scholarly journals Vortex dynamics under pulsatile flow in axisymmetric constricted tubes

2020 ◽  
Vol 12 ◽  
pp. 120002
Author(s):  
Nicasio Barrere ◽  
Javier Brum ◽  
Alexandre L'her ◽  
Gustavo L. Sarasúa ◽  
Cecilia Cabeza
Keyword(s):  
Flow Pattern ◽  
Pulsatile Flow ◽  
Scaling Law ◽  
Transport Processes ◽  
Turbulent Regime ◽  
Dimensionless Variable ◽  
Image Velocimetry ◽  
Pulsatile Flows ◽  
Rigid Model

Improved understanding of how vortices develop and propagate under pulsatile flow can shed important light on the mixing and transport processes occurring in such systems, including the transition to turbulent regime. For example, the characterization of pulsatile flows in obstructed artery models serves to encourage research into flow-induced phenomena associated with changes in morphology, blood viscosity, wall elasticity and flow rate. In this work, an axisymmetric rigid model was used to study the behaviour of the flow pattern with varying degrees constriction  ($d_0$) and mean Reynolds ($\bar{Re}$) and Womersley numbers ($\alpha$). Velocity fields were obtained experimentally using Digital Particle Image Velocimetry and generated numerically. For the acquisition of data, $\bar{Re}$ was varied from 385 to 2044, $d_0$ was 1.0 cm and 1.6 cm, and $\alpha$ was varied from 17 to 33 in the experiments and from 24 to 50 in the numerical simulations. Results for the Reynolds number considered showed that the flow pattern consisted of two main structures: a central jet around the tube axis and a recirculation zone adjacent to the inner wall of the tube, where vortices shed. Using the vorticity fields, the trajectory of vortices was tracked and their displacement over their lifetime calculated. The analysis led to a scaling law equation for maximum vortex displacement as a function of a dimensionless variable dependent on the system parameters Re and $\alpha$.

scholarly journals TR-PIV in highly pulsatile flow: pulsation frequency and wake dynamics case study

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Ian A. Carr ◽  
Michael W. Plesniak
Keyword(s):  
Pulsatile Flow ◽  
High Frequency ◽  
Dynamic Range ◽  
Low Frequency ◽  
Pulsation Frequency ◽  
Time Resolved ◽  
Image Velocimetry ◽  
Pulsatile Flows ◽  
Conceptual Overview

Experimental study of highly pulsatile flows presents a number of challenges, primarily the inherently large dynamic range of velocities. Herein, we use time-resolved particle image velocimetry processed with a technique known as pyramid sum-of-correlation to study highly pulsatile flow around a surface-mounted hemisphere. The frequency of pulsation is varied from low- frequency, quasi-steady pulsation to high frequency pulsation. We present a conceptual overview of the wake regimes observed and compare the flow physics of the high-frequency case to that of a vortex ring produced by a single impulse of fluid.

Development of a prototype for modelling soil–pipe interaction and its application for predicting uplift resistance to buried pipe movements in sand

2018 ◽  
Vol 55 (10) ◽  
pp. 1451-1474 ◽  
Author(s):  
Yousef Ansari ◽  
George Kouretzis ◽  
Scott W. Sloan
Keyword(s):  
Scale Effects ◽  
Reaction Force ◽  
Failure Surface ◽  
Relative Displacement ◽  
Published Data ◽  
Buried Pipe ◽  
Image Velocimetry ◽  
Close Range ◽  
Uplift Resistance

This paper presents a testing rig for measuring the reactions on rigid pipes buried in sand during episodes of relative displacement. Following a detailed presentation of the 1g prototype, the test preparation procedure, and the characterization of the test sand’s shear strength and dilation potential under the low confining stresses pertinent to the problem, the paper focuses on the workflow devised to obtain accurate measurements of friction and arching effects, and accordingly normalize them to account for scale (stress level) effects. Emphasis is put on demonstrating the effectiveness of the sand deposition method for accurately controlling the density of the sample, and on quantitatively assessing its uniformity. Measurements obtained during a series of uplift tests, including reaction force – pipe displacement curves and images of the developing failure surface, facilitated by particle image velocimetry and close-range photogrammetry techniques, are compared against published data and analytical methods. The results lead to the development of a new simplified formula for calculating the uplift resistance to buried pipe movements in sand: capable of accounting for scale effects, yet simple enough to be used for the analysis of pipes in practice.

scholarly journals Turbulent drag in a rotating frame

2016 ◽  
Vol 794 ◽  
Author(s):  
Antoine Campagne ◽  
Nathanaël Machicoane ◽  
Basile Gallet ◽  
Pierre-Philippe Cortet ◽  
Frédéric Moisy
Keyword(s):  
Large Scale ◽  
Scaling Law ◽  
Stereoscopic Particle Image Velocimetry ◽  
Turbulence Theory ◽  
Water Tank ◽  
Wave Interactions ◽  
Turbulent Drag ◽  
Image Velocimetry ◽  
Weak Turbulence Theory ◽  
Large Scale Flow

What is the turbulent drag force experienced by an object moving in a rotating fluid? This open and fundamental question can be addressed by measuring the torque needed to drive an impeller at a constant angular velocity ${\it\omega}$ in a water tank mounted on a platform rotating at a rate ${\it\Omega}$. We report a dramatic reduction in drag as ${\it\Omega}$ increases, down to values as low as 12 % of the non-rotating drag. At small Rossby number $Ro={\it\omega}/{\it\Omega}$, the decrease in the drag coefficient $K$ follows the approximate scaling law $K\sim Ro$, which is predicted in the framework of nonlinear inertial-wave interactions and weak-turbulence theory. However, stereoscopic particle image velocimetry measurements indicate that this drag reduction instead originates from a weakening of the turbulence intensity in line with the two-dimensionalization of the large-scale flow.

