scholarly journals PIV-Based Acoustic Pressure Measurements of a Single Bubble near the Elastic Boundary

Micromachines ◽  
2020 ◽  
Vol 11 (7) ◽  
pp. 637
Author(s):  
Qidong Yu ◽  
Zhicheng Xu ◽  
Jing Zhao ◽  
Mindi Zhang ◽  
Xiaojian Ma
Keyword(s):  
Flow Structure ◽  
Acoustic Pressure ◽  
Transient Flow ◽  
Single Bubble ◽  
Rigid Boundary ◽  
Inverted Cone ◽  
Migration Direction ◽  
Elastic Boundary ◽  
Image Velocimetry ◽  
Spark Bubble

The objective of this paper was to investigate acoustic pressure waves and the transient flow structure emitted from the single bubble near an elastic boundary based on the particle image velocimetry (PIV). A combination of an electric-spark bubble generator and PIV were used to measure the temporal bubble shapes, transient flow structure, as well as the mid-span deflection of an elastic boundary. Results are presented for three different initial positions near an elastic boundary, which were compared with results obtained using a rigid boundary. A formula relating velocity and pressure was proposed to calculate the acoustic pressure contours surrounding a bubble based on the velocity field of the transient flow structure obtained using PIV. The results show the bubbles near the elastic boundary presented a “mushroom” bubble and an inverted cone bubble. Based on the PIV-measured acoustic pressure contours, a significant pressure difference is found between the elastic boundary and the underside of the bubble, which contributed to the formation of the “mushroom” bubble and inverted cone bubble. Furthermore, the bubbles had opposite migration direction near rigid and elastic boundaries, respectively. In detail, the bubble was repelled away from the elastic boundary and the bubble was attracted by the rigid boundary. The resultant force made up of a Bjerknes force and buoyancy force dominated the migration direction of the bubble.

Investigation of Combustion Oscillations in a Lean Gas Turbine Model Combustor

2007 ◽  
Author(s):  
Olaf Diers ◽  
Denis Schneider ◽  
Melanie Voges ◽  
Peter Weigand ◽  
Christoph Hassa
Keyword(s):  
Atmospheric Pressure ◽  
Acoustic Pressure ◽  
Particle Image ◽  
Operating Conditions ◽  
Operating Point ◽  
Image Velocimetry ◽  
Different Types ◽  
Mass Flows ◽  
Combined Data

This contribution is a continuation of ASME-GT2006-90300. While still working at atmospheric pressure, the range of operating conditions was extended to more realistic reduced mass flows to reproduce the engine pressure loss and air preheat up to 700K. The thermoacoustic behaviour of the burner was mapped over that operating range. Two different types of oscillations were observed for flames anchored at the nozzle or lifted from it. Both exhibited a frequency dependence on the Strouhal number for constant reduced mass flows. For a selected operating point with the lifted flame at a preheat temperature of 600K and a reduced mass flow of 0.3kg K0.5/(s bar), the thermoacoustic behaviour of the burner was characterised by phase locked Particle Image Velocimetry as well as phase locked OH- and OH-T- LIF measurements and correlated to the acoustic pressure signal obtained by microphones. The combined data showed pulsating combustion being supported through periodic reignition of the main flame zone by a recirculating volume of hot, OH-rich gas, the cycle time being connected to the observed frequency. The characterization of the preheated operating point was completed with a heat balance investigation quantifying the non-adiabatic combustion conditions of the uncooled combustor.

Different Modes of Gas Entrainment Through Bottom Discharge Branch by Using Three Dimensional Particle Image Velocimetry System

2007 ◽  
Author(s):  
Wael Fairouz Saleh ◽  
Ibrahim Galal Hassan
Keyword(s):  
Particle Image Velocimetry ◽  
Flow Structure ◽  
Particle Image ◽  
Three Dimensional ◽  
Industrial Applications ◽  
Particle Image Velocimetry System ◽  
Three Dimension ◽  
Two Phase ◽  
Mean Velocity ◽  
Image Velocimetry

