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Effect of bleed opening ratio on flow structure of a nonslender delta wing

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2019
Kestel, Kayaca
Boundaries of the aircraft industry need to expand since both economic and ecologic constraints are getting more challenging. The usage of Unmanned Air Vehicles(UAV), Unmanned Combat Air Vehicles(UCAV), and Micro Air Vehicles(MAV) which can be simplified as non-slender delta wing plan-forms has been increasing during the last few decades, primarily due to their superiority over commercial airplanes. Hence, researchers have aimed to control the complex flow structures on non-slender delta wings with particular interest on elimination of large-scale, three dimensional surface separation indication of pre-stall/stall regime, which appears at sufficiently high angle of attacks. Recently, it is proposed that passive bleeding, which utilizes passage inside the wing in order to allow the fluid to flow from the pressure side to suction side by using inherent pressure difference, have potential to be used as a flow control method to eliminate large-scale surface separation. The aim of the present study is to understand the effect of bleed opening ratio on flow structure and aerodynamic forces of a non-slender, 45 degree swept delta wing. For that purpose, the delta wings with four different bleed opening ratios, bor, varying from 0.35 to 1.00, have been tested in a low-speed wind tunnel using surface pressure measurement, Particle Image Velocimetry (PIV), and force measurement. The experiments were conducted in a broad range of angles of attack 0≤α≤36 degree and at two different Reynolds number Re = 5 x 10^4 and 1 x 10^5. The results indicate that at high angles of attack where the pronounced surface separation appears on the plan-form, wing with bor=1.00 is the most successful in the elimination of the of large-scale, three-dimensional surface separation, albeit that the lift force over the wing decreases. Moreover, the wing with bor=0.85 exhibits the best performance considering the lift coefficients and the stall angle. Further studies are needed to effectively use bleeding as a flow control technique.