Centreline velocity decay measurements in 

low-velocity axisymmetric jets

Malmström, Tor G.; Kirkpatrick, Allan; Christensen, B.; Knappmiller, K.

doi:10.1017/s0022112097006368

Cited by 95 publications

(49 citation statements)

References 9 publications

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“…Indeed, this entrainment coefficient definition reflects that the air entrainment rate is responsible for the increase of the total jet flow rate with downstream distance. This is further confirmed by the experiments by Crow et al [5] or Malmström et al [35] in the twophase jet flow near field region, i.e., at a downstream distance of less than ten nozzle outlet diameters, elucidating that the entrainment coefficient in this region is lower than that in the Similarity region of the jet, i.e., at a downstream distance of greater than thirty nozzle outlet diameters.…”

Section: Literature Surveysupporting

confidence: 70%

Prediction of Droplet Velocities and Rain Out in Horizontal Isothermal Free Jet Flows of Air and Viscous Liquid in Stagnant Ambient Air

Rabadi

Friedel

Surma³

2007

Chem Eng & Technol

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Two-dimensional phase Doppler anemometer measurements of droplet size and velocity conducted under several nozzle conditions and a systematic variation of the air mass flow quality and liquid phase viscosity show that the air entrainment process is enhanced when keeping all test conditions constant except for increasing the Newtonian liquid viscosity above of that of water. A two-zone entrainment model based on a variable two-phase entrainment coefficient is proposed with the normalized axial distance allowing for a change in the jet angle. Thus, the jet perimeter is lower and the breakup length is longer in the case of air/relatively higher viscosity liquid phase. It provides the most accurate reproduction of the experimental droplet velocity in comparison with that of other models in the literature and, hence, is recommended for the prediction of the droplet velocity in the case of two-phase air/liquid phase free jet flow in stagnant ambient air. A model for predicting the droplet rain out, considering the droplet trajectories in the free jet flow, allows also for an adequate reproduction of the experimental data.

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Section: Literature Surveysupporting

confidence: 70%

Prediction of Droplet Velocities and Rain Out in Horizontal Isothermal Free Jet Flows of Air and Viscous Liquid in Stagnant Ambient Air

Rabadi

Friedel

Surma³

2007

Chem Eng & Technol

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“…The reported values on K commonly span between 4.0 -6.7 (see for example the review articles by Lipari and Stansby (2011) and Abdel-Rahman (2010)), although Malmström et al (1997) reported values below 4 for jets with very low inlet velocity. For the virtual origin ( ) reported values in the literature show significant spread.…”

Section: Research Questionmentioning

confidence: 99%

“…The spreading rate of a single round jet is in the order of 0.1 (see for example Malmström et al (1997)). …”

Section: Research Questionmentioning

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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“…Son Siebers y Higgins a lo largo de una serie de trabajos experimentales [69][70][71] los que estudian el fenómeno con detalle para un chorro Diesel inyectado en una cámara de volumen constante. Estos autores miden la longitud de lift-off a partir de la quimioluminiscencia del OH [72], y no a partir de la incandescencia del hollín como habían hecho Winklhofer o Larsson. En realidad, la longitud de lift-off indica la distancia a la cual está ubicada la zona de reacción premezclada que presenta el modelo conceptual de combustión en la fase cuasi-estacionaria, y a dicha distancia no hay hollín presente, sino que este aparece aguas abajo de esa zona (figura 2.8 30 ) y del aire en cámara (densidad, temperatura y concentración de oxígeno) que cubren, de manera más completa que Bergstrand et al, el rango esperable de condiciones en un motor Diesel de inyección directa.…”

Section: Lift-offunclassified

“…Se observa que, en una posición axial dada, la velocidad y la fracción de mezcla toman valores más elevados en el caso de combustión que en el de mezcla. Dicho de otra forma, la coordenada axial para la cual se alcanza un determinado grado de mezcla es mayor en el caso de un chorro en combustión que en el de mezcla 72 . En consecuencia, existen cambios en el tamaño del chorro y en el proceso de mezcla que las leyes de escalado desarrolladas hasta ahora no pueden tener en cuenta, y que dependen fundamentalmente del proceso de combustión.…”

Section: La Fracción De Mezcla Y Las Relaciones De Estadounclassified

Aportaciones al estudio del proceso de combustión turbulenta de chorros en motores diesel de inyección directa.

Oliver¹,

María²

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Aquestos conceptes han sigut estesos posteriorment al cas del doll Diesel. D'aquesta manera s'han estudiat en apartats successius els problemes de l'evaporació, l'autoencés i la flama de difussió Diesel mitjançant resultats experimentals obtesos a partir de tècniques convencionals iòptiques. Els raonaments recolzats sobre els conceptes de doll gasós han permés acompletar una descripció senzilla però rigurosa dels processos físics relevants per a l'evol·lució dels dolls de combustible. AbstractThe overall objective of this thesis is aimed at the construction of the necessary conceptual tools in order to analyse in a simple way the physical mechanisms that govern the fuel spray combustion process under boundary conditions found in a Diesel direct injection engine with a 2-litre per cylinder displacement that is highly supercharged. The work stems from the knowledge of the isothermal Diesel spray behaviour existing in the research group where it has been developed. In the first place, a review has been carried out in order to identify aspects of the Diesel injection-combustion process that have to be taken into account in order to develop this simple description.On the other hand, the work is based on the widely accepted assumption that this description can be based on the analysis of the Diesel spray from the point of view of gas jets. According to this, an in-depth study on the gas jet has been carried out, based on numerical simulations and theoretical deductions. The mixture fraction, the state relationships and the equivalent diameter concepts have been adapted in a simple way in order to describe the gaseous jets from the most general perspective, both under inert and reacting conditions. Such concepts have been extended to the Diesel spray. In this way, the evaporation, autoignition and difusion flame processes have been studied by means of experimental results obtained from both conventional and optical techniques. Arguments based on gas jet concepts have made it possible to compile a simple but rigourous description of the physical processes relevant to the evolution of fuel sprays. AgradecimientosMe gustaría en estas líneas agradecer a mucha gente su colaboración directa o indirecta en esta tesis doctoral, y en cualquier otro aspecto de mi trabajo en la CMT. En primer lugar, agradezco a José María Desantes y a José Vicente Pastor por todo lo que de ellos he aprendido en todos estos años. Al primero, gracias por enseñarme a pensar y a razonar la Física, para poder analizar algo tan complicado como un chorro de forma sencilla, pero a la vez sin dejar de ser estrictos. A José Vicente, por haberme enseñado una gran parte de la (poca) Optica que sé.También quisiera agradecer al Dr. Franz Chmela la oportunidad que nos ha ofrecido de trabajar en un proyecto en el que probablemente lo principal era aprender, imaginar, pensar. . . . Muchos conceptos de esta tesis doctoral son fruto de esas horas dedicadas, en el sentido estricto de la palabra, a investigar.En la parte experimental es donde uno se da cuenta de la c...

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Centreline velocity decay measurements in low-velocity axisymmetric jets

Cited by 95 publications

References 9 publications

Prediction of Droplet Velocities and Rain Out in Horizontal Isothermal Free Jet Flows of Air and Viscous Liquid in Stagnant Ambient Air

Prediction of Droplet Velocities and Rain Out in Horizontal Isothermal Free Jet Flows of Air and Viscous Liquid in Stagnant Ambient Air

Experimental and Numerical Investigations of Confluent Round Jets

Aportaciones al estudio del proceso de combustión turbulenta de chorros en motores diesel de inyección directa.

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