Resonance dynamics in compressible cavity flows using time-resolved velocity and surface pressure fields

2017 ◽  
Vol 830 ◽  
pp. 494-527 ◽  
Author(s):  
Justin L. Wagner ◽  
Steven J. Beresh ◽  
Katya M. Casper ◽  
Edward P. DeMauro ◽  
Srinivasan Arunajatesan
Keyword(s):  
Velocity Field ◽  
Shear Layer ◽  
Surface Pressure ◽  
Coherent Structures ◽  
Acoustic Waves ◽  
Mode Switching ◽  
Recirculation Region ◽  
Mean Flow ◽  
Time Resolved ◽  
Phase Velocities

The resonance modes in Mach 0.94 turbulent flow over a cavity having a length-to-depth ratio of five were explored using time-resolved particle image velocimetry (TR-PIV) and time-resolved pressure sensitive paint (TR-PSP). Mode switching was quantified in the velocity field simultaneous with the pressure field. As the mode number increased from one through three, the resonance activity moved from a region downstream within the recirculation region to areas further upstream in the shear layer, an observation consistent with linear stability analysis. The second and third modes contained organized structures associated with shear layer vortices. Coherent structures occurring in the velocity field during modes two and three exhibited a clear modulation in size with streamwise distance. The streamwise periodicity was attributable to the interference of downstream-propagating vortical disturbances with upstream-travelling acoustic waves. The coherent structure oscillations were approximately $180^{\circ }$ out of phase with the modal surface pressure fluctuations, analogous to a standing wave. Modal propagation (or phase) velocities, based on cross-correlations of bandpass-filtered velocity fields were found for each mode. The phase velocities also showed streamwise periodicity and were greatest at regions of maximum constructive interference where coherent structures were the largest. Overall, the phase velocities increased with modal frequency, which coincided with the modal activity residing at higher portions of the cavity where the local mean flow velocity was elevated. Together, the TR-PIV and TR-PSP provide unique details not only on the distribution of modal activity throughout the cavity, but also new understanding of the resonance mechanism as observed in the velocity field.

The Role of Streamwise Vorticity in the Control of Impinging Jets

2003 ◽  
Author(s):  
F. S. Alvi ◽  
H. Lou ◽  
C. Shih
Keyword(s):  
Velocity Field ◽  
Shear Layer ◽  
Acoustic Waves ◽  
High Speed ◽  
Feedback Loop ◽  
Large Scale ◽  
Field Measurements ◽  
Impinging Jets ◽  
Streamwise Vorticity

Supersonic impinging jets produce a highly unsteady flowfield leading to very high dynamic pressure loads on nearby surfaces. In earlier studies, we conclusively demonstrated that arrays of supersonic microjet, 400 μm in diameter, effectively disrupted the feedback loop inherent in high-speed impinging jet flows. This feedback disruption results in significant reductions in the adverse effects associated with such flows. In this paper, by primarily using detailed velocity field measurements, we examine the role of streamwise vorticity in order to better understand the mechanisms behind this control scheme. The velocity field measurements clearly reveal the presence of well-organized, streamwise vortices with the activation of microjets. This increase in streamwise vorticity is concomitant with a reduction in the azimuthal vorticity of the primary jet. We propose that the streamwise vorticity is mainly a result of the redirection of the azimuthal vorticity, which leads to a weakening of the large-scale structures in the primary jet. The appearance of strong vortices in the shear layer near the nozzle exit due to microjets further weakens the spatial coherence of the coupling between the acoustic waves and shear layer instability, while thickening the jet shear layer. All these effects are thought to be collectively responsible for the efficient disruption of the feedback loop using microjets.

