Passive scalar mixing in vortex rings

Sau, Rajes; Mahesh, Krishnan

doi:10.1017/s0022112007006349

Cited by 52 publications

(26 citation statements)

References 23 publications

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“…Usually, the centre C of the vortex is first located as the point of the maximum vorticity ω max ; the vortex core is then defined as the inner domain bounded by the vorticity contour ω/ω max = 0.05 that encircles the centre C. The cutoff level is set based on trial and error, to the best satisfaction of the authors. Threshold values ranged from 2% (Mohseni 2001) and 5% (Rosenfeld et al 1998;Zhao et al 2000;Sau & Mahesh 2007) in numerical studies, to approximately 10% (Dabiri & Gharib 2004) in experiments.…”

Section: Numerical Resultsmentioning

confidence: 92%

Modelling of confined vortex rings

2015

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Section: Numerical Resultsmentioning

confidence: 92%

Modelling of confined vortex rings

2015

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“…The algorithm has been validated for a wide range of complex problems which include a gas turbine combustor geometry ) and predicting propeller crashback (Verma, Jang & Mahesh 2012;Jang & Mahesh 2013). It has been used to study the entrainment from free jets by (Babu & Mahesh 2004) and was applied to transverse jets by Muppidi & Mahesh (2005 and Sau & Mahesh (2007. DNS of a round turbulent jet in crossflow was performed by Muppidi & Mahesh (2007) under the same conditions as Su & Mungal's (2004) experiments, and very good agreement with the experimental data was obtained.…”

Section: Numerical Algorithmmentioning

confidence: 97%

A numerical study of shear layer characteristics of low-speed transverse jets

Iyer

Mahesh

2016

J. Fluid Mech.

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Direct numerical simulation (DNS) and dynamic mode decomposition (DMD) are used to study the shear layer characteristics of a jet in a crossflow. Experimental observations by Megerian et al. (J. Fluid Mech., vol. 593, 2007, pp. 93-129) at velocity ratios (R = v j /u ∞ ) of 2 and 4 and Reynolds number (Re = v j D/ν) of 2000 on the transition from absolute to convective instability of the upstream shear layer are reproduced. Point velocity spectra at different points along the shear layer show excellent agreement with experiments. The same frequency (St = 0.65) is dominant along the length of the shear layer for R = 2, whereas the dominant frequencies change along the shear layer for R = 4. DMD of the full three-dimensional flow field is able to reproduce the dominant frequencies observed from DNS and shows that the shear layer modes are dominant for both the conditions simulated. The spatial modes obtained from DMD are used to study the nature of the shear layer instability. It is found that a counter-current mixing layer is obtained in the upstream shear layer. The corresponding mixing velocity ratio is obtained, and seen to delineate the two regimes of absolute or convective instability. The effect of the nozzle is evaluated by performing simulations without the nozzle while requiring the jet to have the same inlet velocity profile as that obtained at the nozzle exit in the simulations including the nozzle. The shear layer spectra show good agreement with the simulations including the nozzle. The effect of shear layer thickness is studied at a velocity ratio of 2 based on peak and mean jet velocity. The dominant frequencies and spatial shear layer modes from DNS/DMD are significantly altered by the jet exit velocity profile.

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“…9, in which a trailing column [16][17][18][19][36][37][38] of hot gas is evident. The creation of the trailing column was the result of exceeding the critical formation number of a vortex ring [17,18].…”

Section: Resultsmentioning

confidence: 99%

Temperatures of Spark Kernels Discharging into Quiescent or Crossflow Conditions

Okhovat

Hauth

Blunck

2017

Journal of Thermophysics and Heat Transfer

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This work determines how the temperature of spark kernels changes for quiescent and crossflow conditions. Previous efforts have primarily considered kernels in quiescent conditions and typically neglected how the temperature changes with time. The latter is significant because the temperature evolution is critical for determining if reactions become self-sustaining. Kernels were generated using a gas turbine engine igniter. Temperatures were determined from radiation intensity measurements (FLIR SC6700) and by solving the radiation transfer equation. Kernels were discharged into a wind tunnel with crossflow velocities between 0 and 15.6 m∕s. Kernels developed into toroidal vortices for all conditions. The average peak temperature in quiescent conditions was near 950 K and nearly 1250 K at the highest crossflow velocity. Higher temperatures were observed at the upstream side of kernels when ejecting into a crossflow. The changes in temperatures observed with crossflow are explained by fluid mechanic literature; vortex crossflow interaction alters entrainment into kernels. The sensible energy of kernels, determined from the temperatures, decreased roughly linearly with time for all flow conditions. The highest crossflow velocity had the lowest sensible energy as a result of reduced apparent volume of the kernel. The trajectory of kernels in a crossflow matches that from pulsed jet literature.

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Passive scalar mixing in vortex rings

Cited by 52 publications

References 23 publications

Modelling of confined vortex rings

Modelling of confined vortex rings

A numerical study of shear layer characteristics of low-speed transverse jets

Temperatures of Spark Kernels Discharging into Quiescent or Crossflow Conditions

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