Effects of Exit Geometry on the Propulsive Characteristics of the Starting Jet

2019 ◽  
Vol 09 (04) ◽  
pp. 197-206
Author(s):  
鑫 王
Keyword(s):  
Starting Jet

scholarly journals Compressible starting jet: pinch-off and vortex ring–trailing jet interaction

2017 ◽  
Vol 817 ◽  
pp. 560-589 ◽  
Author(s):  
Juan José Peña Fernández ◽  
Jörn Sesterhenn
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Vortex Ring ◽  
Pressure Ratio ◽  
Reynolds Numbers ◽  
Chamber Pressure ◽  
Vortex Interaction ◽  
Dominant Feature ◽  
Chamber Temperature ◽  
Starting Jet

The dominant feature of the compressible starting jet is the interaction between the emerging vortex ring and the trailing jet. There are two types of interaction: the shock–shear layer–vortex interaction and the shear layer–vortex interaction. The former is clearly not present in the incompressible case, since there are no shocks. The shear layer–vortex interaction has been reported in the literature in the incompressible case and it was found that compressibility reduces the critical Reynolds number for the interaction. Four governing parameters describe the compressible starting jet: the non-dimensional mass supply, the Reynolds number, the reservoir to unbounded chamber temperature ratio and the reservoir to unbounded chamber pressure ratio. The latter parameter does not exist in the incompressible case. For large Reynolds numbers, the vortex pinch-off takes place in a multiple way. We studied the compressible starting jet numerically and found that the interaction strongly links the vortex ring and the trailing jet. The shear layer–vortex interaction leads to a rapid breakdown of the head vortex ring when the flow impacted by the Kelvin–Helmholtz instabilities is ingested into the head vortex ring. The shock–shear layer–vortex interaction is similar to the noise generation mechanism of broadband shock noise in a continuously blowing jet and results in similar sound pressure amplitudes in the far field.

High-resolution LES of a starting jet

2016 ◽  
Vol 140 ◽  
pp. 435-449 ◽  
Author(s):  
E. Inanc ◽  
M.T. Nguyen ◽  
S. Kaiser ◽  
A.M. Kempf
Keyword(s):  
High Resolution ◽  
Starting Jet

Modelling circulation, impulse and kinetic energy of starting jets with non-zero radial velocity

2013 ◽  
Vol 719 ◽  
pp. 488-526 ◽  
Author(s):  
Michael Krieg ◽  
Kamran Mohseni
Keyword(s):  
Kinetic Energy ◽  
Radial Velocity ◽  
Jet Flows ◽  
Axisymmetric Jet ◽  
Image Velocimetry ◽  
Energy Modelling ◽  
Powerful Analytical Tool ◽  
Drastic Effect ◽  
Specific Configuration ◽  
Starting Jet

AbstractThe evolution of starting jet circulation, impulse and kinetic energy are derived in terms of kinematics at the entrance boundary of a semi-infinite axisymmetric domain. This analysis is not limited to the case of parallel jet flows; and the effect of non-zero radial velocity is specifically identified. The pressure distribution along the entrance boundary is also derived as it is required for kinetic energy modelling. This is done without reliance on an approximated potential function (i.e. translating flat plate), making it a powerful analytical tool for any axisymmetric jet flow. The pressure model indicates that a non-zero radial velocity is required for any ‘over-pressure’ at the nozzle exit. Jet flows are created from multiple nozzle configurations to validate this model. The jet is illuminated in cross-section, and velocity and vorticity fields are determined using digital particle image velocimetry (DPIV) techniques and circulation, impulse and kinetic energy of the jet are calculated from the DPIV data. A non-zero radial velocity at the entrance boundary has a drastic effect on the final jet. Experimental data showed that a specific configuration resulting in a jet with a converging radial velocity, with a magnitude close to 40 % of the axial velocity at its maximum, attains a final circulation which is 90–100 % larger than a parallel starting jet with identical volume flux and nozzle diameter, depending on the stroke ratio. The converging jet also attains a final impulse which is 70–75 % larger than the equivalent parallel jet and a final kinetic energy 105–135 % larger.

