Dynamic-mode decomposition based analysis of shear coaxial jets with and without transverse acoustic driving

2016 ◽  
Vol 790 ◽  
pp. 5-32 ◽  
Author(s):  
Jia-Chen Hua ◽  
Gemunu H. Gunaratne ◽  
Douglas G. Talley ◽  
James R. Gord ◽  
Sukesh Roy
Keyword(s):  
Coherent Structures ◽  
Flux Ratio ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Oscillatory Behaviour ◽  
Natural Approach ◽  
Coaxial Jets ◽  
Mode Decomposition ◽  
Transverse Acoustic ◽  
Injector Flows

Modal decompositions of unperturbed and acoustically driven injector flows from shear coaxial jets are implemented using dynamic-mode decomposition, which is a natural approach in the search for collective oscillatory behaviour in nonlinear systems. Previous studies using proper orthogonal decomposition had revealed the most energetic pairs of coherent structures in injector flows. One of the difficulties in extracting lower-energy coherent structures follows from the need to differentiate robust flow constituents from noise and other irregular facets of a flow. The identification of robust features is critical for applications such as flow control as well, since only they can be used for the tasks. A dynamic-mode decomposition based algorithm for this differentiation is introduced and used to identify different classes of robust dynamic modes. They include (1) background modes located outside the injector flow that decay rapidly, (2) injector modes – including those presented in earlier studies – located in the vicinity of the flow, (3) modes that persist under acoustic driving, (4) modes responding linearly to the driving and, most interestingly, (5) a mode whose density exhibits antiphase oscillatory behaviour in the observation plane and that appears only when $J$, the outer-to-inner-jet momentum flux ratio, is sufficiently large; we infer that this is a projection of a mode rotating about the symmetry axis and born via a spontaneous symmetry breaking. Each of these classes of modes is analysed as $J$ is increased, and their consequences for the flow patterns are discussed.

Quantitative Analysis of Forced and Unforced Turbulent Multiphase Coaxial Jets

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
D. J. Forliti ◽  
J. Wegener ◽  
C. Min ◽  
I. A. Leyva
Keyword(s):  
Acoustic Waves ◽  
Acoustic Resonance ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Confined Space ◽  
Coaxial Jets ◽  
Mode Decomposition ◽  
Global Signal ◽  
Background Turbulence ◽  
Signal Processing Methods

Abstract This study explores the structure of liquid/gas coaxial jets under forced and unforced conditions. The forcing is in the form of a transverse acoustic resonance within the confined space where the mixing occurs. The studied flows are relevant to combustion instabilities which involve an interaction between acoustic waves and reactant mixing. A variety of local and global signal processing methods were applied to digital flow visualization data to identify spatial and temporal features. The unforced case is in particular chaotic and influenced by a broad range of spatial and temporal phenomena. Proper orthogonal decomposition (POD) was able to extract flapping and convecting features, and spectral content of these behaviors is presented. The forced case results in organized structures that emerge above the background turbulence, including harmonics of the forcing frequency and nonlinear interactions between specific frequencies. The dynamic mode decomposition (DMD) performs the best in the forced case, clearly isolating all of these features. Wavelet analysis showed that forcing tended to reorganize energy from longer to shorter time scales. Bicoherence analysis of the data showed that the forcing causes a much different energy exchange in the outer and inner shear layers. The outer-to-inner jet coupling during forced conditions appears to be limited to an axial extent of about one to three inner jet diameters downstream of the jet exit. The recirculation zone between the inner and outer jet, extending about one inner jet diameter downstream, appears to disrupt the influence of forcing on the inner jet.

Experimental Investigation of Coherent Structure Dynamics in a Submerged Forced Jet

2013 ◽  
Vol 8 (1) ◽  
pp. 56-64
Author(s):  
Sergey Abdurakipov ◽  
Vladimir Dulin ◽  
Dmitriy Markovich
Keyword(s):  
Coherent Structures ◽  
Vortex Formation ◽  
Velocity Fields ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Analysis Tool ◽  
Modulation Amplitude ◽  
Mode Decomposition ◽  
Image Velocimetry ◽  
Statistical Analysis Tool

The present work investigates the dynamics of coherent structures, including their scales and intensity, in an initial region of a submerged round forced jet by a Particle Image Velocimetry (PIV) technique for measurements of instantaneous velocity fields and statistical analysis tool Dynamic Mode Decomposition (DMD). The PIV measurements were carried out with 1,1 kHz acquisition rate. Application of DMD to the measured set of the velocity fields provided information about dominant frequencies, contained in DMD spectrum, of velocity fluctuations in different flow regions and about scales of the corresponding spatial coherent structures, contained in DMD modes. Additional calculations of time-spectra from turbulent fluctuations showed good agreement between frequencies of the main harmonics and characteristic frequencies of the dominant dynamic modes. Superposition of relevant DMD modes approximately described nonlinear interaction of coherent structures: vortex formation, their quasi-periodic pairing with modulation amplitude of generated harmonics

scholarly journals Dynamic Mode Decomposition of Elliptical Liquid Jets in Crossflow

