Further Characterization of the Disturbance Field in a Transversely Excited Swirl-Stabilized Flame

2011 ◽  
Author(s):  
Jacqueline O’Connor ◽  
Tim Lieuwen
Keyword(s):  
Acoustic Waves ◽  
High Speed ◽  
Flow Direction ◽  
Rocket Engines ◽  
Velocity Data ◽  
Image Velocimetry ◽  
Transverse Acoustic ◽  
Field Fluctuations ◽  
Disturbance Field

Transverse instabilities in annular gas turbine combustors are an important problem for both power generation and aircraft applications. These instabilities, also found in afterburners and rocket engines, are manifested as strong acoustic field fluctuations perpendicular to the flow direction. Transverse acoustic waves not only directly perturb the flame, but also couple with nozzle acoustics and inherent fluid mechanic instabilities. As such, the unsteady flow field that disturbs the flame is a complex superposition of transverse and longitudinal disturbances associated with both acoustic and vortical waves. This study closely follows prior work of the authors, which overviewed the disturbance field characteristics of a transversely forced, swirling nozzle flow. Velocity data from a transversely forced, swirl-stabilized flame was taken using high-speed particle image velocimetry (PIV). The topology of the velocity and vorticity field is compared between the inphase and out-of-phase forcing cases using both filtered and instantaneous data. These data also show that the acoustic and vortical disturbances are comparable in amplitude and, because they propagate at very different speeds, their superposition leads to prominent interference patterns in the fluctuating velocity. Data from both non-reacting and reacting test cases are presented to show that many features of the unsteady shear layers are quite similar.

Experimental Characterization of a Liquid Jet Emanating From An Effervescent Atomizer

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
V. Sivadas ◽  
K. Balaji ◽  
Antriksha Vishwakarma ◽  
Sundar Ram Manikandan
Keyword(s):  
High Speed ◽  
Flow Direction ◽  
Low Frequency ◽  
Intrinsic Property ◽  
Liquid Jet ◽  
Experimental Characterization ◽  
Jet Breakup ◽  
Effervescent Atomizer ◽  
Visualization Techniques

Abstract The study focuses on experimental characterization of the primary atomization associated with an effervescent atomizer. Unlike the existing designs available in the literature that inject air perpendicular to the liquid flow direction, the present atomizer design utilizes coflowing air configuration. In doing so, the aerodynamic shear at the liquid–gas interface create instability and enhance the subsequent jet breakup. Both integrated and intrinsic properties of the liquid jet were extracted by utilizing high-speed flow visualization techniques. The integrated property consists of breakup length, while the intrinsic property involves primary and intermediate breakup frequencies. The primary instability is characterized by low-frequency sinusoidal mode, whereas the intermediate instability consists of high-frequency dilatational mode. Dimensionless plots of these parameters with Weber number ratio leads to a better collapse of data, thereby generating appropriate universal functions. The combined diagram of frequencies converge with increasing relative velocity. This may be due to the dominance of energy consuming sinusoidal wave as the aerodynamic shear increases.

Disturbance Field Characteristics of a Transversely Excited Annular Jet

2010 ◽  
Author(s):  
Jacqueline O’Connor ◽  
Shweta Natarajan ◽  
Michael Malanoski ◽  
Tim Lieuwen
Keyword(s):  
Acoustic Waves ◽  
Swirling Flow ◽  
Near Field ◽  
Acoustic Mode ◽  
Response Characteristics ◽  
Annular Jet ◽  
Transverse Acoustic ◽  
Left And Right ◽  
Acoustic Instabilities ◽  
Disturbance Field

