Investigation of Flow Structure to Prevent Thermal Fatigue in a Downward Branch Pipe With a Closed End

2017 ◽  
Author(s):  
Koji Miyoshi ◽  
Akira Nakamura
Keyword(s):  
Penetration Depth ◽  
Flow Structure ◽  
Thermal Fatigue ◽  
Branch Pipe ◽  
Swirl Flow ◽  
Main Flow ◽  
Cross Sectional ◽  
Fluctuation Range ◽  
Sectional Plane ◽  
The Cross

Many pipes branch off from the main pipes in power plants. Main flow with high velocity initiates a cavity flow in a downward branch pipe with a closed end. Hot water penetrates into the branch pipe and a thermally stratified layer forms in the branch pipe if the main flow is hot. Fluctuations of the thermally stratified layer may initiate wall temperature fluctuations and thermal fatigue cracks in the branch pipe. Penetration depth of the main flow and the fluctuation characteristics into the branch pipe with a closed end were investigated by experiments. Experiments were conducted for various inner diameters of a branch pipe and main flow velocities under room temperature conditions. Flow structure was observed by test section made of acrylic resin. A tracer method was used to measure the penetration depth of the main flow. The penetration depth of the main flow changed periodically. The maximum penetration depth of the main flow was correlated by the Reynolds number. The fluctuation range and period of the penetration depth were also investigated. Next, the flow patterns on the cross-sectional plane in the branch pipe were observed to investigate the fluctuation mechanism of penetration depth. Three flow patterns were observed on the cross-sectional plane in the branch pipe. They were flow parallel to the cross-sectional direction, flow consisting of small vortexes and large swirl flow. The generation period of the large swirl flow was nearly equal to the fluctuation period of the penetration depth. The fluctuation range of the penetration depth and the duration showed similar trends for different inner diameters of the branch pipe. These results showed that the fluctuation of the penetration depth was caused by the periodic generation of the large swirl flow.

Formation and decay of coherent structures in pipe flow

2010 ◽  
Vol 655 ◽  
pp. 258-279 ◽  
Author(s):  
JIMMY PHILIP ◽  
JACOB COHEN
Keyword(s):  
Coherent Structures ◽  
Pipe Flow ◽  
Three Dimensional ◽  
Vortex Pair ◽  
Hairpin Vortices ◽  
Cross Sectional ◽  
Instability Waves ◽  
Sectional Plane ◽  
The Cross ◽  
Three Dimensional Coordinate

Experimental investigation of the generation and decay of coherent structures, namely, streaks (accompanied by a counter-rotating vortex pair) and hairpin vortices in pipe flow, is carried out by artificial injection of continuous disturbances. Flow visualization and velocity measurements show that for small amplitudes of disturbances (v0) streaks are produced, and increasing v0 produces instability waves on the streaks, which further break down into an array of hairpin vortices. However, the streaks and hairpins decay along the downstream direction (X). In fact, the critical value of v0 required for the initiation of hairpins at a given Re (Reynolds number) varies with the streamwise distance (in contrast to the previously found scaling of v0 ~ Re−1, valid only close to the location of injection, i.e. smaller X). This is a consequence of the decay of the coherent structures in the pipe. Moreover, the hairpins have been found to decay more slowly with increasing Re. Measurements of energy in the cross-sectional plane of the pipe, and maps of disturbance velocity at various X-locations show the transient growth and decay of energy for relatively low v0. For higher v0 and Re the energy has been seen to increase continuously along the length of the pipe under observation. Owing to the increase in the cross-sectional area occupied by the disturbance along the X-direction, it is observed that energy can transiently increase even when the total disturbance magnitude is decreasing. Observing the similarity of the present work and other investigations wherein decay of turbulence in pipe flow is found, a schematic illustration of the transition surface for pipe flow on a v0−Re−X, three-dimensional coordinate system is presented.

scholarly journals A Spectral Finite Element Model for Vibration Analysis of a Beam Based on General Higher-Order Theory

2008 ◽  
Vol 15 (2) ◽  
pp. 179-192 ◽  
Author(s):  
Jiao Sujuan ◽  
Li Jun ◽  
Hua Hongxing ◽  
Shen Rongying
Keyword(s):  
Cross Section ◽  
Spectral Element ◽  
Higher Order ◽  
Cross Sectional ◽  
Elliptical Cross ◽  
Coupled Equations ◽  
Aspect Ratios ◽  
Sectional Plane ◽  
The Cross ◽  
Element Matrix

The spectral element matrix is derived for a straight and uniform beam element having an arbitrary cross-section. The general higher-order beam theory is used, which accurately accounts for the transverse shear deformation out of the cross-sectional plane and antielastic-type deformation within the cross-sectional plane. Two coupled equations of motion are derived by use of Hamilton's principle along with the full three-dimensional constitutive relations. The theoretical expressions of the spectral element matrix are formulated from the exact solutions of the coupled governing equations. The developed spectral element matrix is directly applied to calculate the exact natural frequencies and mode shapes of the illustrative examples. Numerical results of the thick isotropic beams with rectangular and elliptical cross-sections are presented for a wide variety of cross-section aspect ratios.