scholarly journals PERIODIC FLOWS FROM TIDAL INLETS

1978 ◽  
Vol 1 (16) ◽  
pp. 78
Author(s):  
D.L. Wilkinson
Keyword(s):  
Bottom Topography ◽  
Vortex Pair ◽  
Periodic Flows ◽  
Variable Bottom ◽  
Dominant Feature ◽  
Coastal Inlet ◽  
Offshore Flow ◽  
Rotational Motions ◽  
Starting Jet ◽  
Coastal Inlets

A study was undertaken of the flow produced in the offshore region by tidal currents at the entrance of a coastal inlet. The gross features of the offshore flow structure were examined in an idealised two dimensional model in which a sinusoidally reversing flow was discharged from an open channel into a large stagnant basin. During each period of ebb flow, the discharge from the simulated inlet developed a structure very similar to that of a starting jet, and a vortex pair was observed to form and ultimately became the dominant feature of the flow. Although variable bottom topography and long shore currents will distort the flow pattern, the rotational motions observed in these experiments would be expected to persist. The study was restricted to coastal inlets in which the sectional area of the entrance channel is several orders of magnitude smaller the area of water surface inside the inlet.

scholarly journals Modeling Aerial Transmission of Pathogens (Including the SARS-CoV-2 Virus) through Aerosol Emissions from E-Cigarettes

2021 ◽  
Vol 11 (14) ◽  
pp. 6355
Author(s):  
Roberto A. Sussman ◽  
Eliana Golberstein ◽  
Riccardo Polosa
Keyword(s):  
Cigarette Smoking ◽  
Theoretical Modeling ◽  
Horizontal Distance ◽  
Axially Symmetric ◽  
Low Intensity ◽  
Direct Exposure ◽  
Submicron Droplets ◽  
Starting Jet ◽  
Aerosol Emissions ◽  
Respiratory Droplets

We examine the plausibility of aerial transmission of pathogens (including the SARS-CoV-2 virus) through respiratory droplets that might be carried by exhaled e-cigarette aerosol (ECA). Given the lack of empiric evidence on this phenomenon, we consider available evidence on cigarette smoking and respiratory droplet emission from mouth breathing through a mouthpiece as convenient proxies to infer the capacity of vaping to transport pathogens in respiratory droplets. Since both exhaled droplets and ECA droplets are within the Stokes regime, the ECA flow acts effectively as a visual tracer of the expiratory flow. To infer quantitatively the direct exposure distance, we consider a model that approximates exhaled ECA flow as an axially symmetric intermittent steady starting jet evolving into an unstable puff, an evolution that we corroborate by comparison with photographs and videos of actual vapers. On the grounds of all this theoretical modeling, we estimate for low-intensity vaping (practiced by 80–90% of vapers) the emission of 6–210 (median 39.9, median deviation 67.3) respiratory submicron droplets per puff and a horizontal distance spread of 1–2 m, with intense vaping possibly emitting up to 1000 droplets per puff in the submicron range with a distance spread over 2 m. The optical visibility of the ECA flow has important safety implications, as bystanders become instinctively aware of the scope and distance of possible direct contagion through the vaping jet.

scholarly journals Experimental characterization of starting jet dynamics

2007 ◽  
Vol 39 (11-12) ◽  
pp. 711-730 ◽  
Author(s):  
Geno Pawlak ◽  
Carolina Marugan Cruz ◽  
Carlos Martínez Bazán ◽  
Pedro García Hrdy
Keyword(s):  
Experimental Characterization ◽  
Starting Jet

scholarly journals Structure and evolution of tidal starting jet vortices at idealized barotropic inlets

2009 ◽  
Vol 114 (C5) ◽  
Author(s):  
Francisco Nicolau del Roure ◽  
Scott A. Socolofsky ◽  
Kuang-An Chang
Keyword(s):  
Starting Jet
Sign in / Sign up

Export Citation Format

Share Document