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Visualization and structure of confined, milliscale, unsteady impinging slot jets and associated vortices

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Abstract

Flow characteristics of confined, laminar milliscale slot jets are investigated from visualizations, as they impinge upon a flat target plate, with a fully developed velocity profile at the nozzle exit. The effects of Reynolds number Re and normalized nozzle-to-plate distance H/B are considered for a nozzle width B of 1.0 mm. Transition from a stable symmetric jet to an unsteady oscillating jet is observed as the Reynolds number increases (with H/B constant), where the Reynolds number associated with this transition decreases as the normalized nozzle-to-plate distance H/B increases. Instantaneous visualizations show unsteady lateral distortions of jet columns at experimental conditions corresponding to the presence of continuous sinusoidal oscillations, intermittent oscillating motion of the jet column, and jet flow fluctuation/flapping motion. Also apparent in flow visualization sequences are smoke signatures associated with instantaneous vortex structures, which form as secondary flows develop in fluid which, initially, is just adjacent to and within the jet column. Associated jet and vortex structural changes are described as different modes of unsteadiness are present, including characterization of jet column unsteadiness using jet column oscillation frequency, and lateral and streamwise extents of jet distortion.

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Abbreviations

B :

Nozzle width

H :

Nozzle-to-plate distance

N :

Frequency

Re :

Reynolds number based on nozzle width

t :

Time

U :

Average jet velocity

x, X :

Lateral coordinate along the impingement channel, measured from jet centerline

y, Y :

Spanwise coordinate along the slot

z, Z :

Nozzle axis direction coordinate, measured from the target surface

X loc :

Lateral jet column instantaneous distortion

Z loc :

Streamwise jet column instantaneous distortion

RMS :

Root mean square value

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Acknowledgments

The work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (No. 2012-006592). We are grateful for the financial support for this research.

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Authors and Affiliations

  1. Department of Mechanical and Automotive Engineering, High Safety Vehicle Core Technology Research Center, Inje University, 607 Obang-dong, Gimhae, Gyeongnam, 621-749, Korea

    Dae Hee Lee

  2. Bk21 Advanced Vehicle Core Parts Research Group, Inje University, 607 Obang-dong, Gimhae, Gyeongnam, 621-749, Korea

    Hyun Jin Park

  3. Oliver L. Parks Endowed Chair Professor, Parks College of Engineering, Aviation, and Technology, Saint Louis University, 3450 Lindell Boulevard, McDonnell Douglas Hall Room 1033A, St. Louis, MO, 63103, USA

    Phil Ligrani

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  1. Dae Hee Lee
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  2. Hyun Jin Park
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  3. Phil Ligrani
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Correspondence to Phil Ligrani.

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Lee, D.H., Park, H.J. & Ligrani, P. Visualization and structure of confined, milliscale, unsteady impinging slot jets and associated vortices. Exp Fluids 54, 1420 (2013). https://doi.org/10.1007/s00348-012-1420-3

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  • DOI: https://doi.org/10.1007/s00348-012-1420-3

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