Influence of meniscus shape in the cross sectional plane on the knee contact mechanics

2015 ◽  
Vol 48 (8) ◽  
pp. 1356-1363 ◽  
Author(s):  
Piotr Łuczkiewicz ◽  
Karol Daszkiewicz ◽  
Wojciech Witkowski ◽  
Jacek Chróścielewski ◽  
Witold Zarzycki
Keyword(s):  
Contact Mechanics ◽  
Cross Sectional ◽  
Meniscus Shape ◽  
Sectional Plane ◽  
The Cross

scholarly journals Flush Flow Behaviour Affected by the Morphology of Intravascular Endoscope: A Numerical Simulation and Experimental Study

2021 ◽  
Vol 12 ◽  
Author(s):  
Yujie Li ◽  
Mingzi Zhang ◽  
Simon Tupin ◽  
Kohei Mitsuzuka ◽  
Toshio Nakayama ◽  
...  
Keyword(s):  
Computational Models ◽  
Volume Fraction ◽  
High Volume ◽  
Strong Impact ◽  
Cross Sectional ◽  
Injection Speed ◽  
Vascular Segment ◽  
Sectional Plane ◽  
The Cross

Background: Whilst intravascular endoscopy can be used to identify lesions and assess the deployment of endovascular devices, it requires temporary blockage of the local blood flow during observation, posing a serious risk of ischaemia.Objective: To aid the design of a novel flow-blockage-free intravascular endoscope, we explored changes in the haemodynamic behaviour of the flush flow with respect to the flow injection speed and the system design.Methods: We first constructed the computational models for three candidate endoscope designs (i.e., Model A, B, and C). Using each of the three endoscopes, flow patterns in the target vessels (straight, bent, and twisted) under three different sets of boundary conditions (i.e., injection speed of the flush flow and the background blood flowrate) were then resolved through use of computational fluid dynamics and in vitro flow experiments. The design of endoscope and its optimal operating condition were evaluated in terms of the volume fraction within the vascular segment of interest, as well as the percentage of high-volume-fraction area (PHVFA) corresponding to three cross-sectional planes distal to the microcatheter tip.Results: With a mild narrowing at the endoscope neck, Model B exhibited the highest PHVFA, irrespective of location of the cross-sectional plane, compared with Models A and C which, respectively, had no narrowing and a moderate narrowing. The greatest difference in the PHVFA between the three models was observed on the cross-sectional plane 2 mm distal to the tip of the microcatheter (Model B: 33% vs. Model A: 18%). The background blood flowrate was found to have a strong impact on the resulting volume fraction of the flush flow close to the vascular wall, with the greatest difference being 44% (Model A).Conclusion: We found that the haemodynamic performance of endoscope Model B outperformed that of Models A and C, as it generated a flush flow that occupied the largest volume within the vascular segment of interest, suggesting that the endoscope design with a diameter narrowing of 30% at the endoscope neck might yield images of a better quality.

Flow and Mixing in Rotating Zigzag Microchannel

2017 ◽  
Author(s):  
Yong Ren ◽  
Wallace Woon-Fong Leung
Keyword(s):  
Numerical Model ◽  
Cross Flow ◽  
Centrifugal Acceleration ◽  
Cross Sectional ◽  
Coriolis Acceleration ◽  
Rotation Direction ◽  
Mixing Quality ◽  
Sectional Plane ◽  
The Cross