2021 ◽  
Author(s):  
Keivan Mokhtarpour ◽  
Mehdi Jadidi ◽  
Ali Dolatabadi
Keyword(s):  
High Speed ◽  
Flux Ratio ◽  
Open Loop ◽  
Dynamic Mode Decomposition ◽  
Liquid Jets ◽  
Dynamic Mode ◽  
Equivalent Diameter ◽  
Arnoldi Method ◽  
Aspect Ratios ◽  
Mode Decomposition

Dynamics of round and elliptical liquid jets in subsonic crossflow is studied using high-speed imaging technique. The experiments are performed at constant gaseous weber number and liquid-gas momentum flux ratio of 6.45 and 17.87 respectively, with orifices of different aspect ratios having an equivalent diameter of 0.43 mm. All cases are carried out inside an open loop subsonic wind tunnel with a test section of 100*100*750 mm. For each case, dynamic modes are generated directly from the snapshots using a variant of Arnoldi method known as the dynamic mode decomposition (DMD). DMD results indicate that elliptical liquid jets have more small-scaled patterns with higher frequencies compared to the case of round liquid jets. As the first attempt to investigate the dynamics of elliptical liquid jets in crossflow, present work captures the dominant spatio-temporal structures. It is also found that the orifice aspect ratio can alter the jet wavelengths remarkably. The extracted data of this work can provide beneficial information on the behaviour of elliptical liquid jets exposed to the gas crossflow in the enhanced capillary breakup regime.

scholarly journals Data-Driven Pulsatile Blood Flow Physics with Dynamic Mode Decomposition

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 111
Author(s):  
Milad Habibi ◽  
Scott T. M. Dawson ◽  
Amirhossein Arzani
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Coherent Structures ◽  
Dynamic Mode Decomposition ◽  
Data Driven ◽  
Patient Specific ◽  
Dynamic Mode ◽  
Flow Data ◽  
Reduced Order ◽  
Mode Decomposition

Dynamic mode decomposition (DMD) is a purely data-driven and equation-free technique for reduced-order modeling of dynamical systems and fluid flow. DMD finds a best fit linear reduced-order model that represents any given spatiotemporal data. In DMD, each mode evolves with a fixed frequency and therefore DMD modes represent physically meaningful structures that are ranked based on their dynamics. The application of DMD to patient-specific cardiovascular flow data is challenging. First, the input flow rate is unsteady and pulsatile. Second, the flow topology can change significantly in different phases of the cardiac cycle. Finally, blood flow in patient-specific diseased arteries is complex and often chaotic. The objective of this study was to overcome these challenges using our proposed multistage dynamic mode decomposition with control (mDMDc) method and use this technique to study patient-specific blood flow physics. The inlet flow rate was considered as the controller input to the systems. Blood flow data were divided into different stages based on the inlet flow waveform and DMD with control was applied to each stage. The system was augmented to consider both velocity and wall shear stress (WSS) vector data, and therefore study the interaction between the coherent structures in velocity and near-wall coherent structures in WSS. First, it was shown that DMD modes can exactly represent the analytical Womersley solution for incompressible pulsatile flow in tubes. Next, our method was applied to image-based coronary artery stenosis and cerebral aneurysm models where complex blood flow patterns are anticipated. The flow patterns were studied using the mDMDc modes and the reconstruction errors were reported. Our augmented mDMDc framework could capture coherent structures in velocity and WSS with a fewer number of modes compared to the traditional DMD approach and demonstrated a close connection between the velocity and WSS modes.

Temporal and spatial evolution of cavitating bubbles and coherent structures in a confined submerged jet shear layer

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Runqiang Zhang ◽  
Guoyong Sun ◽  
Yuchuan Wang ◽  
Sebastián Leguizamón
Keyword(s):  
Shear Layer ◽  
Coherent Structures ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Content Type ◽  
Cavitation Inception ◽  
Mode Decomposition ◽  
The Relationship