The discharge of two-phase flow from a stratified region through single or multiple branches is an important process in many industrial applications including the pumping of fluid from storage tanks, shell-and-tube heat exchangers, and the fluid flow through small breaks in cooling channels of nuclear reactors during loss-of-coolant accidents (LOCA). Knowledge of the flow phenomena involved along with the quality and mass flow rate of the discharging stream(s) is necessary to adequately predict the different phenomena associated with the process. Particle Image Velocimetry (PIV) in three dimension was used to provide detailed measurements of the flow patterns involving distributions of mean velocity, vorticity field, and flow structure. The experimental investigation was carried out to simulate two phase discharge from a stratified region through branches located on a semi-circular wall configuration during LOCA scenarios. The semi-circular test section is in close dimensional resemblance with that of a CANDU header-feeder system, with branches mounted at orientation angles of zero, 45 and 90 degrees from the horizontal. The experimental data for the phase development (mean velocity, flow structure, etc.) was done during single discharge through the bottom branch from an air/water stratified region over a three selected Froude numbers. These measurements were used to describe the effect of outlet flow conditions on phase redistribution in headers and understand the entrainment phenomena.

Validation of in-cylinder flow structure of controlled auto-ignition engine

2013 ◽  
Vol 10 (4) ◽  
pp. 305-312
Author(s):  
J. Beauquel ◽  
S. Ibrahim ◽  
R. Chen
Keyword(s):  
Experimental Data ◽  
Flow Structure ◽  
Transient Flow ◽  
Laser Doppler Anemometry ◽  
Auto Ignition ◽  
Geometry Configuration ◽  
Turbulent Flow Structure ◽  
Air Intake ◽  
Exhaust Valves ◽  
Actual Geometry

Numerical calculations have been carried out to investigate the in-cylinder transient flow structure of a controlled auto-ignition (CAI) engine running at speeds of 1,500rpm and 2,000rpm. The calculated turbulent flow structure and velocities are validated against published laser doppler anemometry (LDA) experimental data. The experimental data were re-processed to represent the time dependent mean velocities for all measured points. The actual geometry configuration of the engine is imported into the computational fluid dynamics (CFD) code used in this study. The simulations take into account the movement of the inlet, exhaust valves and the piston. The CFD simulations replicate the experimental work where only air was inserted into a driven optical engine. Also, to simulate an engine in controlled auto-ignition (CAI) mode, the same valve timing that allows 36% internal exhaust gas recirculation (IEGR) was applied for the air intake. The calculated results are found to agree well with the LDA measurements with an overall agreement of 75.06% at 1,500 rpm and 73.42% at 2,000 rpm.

Experimental Study on Convolution Flow near Charged Spray Nozzle

2010 ◽  
Vol 29-32 ◽  
pp. 1675-1679
Author(s):  
Zhen Tao Wang ◽  
Jun Feng Wang ◽  
Wei Dong Jia ◽  
Ti Qian Luo
Keyword(s):  
Flow Structure ◽  
Flue Gas ◽  
Particle Image ◽  
Jet Flow ◽  
Dust Particles ◽  
Flow Section ◽  
Spray Nozzle ◽  
Image Velocimetry ◽  
Gas Removal ◽  
Form Development

The electrostatic jet flow has been widely employed to crop-dusting, painting, fuel spray and combustion, electrostatic painting, dust particles and flue gas removal. In order to investigate the convolution flow structure near the nozzle, discuss the effects of electrostatic voltages on convolution flow form, development and the aggrandizement of droplets mass transfer. PIV (Particle Image Velocimetry) was employed to measure and analyze the convolution flow near the nozzle under different voltages, and the velocity vectors and streamlines were gained. Experiment and analysis indicate that convolution flow structure has been existed in electrostatic jet flow brim and the main jet flow section change is inconspicuous with voltages adding; Electrical filed intensity has been enhanced and the droplets convolution flow was picked up with the electrostatic voltages adding. The convolution flow structure could quicken the gas mix into the main jet flow, and enhanced the droplets absorbency.

scholarly journals Forces and Flow Structures on a Simplified Car Model Exposed to an Unsteady Harmonic Crosswind

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Valérie Ferrand
Keyword(s):  
Phase Shift ◽  
Transient Flow ◽  
Measurement Techniques ◽  
Flow Topology ◽  
Average Force ◽  
Ground Vehicle ◽  
Vortical Structures ◽  
Car Model ◽  
Image Velocimetry ◽  
Evolution Phase