The flow and mixing in rotating zigzag microchannel is investigated experimentally and numerically with objective of improving mixing, which is largely due to secondary or cross-flow in the cross-sectional plane of the channel and the bend connecting non-radial angled channel segments. Unlike the conventional stationary zigzag channel, crossflow in the zigzag channel is highly intensified from a combination of (a) centrifugal acceleration component in the cross-sectional plane due to the angled channel segments, (b) centrifugal acceleration generating Görtler vortices at “channel bends”, and (c) Coriolis acceleration. When the channel segment in the zigzag channel is inclined towards rotation direction (prograde), all three accelerations are aligned intensifying the crossflow; however, when it is inclined opposite to rotation (retrograde), Coriolis acceleration negates the other two accelerations reducing mixing. A numerical model has been developed accurately accounting for the interactions of throughflow, crossflow and material dispersion by diffusion and convection in a rotational platform. An experimental microfluidic platform with rotating zigzag microchannel has also been developed. Experimental results on mixing quality carried out at two rotation speeds compared well with prediction from the numerical model. The overall mixing quality of a rotating zigzag channel is much improved compared with that of a stationary zigzag channel.

scholarly journals Effect of inertial lift on a spherical particle suspended in flow through a curved duct

2019 ◽  
Vol 875 ◽  
pp. 1-43 ◽  
Author(s):  
Brendan Harding ◽  
Yvonne M. Stokes ◽  
Andrea L. Bertozzi
Keyword(s):  
Reynolds Number ◽  
Spherical Particle ◽  
Cross Section ◽  
Bend Radius ◽  
Cross Sectional ◽  
Particle Reynolds Number ◽  
Curved Duct ◽  
Sectional Plane ◽  
Flow Through ◽  
The Cross

We develop a model of the forces on a spherical particle suspended in flow through a curved duct under the assumption that the particle Reynolds number is small. This extends an asymptotic model of inertial lift force previously developed to study inertial migration in straight ducts. Of particular interest is the existence and location of stable equilibria within the cross-sectional plane towards which particles migrate. The Navier–Stokes equations determine the hydrodynamic forces acting on a particle. A leading-order model of the forces within the cross-sectional plane is obtained through the use of a rotating coordinate system and a perturbation expansion in the particle Reynolds number of the disturbance flow. We predict the behaviour of neutrally buoyant particles at low flow rates and examine the variation in focusing position with respect to particle size and bend radius, independent of the flow rate. In this regime, the lateral focusing position of particles approximately collapses with respect to a dimensionless parameter dependent on three length scales: specifically, the particle radius, duct height and duct bend radius. Additionally, a trapezoidal-shaped cross-section is considered in order to demonstrate how changes in the cross-section design influence the dynamics of particles.

On Saint-Venant’s Problem for an Inhomogeneous, Anisotropic Cylinder—Part II: Cross-Sectional Properties

2000 ◽  
Vol 68 (3) ◽  
pp. 382-391 ◽  
Author(s):  
J. B. Kosmatka ◽  
H. C. Lin ◽  
S. B. Dong
Keyword(s):  
Cross Section ◽  
Symmetry Plane ◽  
Material Symmetry ◽  
Shear Center ◽  
Cross Sectional ◽  
Mean Values ◽  
Anisotropic Cylinder ◽  
Sectional Plane ◽  
Weighted Integrals ◽  
The Cross

Cross-sectional properties of a prismatic inhomogeneous, anisotropic cylinder are determined from Saint-Venant solutions for extension-bending-torsion and flexure, whose method of construction was presented in a previous paper. The coupling of extensional, bending, and twisting deformations due to anisotropy and inhomogeneity leads to some very interesting features. Herein, it is shown that for an inhomogeneous, anisotropic cylinder whose cross-sectional plane is not a material symmetry plane, distinct modulus-weighted and compliance-weighted centroids and distinct principal bending axes are possible. A line of extension-bending centers is given on which an axial force causes extension and bending only but no twist. Two shear centers are given, one using the Griffith-Taylor definition that ignores cross-sectional warpages and the other by stipulating a zero mean rotation over the cross section. The center of twist is discussed, and this property depends on root end fixity conditions that are prescribed in terms of their mean values based on integrals over the cross section rather than by a pointwise specification. While these shear center and center of twist definitions have some rational bases, it is recognized that other definitions are possible, for example those based on modulus or compliance-weighted integrals. Two examples, an angle and a channel, both composed of a two-layer ±30 deg angle-ply composite material, illustrate the procedures for determining these cross-sectional properties.

scholarly journals A Study on the Evaluation of Flow Distribution Evenness in Parallel-Arrayed Type Low Pressure Membrane Module Piping

2021 ◽  
Vol 43 (5) ◽  
pp. 325-334
Author(s):  
SeokHyun Jang ◽  
Sukmin Yoon ◽  
Si-Yeon Kim ◽  
Young-Joo Lee ◽  
No-Suk Park
Keyword(s):  
Flow Rate ◽  
Cfd Simulation ◽  
Branch Pipe ◽  
Low Pressure ◽  
Cross Sectional Area ◽  
Membrane Module ◽  
Sectional Area ◽  
Cross Sectional ◽  
Actual Measurement ◽  
The Cross

