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TECHNICAL PAPERS

# Investigation of the Large-Scale Flow Structures in the Cooling Jets Used in the Blown Film Manufacturing Process

[+] Author and Article Information
Nan Gao1

Department of Mechanical Engineering,  McMaster University, Hamilton, Ontario, Canada L8S 4L7gaon@mcmaster.ca

Dan Ewing

Department of Mechanical Engineering,  McMaster University, Hamilton, Ontario, Canada L8S 4L7ewingd@mcmaster.ca

1

Author to whom all correspondence should be addressed.

J. Fluids Eng 127(5), 978-985 (Apr 07, 2005) (8 pages) doi:10.1115/1.1989367 History: Received May 14, 2004; Revised April 07, 2005

## Abstract

The development of the flow field produced by concentric jets used in the blown-film manufacturing process was studied experimentally using hot wire anemometry. It was found that the inner jet was entrained into the outer jet before the outer jet attached to the wall. The inner shear layer of the outer jet attached to the surface $3H$ to $5H$ downstream of the jet exit, and the outside shear layer of the outer jet attaches to the surface further downstream of the jet exit. The distribution and spectra of the fluctuating wall pressure was measured using microphones. The pressure fluctuations were largest where the outer jet attached to the surface, and had characteristic frequencies of $100to900Hz$. Measurements of two-point and two-time correlation of the fluctuating pressure were used to characterize the development of the large-scale structures that caused these pressure fluctuations. It was found that the structures were convected along the surface at 0.45 to 0.7 of the outer jet velocity for different ratios between inner and outer jet velocities. The convection velocity of the large scale structures in the region farther than $10H$ downstream of the jet exit was determined by the upper jet velocity.

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Copyright © 2005 by American Society of Mechanical Engineers
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## Figures

Figure 1

Schematic of a typical blown film manufacturing process with a dual lip air ring

Figure 11

Profiles of (a) the mean streamwise velocity and (b) the rms streamwise velocity for a maximum outer jet velocity of ———30.4m∕s, ---39.2m∕s, and -∙-∙-42.6m∕s

Figure 12

Distributions of the static and fluctuating wall pressures normalized by the dynamic head of the outer jet for a maximum outer jet velocity of 엯 30.4m∕s, ◻ 39.2m∕s, and ▵ 42.6m∕s

Figure 13

Distributions of (a) the convection velocity of the large scale structures computed from the cross-spectra of the fluctuating wall pressure and (b) convection velocities for a maximum outer jet velocity of 엯 30.4m∕s, ∎ 39.2m∕s, and ▿ 42.6m∕s

Figure 2

Schematic of the dual-lip air ring and the rigid model used in this investigation

Figure 3

Distributions of (a) the mean velocity vectors above the forming cone (12), (b) the static pressure, and (c) the fluctuating pressure measured on the bubble surface

Figure 4

Distributions of the normalized static and fluctuating pressure on the bubble surface above the forming cone

Figure 5

Contours of (a) the mean streamwise velocity (in m/s) and (b) the rms streamwise velocity (in m/s) for a typical air ring setting, and profiles of (c) the mean streamwise velocity and (d) the rms streamwise velocity, measured at locations shown by the dash lines in the contour plots

Figure 6

Examples of the transient fluctuating wall pressure measured at (a) x∕H=3, (b) x∕H=6, and (c) x∕H=12. The signals are low-pass filtered at 2048Hz.

Figure 7

Spectra of wall fluctuating pressure measured at (a) x∕H=---0, -∙-1, ⋯2, ———3, 엯 4, ● 5, ▵ 6, (b) x∕H=---3, -∙-4, ⋯5, ———6, 엯 7, ● 8, ▵ 9, and (c) x∕H=---6, -∙-8, ⋯10, ———12, 엯 14, ● 16, ▵ 20

Figure 8

Cross-spectra of fluctuating wall pressure measured for (a) x1∕H=3 and x2∕H=---0, -∙-1, ⋯2, ———3, 엯 4, ● 5, ▵ 6, (b) x1∕H=6 and x2∕H=---3, -∙-4, ⋯5, ———6, 엯 7, ● 8, ▵ 9, and (c) x1∕H=12 and x2∕H=---6, -∙-8, ⋯10, ———12, 엯 14, ● 16, ▵ 20

Figure 9

Normalized cross correlation of fluctuating wall pressure measured between (a) x1∕H=3 and x2∕H=---0, -∙-1, ⋯2, ———3, 엯 4, ● 5, ▵ 6, (b) x1∕H=6 and x2∕H=---3, -∙-4, ⋯5, ———6, 엯 7, ● 8, ▵ 9, and (c) x1∕H=12 and x2∕H=---6, -∙-8, ⋯10, ———12, 엯 14, ● 16, ▵ 20

Figure 10

Distribution of the convection velocity computed from the cross-spectra normalized by the maximum outer jet exit velocity

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