Computational study of buoyancy effects in a laminar starting jet

Satti, Rajani; Agrawal, Ajay K.

doi:10.1016/j.ijheatfluidflow.2007.12.002

Cited by 12 publications

(4 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although the transition Re is about a factor of 4 lower than the typical transition value (Re ∼ 1 760 for flow inside a cylindrical pipe, i.e., Poiseuille flow25), our Reynolds number is consistent with other reports (Re ∼ a few hundred) for the flow transition of helium plasma jet in open air 26, 27. This low Reynolds number flow transition was observed and explained in helium gas jets by the buoyancy effect 27–29. According to these reports, the buoyancy effect may be significant for flow transition in the low momentum and momentum dominated helium jet.…”

Section: Resultssupporting

confidence: 90%

A Simple Approach to Surface Modification Using Polytetrafluoroethylene (PTFE) with Laminar and Turbulent Flows of Micro Plasma Jets at Atmospheric Pressure

Jung¹,

Gweon²,

Kim³

et al. 2011

Plasma Processes & Polymers

View full text Add to dashboard Cite

Unlike large area plasmas, small size plasma jets could be useful in treating localized regions. For this reason, we developed a micro plasma jet having a polytetrafluoroethylene (PTFE) part exposed to the discharge inside the plasma source. As the helium gas flow rate was raised from 0.1 to 6.0 slpm, the plasma exhibited a change in characteristic from laminar to turbulent and an abrupt change of appearance at a certain flow rate (2.0–3.0 slpm). The measured rotational temperature was above 500 K under laminar flow conditions, which was a sufficiently high temperature for the pyrolysis of PTFE, and the excitation temperature of the laminar flow was higher than that of the turbulent flow. The corresponding optical emission spectra were different (CN, C2, F I, Hα dominated for laminar conditions while N 2+, OH, O I dominated for turbulent flow conditions). These different plasma characteristics were obtained by simply controlling the gas flow rate. A feasibility study of surface modification demonstrated a change of the surface wettability from hydrophobic to hydrophilic (and vice versa) depending only on the gas flow rate.

show abstract

Section: Resultssupporting

confidence: 90%

A Simple Approach to Surface Modification Using Polytetrafluoroethylene (PTFE) with Laminar and Turbulent Flows of Micro Plasma Jets at Atmospheric Pressure

Jung¹,

Gweon²,

Kim³

et al. 2011

Plasma Processes & Polymers

View full text Add to dashboard Cite

show abstract

“…Iglesias et al [20] and Satti and Agrawal [21,22] simulated helium jets injected into quiescent ambient air, motivated by the objective to improve the ignition of diesel engines. Satti and Agrawal [22] showed that the penetration rate was strongly dependent on buoyancy; they further investigated the effect of buoyancy on developing buoyant jets, focusing on the details of the vortex ring evolution. Despite their pioneering effort, their study did not cover enough scenarios to allow a systematic analysis of the role of the buoyancy flux in the starting phenomenon.…”

Section: Introductionmentioning

confidence: 99%

Large-eddy simulation of starting buoyant jets

et al. 2010

View full text Add to dashboard Cite

A series of Large Eddy Simulations (LES) are performed to investigate the penetration of starting buoyant jets. The LES code is first validated by comparing simulation results with existing experimental data for both steady and starting pure jets and lazy plumes. The centerline decay and the growth rate of the velocity and concentration fields for steady jets and plumes, as well as the simulated transient penetration rate of a starting pure jet and a starting lazy plume, are found to compare well with the experiments. After validation, the LES code is used to study the penetration of starting buoyant jets with three different Reynolds numbers from 2000 to 3000, and with a wide range of buoyancy fluxes from pure jets to lazy plumes. The penetration rate is found to increase with an increasing buoyancy flux. It is also observed that, in the initial Period of Flow Development, the two penetrative mechanisms driven by the initial buoyancy and momentum fluxes are uncoupled; therefore the total penetration rate can be resolved as the linear addition of these two effects. A fitting equation is proposed to predict the penetration rate by combining the two independent mechanisms.

show abstract

“…Satti and Agrawal 13 were also concerned with the variations of vorticity fields due to buoyancy effects in laminar starting jets, although their computational study was focused only on positively buoyant jets.…”

Section: Introductionmentioning

confidence: 99%

Negatively buoyant starting jets

2009

View full text Add to dashboard Cite

The initial development of negatively buoyant jets has been investigated experimentally and numerically, focusing on the role played by gravity in the evolution of the leading vortex ring. Under the experimental conditions considered in this work, the densimetric Froude number, Fr = j U j 2 / ͓͑ 0 − j ͒gD͔, which represents the ratio between the jet momentum and the buoyancy forces, emerges as the most relevant parameter characterizing the dynamics of the flow. Two different flow regimes have been observed depending on the Froude number: for sufficiently small Fr, the vortex ring generated initially is pushed radially away by gravity forces before it has time to detach from the shear layer originating at the orifice. On the other hand, when the Froude number is larger than a critical value, FrϾ Fr c ϳ 1, the vortex ring detaches from the injection orifice and propagates downstream into the stagnant ambient followed by a trailing jet until it eventually reaches a maximum penetration depth. In order to clarify the mechanisms leading to the transition between the two regimes, and to gain physical understanding of the formation dynamics of negatively buoyant starting jets, the total and the vortex circulation, as well as the trajectory of the vortex center, have been measured and compared to the case of neutrally buoyant jets. Finally, based on the experimental measurements and on the results of the numerical computations, a kinematic model that successfully describes the evolution of both total circulation and vortex trajectory is proposed.

show abstract

Computational study of buoyancy effects in a laminar starting jet

Cited by 12 publications

References 30 publications

A Simple Approach to Surface Modification Using Polytetrafluoroethylene (PTFE) with Laminar and Turbulent Flows of Micro Plasma Jets at Atmospheric Pressure

A Simple Approach to Surface Modification Using Polytetrafluoroethylene (PTFE) with Laminar and Turbulent Flows of Micro Plasma Jets at Atmospheric Pressure

Large-eddy simulation of starting buoyant jets

Negatively buoyant starting jets

Contact Info

Product

Resources

About