Objectives : In this study, the degree of uniformity of the flow rate flowing into each module is measured for the external pressure typed low-pressure membrane (microfiltration) filtration process that has been actually applied to water treatment, and computational fluid dynamics (CFD) technique is used to clarify the cause and effect.Methods : Mobile ultrasonic flow meter was used to measure the flow rate flowing from the membrane module pipe to each module, and the CFD technique was used to verify this.Results and Discussion : From the results of the actual measurement using ultrasonic flowmeter and CFD simulation, it was confirmed that the outflow flow rate from the branch pipe located at the end of the header pipe was three times higher than that of the branch pipe near the inlet. The reason was that the differential pressure generated between each membrane module was higher toward the end of the header pipe.Conclusions : When the ratio of the sum of the cross-sectional area of the branch pipe and the cross-sectional area of the header pipe was reduced by about 30 times, it was confirmed that the flow rate flowing from each branch pipe to the membrane module was almost equal. Also, If the flow in the header pipe is transitional or laminar (Reynolds No. is approximately 4,000 or less), the flowrate flowing from each branch pipe to the membrane module can be more even.

scholarly journals The influence of secondary flow in a two-phase gas-solid system in straight channels with a non-circular cross-section

2016 ◽  
Vol 20 (suppl. 5) ◽  
pp. 1419-1434
Author(s):  
Sasa Milanovic ◽  
Milos Jovanovic ◽  
Boban Nikolic ◽  
Vladislav Blagojevic
Keyword(s):  
Turbulent Flow ◽  
Secondary Flow ◽  
Cross Section ◽  
Circular Cross Section ◽  
Channel Cross Section ◽  
Two Phase ◽  
Cross Sectional ◽  
Specific Flow ◽  
Sectional Plane ◽  
The Cross

The paper considers two-phase gas-solid turbulent flow of pneumatic transport in straight horizontal channels with a non-circular cross-section. During turbulent flow, a specific flow phenomenon, known as secondary flow, occurs in these channels in the cross-sectional plane. The existence of strong temperature gradients in the cross-sectional plane of the channel or the cases of curved channels result in the appearance of the secondary flow of the first kind. However, in straight channels with a non-circular cross-section, in the developed turbulent flow mode, a secondary flow, known as Prandtl?s secondary flow of the second kind, is induced. The paper presents a numerical simulation of a developed two-phase turbulent flow by using the PHOENICS 3.3.1 software package. Reynolds stress model was used to model the turbulence. The paper provides the data on the changes in turbulent stresses in the channel cross-section as well as the velocities of solid particles transported along the channel.

Experimental Investigation of Flow Field Structure in Non-Isothermal Mixing Tee

2007 ◽  
Author(s):  
Seyed Mohammad Hosseini ◽  
Kazuhisa Yuki ◽  
Hidetoshi Hashizume
Keyword(s):  
Thermal Fatigue ◽  
Velocity Fluctuation ◽  
Temperature Fluctuation ◽  
Pipe Wall ◽  
Branch Pipe ◽  
Main Flow ◽  
Turbulent Jet ◽  
Junction Area ◽  
Main Pipe ◽  
High Cycle Thermal Fatigue

T-junction is one of familiar components in the cooling system of power plants with enormous capability to high-cycle thermal fatigue. This research tries to investigate fluid mixing mechanism in non-isothermal T-junction area with 90-degree bend upstream. Classification of turbulent jet and effects of 90-degree bend were evaluated previously and re-attached jet was selected as complicated mixing structure with highest velocity fluctuation [4]. For considering the mixing mechanism of re-attached jet, T-junction area is visualized in various lateral and longitudinal sections. The measuring data show the flow of branch pipe acts as turbulent jet in finite space and interaction between the jet and main flow can create various eddies and develops high velocity fluctuation area near the main pipe wall as well as temperature fluctuation. Three regions are more affected by maximum velocity fluctuation in T-junction area near the main pipe wall; the region close to the jet surface (fluctuation mostly is caused by Kelvin-Helmholtz instability), the region above the jet and along the main flow (fluctuation mostly is caused by Karman vortex) and re-attached area (fluctuation mostly is caused by moving the jet body with pressure gradient). Finally, the re-attached area is selected as region with strongest possibility to high cycle thermal fatigue with effective velocity fluctuation on the main pipe wall above the branch nozzle as well as temperature fluctuation.

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