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Research Papers: Fundamental Issues and Canonical Flows

Direct Numerical Simulation of Single and Multiple Square Jets in Cross-Flow

[+] Author and Article Information
Y. Yao1

School of Aerospace and Aircraft Engineering, Faculty of Engineering, Kingston University, Roehampton Vale, Friars Avenue, London SW15 3DW, United Kingdomy.yao@kingston.ac.uk

M. Maidi

School of Aerospace and Aircraft Engineering, Faculty of Engineering, Kingston University, Roehampton Vale, Friars Avenue, London SW15 3DW, United Kingdom

1

Corresponding author.

J. Fluids Eng 133(3), 031201 (Mar 10, 2011) (10 pages) doi:10.1115/1.4003588 History: Received September 28, 2009; Revised December 17, 2010; Published March 10, 2011; Online March 10, 2011

Abstract

Direct numerical simulations (DNSs) have been carried out for single and multiple square jets issuing normally into a cross-flow, with the primary aim of studying the flow structures and interaction mechanisms associated with the jet in cross-flow (JICF) problems. The single JICF configuration follows a similar study previously done by Sau (2004, Phys. Rev. E, 69, p. 066302) and the multiple JICF configurations are arranged side-by-side in the spanwise direction with a jet-to-jet adjacent edge distance (H) for the twin-jet case and an additional third jet downstream along the centerline with a jet-to-jet adjacent edge distance (L) for the triple-jet case. Simulations are performed for two twin-jet cases with $H=1D,2D$, respectively, and for one triple-jet case with $H=1D$, $L=2D$, where D is the jet exit width. Flow conditions similar to Sau et al. are considered, i.e., the jet to the cross-flow velocity ratio $R=2.5$ and the Reynolds number 225, based on the freestream velocity and the jet exit width. For the single jet in cross-flow, the vortical structures from our DNS are in good qualitative agreement with the findings of Sau et al. For the side-by-side twin-jet configuration, results have shown that the merging process of the two initially separated counter-rotating vortex pairs (CRVPs) from each jet hole exit is strongly dependent on the jet-to-jet adjacent edge distance H with earlier merging observed for the case $H=1D$. Downstream, the flow is dominated by a larger CRVP structure, accompanied by a smaller inner vortex pair. The inner vortex pair is found not to survive in the far-field as it rapidly dissipates before exiting the computational domain. These observations are in good agreement with the experimental findings in the literature. Simulations of the triple-jet in cross-flow case have shown some complicated jet-jet and jet-cross-flow interactions with three vortex pairs observed downstream, significantly different from that seen in the twin-jet cases. The evidence of these flow structures and interaction characteristics could provide a valuable reference database for future in-depth flow physics studies of laboratory experimental and numerical investigations.

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Figures

Figure 1

Sketch of the vortex system in a single JICF configuration

Figure 2

Computational domain for the single and the multiple JICF configurations

Figure 3

Isosurfaces of the spanwise vorticity ωz=±0.5, positive in gray color and negative in dark color

Figure 4

Contours of the spanwise vorticity ωz in a vertical plane (x,y,z=3D)

Figure 5

Streamlines from the jet inlet and the cross-flow inlet in the near-wall region

Figure 6

Three-dimensional streamlines participating in the formation of Kelvin–Helmholtz vortex systems

Figure 18

Streamline pattern in a horizontal plane (x,y=0.1D,z) close to the wall

Figure 17

Contours of the streamwise vortices ωx in two x-planes for triple-jet flow: (a) x=18D and (b) x=23D

Figure 11

Velocity vectors for the side-by-side twin jets for the case H=2D at two successive streamwise locations: (a) x=20D and (b) x=23D

Figure 10

Contours of the spanwise vortices ωz in the z=Lz/2 plane: (a) H=2D and (b) H=1D

Figure 16

Velocity vectors for the triple jets in a particular tandem arrangement at a streamwise location of x=20D

Figure 15

Streamlines of triple jets in a particular tandem arrangement (a front view) showing the lateral spreading and the longitudinal evolving of the flow

Figure 14

Isosurfaces of the spanwise vorticity ωz=±0.5 of triple jets in a particular tandem arrangement, positive in gray color and negative in dark color

Figure 13

Streamline pattern in a horizontal plane (x,y,z=0.1D,z) close to the wall: (a) H=2D and (b) H=1D

Figure 12

Velocity vectors for the side-by-side twin jets for the case H=1D at two successive streamwise locations: (a) x=20D and (b) x=23D

Figure 9

Isosurfaces of the spanwise vorticity ωz=±0.5, with positive in gray color and negative in dark color: (a) H=2D and (b) H=1D

Figure 8

Contours of the streamwise vortices ωx at three successive streamwise locations, illustrating the formation of “double-deck” vortex structures by x=20D

Figure 7

Streamline patterns in a vertical plane (x,y,z=3D). (a) An overview with locations of the horseshoe vortex and the wake vortex. (b) A close view near the jet leading-edge with the hovering vortex.

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