This paper describes an investigation of transverse acoustic instabilities in premixed, swirl-stabilized flames. Additional measurements, beyond the scope of the current work, are described in O’Connor et al. [1]. Transverse excitation of swirling flow involves complex interactions between acoustic waves and fluid mechanic instabilities. The flame’s response to transverse acoustic excitation is a superposition of both acoustic and vortical disturbances that fluctuate in both the longitudinal and transverse direction. In the nozzle near field region, the disturbance field is a complex superposition of convecting vortical disturbances, as well as longer wavelength transverse and longitudinal acoustic disturbances. Farther downstream, the disturbance field is dominated by the transverse acoustic field. The phasing between the disturbances on the inside and outside of the burner annulus, as well as the left and right sides of the burner annulus is a strong function of the transverse disturbance field characteristics. For cases where the burner centerline is an approximate pressure node and velocity anti-node, the mass flow out of the left and right sides of the burner actually oscillates out-of-phase with respect to each other. In contrast, for cases where the centerline is a pressure anti-node, the burner responds symmetrically about the burner and annulus centerlines. These results show that the burner response characteristics strongly depend upon their location in the acoustic mode shape.

scholarly journals Experimental characterization of speech aerosol dispersion dynamics

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zu Puayen Tan ◽  
Lokesh Silwal ◽  
Surya P. Bhatt ◽  
Vrishank Raghav
Keyword(s):  
High Speed ◽  
Particle Image ◽  
Experimental Characterization ◽  
Production Rates ◽  
Plume Front ◽  
Fidelity Assessment ◽  
Image Velocimetry ◽  
Aerosol Dispersion ◽  
Primary Transmission

AbstractContact and inhalation of virions-carrying human aerosols represent the primary transmission pathway for airborne diseases including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Relative to sneezing and coughing, non-symptomatic aerosol-producing activities such as speaking are highly understudied. The dispersions of aerosols from vocalization by a human subject are hereby quantified using high-speed particle image velocimetry. Syllables of different aerosol production rates were tested and compared to coughing. Results indicate aerosol productions and penetrations are not correlated. E.g. ‘ti’ and ‘ma’ have similar production rates but only ‘ti’ penetrated as far as coughs. All cases exhibited a rapidly penetrating “jet phase” followed by a slow “puff phase.” Immediate dilution of aerosols was prevented by vortex ring flow structures that concentrated particles toward the plume-front. A high-fidelity assessment of risks to exposure must account for aerosol production rate, penetration, plume direction and the prevailing air current.

High Speed Visualization and PIV Measurements in the Near Field of Spray Produced by Flow-Blurring Atomization

2014 ◽  
Author(s):  
Lulin Jiang ◽  
Ajay K. Agrawal ◽  
Robert P. Taylor
Keyword(s):  
High Speed ◽  
Flow Direction ◽  
Near Field ◽  
Liquid Fuels ◽  
Two Phase ◽  
Time Resolved ◽  
Straight Vegetable Oil ◽  
Image Velocimetry ◽  
Fine Spray ◽  
Field Plots

Clean and stable combustion of alternative liquid fuels, such as biodiesel, straight vegetable oil and glycerol has been achieved in past studies by using a novel flow blurring (FB) injector without fuel pre-processing or combustor hardware modification. FB injector employs aerodynamic principle to form two phase flow immediately upstream of the injector exit. Explosion of air bubbles at the injector exit atomizes the liquid into a fine spray. In this study, the flow field in the near field of the FB injector is investigated by high-speed visualization and time-resolved Particle Image Velocimetry (PIV) techniques. Experiments are performed using water and air for air to liquid mass ratio (ALR) of 2. Flow visualization at the injector exit focused on field of view with the dimension of 2.3 mm × 1.4 mm, spatial resolution of 7.16 μm per pixel, exposure time of 1 μs, and image acquisition rate of 100 k frames per second (fps). Image sequence illustrates fine spray of FB atomization in the near field and the break-down process of larger droplets appearing occasionally. Time-resolved PIV technique is applied to quantify the injector near field. Plots of instantaneous, mean, root-mean-square velocities and turbulence kinetic energy are presented to reveal the droplet characteristics and secondary atomization process. Results show that the majority of the liquid is atomized into fine droplets at the injector exit. The droplet velocity increases in the flow direction and decreases from the center to the periphery of the spray. This result is consistent with the size of the droplets, i.e., the larger droplets move slowly while the finer droplets move faster as they follow the atomizing air flow.

