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Research Papers: Multiphase Flows

A Comparison Between Round Turbulent Jets and Particle-Laden Jets in Crossflow by Using Time-Resolved Stereoscopic Particle Image Velocimetry

[+] Author and Article Information
F. J. Diez, M. M. Torregrosa

Department of Mechanical and Aerospace Engineering,  Rutgers University, Piscataway, NJ 08854

S. Pothos

 TSI Inc, Shoreview, MN 55126

J. Fluids Eng 133(9), 091301 (Sep 12, 2011) (13 pages) doi:10.1115/1.4004815 History: Received December 01, 2010; Revised July 27, 2011; Published September 12, 2011; Online September 12, 2011

Time-resolved stereoscopic particle image velocimetry (TR-ST-PIV) measurements were performed to compare the velocity and vorticity field, and the three-dimensional high intensity vorticity structures between a round turbulent single-phase jet and a particle-laden jet in crossflow. The experiments involved steady fresh water jet sources with a particle mass loading of ∼2.0% injected into steady fresh water crossflows. The TR-ST-PIV system was combined with a phase discrimination method that separates two-phase stereo PIV images into dispersed phase images and continuous phase images that are analyzed by using particle tracking velocimetry and stereo-PIV algorithms, respectively. The analysis shows the importance of phase separation for accurate velocity results. It provides instantaneous velocity fields where the dispersed phase preferentially concentrated in regions of low vorticity with the velocity not matching the continuous phase. The jet and the particle-laden jets trajectories are compared to each other and with results in the literature. Similarly, a comparison of mean velocity and vorticity fields between both flows suggest enhanced mixing in the particle-laden jet due to the effects of the dispersed phased which lowered the centerline velocities and enhanced the penetration in the cross-stream direction of the continuous phase. The Taylor’s frozen flow hypothesis is applied to reconstruct the 3D high intensity vorticity structures in a volume. The visualization of the three-dimensional structures corresponding to the intermediate scales of the flow shows slightly elongated structures preferentially aligned with the jet centerline axis.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 14

Visualization of quasi-instantaneous three-dimensional high intensity vorticity structures reconstructed using (a) the three components of the vorticity magnitude (calculated from the x, y, and z components of the vorticity) and using (b) the swirling strength (λi ) defined in [53] for a particle-laden jet in crossflow at Re = 13,500

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Figure 6

Mean velocity vector field, end view, obtained (a) without and (b) with applying the phase discrimination method to the TR-ST-PIV image pairs

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Figure 7

Jet centerline trajectory in rd-normalized coordinates

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Figure 8

Contour plot of the mean velocity field, side view, (a) for a jet and (b) for a particle-laden jet in crossflow showing the axis normalized by rd. The dashed line corresponds to the jet centerline which represents the line of zero vorticity. Streamlines are shown as solid white lines.

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Figure 9

Contour plot of the mean vorticity field, side view, (a) for a jet and (b) for a particle-laden jet in crossflow showing the axis normalized by rd. The dashed line corresponds to the line of zero vorticity which defines the jet centerline.

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Figure 10

Contour plot of the mean velocity field, end view, (a) for a jet and (b) for a particle-laden jet in crossflow showing the axis normalized by rd. Streamlines are shown as solid black lines.

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Figure 3

Sketch of a particle-laden jet in a crossflow approximately showing the location of the measurement regions. Locations L1 and L2 are in the x-y plane and location L3 is in the y-z plane.

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Figure 4

A graphical chart showing the sequence of filters of the simultaneous two-phase separation method

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Figure 5

Time evolution of the instantaneous (a)–(c) vorticity field and (d)–(f) velocity field from an end view of a particle-laden jet in a crossflow. Vectors shown in black in (a)–(c) and in red in (d)–(f) represent the velocity of the particles in the dispersed phase. In general the dispersed phase particles do not follow the main flow and are preferentially distributed in regions of low vorticity.

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Figure 1

Experimental setup showing the top view of the test section of the water channel

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Figure 2

Velocity profiles measured at different downstream locations close to the nozzle exit along the centerline for both (a) the jet and (b) the particle-laden jet

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Figure 11

Contour plot of the mean vorticity field, end view, (a) for a jet and (b) for a particle-laden jet in crossflow showing the axis normalized by rd

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Figure 12

(a) A sequence of time-resolved velocity field images taken at the same transverse location at times t = 0, 0.02, 0.04, 0.06, and 0.08 s used to reconstruct (b) the velocity field in a volume by applying the Taylor hypothesis

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Figure 13

Visualization of quasi-instantaneous high intensity x-vorticity structures in (a) a jet and (b) a particle-laden jet in crossflow. The normalized x-vorticity, ωx /(U∞ /d), structures are constructed from a set of 40 pairs of instantaneous stereo PIV images taken 2 ms apart from each other (i.e., 500 fps). Iso-surfaces corresponding to normalized vorticity values of ±0.9 are shown (positive vorticity is shown in blue and negative vorticity in red).

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