Variation of drag coefficients in an interacting drop stream

Poo, J. Y.

doi:10.1007/bf00198426

Cited by 18 publications

(6 citation statements)

References 15 publications

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“…19 The droplet stream drag coefficients are more than five times smaller than for isolated droplets and thus droplets are about five times less decelerated. This finding is in accordance with several available studies (Mulholland et al 1988;Poo and Ashgriz 1991;Fieberg et al 2009): All approaches agree that the droplet drag coefficient in an infinite stream depends on aerodynamic forces (Reynolds number), the inter-droplet distance (spacing parameter C) and evaporation (a factor that includes the Spalding mass transfer number). The inter-droplet spacing is the crucial factor for modeling the influence of the stream.…”

Section: Dynamics Of the Droplet Streamsupporting

confidence: 93%

Applicability of pulsed 2cLIF-EET for micro-droplet internal thermometry under evaporation conditions

et al. 2020

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The relatively new thermometry technique "pulsed 2cLIF with MDR-enhanced energy transfer" is tested for the first time on micro-droplet streams in a heated air flow. The method allows simultaneous measurements of the droplet internal temperaturefield, droplet size and droplet velocity. Plausibility of the measurement results is evaluated by comparing results of various experimental conditions among each other and by comparison with analytic modeling. Overall, measurement results are plausible. However, measured temperature-fields are biased by the integral fluorescence signal and initial conditions of the models are limited by the Rayleigh jet breakup that creates the droplet stream.

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Section: Dynamics Of the Droplet Streamsupporting

confidence: 93%

Applicability of pulsed 2cLIF-EET for micro-droplet internal thermometry under evaporation conditions

et al. 2020

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“…Droplets in size bin 20-40 µm with Stk ≈ 1 are still somewhat affected by the airflow while the largest droplets (80-160 µm) with Stk > 10 move almost ballistically. It is well known that the ambient turbulence increases Cd, (Poo & Ashgriz, 1991); therefore, the Stk of droplets of all sizes is rather overestimated in highturbulent spray regions. The overall data inspection shows that the Stk decreases systematically with the axial distance for all size groups.…”

Section: Stokes Number Of Dropletsmentioning

confidence: 99%

“…varies with the droplet concentration or interdroplet spacings (Poo & Ashgriz, 1991) and depends on the turbulence character (S. Lee, 1987). The extent of interactions between droplets has been given up to seven droplet diameters parallel to the airflow and two droplet diameters normal to the airflow (Poo & Ashgriz, 1991).…”

Section: Stokes Number Of Dropletsmentioning

confidence: 99%

Air–liquid interactions in a pressure-swirl spray

Jedelský

Malý

Corral

et al. 2018

International Journal of Heat and Mass Transfer

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The energy transfer between a liquid hollow cone spray and the surrounding air has been studied using both imaging and phase-Doppler techniques. The spray was produced by a pressure-swirl atomizer discharging Jet A-1 fuel at inlet over pressures of p = 0.5, 1.0 and 1.5 MPa into quiescent ambient air. The liquid exits the nozzle as a conical film which thins as it spreads and develops long-and shortwave sinusoidal instabilities with breakup occurring, at the length smaller than that predicted by the inviscid model, to form film fragments and ultimately droplets downstream the spray. The single shot imaging characterised the spray regions of near-nozzle flow, the breakup processes and the developed spray. The phase-Doppler system resolved the three components of velocity and size for the droplet flow as measured on radial profiles for four axial distances from the nozzle exit. A Stokes number, Stk, analysis of the droplets' response times to the airflow timescales showed that droplets < 5 µm followed the airflow faithfully and so were used to estimate the local airflow velocity. This allowed a comparison of both the droplet and airflow fields in terms of their mean and fluctuating velocity components to be made. The formation of the hollow cone spray and the interaction of the fragments and droplets with the air, through viscous drag, induce complex entrained airflows. The airflow was found to be highly anisotropic, fluctuating preferentially in the downstream direction, and spatially varying within three distinct spray regions. The air drag establishes a positive size-velocity correlation of droplets; their Stk reduces with axial distance and increases with droplet size and p; so that Stk ≈ 1 for 20-40 µm droplets and the largest droplets (80-160 µm, Stk > 10) move ballistically. The spatially resolved mean and turbulent kinetic energies of the air and spectra of the droplet velocity fluctuations are detailed in the paper. These findings are relevant to scientists and engineers modelling the complex two-phase flows.

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“…They concluded that the leading droplet is not affected by the trailing in terms of drag force, while the latter experiences reduction in its drag coefficient up to 50% relative to its isolated value. Poo and Ashgriz [24] also investigated the variation of the drag coefficient in a droplet stream present in a turbulent flow and found a decrease in the drag coefficient by a factor of 4 to 5 compared to the drag coefficient of a solid sphere at the same conditions. Nguyen and Dunn-Rankin [25] conducted experiments with droplet packets (1-6 droplets) travelling vertically in an air stream for Re=80 and L/D 0 =5.2, and found that the average drag of the trailing droplet was 25% lower than that of the leading one.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Numerical investigation of the aerodynamic breakup of droplets in tandem

Stefanitsis

Malgarinos

Strotos

et al. 2019

International Journal of Multiphase Flow

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights Numerical examination of the aerodynamic breakup of four Diesel droplets in tandem formation at representative engine conditions. Identification of a new breakup mode in the multi-mode regime, termed as "shuttlecock". Droplet proximity becomes important for non-dimensional distances between the droplets lower than 9. Drag coefficient and liquid surface area of the "representative chain droplet" are lower than the corresponding ones of the isolated droplet; breakup initiation time is longer and the critical We number is higher. Proposed correlations to predict the drag coefficient, liquid surface area, breakup initiation time and critical We of the "representative chain droplet".

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Variation of drag coefficients in an interacting drop stream

Cited by 18 publications

References 15 publications

Applicability of pulsed 2cLIF-EET for micro-droplet internal thermometry under evaporation conditions

Applicability of pulsed 2cLIF-EET for micro-droplet internal thermometry under evaporation conditions

Air–liquid interactions in a pressure-swirl spray

Numerical investigation of the aerodynamic breakup of droplets in tandem

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