Flow Downstream of a Cluster of Nine Jets

Boutazakhti, Mohamed; Sullivan, Pierre E.; Thomson, Murray J.; Yimer, Ibrahim

doi:10.1115/1.2720451

Cited by 3 publications

(4 citation statements)

References 8 publications

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“…Starch granules of 5 lm mean diameter and density of 2.5 · 10 À4 g/mm 3 were used as tracer particles, which had good tracking ability and reflective performance 13,16 for the flow conditions investigated. The seeding density was set so that a The laser pulse energy was approximately 650 MJ.…”

Section: Piv Systemmentioning

confidence: 99%

“…Boutazakhti et al 16 utilized PIV and phase Doppler particle anemometry (PDPA) to map the velocity field downstream of a 3 · 3 square matrix of nine small swirlers, in addition to a single swirler configuration. The experimental results showed that in the merger region close to the swirlers, the characteristics of individual jets were still visible and the expansion rate of the central jet was slowed.…”

Section: Introductionmentioning

confidence: 99%

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Effect of boundary conditions on downstream vorticity from counter-rotating swirlers

Huo

Lin

Zhang

et al. 2015

Chinese Journal of Aeronautics

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Particle image velocimetry (PIV) is utilized to measure the non-reacting flow field in a reflow combustor with multiple and single swirlers. The velocity field, vortex structure and total vorticity levels are experimentally obtained using two different boundary conditions, representing a single confined swirler and multiple swirlers in an annular combustor. The influence of the boundary conditions on the flow field at several locations downstream of the swirlers is experimentally investigated, showing that the central vortex in the multi-swirler case is more concentrated than in the single-swirler case. The vorticity of the central vortex and average cross-sectional vorticity are relatively low at the swirler outlet in both cases. Both of these statistics gradually increase to the maximum values near 20 mm downstream of the swirler outlet, and subsequently decrease. It is also found that the central vortex in the multi-swirler case is consistently greater than the single-swirler case. These results demonstrate the critical influence of boundary conditions on flow characteristic of swirling flow, providing insight into the difference of the experiments on testbed combustor and the full-scale annular combustors. ª 2015 Production and hosting by Elsevier Ltd. on behalf of CSAA & BUAA.

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Section: Piv Systemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of boundary conditions on downstream vorticity from counter-rotating swirlers

Huo

Lin

Zhang

et al. 2015

Chinese Journal of Aeronautics

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“…experimental data for a cluster of nine swirling jets was recently obtained [Boutazakhti et al, 2007], while data for circular, elliptic, square, rectangular, equilateral triangular, and isosceles triangular jets was measured recently [Singh, Sundararajan, Bhaskaran, 2003].…”

Section: Swirling Jetmentioning

confidence: 99%

Swirling jets for the mitigation of hot spots and thermal stratification in the VHTR lower plenum.

Rodríguez¹

2011

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The literature indicates that a prismatic-core very high temperature reactor can experience thermal stratification and hot spot issues in the lower plenum (LP). This research hypothesizes that the complex thermalhydraulic phenomena in the LP requires a sophisticated computational fluid dynamics (CFD) code with state-of-the-art turbulence models and advanced swirling jet technology to mitigate the two issues. The primary research goals were to increase the heat transfer and mixing capacity of swirling jets, extend swirling jet theory, and to apply those advancements for the mitigation of the thermalhydraulic issues. First, it was demonstrated that the Fuego CFD code successfully modeled a set of key LP thermalhydraulic phenomena. Thereafter, a helicoid vortex swirl model was developed to investigate the impact of the swirl number (S) on mixing and heat transfer. The development of azimuthal and axial velocities that are solely functions of S permitted the analysis of the central recirculation zone's (CRZ) impact on the LP flow field. At this point, several characteristics were found in common between the helicoid vortex and other axisymmetric, Newtonian, incompressible vortices found in the literature. This observation resulted in a more fundamental understanding of how vortices behave, and which traits can be exploited for the purpose of maximizing heat transfer and mixing. Because the CRZ is a strong function of the azimuthal and axial velocities, shaping those velocity profiles had a substantial impact. Eventually, this led to the discovery that vortices may be expressed as alternating series that expand geometrically with odd exponents. This helped corroborate that the 15 axisymmetric vortices discussed in this research are part of a vortex family with seven common traits. This also led to the development of new vortices that are based on one or two series terms that satisfy the Navier-Stokes equations and conservation of mass. In addition, the impact of Reynolds number and swirl decay were explored in order to further quantify their impact. Finally, the above theories and modeling insights were applied towards a comprehensive set of LP calculations that showed that the swirling jets mitigated the entrainment and hot spot issues, while resulting in a reasonable pressure drop. Contents

