 104−2 × 105. Measurements were made of the pressure drop, the positions of zero shear stress and maximum velocity, and the velocity distribution in annuli of radius ratios α = 0.02, 0.04 and 0.1, respectively. The results for the key problem in the flow through annuli, the position of zero shear stress, showed that this position is not coincident with the position of maximum velocity. Furthermore, the investigation showed the strong influence of spacers on the velocity and shear-stress distributions. The numerous theoretical and experimental results in the literature which are based on the coincidence of the positions of zero shear stress and maximum velocity are not in agreement with reality.

An Experimental Investigation of Turbulent Water Flow in Concentric Annulus Using Particle Image Velocimetry Technique

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
F. E. Rodriguez-Corredor ◽  
Majid Bizhani ◽  
Mohammad Ashrafuzzaman ◽  
Ergun Kuru
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Maximum Velocity ◽  
Viscous Sublayer ◽  
Reynolds Stresses ◽  
Flow Loop ◽  
Particle Image Velocimetry Technique ◽  
Mean Velocity ◽  
Number Range ◽  
Image Velocimetry

Fully developed turbulent flow of water through a horizontal flow loop with concentric annular geometry was investigated using high resolution particle image velocimetry (PIV). Reynolds number range varied from 17,700 to 66,900. Axial mean velocity profile was found to be following the universal wall law (u+ = y+) in the viscous sublayer (y+ < 10) and log law away from the wall (y+> 30). Radial position of zero shear stress and maximum velocity were found to be slightly different (2%). Root mean square values of velocity fluctuations velocity, Reynolds stresses, vorticity, and turbulent kinetic energy budget were also analyzed.

Analysis of Aerothermal Characteristics of Surface Micro-Structures

2017 ◽  
Author(s):  
M. Kapsis ◽  
L. He
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Computational Study ◽  
Number Range ◽  
High Loss ◽  
Turbulent Flow Regime ◽  
Roughness Elements ◽  
Element Pattern ◽  
Micro Structures

Recent advances in manufacturing technologies, such as additive manufacturing, have raised the potential of choosing surface finish pattern as a design parameter. Hence, understanding and prediction of aerothermal effects of machined micro-structures (‘machined roughness’) would be of great interest. So far, however, roughness has been largely considered as a stochastic attribute and empirically modelled. A relevant question is: if and how would shape of the machined roughness elements matter at such fine scales? In this paper, a systematic computational study has been carried out on the aerothermal behaviour and impact of some discrete micro-structures. Two shapes of micro-structure configurations are considered: hemispherical and rectangular elements for a Reynolds number range typical for those roughness elements (Re<5000). Several validation cases are studied as well as the turbulence modelling and grid sensitivities are examined to ensure the consistence of the numerical results. Furthermore, LES analyses are performed to contrast the behaviour in a well-established turbulent flow regime to a transitional one. The present results reveal a distinctive common flow pattern change (from an ‘open separation’ to a ‘reattached separation’) associated with a drastic change of drag/loss correlation from a low to a high loss regime. The results also indicate a clear dependence of drag and heat transfer characteristics on the element pattern and orientation relative to the flow. The distinctive performance correlations with Reynolds number can be affected considerably by the element shape, for both a transitional and a turbulent flow regime. The results also consistently illustrate that conventional empirical stochastic roughness parameters would be unable to predict these trends.