PurposeThe study aims to display the bubbles' evolution in the shear layer and their relationship with the pressure fluctuations. Furthermore, the coherent structures of the first six modes are extracted, in order to provide insight into their temporal and spatial evolution and determine the relationship between cavitating bubbles and coherent structures.Design/methodology/approachIn the present study, numerical simulations of submerged jet cavitating flow were carried out at a cavitation inception condition inside an axisymmetric cavity using the large eddy simulation (LES) turbulence model and the Schnerr–Sauer (S–S) cavitation model. Based on snapshots produced by the numerical simulation, dynamic mode decomposition (DMD) was performed to extract the three-dimensional coherent structures of the first six modes in the shear layer.FindingsThe cavitating bubbles in the shear layer are deformed to elongated ellipsoid shapes by shear forces. The significant pressure fluctuations are induced by the collapse of the biggest bubble in the group. The first mode illustrates the mean characteristics of the flow field. The flow in the peripheral region of the shear layer is mainly dominated by large-scale coherent structures revealed by the second and third modes, while different small-scale coherent structures are contained in the central region. The cavitating bubbles are associated with small size coherent structures as the sixth or higher modes.Practical implicationsThis work demonstrates the feasibility of LES for high Reynolds number shear layer flow. The dynamic mode decomposition method is a novel method to extract coherent structures and obtain their dynamic information that will help us to optimize and control the flow.Originality/value(1) This paper first displays the three-dimensional coherent structures and their characteristics in the shear layer of confined jet flow. (2) The relationship of bubbles shape and pressure fluctuations is illustrated. (3) The visualization of coherent structures benefits the understanding of the mixing process and cavitation inception in jet shear layers.

scholarly journals Tomographic Particle Image Velocimetry and Dynamic Mode Decomposition (DMD) in a Rectangular Impinging Jet: Vortex Dynamics and Acoustic Generation

Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 429
Author(s):  
Hassan H. Assoum ◽  
Jana Hamdi ◽  
Marwan Alkheir ◽  
Kamel Abed Meraim ◽  
Anas Sakout ◽  
...  
Keyword(s):  
Particle Image Velocimetry ◽  
Acoustic Field ◽  
Coherent Structures ◽  
Particle Image ◽  
Flow Dynamics ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
Tomographic Particle Image Velocimetry ◽  
Mode Decomposition ◽  
Image Velocimetry

Impinging jets are encountered in ventilation systems and many other industrial applications. Their flows are three-dimensional, time-dependent, and turbulent. These jets can generate a high level of noise and often present a source of discomfort in closed areas. In order to reduce and control such mechanisms, one should investigate the flow dynamics that generate the acoustic field. The purpose of this study is to investigate the flow dynamics and, more specifically, the coherent structures involved in the acoustic generation of these jets. Model reduction techniques are commonly used to study the underlying mechanisms by decomposing the flow into coherent structures. The dynamic mode decomposition (DMD) is an equation-free method that relies only on the system’s data taken either through experiments or through numerical simulations. In this paper, the DMD technique is applied, and the spatial modes and their frequencies are presented. The temporal content of the DMD’s modes is then correlated with the acoustic signal. The flow is generated by a rectangular jet impinging on a slotted plate (for a Reynolds number Re = 4458) and its kinematic field is obtained via the tomographic particle image velocimetry technique (TPIV). The findings of this research highlight the coherent structures signature in the DMD’s spectral content and show the cross correlations between the DMD’s modes and the acoustic field.

Experimental Measurement of In-Plane Rolling Nonpneumatic Tire Vibrations Using High-Speed Imaging

2019 ◽  
Vol 47 (3) ◽  
pp. 196-210
Author(s):  
Meghashyam Panyam ◽  
Beshah Ayalew ◽  
Timothy Rhyne ◽  
Steve Cron ◽  
John Adcox
Keyword(s):  
High Speed ◽  
Image Correlation ◽  
Dynamic Mode Decomposition ◽  
Dynamic Mode ◽  
High Speed Imaging ◽  
Correlation Algorithm ◽  
Mode Decomposition ◽  
Series Of Experiments ◽  
Plane Deformations ◽  
Dominant Frequencies

ABSTRACT This article presents a novel experimental technique for measuring in-plane deformations and vibration modes of a rotating nonpneumatic tire subjected to obstacle impacts. The tire was mounted on a modified quarter-car test rig, which was built around one of the drums of a 500-horse power chassis dynamometer at Clemson University's International Center for Automotive Research. A series of experiments were conducted using a high-speed camera to capture the event of the rotating tire coming into contact with a cleat attached to the surface of the drum. The resulting video was processed using a two-dimensional digital image correlation algorithm to obtain in-plane radial and tangential deformation fields of the tire. The dynamic mode decomposition algorithm was implemented on the deformation fields to extract the dominant frequencies that were excited in the tire upon contact with the cleat. It was observed that the deformations and the modal frequencies estimated using this method were within a reasonable range of expected values. In general, the results indicate that the method used in this study can be a useful tool in measuring in-plane deformations of rolling tires without the need for additional sensors and wiring.

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