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Aerodynamics of battle damaged finite aspect ratio wings

By Mujahid Samad-Suhaeb

Abstract

A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.When an aircraft is aerodynamically or structurally damaged in battle, it may not able to\ud complete the mission and the damage may cause its loss. The subject of aircraft battle\ud survivability is one of critical concern to many disciplines, whether military or civil.\ud This thesis considered and focused on Computational Fluid Dynamics [CFD] predictions and\ud experimental investigations into the effects of simulated battle damage on the low-speed\ud aerodynamics of a fmite aspect ratio wing.\ud Results showed that in two-dimensional [2d] and three-dimensional [3D] CFD simulations,\ud Fluent's® models work reasonably well in predicting jets flow structures, pressure distributions,\ud and pressure-coefficient Cp's contours but not for aerodynamic coefficients. The consequences\ud were therefore that CFD prediction was poor on aerodynamic-coefficients increments. The\ud prediction of Cp's achieved good agreement upstream and near the damage hole, but showed\ud poor agreement at downstream of the hole. For the flow structure visualisation, at both weak and\ud strong jet incidences, the solver always predicted pressure-distribution-coefficient lower at\ud upstream and higher at downstream. The results showed relatively good agreement for the case\ud of transitional and strong jet incidences but slightly poor for weak jet incidences.\ud From the experimental results of Finite Wing, the increments for Aspect-ratio, AR6, AR8 and\ud ARIO showed that as damage moves out towards the tip, aerodynamic-coefficients increments\ud i.e. lift-loss and drag-rise decreased, and pitching-moment-coefficient increment indicated a\ud more positive value at all incidence ranges and at all aspect ratios. Increasing the incidence\ud resulted in greater magnitudes of lift-loss and drag-rise for all damage locations and aspect\ud ratios. At the weak jet incidence 4° for AR8 and in all of the three damage locations, the main\ud characteristics of the weak-jet were illustrated clearly. The increments were relatively small.\ud Whilst at 8°, the flow structure was characterised as transitional to stronger-jet. In Finite Wing\ud tests and for all damage locations, there was always a flow structure asymmetry. This was\ud believed to be due to gravity, surface imperfection, and or genuine feature. An 'early strong jet'\ud that indicated in Finite Wing-AR8 at 'transitional' incidence of 8°, also indicated in twodimensional\ud results but at the weak-jet incidence of 4°.\ud For the application of 2d data to AR6, AR8, and ARIO, an assessment of 2d force results led to\ud the analysis that the tests in the AAE's Low Turbulence Tunnel for 2d were under-predicting the\ud damage effects at low incidence, and over-predicting at high incidences. This suggested\ud therefore that Irwin's 2d results could not be used immediately to predict three-dimensional

Topics: Battle damage, Survivability, Jets-in-crossflow, Cavity, Weak-jet, Strong-jet, Low speed wind tunnel, Force measurement, Surface pressure measurements, Flow visualisation, Finite aspect ratio wing, CFD, Fluent®
Publisher: © M.Samad-Subaeb
Year: 2005
OAI identifier: oai:dspace.lboro.ac.uk:2134/10736

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