Nonlinear evolution of spiral density waves generated by the instability of the shear layer in a rotating compressible fluid

1991 ◽  
Vol 233 ◽  
pp. 587-612 ◽  
Author(s):  
I. G. Shukhman
Keyword(s):  
Shear Layer ◽  
Compressible Fluid ◽  
Acoustic Waves ◽  
Evolution Equations ◽  
Nonlinear Evolution ◽  
Density Wave ◽  
Mixing Layer ◽  
Mean Flow ◽  
Spiral Density Waves ◽  
Corotation Radius

In a previous paper we considered the nonlinear stability of a cylindrical mixing layer in an incompressible fluid at large Reynolds numbers. Nonlinear evolution results in the formation of vortex structures in the vicinity of the corotation radius rc. This paper considers the same model but in a compressible fluid. A fundamental difference implied by the presence of compressibility is the possibility of the generation of disturbances which are no longer localized near the shear layer but embrace the entire region. These are acoustic waves generated in the region of corotation resonance and emitted into the periphery. In the r > rc region lines of equal density are trailing spirals. The nonlinear evolution of such disturbances is determined by redistribution of the mean flow inside the critical layer (CL). It is shown that only two possible types of CL, viscous and unsteady, can be realized here. For both types of these regimes, evolution equations describing the dynamics of a spiral density wave amplitude are obtained and their solutions analysed. It appears that at any values (provided that they are small enough) of initial supercriticality of the flow, an explosive growth of amplitude occurs which continues as long as values comparable with background ones are reached.

scholarly journals Numerical investigation of a jet from a blunt body opposing a supersonic flow

2011 ◽  
Vol 684 ◽  
pp. 85-110 ◽  
Author(s):  
Li-Wei Chen ◽  
Guo-Lei Wang ◽  
Xi-Yun Lu
Keyword(s):  
Supersonic Flow ◽  
Shear Layer ◽  
Numerical Investigation ◽  
Coherent Structures ◽  
Blunt Body ◽  
Free Stream ◽  
Mach Disk ◽  
Recirculation Region ◽  
Small Scale ◽  
Flow States

AbstractNumerical investigation of a sonic jet from a blunt body opposing a supersonic flow with a free stream Mach number ${M}_{\infty } = 2. 5$ was carried out using large-eddy simulation for two total pressure ratios of the jet to the free stream, i.e. $\mathscr{P}= 0. 816$ and 1.633. Results have been validated carefully against experimental data. Various fundamental mechanisms dictating the flow phenomena, including shock/jet interaction, shock/shear-layer interaction, turbulent shear-layer evolution and coherent structures, have been studied systematically. Based on the analysis of the flow structures and features, two typical flow states, i.e. unstable and stable states corresponding to the two values of $\mathscr{P}$, are identified and the behaviours relevant to the flow states are discussed. Small-scale vortical structures mainly occur in the jet column, and large-scale vortices develop gradually in a recirculation region when the jet terminates through a Mach disk and reverses its orientation as a conical free shear layer. The turbulent fluctuations are enhanced by the rapid deviation of the shear layer and the interaction with shock waves. Moreover, the coherent structures of the flow motion are analysed using the proper orthogonal decomposition technique. It is found that the dominant mode in the cross-section plane exhibits an antisymmetric character for the unstable state and an axisymmetric one for the stable state, while statistical analysis of unsteady loads indicates that the side loads can be seen as a rotating vector uniformly distributed in the azimuthal direction. Further, we clarify a feedback mechanism whereby the unsteady motion is sustained by the upstream-propagating disturbance to the Mach disk through the recirculation subsonic region and downstream propagation in the conical shear layer. Feedback models are then proposed which can reasonably well predict the dominant frequencies of the two flow states. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the opposing jet/supersonic flow interaction.

scholarly journals Nonlinear self-excited thermoacoustic oscillations of a ducted premixed flame: bifurcations and routes to chaos

2014 ◽  
Vol 761 ◽  
pp. 399-430 ◽  
Author(s):  
Karthik Kashinath ◽  
Iain C. Waugh ◽  
Matthew P. Juniper
Keyword(s):  
Acoustic Waves ◽  
Stable State ◽  
Period Doubling ◽  
Premixed Flame ◽  
Mode Switching ◽  
Multiple Time ◽  
Flame Surface ◽  
Nonlinear Behaviour ◽  
Mean Flow ◽  
Routes To Chaos

