Determination of single and double helical structures in a swirling jet by spectral proper orthogonal decomposition

Zhang, Yang; Vanierschot, Maarten

doi:10.1063/5.0032985

Cited by 26 publications

(5 citation statements)

References 62 publications

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“…The subgrid-scale stress tensor τ ij = u i u j − u i u j in the above formulation is modeled by the localized dynamic k model introduced by Kim and Menon [19][20] . Recently, we have used the same numerical approach to simulate the turbulent annular swirling jet flow in a similar configuration to identify the helical vortex cores in the flow field [21] . It was found that the numerical results were in line with experimental measurements, validating the approach.…”

Section: Methodsmentioning

confidence: 99%

“…The time step is fixed at 8 × 10 −6 s to meet the Courant-Friedrichs-Lewy condition, and the maximum Courant number is less than 0.55 during the simulation. The detailed information about the numerical method and its validation can be found in our previous work [21] . can see that the recirculation zone behind the inner cylinder is asymmetric although the flow configuration has an axisymmetric geometry.…”

Section: Movable Blocksmentioning

confidence: 99%

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Proper orthogonal decomposition analysis of coherent motions in a turbulent annular jet

Zhang

Vanierschot

2021

Appl. Math. Mech.-Engl. Ed.

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A three-dimensional incompressible annular jet is simulated by the large eddy simulation (LES) method at a Reynolds number Re = 8 500. The time-averaged velocity field shows an asymmetric wake behind the central bluff-body although the flow geometry is symmetric. The proper orthogonal decomposition (POD) analysis of the velocity fluctuation vectors is conducted to study the flow dynamics of the wake flow. The distribution of turbulent kinetic energy across the three-dimensional POD modes shows that the first four eigenmodes each capture more than 1% of the turbulent kinetic energy, and hence their impact on the wake dynamics is studied. The results demonstrate that the asymmetric mean flow in the near-field of the annular jet is related to the first two POD modes which correspond to a radial shift of the stagnation point. The modes 3 and 4 involve the stretching or squeezing effects of the recirculation region in the radial direction. In addition, the spatial structure of these four POD eigenmodes also shows the counter-rotating vortices in the streamwise direction downstream of the flow reversal region.

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Section: Methodsmentioning

confidence: 99%

Section: Movable Blocksmentioning

confidence: 99%

Proper orthogonal decomposition analysis of coherent motions in a turbulent annular jet

Zhang

Vanierschot

2021

Appl. Math. Mech.-Engl. Ed.

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“…Only very few numerical works have reported the double helix structure. Zhang and Vanierschot (2021) used incompressible LES to predict single and double PVC in the iso-thermal flow investigated by Vanierschot et al (2020). Mansouri et al (2016) studied a double helical vortex structure and its interaction with a premixed propane flame in a swirl-stabilised burner using Detached Eddy Simulation.…”

Section: Temporal Evolution Of Vortical Structuresmentioning

confidence: 99%

Numerical Investigation of Combustion Instabilities in Swirling Flames with Hydrogen Enrichment

Gong,

Fredrich,

Marquis

et al. 2023

Flow Turbulence Combust

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This work presents a numerical study on technically premixed, swirl-stabilised flames in the PRECCINSTA model combustor. The employed method, BOFFIN-LES, comprises a fully compressible formulation to study unsteady combustion with thermo-acoustic instabilities. To allow for this, the iso-thermal flows are first investigated, based on which three reacting cases are established. The investigation delves into various aspects including flame topology, flow characteristics, and the related thermo-acoustic and hydrodynamic instabilities are studied and results are benchmarked against available measurement data. The dominant feedback mechanism of the observed thermo-acoustic fluctuations is identified; the evolution of the helical vortex is discussed together with the related flame stabilisation process. Furthermore, the interplay of the thermo-acoustic oscillations, helical structure, and the flame stabilisation process is summarised in the end, with the potential effect of the wall-heat transfer on them discussed. This work establishes that the Large Eddy Simulation (LES) effectively captures the iso-thermal flow dynamics and the flame topology under various operating conditions, with a good prediction of the thermo-acoustic frequencies in all the cases. The dominant driving mechanism of the observed thermo-acoustic fluctuations was identified as a combined effect of equivalence ratio and velocity fluctuations in all the cases investigated. The effect of Hydrogen enrichment on modifying the flame topology and changing the thermo-acoustic instability features are well predicted by the simulations. Moreover, different modes of the helical vortex are detected, and their periodic excitement, evolution, and effect on flame stabilisation are discussed in great detail. To conclude, this LES-based investigation offers valuable insights into the complex interplay of unsteady combustion, acoustic fluctuations, flow dynamics, and solid boundaries within swirling flames subjected to unsteady conditions.

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“…To capture the relevant flow dynamics of the jet flow, we apply snapshot SPOD as reduced order modelling technique (24). Snapshot SPOD has already shown its capabilities for both swirling and non-swirling jet flows (21,28,29,32). The velocity field is decomposed into a mean and fluctuating part:…”

Section: Spectral Proper Orthogonal Decomposition (Spod)mentioning

confidence: 99%

Experimental study of a self-excited jet precession in a sudden expansion flow

Holemans

Zhu

Greef

et al. 2022

Preprint

Self Cite

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Stereoscopic Particle Image Velocimetry (S-PIV) measurements are performed to analyse the flow field in a sudden expansion with an expansion ratio of 4.9:1. The velocity profile in the inlet tube is measured using Laser Doppler Anemometry (LDA) and the Reynolds number (Re) is varied from 3150 till 63300. The time-averaged flow field is found to be axisymmetric and has a jet-like velocity profile near the nozzle with a spreading rate comparable to free round jets. Despite the axisymmetric nature of the mean flow field, it contains unsteady coherent structures, which are analysed using both Spectral Proper Orthogonal Decomposition (SPOD) and phase averaging. It is found that the instantaneous flow field is asymmetric and it precesses around the central axis of the geometry. The structure of this precession is similar for all Reynolds numbers investigated and the Strouhal number increases with increasing Reynolds number till Re= 26000, after which it reaches a constant value of around 3 × 10−3. These precessing structures were previously only reported for swirling sudden expansion flows or flows in dedicated free jet nozzles, but this study shows they also exist in confined non swirling sudden expansion flows.

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Determination of single and double helical structures in a swirling jet by spectral proper orthogonal decomposition

Cited by 26 publications

References 62 publications

Proper orthogonal decomposition analysis of coherent motions in a turbulent annular jet

Proper orthogonal decomposition analysis of coherent motions in a turbulent annular jet

Numerical Investigation of Combustion Instabilities in Swirling Flames with Hydrogen Enrichment

Experimental study of a self-excited jet precession in a sudden expansion flow

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