Measurement in the Wake Region of Two Bubbles in Close Proximity by Combined Shadow-Image and PIV Techniques

1999 ◽  
Vol 121 (1) ◽  
pp. 191-197 ◽  
Author(s):  
A. Tokuhiro ◽  
A. Fujiwara ◽  
K. Hishida ◽  
M. Maeda
Keyword(s):  
Ccd Camera ◽  
Shadow Image ◽  
Wake Flow ◽  
Air Bubbles ◽  
Velocity Measurements ◽  
Square Channel ◽  
Image Velocimetry ◽  
Close Proximity ◽  
Spatio Temporal ◽  
Two Bubbles

An experimental study on flow around two similarly-sized, adjacent air bubbles confined in a 1000 mm vertical, square channel (100 × 100 mm2) with downward flow of water was conducted. The bubbles were D = 11.7 mm in major diameter, ellipsoidal in shape (0.4 ml volume) and 12 mm apart. The Reynolds and Eo¨tvo¨s numbers were 1950 < ReD < 2250, 11 < Eo < 11.5 such that the bubbles oscillated. Velocity measurements were taken using Digital Particle Image Velocimetry, Complemented by Laser Induced Fluorescence. Simultaneously, a second CCD camera recorded the shadow image of the bubble pair’s motions. Visualization revealed that the bubbles move out of phase and do not collide nor coalesce. The velocity data revealed the dynamic interaction of two wake-flow velocity fields with a jet-like flow in-between. From the DPIV data, estimates of the vorticity, Reynolds-stress and turbulent kinetic energy (TKE) distributions confirmed the spatio-temporal nature of the flow. Details will be presented.

Comparison of Near Wake-Flow Structure Behind a Solid Cap With an Attached Bubble and a Solid Counterpart

2003 ◽  
Author(s):  
Hidekazu No ◽  
Michel Call ◽  
Akira T. Tokuhiro
Keyword(s):  
Flow Structure ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Equivalent Diameter ◽  
Velocity Measurements ◽  
Near Wake ◽  
Downward Flow ◽  
Air Bubble ◽  
Square Channel ◽  
Image Velocimetry

An experimental study was conducted on the flow structure in the near-wake of a hollow cap with an air bubble attached underneath and a solid object possessing a bubble-like shape. The objective of the study was to elucidate distinguishing wake flow characteristics of the capped bubble relative to the solid. The experiment was performed in a square channel, 80×80mm2 in cross section. The bubble and solid were separately suspended in downward flow of purified water. Both the capped bubble and the solid were ellipsoidal in shape (the cap was shaped to represent the front of an ellipsoidal bubble) and had an approximate volume of 0.8ml. The Reynolds number for the flow, based on the objects’ equivalent diameter and average downward flow velocity (U = 25cm/s), was Re ≅ 2800. Velocity measurements were taken using Particle Image Velocimetry. The obtained velocity data were analyzed to deduce vorticity, turbulent kinetic energy, production, and Reynolds stress. Graphic and numerical comparisons between the two cases were made. The results to date are discussed.

High Spatio-Temporal Resolution Digital Particle Image Velocimetry Near Compliant, Dynamically Moving Boundaries

2002 ◽  
Author(s):  
Ali Etebari ◽  
Claude Abiven ◽  
Olga Pierrakos ◽  
Pavlos P. Vlachos
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
State Of The Art ◽  
Digital Particle Image Velocimetry ◽  
Moving Boundaries ◽  
Global Flow ◽  
Velocity Measurements ◽  
Non Invasive ◽  
Image Velocimetry ◽  
Spatio Temporal

Digital Particle Image Velocimetry (DPIV) currently represents the state of the art for non-invasive global flow velocity measurements. The instantaneous velocities are determined by cross-correlating patterns of particles between consecutive images, thus mapping in space and time the velocity distribution for thousands of points in the flow field simultaneously.

scholarly journals Investigation of bubbles interaction and coalescence boiling in the boiling heat transfer process

2019 ◽  
Vol 23 (5 Part A) ◽  
pp. 2605-2611 ◽  
Author(s):  
Zhixin Zhao ◽  
Xudong Xue ◽  
Kun Wang
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Influencing Factor ◽  
Ccd Camera ◽  
Heat Transfer Process ◽  
Wake Flow ◽  
Rising Bubble ◽  
Influence Area ◽  
Two Bubbles

This paper presents a new approach to investigate the bubbles movements and their interaction in the boiling heat transfer proess. Based on the study of the wake flow of single rising bubble, the interaction of bubble pairs, such as interaction and coalescenceboiling, is experimentally and numerically simulated. The validity of the numerical simulation was verified by the experimental pictures captured by high-speed CCD camera. The wakes of two bubbles was revealed by obtatined velocity field, and the interaction between two bubbles was analyzed in fluid dynamics. The simulations shows that the coalescence of bubbles may happen when one bubble enters the wake influence area of the main bubble. The velocity vector field shows that wake flow of the bubble is the major influencing factor determining the interaction between bubbles.

Wing tip vortex control using synthetic jets

2006 ◽  
Vol 110 (1112) ◽  
pp. 673-681 ◽  
Author(s):  
P. Margaris ◽  
I. Gursul
Keyword(s):  
Synthetic Jet ◽  
Synthetic Jets ◽  
Tip Vortex ◽  
Particle Image Velocimetry System ◽  
Driving Frequency ◽  
Velocity Measurements ◽  
Vortex Control ◽  
Image Velocimetry ◽  
Wing Tip ◽  
Jet Blowing

AbstractAn experimental investigation was conducted to study the effect of synthetic jet (oscillatory, zero net mass flow jet) blowing near the wing tip, as a means of diffusing the trailing vortex. Velocity measurements were taken, using a Particle Image Velocimetry system, around the tip and in the near wake of a rectangular wing, which was equipped with several blowing slots. The effect of the synthetic jet was compared to that of a continuous jet blowing from the same configurations. The results show that the use of synthetic jet blowing is generally beneficial in diffusing the trailing vortex and comparable to the use of continuous jet. The effect was more pronounced for the highest blowing coefficient used. The driving frequency of the jet did not generally prove to be a significant parameter. Finally, the instantaneous and the phase-locked velocity measurements helped explain the different mechanisms employed by the continuous and synthetic jets in diffusing the trailing vortex.

