Particle Image Velocimetry (PIV) has been used to map the complex
flow field generated
by simulated battle damage to a two-dimensional wing. Previous studies have relied on
surface
flow visualisation techniques to study the
flow but here PIV data has enabled the
flow field away from the surface to be analysed for the first time. Damage was simulated
by a single hole with a diameter equal to 20% of the chord, located at mid-chord. Wind
tunnel tests were conducted at a Reynolds number of 500,000 over a range of incidences
from 0-10 with two-component PIV measurements made on three span-wise planes; on the
damage centre line and o set by 0.5 and 1.0 hole radii. The PIV data was seen to be
in good agreement with existing surface
flow visualisation showing strong evidence of the
formation of a horse shoe vortex, a counter-rotating vortex pair and reverse
flow regions.
Large variations in the
flow structure were observed over the range of incidences tested as
the jet transitioned from weak at lower angles to strong at higher angles. The data also
revealed some significant differences in the
flow compared to classic Jets In Cross-Flow
(JICF) behaviour. Notably in the case of battle damage the jet never fully occupies the
hole and jet velocity pro le is highly skewed towards the rear of the hole. Additionally,
the measured velocity ratios are much less than would be expected for typical JICF. For
example, strong jet behaviour is observed at a velocity ratio as low as 0.22 whereas JICF
studies would suggest a much higher ratio (> 2) is required. Increasing velocity ratio has
been related to a reduction in lift and an increase in drag. At the highest incidence tested
(10 ) the velocity ratio of 0.32 resulted in a reduction of the lift coe fficient by 0.18 and an
increase in the drag coeffi cient of 0.035
