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.

scholarly journals CFD Analysis of Dynamics of Interaction of ShockWave -Vortex Core over Flapped Wing of Supersonic Aircraft at different angle of attack & Mach number

2019 ◽  
Vol 9 (2) ◽  
pp. 5578-5589
Keyword(s):  
Shock Wave ◽  
Flow Field ◽  
Strong Interaction ◽  
Vortex Core ◽  
Acoustic Waves ◽  
Vortex Breakdown ◽  
Pressure Coefficient ◽  
Angle Of Attack ◽  
Strong Shock ◽  
Supersonic Aircraft

The objective of this paper was to analysis the condition for the appearance of the many types of interaction of a vortex core with shock wave over a flapped wing of a supersonic aircraft. A five digit NACA 23012 aerofoil was selected for this work. Structured Mesh was generated by Quadrilaterals Method. Steady-state density based implicit solver and K-ω SST turbulent model was selected. Q criterion method with vorticity magnitude was used to calculate the vortex core. NACA aerofoil Scaled model was manufactured by using NACA profile for experimental work and CFD results were validated by pressure coefficient calculated by wind tunnel setup. Finally, concluded that weak interaction with no vortex breakdown was observed at M= 1.4 and a strong interaction with a bubble-like vortex breakdown formed at M= 1.8 and It found that when a shock wave interact with vortex core, disturbance is generated, which expands along the shock wave and deformed into many small vortices. The flow field is compressed behind the curved shock wave which is reason of acoustic waves. This principle are related to the shock–turbulence interaction which is one of major source of noise. Also concluded that initially at low angle of attack,it observed a strong organized flow field in the downstream region which is due to less strength of the shock. The development of a transmitted shock wave across the vortex core was observed because of shock scattering phenomenon. The moderate breakdown of the vorticity field that occurs after a very strong shock at M =1.4 also observed and the breakdown was more intense when increased Mach No. up to 1.8. Weak and strong interaction region were observed and three stages of interaction found by the flow field over aerofoil at high Mach No. =1.8.

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.

Methodology to Identify the Unsteady Flow Field Associated With the Loss of Acoustic Energy in the Vicinity of Circular Holes

2010 ◽  
Author(s):  
Jochen Rupp ◽  
Jon Carrotte ◽  
Adrian Spencer
Keyword(s):  
Velocity Field ◽  
Flow Field ◽  
Unsteady Flow ◽  
Acoustic Field ◽  
Acoustic Waves ◽  
Large Scale ◽  
Acoustic Power ◽  
Acoustic Energy ◽  
Absorption Mechanism ◽  
Linear Absorption

Thermo-acoustic instabilities in lean gas turbine combustors have been well reported over the past decade. One option by which the generation of potentially damaging, large scale, pressure amplitudes can be avoided is to increase the amount of damping within the combustion system using passive damping devices. Common to these devices is the absorption mechanism by which acoustic energy, associated with incident pressure fluctuations onto an orifice, generates an unsteady flow that cannot be converted back into acoustic energy. This paper is concerned with providing a greater understanding of this fundamental process. Experimental results are presented for a single orifice that is exposed to plane acoustic waves within a rectangular duct. Measurements of unsteady pressure enable the acoustic power absorbed by the orifice to be determined, whilst Particle Image Velocimetry (PIV) is used to measure the unsteady flow field. A method is outlined for identifying those features within the measured unsteady flow field that are responsible for absorption of the acoustic energy. This is based on a Proper Orthogonal Decomposition (POD) analysis of the velocity field and identification of the relevant modes. The method is validated for the non-linear and linear absorption regimes by comparing the energy of the relevant velocity field features with the energy absorbed from the acoustic field. The good agreement obtained indicates the success of the technique presented. The improved understanding of the mechanisms by which energy is transferred out of the acoustic field, and into the unsteady velocity field, explains many of the observed absorption characteristics. This improved understanding should lead to the design of optimized damping systems. The presented methodology is also thought to be the basis by which numerical, CFD based, predictions relating to the absorption of acoustic waves should be analyzed and validated.

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.

