Concentration Field Measurements Within Isolated Turbulent Puffs

[+] Author and Article Information
E. Ghaem-Maghami

Mechanical Engineering Department, Worcester Polytechnic Institute, Worcester, MA 01609

H. Johari1

Mechanical Engineering Department, Worcester Polytechnic Institute, Worcester, MA 01609hjohari@csun.edu


Corresponding author.

J. Fluids Eng 129(2), 194-199 (Jul 06, 2006) (6 pages) doi:10.1115/1.2409348 History: Received August 17, 2005; Revised July 06, 2006

The structure of passive scalar concentration field within isolated turbulent puffs was measured using the planar laser Mie scattering technique. Puffs were generated by injecting seeded air through a 5-mm-diameter nozzle into a chamber with a weak air co-flow. The injection time and volume was varied by the use of a fast-response solenoid valve. Puffs were examined in the range of 25–55 diameters downstream of the nozzle. The Reynolds number based on the average velocity and nozzle diameter was 5000. The results indicate that as the injection volume increases, puffs evolve from a spherical geometry to that with a tail. The half-width of radial concentration profiles through the puff center decrease as the injection volume increases. On the other hand, the puff length in the axial direction increases with the injection volume. The volume of ambient fluid entrained by the puff, and normalized by the injected volume, decreases with increasing injection volume.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Schematic of isolated turbulent puffs: (a) short injection time; and (b) long injection time. An elongated puff with a tail in (b) is distinguished from a compact puff in (a).

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Figure 2

Flow chamber schematic

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Figure 3

Time trace of jet velocity for an injection time of 23ms corresponding to P=4

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Figure 4

Sample instantaneous images of individual puffs: (a) P=4; (b) P=5; (c) P=6; and (d) P=8. The arrows indicate the approximate location where the tail can be differentiated from the leading structure.

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Figure 5

Average passive scalar concentration field, normalized by the peak value, for isolated puffs: (a) P=4; and (b) P=6. The maximum contour has a relative concentration of 0.9 and the adjacent contours are spaced by 0.1.

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Figure 11

Normalized entrained volume as a function of P

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Figure 10

Variation of puff aspect ratio with P

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Figure 9

Puff length as a function of P

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Figure 8

Axial concentration profiles through puff center: (a) P=4; and (b) P=6

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Figure 7

Puff width as a function of P: (a) full width at half height; and (b) full width at 10% height

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Figure 6

Radial concentration profiles (solid line) through puff center: (a) P=4; and (b) P=6. Dashed curves represent Gaussian curve fits to the data.




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