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An experimental study on jets issuing from elliptic inclined nozzles

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Abstract

This paper reports on an experimental flow visualisation and digital particle image velocimetry investigation on forced jets exhausting from aspect ratio equal to three elliptic nozzles with exits inclined at 30° and 60°. Flow images show that shear layer instabilities and subsequent vortex roll-ups are formed parallel to the inclined nozzle exits at 30° incline and that rapid re-orientation of the vortex roll-ups occurs at 60° incline. Flow observations also show that strong axis-switching occurs in a non-inclined elliptic nozzle. However, 30° and 60° elliptic inclined nozzles produce significant distortions to and suppression of the axis-switching behaviour, respectively. As a result, flow stresses and turbulent kinetic energy distributions become increasingly asymmetric. Their coherency and magnitudes along the shorter nozzle lengths also vary significantly. This can be attributed to the dissimilar formations of vortex roll-ups and rib structures, as well as unequal mutual interactions between them as the incline-angle increases. Lastly, results also show that unlike circular inclined nozzles, elliptic inclined nozzles do not produce serpentine-shaped jet columns nor lead to significant lateral jet-spread at large incline-angles.

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Abbreviations

D :

Particle diameter

D h :

Hydraulic diameter of elliptic nozzle

D major :

Major diameter of elliptic nozzle

D minor :

Minor diameter of elliptic nozzle

f :

Forcing frequency

H :

Nozzle mean height

U cl :

Local centerline velocity in the streamwise direction

U e :

Mean jet exit velocity

U f :

Forcing amplitude

U m :

Mean jet velocity

u′:

Streamwise velocity fluctuation

v′:

Cross-stream velocity fluctuation

u′u′:

Streamwise flow stress

u′v′:

Reynolds shear stress

v′v′:

Cross-stream flow stress

x :

Streamwise distance from nozzle mean height

y :

Cross-stream distance from nozzle center

δ:

Jet exit shear layer thickness

ρ:

Particle density

τparticle :

Particle time scale τparticle = ρD 2/18μ

τflow :

Jet flow time scale τflow = δ/U cl

μ:

Dynamic viscosity of water

ν :

Kinematic viscosity of water

Re :

Reynolds number Re = U e D h/ν

St :

Strouhal number St = fD h/U e

Stk :

Stokes number Stk = τparticle/τflow

AR:

Aspect ratio

DPIV:

Digital particle image velocimetry

Px:

Pixel

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Acknowledgments

The author gratefully acknowledges D. Tsovolos for his assistance in the flow visualisation and DPIV experiments and the Research Support Budget from the Department of Engineering at the University of Liverpool for the study.

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Authors and Affiliations

  1. Department of Engineering, University of Liverpool, Liverpool, L69 3GH, UK

    T. H. New

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  1. T. H. New
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Correspondence to T. H. New.

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New, T.H. An experimental study on jets issuing from elliptic inclined nozzles. Exp Fluids 46, 1139–1157 (2009). https://doi.org/10.1007/s00348-009-0622-9

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  • DOI: https://doi.org/10.1007/s00348-009-0622-9

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