Investigation of the effect of passive bleeding technique on the aerodynamic performance of a non-slender delta wing in ground effect

Non-slender delta wings are widely used in Unmanned Aerial Vehicles (UAV), Unmanned Combat Aerial Vehicles (UCAV), Micro Aerial Vehicles (MAV), and fighter aircraft due to their maneuverability and providing a large surface area for system integration. Therefore, the aerodynamics and flow structures of non-slender delta wings are a research area of great interest. Ground effect is an aerodynamic phenomenon that introduces an additional boundary condition to the flow field of wings moving close to the ground plane. As aircraft enter ground effect, flow structures and aerodynamic parameters are significantly affected compared to the free stream condition. Especially in landing/take-off scenarios, aircraft are in-ground effect and it is one of the most critical parts of their flight times. Therefore, a thorough understanding of the aerodynamic behavior of delta wings in- ground effect gains importance. In this study, the aerodynamic parameters of non-slender delta wings with sweep angle of Λ= 45^° in-ground effect were investigated experimentally. In recent years, it has shown that the passive bleeding technique, which takes advantage of the pressure difference between the pressure and suction sides of the wing, can be an effective method of flow control. Therefore, the Base wing without any bleed opening applied and two different bleed opening ratios, BOR = 0.85 & 1.00 wings, were compared both in-ground effect and out of ground effect. The experiments were conducted by taking force and moment measurements using an external balance and surface measurements in a low speed wind tunnel. The experiments were performed in a range of angles of attack 0^° ≤ α ≤ 29^°, in a range of dimensionless ground height 13 % ≤ h⁄c ≤110 %, and in a single Reynolds number, Re=9 × 10^4. The dimensionless ground height is defined as the ratio of the distance between the trailing edge of the wing and the ground plane to the wing's chord length. Considering the out of ground effect results, BOR wings delay the stall angle of attack. BOR = 0.85 wing provides a delay of about 4 degrees, and the fact that it can do this without sacrificing too much on the lift coefficient increases its maneuverability. It is seen that the ground effect increases the aerodynamic coefficients. However, as the bleed opening ratio increases, the aerodynamic coefficients become a weaker function of ground effect. All three of the Base, BOR = 0.85 & 1.00 wings are longitudinally unstable in all cases. Moreover, the increase in bleed opening ratio further increases this unstability. When the short distance take-off is considered, the fact that the BOR = 0.85 wing can delay the stall angle of attack by 4 degrees and the lift coefficient increases with the ground effect makes the BOR = 0.85 wing appealing.