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Unsteady characteristics of inlet vortices

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Abstract

An experimental study of the unsteady characteristics of inlet vortices has been conducted using a high-frame rate digital particle image velocimetry system. The results revealed the formation of a pair of counter-rotating inlet vortices for the no-wind configuration and one single inlet vortex when there was crosswind. In all measurement planes, from near the ground to the inlet, evidence of vortex meandering with quasi-periodicity was found. The vortex meander is dominant in the direction of the crosswind, and its amplitude increases with crosswind velocity. The proper orthogonal decomposition analysis of the instantaneous velocity field suggested that the most energetic mode was a helical displacement wave, corresponding to the first helical mode. Similarities with the meandering of the trailing vortices from wings were noted. The present results also suggest that the unsteady characteristics of the focus of separation formed on the ground might be responsible for the unsteady nature of the inlet vortex.

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Abbreviations

a M :

Meandering amplitude of inlet vortex (mm)

D i :

Inlet diameter (mm)

D 0 :

Outer diameter of the inlet tube (mm)

E :

Spectral density (dB/Hz)

f :

Frequency (Hz)

H :

Inlet height (mm)

N :

Number of snapshots of the inlet vortex

P :

Probability of instantaneous inlet vortex locations (%)

Q :

The inlet volumetric flow rate (LPM)

r i :

Radius of the instantaneous inlet vortex (mm)

r oi :

Σ r i /N, Conditionally averaged radius of the instantaneous inlet vortex (mm)

r o :

Radius of the time-averaged inlet vortex (mm)

t :

Time (s)

U i :

Inlet velocity (m/s)

U ∞ :

Crosswind velocity (m/s)

x :

Coordinate in the direction of the crosswind

x c :

Coordinate of the location of the time-averaged inlet vortex in the direction of the crosswind (mm)

x i :

Coordinate of the location of the instantaneous inlet vortex in the direction of the crosswind (mm)

y :

Coordinate in the direction perpendicular to the crosswind

y c :

Coordinate of the location of the time-averaged inlet vortex in the direction perpendicular to the crosswind (mm)

y i :

Coordinate of the location of the instantaneous inlet vortex in the direction perpendicular to the crosswind (mm)

z :

Vertical coordinate

Γ:

Circulation (m2/s)

ω y :

Vorticity in the vertical plane perpendicular to the axis of the inlet model (s−1)

ω z :

Vorticity in the horizontal planes parallel to the ground (s−1)

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Acknowledgments

The authors would like to thank the RCUK Academic Fellowship and also the EPSRC Engineering Instrument Pool of the United Kingdom.

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Authors and Affiliations

  1. Department of Mechanical Engineering, University of Bath, Bath, UK

    Z. Wang & I. Gursul

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  1. Z. Wang
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  2. I. Gursul
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Correspondence to I. Gursul.

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Wang, Z., Gursul, I. Unsteady characteristics of inlet vortices. Exp Fluids 53, 1015–1032 (2012). https://doi.org/10.1007/s00348-012-1340-2

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