Experimental analysis on the inner vortices interaction above diamond wing model in low speed aerodynamics

Abstract

Every country needs a high-speed Unmanned Air Vehicle (UAV) to monitor territory especially their ocean. One of the best UAV that can perform this mission is Unmanned Combat Air Vehicle (UCAV). The main advantage of the UCAV is a kind of delta-shaped drone that can fly at high speed and greater altitude. For a high-speed plane, there are always issues in the take-off and landing segments, as it need a longer runway. Thus, the aerodynamic performances at these conditions were always in transitional and not stable when it manoeuvres. North Atlantic Treaty Organisation (NATO) has initiated a task group of AVT- 183 to perform the aerodynamic analysis on UCAV related profile recently. The flow above of Stability And Control CONfiguration (SACCON) wing is very complicated and a simplified model called Diamond wing was introduced for the aerodynamic studies. Diamond wing is also a kind of delta-shaped wing where at certain angle of attack, the primary vortex and other separation occur on the wing. The outcomes from the AVT-183 group were the flow on the upper surface of the Diamond flow field such as the vortical structures interaction, formation and progression are complicated, disorganised and unknown. Although many computer fluid dynamic researches have been conducted during the campaign, the data from the experiment or wind tunnel testing to validate the simulation is very limited especially in the inboard region. Thus, the numerical prediction of aerodynamic performance for the wing is not well predicted. The aim of this study was to provide the experimental data on the Diamond wing that can improve the understanding of the aerodynamic characteristics and the flow topology above the Diamond wing. This study assessed the formation, progression and interaction of vortices above the Diamond wing. A half-span NATO configuration Diamond-shaped wing model was designed and manufactured. The model was then tested in UTM – Aerolab subsonic wind tunnel at the Reynolds number of 1×106, 2×106 and 3×106, respectively. Four measurement techniques were employed on the wing, i.e., steady/unsteady force measurement, flow visualization, surface pressure measurement and finally the off-surface pressure study. The data obtained from the Diamond wing were compared with another delta-shaped NATO standard profile called VFE-2 wing. A model of VFE-2 wing was also fabricated in UTM, and several measurement techniques such as flow visualization and pressure measurements were performed on this wing. The main flow characteristics above the Diamond and VFE-2 wing were the primary vortex that occurred in the leading edge of the wing. The results from the tuft technique carried out in UTM has identified several relationships between the attached flow, primary and inner vortices. The results obtained have shown that lift and drag (L/D) ratio for the Diamond in the subsonic region has not been affected by the Reynolds number variation. The optimum lift is produced at angle of attack ranges between 3° < a < 5° where the lift is 8 times higher than the drag. The lift for Diamond wing has increased by 9% when compared to the VFE-2 wing in the region where inner vortex was developed. However, the drag for the Diamond wing increased by up to 15% when compared to VFE-2 wing at the angle of attack 12° and above. The onset of the primary vortex for Diamond wing occurred at 20% chord-wise position earlier compared to VFE-2 wing. Interestingly, further inboard of the wing, several other vortices have been found. The number of vortices is depending on the flow conditions and these vortices have the same attributes as the inner vortex. This new discovery vortex is termed as multi - inner vortex. For the VFE-2 wing, there is only one single inner vortex developed inboard of the wing. It happened in the region 30% inboard of the wing span. The inner vortex has low intensity, which has about 85% pressure difference when compared to the corresponding primary vortex. This thesis provides a complete experimental data on flow above the Diamond wing. It also provided a better insight on the flow topology above the Diamond wing.