A ground vehicle traveling along a road is subject to unsteady crosswinds in a number of situations. In windy conditions, for example, the natural atmospheric wind can exhibit strong lateral gusts. Other situations, such as tunnel exits or overtaking induce sudden changes in crosswinds, as well. The interaction of this unsteady oncoming flow with the vehicle and the resulting aerodynamic forces and moments affect the vehicle stability and comfort. The objectives of the current study are to improve the understanding of flow physics of such transient flow and ultimately to develop measurement techniques to quantify the vehicle’s sensitivity to unsteady crosswind. A square back simplified car model is exposed to a forced oscillating yaw and results are compared to static measurements. Tests are conducted at Reynolds number Re = 3.7 × 105 and reduced frequencies ranging from 0.265 × 10−2 to 5.3 × 10−2. Unsteady side force and yawing moment measurements are associated with particle image velocimetry flow fields to interpret dynamic loads in link with flow topology evolution. Phase average force and moment measurements are found to exhibit a phase shift between static and dynamic tests that increases with oscillating frequency. Velocity fields reveal that the phase-shift seems to originate from the rear part of the car model. Moreover, lateral vortical structures appearing on the lee side from β = 15 deg increase this phase-shift and consequently appear to be favorable to the lateral stability of the vehicle.

Seismic Response Analysis of Twin-Tower Building with Enlarged Base

2014 ◽  
Vol 912-914 ◽  
pp. 1534-1537
Author(s):  
Shao Bo Zhang ◽  
Ke Lun Wei ◽  
Bi Jian Xiao
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Boundary Conditions ◽  
Seismic Response ◽  
Time History ◽  
Response Analysis ◽  
Rigid Boundary ◽  
Finite Element Software ◽  
Elastic Boundary ◽  
Elastic Boundary Conditions

This paper adopts large finite element software ANSYS to establish finite element model of twin-tower building with enlarged base, uses dynamic time history analysis method for seismic response calculation, compare and analyze the calculation results of twin-tower building with enlarged base under elastic boundary conditions and rigid boundary conditions. The results showe that dynamic response for model under elastic boundary conditions is larger than dynamic response for model under rigid boundary conditions, and elastic boundary conditions is more close to the actual situation.

scholarly journals Vortices, dissipation and flow transition in volatile binary drops

2014 ◽  
Vol 749 ◽  
pp. 649-665 ◽  
Author(s):  
R. Bennacer ◽  
K. Sefiane
Keyword(s):  
Viscous Dissipation ◽  
Flow Structure ◽  
Volatile Component ◽  
Internal Flow ◽  
Reynolds Numbers ◽  
Local Concentration ◽  
Water Mixture ◽  
Concentration Gradients ◽  
Image Velocimetry ◽  
Good Agreement

AbstractDespite its fundamental and practical relevance, flow structure and evolution within volatile mixture drops remains largely unexplored. We study experimentally, using particle image velocimetry (PIV), the evolution of internal flow during the evaporation of ethanol–water mixture drops for different initial concentrations. The investigation revealed the existence of three stages in the evolving flow behaviour within these binary volatile drops. We propose an analysis of the nature of the flow and focus on understanding successive flow stages as well as transition from multiple vortices to a monotonic outward flow. We show that the existence of multiple vortices during the first stage is driven by local concentration gradients along the interface. When the more volatile component (in this case ethanol) is depleted, the intensity of this Marangoni flow abruptly declines. Towards the end of the first stage, ethanol is driven from the bulk of the drop to the interface to sustain weakening concentration gradients. Once these gradients are too weak, the solutal Marangoni number becomes sub-critical and the driving force for the flow switches off. The evolution of flow structure and transition between stages is found to be well correlated with the ratio of Marangoni and Reynolds numbers. Furthermore, we argue that whilst the observed vortices are driven by surface tension shear stress originating at the liquid/vapour interface, the transition in flow and its dynamics is entirely determined by viscous dissipation. The comparison between the analytical expression for vorticity decay based on viscous dissipation and the experimental data shows a very good agreement. The analysis also shows that regardless of the initial concentration, for same sized drops, the transition in flow follows exactly the same trend. This further supports the hypothesis of a viscous dissipation transition of the flow. The last stage is satisfactorily explained based on non-uniform evaporation and continuity-driven flow.

Sign in / Sign up

Export Citation Format

Share Document