An explanation for the phase lag in supersonic jet impingement

2017 ◽  
Vol 815 ◽  
Author(s):  
Joel L. Weightman ◽  
Omid Amili ◽  
Damon Honnery ◽  
Julio Soria ◽  
Daniel Edgington-Mitchell
Keyword(s):  
Acoustic Waves ◽  
High Speed ◽  
Feedback Loop ◽  
Supersonic Jet ◽  
Jet Impingement ◽  
Phase Lag ◽  
Loop Equation ◽  
Image Velocimetry ◽  
Impinging Flows ◽  
First Time

For the first time, a physical mechanism is identified to explain the phase lag term in Powell’s impinging feedback loop equation (Powell, J. Acoust. Soc. Am., vol. 83 (2), 1988, pp. 515–533). Ultra-high-speed schlieren reveals a previously unseen periodic transient shock in the wall jet region of underexpanded impinging flows. The motion of this shock appears to be responsible for the production of the acoustic waves corresponding to the impingement tone. It is suggested that the delay between the inception of the shock and the formation of the acoustic wave explains the phase lag in the aeroacoustic feedback process. This suggestion is quantitatively supported through an assessment of Powell’s feedback equation, using high-resolution particle image velocimetry and acoustic measurements.

Further Characterization of the Disturbance Field in a Transversely Excited Swirl-Stabilized Flame

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Jacqueline O’Connor ◽  
Tim Lieuwen
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Acoustic Waves ◽  
Vortex Breakdown ◽  
Primary Source ◽  
Base Flow ◽  
Acoustic Fluctuations ◽  
Transverse Acoustic ◽  
Flame Region ◽  
Disturbance Field

This paper describes an analysis of the unsteady flow field in swirl flames subjected to transverse acoustic waves. This work is motivated by transverse instabilities in annular gas turbine combustors, which are a continuing challenge for both power generation and aircraft applications. The unsteady flow field that disturbs the flame consists not only of the incident transverse acoustic wave, but also longitudinal acoustic fluctuations and vortical fluctuations associated with underlying hydrodynamic instabilities of the base flow. We show that the acoustic and vortical velocity fluctuations are of comparable magnitude. The superposition of these waves leads to strong interference patterns in the velocity field, a result of the significantly different wave propagation speeds and axial phase dependencies of these two disturbance sources. Vortical fluctuations originate from the convectively unstable shear layers and absolutely unstable swirling jet. We argue that the unsteady shear layer induced fluctuations are the most dynamically significant, as they are the primary source of flame fluctuations. We also suggest that vortical structures associated with vortex breakdown play an important role in controlling the time-averaged features of the central flow and flame spreading angle, but do not play an important role in disturbing the flame at low disturbance amplitudes. This result has important implications not only for our understanding of the velocity disturbance field in the flame region, but also for capturing important physics in future modeling efforts.

Characterization of RF Sputtered ZnO Piezoelectric Films Using Transmission Electron Microscope

1975 ◽  
Vol 33 ◽  
pp. 86-87
Author(s):  
Kemining W. Yeh ◽  
Richard S. Muller ◽  
Wei-Kuo Wu ◽  
Jack Washburn
Keyword(s):  
Integrated Circuit ◽  
Acoustic Waves ◽  
New Technology ◽  
Surface Acoustic Waves ◽  
Electromechanical Properties ◽  
Leading Role ◽  
Saw Devices ◽  
Transmission Electron ◽  
High Degree

Considerable and continuing interest has been shown in the thin film transducer fabrication for surface acoustic waves (SAW) in the past few years. Due to the high degree of miniaturization, compatibility with silicon integrated circuit technology, simplicity and ease of design, this new technology has played an important role in the design of new devices for communications and signal processing. Among the commonly used piezoelectric thin films, ZnO generally yields superior electromechanical properties and is expected to play a leading role in the development of SAW devices.

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