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“…Further analysis on multiple jets has been conducted within research related to combustion or chemical mixing in Tatsumi et al (2010) and Boutazakhti et al (2007) and for ventilation supply devices by Meslem et al (2010). The study by Meslem et al (2010) showed that for an array of round jets the entrainment rate was higher close to the inlet and reducing in the downstream direction, contrary to twin round jets.…”

Section: 3mentioning

confidence: 99%

Experimental and Numerical Investigations of Confluent Round Jets

Svensson¹

2015

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Unconfined multiple interacting confluent round jets are interesting from a purely scientific point of view, as interaction between neighboring jets brings additional complexity to the flow field. Unconfined confluent round jets also exist in various engineering applications, such as ventilation supply devices, sewage disposal systems, combustion burners, chemical mixing or chimney stacks. Even so, little scientific attention has been paid to unconfined confluent round jets, and detailed investigations on the complete three-dimensional turbulent flow field of confluent jet configurations issuing into an unconfined stagnant environment are scarce.The present work uses both advanced measurement techniques and computational models to provide deeper understanding of the turbulent flow field development of unconfined confluent round jets. Both Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV) have been used to measure mean velocity and turbulence properties within two setups, consisting of a single row of 1×6 jets and a square in-line array of 6×6 confluent jets. LDA was used for measurements very close to the nozzle inlets and to verify the main findings made with PIV. A comparison between LDA and PIV results showed that the two measurement techniques produced results that are in good agreement with each other.Simulations using Computational Fluid Dynamics (CFD) of the 6×6 setup were conducted using three different Reynolds Averaged Navier-Stokes (RANS) turbulence models: the standard k-ε, the RNG k-ε and the Reynolds Stress Model (RSM). The results from the CFD simulations were compared with the experimental PIV data. The employed RANS turbulence models were all capable of accurately predicting mean velocities and turbulent properties in the investigated confluent jet array. In general the RSM and the standard k-ε model provided smaller deviations between numerical and experimental results than the RNG k-ε model. In terms of mean velocity the second-order closure model (RSM) was not found to be superior to the less complex standard k-ε model.The validated CFD results provide data at all locations in the solution domain and the computational results were used to further analyze the investigated confluent jet array. The validated CFD model was also employed in a parametrical investigation, including five independent variables: inlet velocity, nozzle diameter, nozzle edge-toedge spacing, nozzle height and the number of jets in the array. The parametrical investigations made use of statistical methods in the form of Response Surface Methodology and Box-Behnken Design of Experiments. The derived response surface models provided information on the principal influence and relative importance of the investigated parameters within the design limits.ii The positions of the jets within the array strongly influence both mean velocity and turbulence. In all investigated setups the jets experience merging and combining. Square arrays also include considerable jet convergence, which was not present in th...

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Flow Downstream of a Cluster of Nine Jets

Cited by 3 publications

References 8 publications

Effect of boundary conditions on downstream vorticity from counter-rotating swirlers

Effect of boundary conditions on downstream vorticity from counter-rotating swirlers

Swirling jets for the mitigation of hot spots and thermal stratification in the VHTR lower plenum.

Experimental and Numerical Investigations of Confluent Round Jets

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