An Experimental Investigation of Turbulent Flow in Concentric Annulus Using Particle Image Velocimetry Technique

2012 ◽  
Author(s):  
Fabio Ernesto Rodriguez Corredor ◽  
Majid Bizhani ◽  
Mohammad Ashrafuzzaman ◽  
Ergun Kuru
Keyword(s):  
Shear Stress ◽  
Particle Image Velocimetry ◽  
Turbulent Flow ◽  
Particle Image ◽  
Maximum Velocity ◽  
Wall Region ◽  
Number Range ◽  
Concentric Annulus ◽  
Image Velocimetry ◽  
Fully Developed Turbulent Flow

Fully developed turbulent flow in a concentric annulus is encountered in many engineering problems including food, chemical as well as oil industry applications. Because of nonlinear radial variation of total shear stress with the distance from the pipe wall, the analysis for the flow in annulus is more complex than in a round tube or parallel plate channel. In this study, fully developed turbulent flow of water through a horizontal flow loop with concentric annular geometry (inner to outer pipe radius ratio = 0.4) was investigated. Reynolds number range varied from 17,700 to 66,900. Velocity near the wall region was measured using high resolution particle image velocimetry (PIV) system. Axial mean velocity profile was found to be following the universal wall law (i.e., u+ = y+) close to the wall (for y+ < 10) and log law away from the wall (y+>10). For all the cases investigated, radial positions of the maximum velocity and zero shear stress were very close to each other (± 0.5 mm). The difference between the both locations were found to be varying from 1.3 to 3.3% ( 2% on the average).

Measurements and predictions of fully developed turbulent flow in a simulated rod bundle

1982 ◽  
Vol 123 ◽  
pp. 399-423 ◽  
Author(s):  
W. J. Seale
Keyword(s):  
Reynolds Number ◽  
Axial Velocity ◽  
Friction Velocity ◽  
Reynolds Stresses ◽  
Number Range ◽  
Law Of The Wall ◽  
Rod Bundle ◽  
Friction Factors ◽  
Fully Developed Turbulent Flow ◽  
The Mean

Fully developed air flow has been investigated over a Reynolds-number range of 82800-346700 in a duct that simulates two interconnected subchannels of a rod bundle with a pitchldiameter ratio of 1.20. Based on equivalent hydraulic diameter, friction factors were found to be 2% lower than for pipe flow. Detailed measurements were made at a Reynolds number of 200000 of axial velocities, secondary velocities, and the Reynolds stresses. The distribution of axial velocity near the walls (normalized with the local friction velocity) could be expressed by an inner law of the wall for y+ up to 1500. Distributions of the normal Reynolds stresses and the mean turbulence kinetic energy were similar to those observed in a number of pipe and two-dimensional channel flows and could be correlated using the axial-velocity fluct,uations normalized with the local friction velocity. Maximum secondary velocities were about 1.5 % of the bulk axial velocity. The ‘k-ε’ turbulence model and an algebraic vorticity source for generating secondary velocities enabled the computation of axial velocities, secondary velocities, and mean turbulence kinetic energies that are in satisfactory agreement with those measured.

scholarly journals Numerical Simulation of the Coagulation Dynamics of Blood

2008 ◽  
Vol 9 (2) ◽  
pp. 83-104 ◽  
Author(s):  
T. Bodnár ◽  
A. Sequeira
Keyword(s):  
Blood Coagulation ◽  
Computational Study ◽  
Time Integration ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Clot Formation ◽  
Diffusion Reaction ◽  
Numerical Code ◽  
Injured Region ◽  
Reaction Equations

The process of platelet activation and blood coagulation is quite complex and not yet completely understood. Recently, a phenomenological meaningful model of blood coagulation and clot formation in flowing blood that extends existing models to integrate biochemical, physiological and rheological factors, has been developed. The aim of this paper is to present results from a computational study of a simplified version of this coupled fluid-biochemistry model. A generalized Newtonian model with shear-thinning viscosity has been adopted to describe the flow of blood. To simulate the biochemical changes and transport of various enzymes, proteins and platelets involved in the coagulation process, a set of coupled advection–diffusion–reaction equations is used. Three-dimensional numerical simulations are carried out for the whole model in a straight vessel with circular cross-section, using a finite volume semi-discretization in space, on structured grids, and a multistage scheme for time integration. Clot formation and growth are investigated in the vicinity of an injured region of the vessel wall. These are preliminary results aimed at showing the validation of the model and of the numerical code.

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