Analysis of Single Hole Simulated Battle Damage on a Wing Using Particle Image Velocimetry

Abstract

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.