Experimental Investigation on Blunt-Edged UTM Delta Wing VFE-2 Configurations at Low Reynolds Number

Abstract

The flow behaviour over the upper surface of a blunt-edged delta wing is mainly governed by a complicated leading edge vortex. This paper presents an experimental investigation on blunt-edged UTM VFE-2 delta wing model at low Reynolds numbers. The primary vortex for sharp-edged delta wing develops in the apex region even at low angles of attack. However, this situation does not happen for blunt-edged wings; the primary vortex in the leading edge region develops at a certain chordwise position on the wing. The primary vortex progresses upstream or downstream depending on the leading edge profile, the angle of attack and Reynolds number. A decrease in Reynolds number will accelerate the upstream progression of the primary vortex towards the wing apex. In the VFE-2 research group, many experiments were conducted at Reynolds number of 1×10^6 and above. Thus, the main objective of this study was to investigate the upstream progression of leading edge primary vortex on a blunt-edged delta wing at Reynolds numbers of 0.5×10^6, 0.75×10^6 and 1.0×10^6. Wind tunnel experiments were performed at three different flow velocities, 8.7 m/s, 13.1 m/s and 17.5 m/s corresponding to Reynolds numbers of 0.5×10^6, 0.75×10^6 and 1.0×10^6. Two measurement techniques were employed on the upper surface of the wing, i.e. experimental surface pressure and tuft techniques. Experiments were also conducted on two different leading edge profiles namely medium and large radius profiles with different leading edge radius-to-wing chord ratio. Pressure coefficients on the upper surface of the wing were plotted to observe the characteristic primary vortex, the upstream progression of the primary vortex and also the characteristics of vortex breakdown. The results obtained indicate that the primary vortex rapidly formed when the Reynolds number was decreased. Analysis in the apex region showed that the attached flow still existed even at a very low Reynolds number of 0.5 × 10^6.