Confined axisymmetric laminar jets with large expansion ratios

Revuelta, Antonio; Sánchez, Antonio L.; Liñán, A.

doi:10.1017/s0022112001007601

Cited by 15 publications

(16 citation statements)

References 39 publications

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“…It can be expected that the accuracy of the BL approximation would improve for larger R j , a point supported by comparisons with integrations of the complete Navier-Stokes equations computed in Ref. 5 for confined jets with no coflow. Nevertheless, considering the moderate values of the parameters R j ϭ35 and Ϫ1 Ӎ34.8 used in the experiment, the comparisons of Fig.…”

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confidence: 79%

“…In the analysis, the ratio of the inner to the outer radii will be assumed to be very small, as done in Ref. 5 for the confined jet with no coflow, and the momentum flux of the coflow J c will be assumed to be comparable to that of the jet, i.e., Craya-Curtet numbers Cϭ(J c /J j ) 1/2 of order unity, the latter being the appropriate distinguished limit for studying the emergence of reverse flow. Although much research has been done on confined laminar jets ͑see, e.g., the literature review given in Ref.…”

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confidence: 99%

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Laminar Craya–Curtet jets

et al. 2004

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This Brief Communication investigates laminar Craya-Curtet flows, formed when a jet with moderately large Reynolds number discharges into a coaxial ducted flow of much larger radius. It is seen that the Craya-Curtet number, Cϭ(J c /J j ) 1/2 , defined as the square root of the ratio of the momentum flux of the coflowing stream to that of the central jet, arises as the single governing parameter when the boundary-layer approximation is used to describe the resulting steady slender jet. The numerical integrations show that for C above a critical value C c the resulting streamlines remain aligned with the axis, while for CϽC c the entrainment demands of the jet cannot be satisfied by the coflow, and a toroidal recirculation region forms. The critical Craya-Curtet number is determined for both uniform and parabolic coflow, yielding C c ϭ0.65 and C c ϭ0.77, respectively. The streamlines determined numerically are compared with those obtained experimentally by flow visualizations, yielding good agreement in the resulting flow structure and also in the value of Confined jet flows are of interest for many practical engineering applications. The configuration shown in Fig. 1, in which an axisymmetric jet of radius a, with Ӷ1, discharges into a coaxial ducted stream of radius a, is relevant in particular to ejector systems and combustion chambers. Most of the previous works have been devoted to the case of turbulent flows, corresponding to the high-Reynolds-number jets most often encountered in applications. Of particular relevance are the pioneering experimental and theoretical analyses of Craya and Curtet 1 and Curtet, 2 which addressed as a central issue the emergence of regions of reverse flow near the confining wall when sufficiently weak coflow is present. A dimensionless parameter based on similarity considerations was proposed to characterize the resulting flow, similar to that previously proposed by Thring and Newby in their study of turbulent, coflow diffusion flames, 3 for which the recirculating flow provides a key stabilizing mechanism. For the case of uniform coflow investigated by Craya and Curtet, their parameter reduces to Cϭ(J c /J j ) 1/2 in the limit →0 of small inner jet radius, where J c and J j represent the momentum fluxes of the coflow and of the jet, respectively. A detailed account of experimental results, theoretical analyses and approximate integral solutions for turbulent CrayaCurtet jets can be found in Ref. 4. Unlike the above mentioned studies, we address here the laminar flow arising for values of the jet Reynolds number R j ϭ͓J j /()͔ 1/2 /ӷ1 below a certain critical value, when the resulting symmetric solution remains steady, giving a slender jet of characteristic length R j a that can be described with relative errors of order R j Ϫ2 with the boundary-layer ͑BL͒ approximation. The same incompressible fluid of density and kinematic viscosity is assumed to be present in both streams. In the analysis, the ratio of the inner to the outer radii will be assumed to be very small, as done...

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Laminar Craya–Curtet jets

et al. 2004

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“…From the critical injection velocities, it is possible to calculate the local velocity in the jet centreline, ‫ݑ‬ * , at the distance ℎ between the nozzle and the granular bed by a theoretical relation given by [6] for a self-similar laminar jet model and validated for the present jet configuration:…”

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confidence: 99%

Experimental investigation of impinging jet erosion on model cohesive granular materials

Brunier-Coulin¹,

Sarrat²,

Cuéllar³

et al. 2017

EPJ Web Conf.

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Abstract. Erosion of soils affects both natural landscapes and engineering constructions as embankment dams or levees. Improving the safety of such earthen structures requires in particular finding out more about the elementary mechanisms involved in soil erosion. Towards this end, an experimental work was undertaken in three steps. First, several model materials were developed, made of grains (mostly glass beads) with solid bridges at particle contacts whose mechanical yield strength can be continuously varied. Furthermore, for most of them, we succeeded in obtaining a translucent system for the purpose of direct visualization. Second, these materials were tested against surface erosion by an impinging jet to determine a critical shear stress and a kinetic coefficient [2,3]. Note that an adapted device based on optical techniques (combination of Refractive Index Matching and Planar Laser Induced Fluorescence [3]) was used specifically for the transparent media. Third, some specifically developed mechanical tests, and particularly traction tests, were implemented to estimate the mechanical strength of the solid bridges both at micro-scale (single contact) and at macro-scale (sample) and to investigate a supposed relationship with soil resistance to erosion.

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“…walls and deviates from free jet predictions. While some previous mathematical analyses [11] have investigated flow behavior, they have not presented compact correlations to predict the flow, while other experimental investigations [12] did not investigate large expansion ratios. The transition regions identified in this work include the location where the jet begins to deviate from the linear behavior associated with a free jet, the location where the flow reattaches to the confinement wall, known as the reattachment length, and the location where flow in the confinement becomes fully developed.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the Behavior of Confined Laminar Round Jets

Landfried

Jana

Kimber

2012

Volume 1: Symposia, Parts a and B

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Confined laminar fluid jets have many practical applications in industry. Several examples include expansions in pipes and flow of gas into a large plenum. While much consideration has been given experimentally to heat transfer and pressure gradients within the confinement, little attention has been paid to quantify the velocity profiles and transitions between various flow behaviours. Using a finite volume CFD code, OpenFOAM ®, the Navier-Stokes equations were solved for varying expansion ratio, 1/ε = renclosure/rj, and varying Reynolds numbers. In the present analysis, Reynolds number based on the inlet jet diameter is varied from 30 to 70, well within the accepted range for laminar jet behavior. The expansion ratio, 1/ε is varied from 20–200. Of primary focus in the current study are compact correlations for the jet centreline velocity as a function of jet Reynolds number, Rej and expansion ratio. Similar functional dependences for the “linear” decay region of the jet, and the location of the stagnation point on the enclosure wall, are also investigated. These are all important features of the global flow field for the confined jet. Results suggest that initially, the flow characteristics are identical to a free jet. At some downstream location, the presence of the enclosure is felt by the jet and deviations begin to be seen from free jet behavior. This transition region continues until at a sufficiently large downstream location, the flow becomes fully developed, internal Poiseuille flow. In this paper, we analyse these transition regions and offer explanations and practical correlations to successfully predict the important flow physics that occur between free jet behavior and Poiseuille flow. Key dimensionless parameters are identified, the magnitude of which can be used to classify the flow conditions.

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Confined axisymmetric laminar jets with large expansion ratios

Cited by 15 publications

References 39 publications

Laminar Craya–Curtet jets

Laminar Craya–Curtet jets

Experimental investigation of impinging jet erosion on model cohesive granular materials

Characterization of the Behavior of Confined Laminar Round Jets

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