AbstractThermoacoustic systems can oscillate self-excitedly, and often non-periodically, owing to coupling between unsteady heat release and acoustic waves. We study a slot-stabilized two-dimensional premixed flame in a duct via numerical simulations of a $G$-equation flame coupled with duct acoustics. We examine the bifurcations and routes to chaos for three control parameters: (i) the flame position in the duct, (ii) the length of the duct and (iii) the mean flow velocity. We observe period-1, period-2, quasi-periodic and chaotic oscillations. For certain parameter ranges, more than one stable state exists, so mode switching is possible. At intermediate times, the system is attracted to and repelled from unstable states, which are also identified. Two routes to chaos are established for this system: the period-doubling route and the Ruelle–Takens–Newhouse route. These are corroborated by analyses of the power spectra of the acoustic velocity. Instantaneous flame images reveal that the wrinkles on the flame surface and pinch-off of flame pockets are regular for periodic oscillations, while they are irregular and have multiple time and length scales for quasi-periodic and aperiodic oscillations. This study complements recent experiments by providing a reduced-order model of a system with approximately 5000 degrees of freedom that captures much of the elaborate nonlinear behaviour of ducted premixed flames observed in the laboratory.

Jet-noise control by fluidic injection from a rotating plug: linear and nonlinear sound-source mechanisms

2016 ◽  
Vol 788 ◽  
pp. 358-380 ◽  
Author(s):  
Maxime Kœnig ◽  
Kenzo Sasaki ◽  
André V. G. Cavalieri ◽  
Peter Jordan ◽  
Yves Gervais
Keyword(s):  
Coherent Structures ◽  
Stereoscopic Particle Image Velocimetry ◽  
Linear Stability Theory ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Wave Interactions ◽  
Time Resolved ◽  
Source Mechanisms ◽  
The Mean ◽  
Flow Deformation

We present a study of the turbulent and acoustic fields of subsonic jets, controlled by means of a novel actuator that introduces perturbations via steady-fluidic actuation from a rotating centrebody. The actuation can produce louder or quieter jets, and these are analysed using time-resolved stereoscopic particle image velocimetry and a hot-wire anemometer. We place the analysis in the framework of wavepackets and linear stability theory, whence we show, using solutions of the linear parabolised stability equations, that the quieter flows can be understood to result from a mean-flow deformation that modifies wavepacket dynamics, and in particular their phase velocities, which are significantly reduced. The mean-flow deformation is shown, by a triple decomposition, to be due to the generation of Reynolds stresses associated with incoherent turbulence (rather than coherent structures) which arises when the actuation energises the flow with a frequency–azimuthal wavenumber (${\it\omega}$–$m$) combination to which the mean flow is stable. When the actuation excites the flow with an ${\it\omega}$–$m$ combination to which the mean flow is unstable, the response is dominated by coherent structures, whose rapid growth takes them beyond the linear limit, where they undergo quadratic wave interactions and lead, consequently, to a louder flow.

Effect of Fineness Ratio of 0.5 - 2.0 on the Wake Structure Around a Circular Cylinder Measured Using Time-Resolved PIV

2019 ◽  
Author(s):  
Sho Yokota ◽  
Taku Ochiai ◽  
Takumi Ambo ◽  
Yuta Ozawa ◽  
Taku Nonomura ◽  
...  
Keyword(s):  
Velocity Field ◽  
Large Scale ◽  
Vertical Component ◽  
Aerodynamic Characteristics ◽  
Magnetic Suspension ◽  
Recirculation Region ◽  
Mean Velocity ◽  
Wake Structure ◽  
Time Resolved ◽  
Recirculation Bubble

Abstract In this study, the wake structure around freestream-aligned cylinder is investigated and its aerodynamic characteristics are discussed. A magnetic suspension and balance system (MSBS) was used to support a model without interference from a mechanical support device. Seven models with the fineness ratio (length to diameter, L/D) of 0.5, 1.0, 1.25, 1.5, 1.75, 2.0, and 2.25 were used. Reynolds number based on the cylinder diameter were 3.2 × 104 and 6.3 × 104. The velocity field was obtained by particle image velocimetry (PIV) in the center plane of the cylinder. In the case of fineness ratio over 1.5, the reattachment of shear layer was observed from the mean velocity field. The characteristic fluctuation of velocity was confirmed in power spectral density of streamwise component and vertical component. The length of the recirculation region is different depending on fineness ratio. The characteristic frequencies of the velocity fluctuation which seems to be due to recirculation bubble pumping and large-scale structure are observed from power spectrum density.

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

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