NEAR-WAKE BEHAVIOR BEHIND TWO FLAT PLATES ARRANGED SIDE-BYSIDE NORMAL TO FLOW

Ibrahim A. M. Gad

Abstract


Two flat plates arranged side by side normal to air flow at high subcritical Reynolds number 20000 are
investigated for near wake behavior by mean of three ways: 1) discrete vortex method (DVM) calculations,
2) smoke tunnel for near-wake visualizations and 3) wind tunnel for surface pressure measurements.
FORTRAN computer language program is constructed for implementation of DVM calculations. Applying
necessary refinements of some spectral techniques of DVM reduced the maximum differences between
experimental and predicted results from 24.54% to 4.68%. The time variant and averaged aerodynamic
forces, Strouhal number and near-wake configuration are investigated versus normalized time t and gap ratio
(g/h) to understand the phenomena. The results agree satisfactory the previous literatures.
At g/h  (0.05:0.١5) irregular mean drag observed, no biased gap flow pattern appears. The biased gapflow
pattern begin appears. At g/h=0.2: 0.3 the gap flow shows no any reattachment to the rear faces of
plates occurred and the direction of the biasing remains the same unless some disturbance forms are
introduced. The Coanda effect may be omitted from the principal causes of the biasing phenomenon. At g/h
 (0.3:0.6) the gap flows appears always to be biased and flip-flops to the preferred side non-periodically
with respect to time. At g/h  (0.6:1.25) the percentage of time occupied by the gap flow in the biased state
decreases and the non-biased state of the gap flow becomes prevalent. At g/h>1.25 the individual wakes of
the plates behave independently. Generally the plate on the biased side showed high and regular vortex
shedding, while those on the biased side showed the opposite

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