Modal characteristics and fluid–structure interaction vibration response of submerged impeller

2021 ◽  
pp. 107754632110036
Author(s):  
Shihui Huo ◽  
Hong Huang ◽  
Daoqiong Huang ◽  
Zhanyi Liu ◽  
Hui Chen
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Damping Ratio ◽  
Pure Water ◽  
Vibration Response ◽  
Modal Identification ◽  
Liquid Oxygen ◽  
Modal Characteristics ◽  
Oxygen Pump ◽  
Turbo Pump

Turbo pump is one of the elements with the most complex flow of liquid rocket engine, and as an important component of turbo pump, an impeller is the weak point affecting its reliability. In this study, a noncontact modal characteristic identification technique was proposed for the liquid oxygen pump impeller. Modal characteristics of the impeller under three different submerged media, air, pure water, and brine with same density as liquid oxygen, were tested based on the noncontact modal identification technology. Submersion state directly affects the modal frequencies and damping ratio. The transient vibration response characteristics of the impeller excited by the unsteady flow field was achieved combining with unsteady flow field analysis and transient dynamic analysis in the whole flow passage of the liquid oxygen pump. Vibration responses at different positions of the impeller show 10X and 20X frequencies, and the amplitude at the root of short blade is significant, which needs to be paid more attention in structural design and fatigue evaluation.

scholarly journals Photoacoustic 3-D imaging of polycrystalline microstructure improved with transverse acoustic waves

2021 ◽  
pp. 100286
Author(s):  
Théo Thréard ◽  
Elton de Lima Savi ◽  
Sergey Avanesyan ◽  
Nikolay Chigarev ◽  
Zilong Hua ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Transverse Acoustic ◽  
Polycrystalline Microstructure

scholarly journals Analysis of transonic buffet using dynamic mode decomposition

2021 ◽  
Vol 62 (4) ◽  
Author(s):  
Antje Feldhusen-Hoffmann ◽  
Christian Lagemann ◽  
Simon Loosen ◽  
Pascal Meysonnat ◽  
Michael Klaas ◽  
...  
Keyword(s):  
Shock Wave ◽  
Flow Field ◽  
Acoustic Waves ◽  
Feedback Loop ◽  
Measurement Data ◽  
Dynamic Mode Decomposition ◽  
Recirculation Region ◽  
Dynamic Mode ◽  
Mode Decomposition ◽  
Transonic Buffet

AbstractThe buffet flow field around supercritical airfoils is dominated by self-sustained shock wave oscillations on the suction side of the wing. Theories assume that this unsteadiness is driven by a feedback loop of disturbances in the flow field downstream of the shock wave whose upstream propagating part is generated by acoustic waves. High-speed particle-image velocimetry measurements are performed to investigate this feedback loop in transonic buffet flow over a supercritical DRA 2303 airfoil. The freestream Mach number is $$M_{\infty } = 0.73$$ M ∞ = 0.73 , the angle of attack is $$\alpha = 3.5^{\circ }$$ α = 3 . 5 ∘ , and the chord-based Reynolds number is $${\mathrm{Re}}_{c} = 1.9\times 10^6$$ Re c = 1.9 × 10 6 . The obtained velocity fields are processed by sparsity-promoting dynamic mode decomposition to identify the dominant dynamic features contributing strongest to the buffet flow field. Two pronounced dynamic modes are found which confirm the presence of two main features of the proposed feedback loop. One mode is related to the shock wave oscillation frequency and its shape includes the movement of the shock wave and the coupled pulsation of the recirculation region downstream of the shock wave. The other pronounced mode represents the disturbances which form the downstream propagating part of the proposed feedback loop. The frequency of this mode corresponds to the frequency of the acoustic waves which are generated by these downstream traveling disturbances and which form the upstream propagating part of the proposed feedback loop. In this study, the post-processing, i.e., the DMD, is highlighted to substantiate the existence of this vortex mode. It is this vortex mode that via the Lamb vector excites the shock oscillations. The measurement data based DMD results confirm numerical findings, i.e., the dominant buffet and vortex modes are in good agreement with the feedback loop suggested by Lee. Graphic abstract

scholarly journals Unsteady flow field around a human hand and propulsive force in swimming

2009 ◽  
Vol 42 (1) ◽  
pp. 42-47 ◽  
Author(s):  
K. Matsuuchi ◽  
T. Miwa ◽  
T. Nomura ◽  
J. Sakakibara ◽  
H. Shintani ◽  
...  
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Human Hand ◽  
Propulsive Force
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