Experimental analysis of low-Reynolds number free jets

Todde, Valentino; Spazzini, Pier Giorgio; Sandberg, Mats

doi:10.1007/s00348-009-0655-0

Cited by 55 publications

(32 citation statements)

References 19 publications

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“…For example, jets issued from different nozzle configuration have different mixing effect. Therefore, depending on initial conditions, the interaction between the jet flow and the ambient will affect jet development with regard to vortex separation, roll up and pairing, free turbulence evolution, and viscous/inviscid interactions . This in turn will influence the rate of ambient entrainment into the jet.…”

Section: Introductionmentioning

confidence: 99%

Entrainment and its implications on microclimate ventilation systems: Scaling the velocity and temperature field of a round free jet

Kabanshi

Sandberg

2019

Indoor Air

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Research on microclimate ventilation systems, which mostly involve free jets, points to delivery of better ventilation in breathing zones. While the literature is comprehensive, the influence of contaminant entrainment in jet flows and its implications on the delivery of supplied air is not fully addressed. This paper presents and discusses entrainment characteristics of a jet issued from a round nozzle (0.05 m diameter), in relation to ventilation, by exploring the velocity and temperature fields of the jet flow. The results show a trend suggesting that increasing the Reynold number (Re) reduces ambient entrainment. As shown herein, about 30% concentration of ambient air entrained into the bulk jet flow at Re 2541 while Re 9233 had about 13% and 19% for Re = 6537/12 026 at downstream distance of 8 diameters (40 cm). The study discusses that “moderate to high” Re may be ideal to reduce contaminant entrainment, but this is limited by delivery distance and possibly the risk of occupant discomfort. Incorporating the entrainment mixing factor (the ratio of room contaminants entrained into a jet flow) in performance measurements is proposed, and further studies are recommended to verify results herein and test whether this is general to other nozzle configurations.

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Section: Introductionmentioning

confidence: 99%

Entrainment and its implications on microclimate ventilation systems: Scaling the velocity and temperature field of a round free jet

Kabanshi

Sandberg

2019

Indoor Air

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“…Drazin and Reid, 1981). Photographs of free submerged jets often show a laminar "potential core" emerging from the nozzle, with growing waves downstream rolling up into ring vortices along the edges due to Kelvin-Helmholtz instability driven by the local velocity gradients (Todde et al, 2009). The spatial distances for evolution from the nozzle exit, to rolling up of the vortex layer, to coalescence of ring vortex pairs, and eventually to the development of turbulent eddies, were found to shorten with increasing Reynolds number (Becker and Massaro, 1968;Kwon and Seo, 2005;Abdel-Rahman, 2010).…”

Section: Introductionmentioning

confidence: 99%

Mist flow visualization for round jets in Aerosol Jet^®printing

Feng

2018

Aerosol Science and Technology

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With the microdroplets of water serving as light scattering particles, the mist flow patterns of round micro-jets can be visualized using the Aerosol Jet ® direct-write system. The visualization images show that the laminar mist jet (with sheath-to-mist ratio Y = 1:1) appears to extend to more than 20 times the diameter of nozzle orifice D for jet Reynolds number Re < 600, especially with D = 0.3 mm and less. For smaller jets (e.g., with D = 0.15 mm), laminar collimated mist flow might be retained to 40xD for Re < 600 and for Re ~ 1500 within 20xD from the nozzle. The laminar part of mist flow associated with larger jets (e.g., with D = 1.0 mm for Re < 600) tends to exhibit noticeable gradual widening due to viscous diffusion. For free jets, their breakdown length-the distance from nozzle where transition from laminar to turbulent mist flow takes place as signaled by a rapid widening of mist stream-is shown to decrease with increasing Re . The presence of impingement wall tends to prevent turbulence development, even when the wall is placed further downstream of the free-jet breakdown length for a given Re . The critical Re for an impinging jet to develop turbulence increases as the standoff S is reduced. The mist flow of impinging jet of D = 1.0 mm seems to remain laminar even for Re > 4000 at S = 12 mm.

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“…By reviewing some of the experimental work regarding turbulent round jets with smoothly contracting jet nozzles with various Re ranges [18,[24][25][26][27][28][29], it can be concluded that there is no universal Re dependency of the jet mean centerline decay either. For jets with low Re, as stated in Todde et al [24], the mean decay rate 1/B and the virtual origin have different Re dependencies. e decay rate 1/B decreases with Re until about Re � 1600, then remains constant until Re � 4000, and eventually increases again above 4000.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study

Teng

Larsson

Lundström

et al. 2018

International Journal of Chemical Engineering

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In rotary kilns in grate-kiln systems for iron ore pelletizing, a long and stable jet flame is needed to ensure a high quality of the pellets. The primary jet issuing from the nozzle interacts with two asymmetric co-flows creating a very complex flow. In order to better understand and eventually model this flow with quality and trust, simplified cases need to be studied. In this work, a simplified and virtual model is built based on a down-scaled kiln model established in a previous experimental work. The aim is to numerically study the jet development as a function of position and Reynolds number (Re). The numerical simulations are carried out with the standardk-εmodel, and quite accurate velocity profiles are obtained while the centerline decays and spreading of the passive scalars are over predicted. The model is capable of predicting a Re dependency of the jet development. With increasing Re, the jet is longer while it generally decays and spreads faster resulting from the stronger shear between the jet and co-flows and the stronger entrainment from the recirculation zone. This recirculation found in the simulations restrain the momentum spreading in the spanwise direction, leading to a slower velocity spreading with higher Re. For further validation and understanding, more measurements in the shear layer and simulations with more advanced turbulence models are necessary.

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Experimental analysis of low-Reynolds number free jets

Cited by 55 publications

References 19 publications

Entrainment and its implications on microclimate ventilation systems: Scaling the velocity and temperature field of a round free jet

Entrainment and its implications on microclimate ventilation systems: Scaling the velocity and temperature field of a round free jet

Mist flow visualization for round jets in Aerosol Jet^®printing

The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study

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Experimental analysis of low-Reynolds number free jets

Cited by 55 publications

References 19 publications

Entrainment and its implications on microclimate ventilation systems: Scaling the velocity and temperature field of a round free jet

Entrainment and its implications on microclimate ventilation systems: Scaling the velocity and temperature field of a round free jet

Mist flow visualization for round jets in Aerosol Jet®printing

The Effect of Reynolds Number on Jet in Asymmetric Co-Flows: A CFD Study

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Mist flow visualization for round jets in Aerosol Jet^®printing