Unsteady Hemodynamics in Intracranial Aneurysms With Varying Dome Orientations

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Abdullah Y. Usmani ◽  
K. Muralidhar
Keyword(s):  
Intracranial Aneurysm ◽  
Three Dimensional ◽  
Parent Artery ◽  
Fluid Loading ◽  
Image Velocimetry ◽  
Flow Reynolds Number ◽  
Fatal Hemorrhage ◽  
Wall Loading ◽  
Spatio Temporal ◽  
Finite Volume Simulation

Abstract Fluid loading within an intracranial aneurysm is difficult to measure but can be related to the shape of the flow passage. The outcome of excessive loading is a fatal hemorrhage, making it necessary for early diagnosis. However, arterial diseases are asymptomatic and clinical assessment is a challenge. A realistic approach to examining the severity of wall loading is from the morphology of the aneurysm itself. Accordingly, this study compares pulsatile flow (Reynolds number Re = 426, Womersley number Wo = 4.7) in three different intracranial aneurysm geometries. Specifically, the spatio-temporal movement of vortices is followed in high aspect ratio aneurysm models whose domes are inclined along with angles of 0, 45, and 90 deg relative to the plane of the parent artery. The study is based on finite volume simulation of unsteady three-dimensional flow while a limited set of particle image velocimetry experiments have been carried out. Within a pulsatile cycle, an increase in inclination (0–90 deg) is seen to shift the point of impingement from the distal end toward the aneurysmal apex. This change in flow pattern strengthens helicity, drifts vortex cores, enhances spatial displacement of the vortex, and generates skewed Dean's vortices on transverse planes. Patches of wall shear stress and wall pressure shift spatially from the distal end in models of low inclination (0–45 deg) and circumscribe the aneurysmal wall for an inclination angle of 90 deg. Accordingly, it is concluded that high angles of inclination increase rupture risks while lower inclinations are comparatively safe.

Two-Dimensional Experimental Investigation on the Effects of a Fowler Flap Gap and Overlap Size on the Wake Flow Field

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
David Demel ◽  
Mohsen Ferchichi ◽  
William D. E. Allan ◽  
Marouen Dghim
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Angle Of Attack ◽  
Wake Flow ◽  
Two Dimensional ◽  
Edge Region ◽  
Suction Surface ◽  
Trailing Edge ◽  
Piv Measurements ◽  
Image Velocimetry

This work details an experimental investigation on the effects of the variation of flap gap and overlap sizes on the flow field in the wake of a wing-section equipped with a trailing edge Fowler flap. The airfoil was based on the NACA 0014-1.10 40/1.051 profile, and the flap was deployed with 40 deg deflection angle. Two-dimensional (2D) particle image velocimetry (PIV) measurements of the flow field in the vicinity of the main wing trailing edge and the flap region were performed for the optimal flap gap and overlap, as well as for flap gap and overlap increases of 2% and 4% chord beyond optimal, at angles of attack of 0 deg, 10 deg, and 12 deg. For all the configurations investigated, the flow over the flap was found to be fully stalled. At zero angle of attack, increasing the flap gap size was found to have minor effects on the flow field but increased flap overlap resulted in misalignment between the main wing boundary layer (BL) flow and the slot flow that forced the flow in the trailing edge region of the main wing to separate. When the angle of attack was increased to near stall conditions (at angle of attack of 12 deg), increasing the flap gap was found to energize and improve the flow in the trailing edge region of the main wing, whereas increased flap overlap further promoted flow separation on the main wing suction surface possibly steering the wing into stall.

Free surface over a horizontal shear layer: vorticity generation and air entrainment mechanisms

2017 ◽  
Vol 813 ◽  
pp. 1007-1044 ◽  
Author(s):  
Matthieu A. André ◽  
Philippe M. Bardet
Keyword(s):  
Free Surface ◽  
Shear Layer ◽  
Air Entrainment ◽  
Horizontal Shear ◽  
Vortex Instability ◽  
Image Velocimetry ◽  
Planar Laser ◽  
Spatio Temporal ◽  
The Waves

Two air entrainment mechanisms driven by vortex instability are reported in the unstable relaxation of a horizontal shear layer below a free surface. This flow is experimentally investigated by means of planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) coupled with surface profilometry. PLIF identifies counter-rotating vortex pairs (CRVP) emanating from the surface following the growth of high steepness two-dimensional millimetre-size waves for Reynolds and Weber numbers based on the momentum thickness of 177 to 222 and 7.59 to 13.9, respectively. High spatio-temporal resolution PIV reveals the role of surface-generated vorticity and flow separation in the highly curved trough of the waves on the injection of a CRVP. Air bubbles are entrapped in the wake of these CRVPs at Reynolds number above 190. PIV data and spanwise PLIF images show two initiation mechanisms: primary vortex instability modulating the spanwise location where the flow separates, resulting in the pinch off of an air ligament, and secondary vortex instability turning a CRVP into$\unicode[STIX]{x1D6FA}$-shaped loops pulling the surface down. Instability wavelengths agree with linear stability analysis, and models for these new air entrainment mechanisms are proposed.

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