2013 Mazaheri and Ebrahimi 2011), among them also the DelFly of TU Delft (de Croon et al. Multiple bio-inspired FWMAVs have been developed worldwide (e.g., Nakata et al. 2018), thus serving as an inspiration to the development of flapping-wing MAV (FWMAV) designs (Shyy et al. On the other hand, flapping-wing propulsion of natural fliers has shown extraordinary flight capabilities at low Reynolds numbers (Cheng et al. Well-established aircraft design concepts apply to fixed and rotatory wing configurations, but these suffer from a degradation in performance when scaled down in size (Jones and Babinsky 2010). Different classes of MAVs can be distinguished: fixed wing, rotatory wing, and flapping wing (Mueller 2001 Mueller and DeLaurier 2003). These MAVs typically fly at very low speeds or even in hovering conditions, but high manoeuvrability and flight efficiency are desirable for wind gusts rejection and increased flight endurance, respectively. Graphic abstractĪn increasing interest in the development of micro air vehicles (MAVs) has been seen in recent years due to the wide range of missions, where they can be employed, from search and rescue activities to security and surveillance applications. Furthermore, experiments have been carried out in both tethered and free-flight conditions, allowing an unprecedented comparison between the aerodynamics of the two conditions. Experiments have been performed at different settings (flow speed, flapping frequency, and body angle) that are representative of actual flight conditions, and the effect of reduced frequency on the wake topology is investigated. Particle trajectories are determined via Lagrangian particle tracking and information of different phases throughout the flapping cycle is obtained by means of a phase-averaging procedure applied to the particle tracks. To achieve the required visualization domain (which in the present experiments amounts to a size of 60,000 cm 3), use is made of robotic particle image velocimetry, which implements coaxial illumination and imaging in combination with the use of helium-filled soap bubbles as tracer particles. The experimental data are being used to improve computational tools for high-lift wings with integrated powered-lift technologies.The objective of this experimental investigation is the volumetric visualization of the near wake topology of the vortex structures generated by a flapping-wing micro air vehicle. Jet-induced effects are the largest at the most inboard station for all (three) velocity components due in part to the larger inboard slot height. High downwash velocities correlated with the enhanced lift for the 60deg flap cases with blowing. Flowfield results and the general trends are very similar for the two blowing cases at nozzle pressure ratios of 1.37 and 1.56. The 7-hole probe results further quantified two known swirling regions (downstream of the outboard flap edge and the inboard/outboard flap juncture) for the 60deg flap cases with blowing. At 10deg angle of attack the wake surveys were completed with a slat and a 60deg flap deflection. At 0deg angle of attack the surveys were completed with 0deg and 60deg flap deflections. Three model configurations were investigated. Off-body measurements were obtained with a 7-hole probe rake survey system. The test was performed at the NASA Langley 14 x 22 Foot Subsonic Tunnel at low speeds. Wake Measurement Downstream of a Hybrid Wing Body Model with Blown Flaps Flow-field measurements were obtained in the wake of a full-span Hybrid Wing Body model with internally blown flaps.
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