A particle image velocimetry study on the pulsatile flow characteristics in straight tubes with an asymmetric bulge

2000 ◽  
Vol 214 (5) ◽  
pp. 655-671 ◽  
Author(s):  
S C M Yu ◽  
J B Zhao
Keyword(s):  
Particle Image Velocimetry ◽  
Steady Flow ◽  
Pulsatile Flow ◽  
Flow Condition ◽  
Particle Image ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Flow Conditions ◽  
Image Velocimetry

Flow characteristics in straight tubes with an asymmetric bulge have been investigated using particle image velocimetry (PIV) over a range of Reynolds numbers from 600 to 1200 and at a Womersley number of 22. A mixture of glycerine and water (approximately 40:60 by volume) was used as the working fluid. The study was carried out because of their relevance in some aspects of physiological flows, such as arterial flow through a sidewall aneurysm. Results for both steady and pulsatile flow conditions were obtained. It was found that at a steady flow condition, a weak recirculating vortex formed inside the bulge. The recirculation became stronger at higher Reynolds numbers but weaker at larger bulge sizes. The centre of the vortex was located close to the distal neck. At pulsatile flow conditions, the vortex appeared and disappeared at different phases of the cycle, and the sequence was only punctuated by strong forward flow behaviour (near the peak flow condition). In particular, strong flow interactions between the parent tube and the bulge were observed during the deceleration phase. Stents and springs were used to dampen the flow movement inside the bulge. It was found that the recirculation vortex could be eliminated completely in steady flow conditions using both devices. However, under pulsatile flow conditions, flow velocities inside the bulge could not be suppressed completely by both devices, but could be reduced by more than 80 per cent.

Experimental Characterization of a Swirl Stabilized MGT Combustor

2015 ◽  
Author(s):  
T. O. Monz ◽  
M. Stöhr ◽  
W. O’Loughlin ◽  
J. Zanger ◽  
M. Hohloch ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow Pattern ◽  
Flame Stabilization ◽  
Main Stage ◽  
Exhaust Gas ◽  
Test Rig ◽  
Gas Emissions ◽  
Preheating Temperature ◽  
Exhaust Gas Emissions

A swirl stabilized MGT combustor (Turbec T100) was operated with natural gas and was experimentally characterized in two test rigs, a pressurized and optically accessible MGT test rig and an atmospheric combustor test rig. For the detailed characterization of the combustion processes, planar OH-PLIF and simultaneous 3D-stereo PIV measurements were performed in the atmospheric combustor test rig. Flow fields, reaction zones and exhaust gas emissions are reported for a range of pressure scaled MGT load points. Parameter studies on combustor inlet conditions (e.g. air preheating temperature, air and fuel mass flow rates and fuel split) were conducted in the atmospheric combustor test rig. From the parameters studies the fuel split between the pilot and the main stage and the air preheating temperature were found to have the biggest impact on the flame shape, flame stabilization and exhaust gas emissions. The measurements of the ATM test rig are compared with measurements of the pressurized MGT test rig with and without an optically accessible combustion chamber. Opened and closed conical flame and flow pattern were found in both test rigs. Reasons for the two flame and flow pattern are supposed to be the interaction of pilot stage combustion and flow field and the interaction of the dilution air with the combustion and the flow field. The results are discussed and compared with repect to a transferability of combustion characteristics from the ATM test rig to the MGT test rigs.

scholarly journals Flow-Pattern Characterization of Biphasic Electrochemical Cells by Magnetic Resonance Imaging under Forced Hydrodynamic Conditions

ChemPhysChem ◽  
2017 ◽  
Vol 18 (23) ◽  
pp. 3469-3477 ◽  
Author(s):  
María R. Serial ◽  
Manuel I. Velasco ◽  
Emilia V. Silletta ◽  
Franco M. Zanotto ◽  
Sergio A. Dassie ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Flow Pattern ◽  
Electrochemical Cells ◽  
Hydrodynamic Conditions ◽  
Resonance Imaging

scholarly journals A MONTE-CARLO MODEL FOR CAISSON OVERTURNING BY TSUNAMIS

2020 ◽  
pp. 1
Author(s):  
Jennifer L. Irish ◽  
Robert Weiss ◽  
Beverly Goodman-Tchernov
Keyword(s):  
Monte Carlo ◽  
Scaling Law ◽  
Monte Carlo Model ◽  
Community Resilience ◽  
Coastal Inundation ◽  
Hazard Exposure ◽  
Hydrodynamic Loading ◽  
Robust Planning

Robust planning, engineering, and design in regions exposed to coastal inundation and wave extremes are critically important for ensuring economic and community resilience. To address this need, the profession is moving toward multi-faceted, risk-based approaches based on probabilistic hazard exposure that account for uncertainty. Herein, a Monte-Carlo model for sliding and overturning of caissons under extreme hydrodynamic loading is presented. The model may be used to support risk-based analyses during caisson design as well as in the characterization of inundation extremes from contemporary hazard reconnaissance and from the geological and archaeological records. Herein, model applications are presented (1) to characterize the 2nd century AD Mediterranean tsunami that damaged the ancient harbor of Caesarea, Israel and (2) to develop a scaling law for overturning.

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