Passive flow control over a duct and ducted fan and evaluation of the performance

Ducted propeller systems have been explored and used in many areas throughout the history of aviation, including the prevention of rotor tip losses, noise reduction, flow guidance for proper operation of the propeller and safety. Particularly when the turbofan engines used in today's commercial planes which are equipped with a high by-pass fan in the channel and 80% of the the total thrust of turbofan engine generated from this duct and fan combination, the prominence of the ducted fan systems once again. On the other hand, ducted fan systems have played an important role in the development of air vehicles with increased personal use air vehicles and VTOL capability, especially after World War II. Today, the introduction of taxi drones as electric aerial vehicles with VTOL feature, especially electric duct fan (EDF) systems, has been renewed. Ducted fan systems suffer from considerable performance problems in certain forward-speed regimes, where efficiency, thrust, or size reduction, noise suppression, safety, etc., remain in cross flow. There is a problem in many subjects such as an undesirable turbulence, vibration and unwanted moments on micro unmanned aerial vehicles; suction and safety problems of the turbofan engines of a passenger plane while taking off and landing with a high angle of attack. Considering that the duct structure is also a wing profile, the auxiliary aerodynamic strains and methods used by the planes during their ascents to the high angle of attack fields were investigated and concepts like slot, slat and directed jet flow guidance were found. Considering the difficulties of using mechanical moving surfaces in such circular structures and the weights that these systems will create, the slot design logic has been chosen as the aerodynamic directional design of the MAV systems. The slot system designed on the NACA 4312 standart profile used for the duct is designed circularly to direct the flow from each side on the duct axis. In the study, the ducted electric fan system is modeled for a MAV and it is tested with a 3 blade 5 inches diameter polycarbonate propeller and design boundaries are low drag at the forward flight and performing better than the standard duct structure under cross flow and will not have as much mechanical structure as possible. As a solution, slotted ducted fan design was developed. This design has been tested and evaluated in comparison with open propeller, standard channel design and toroidal channel design. A thrust test system capable of receiving semi-automatic data has been developed due to get high amount of data to be received during the execution of experiments. In this thrust test system, the throttle tunnel speed is set manually and the thrust, speed, voltage and current values ​​are automatically recorded on a SD card an. The main structure of the thrust test stand is carbon tubes and 3 printed structure parts and sensors used for developing a sensitive system for measurements. Design of the system is based on a moment arm connected to a load cell, microcontroller, encoders, voltage and current sensros. During the experiments of the standard duct design, it performed very well compared to the open rotor propeller; but the free flow velocity has reduced the performance acoording to the increasing free stream so the performance of the duct decreasşng at one point duct became only have negative effects over whole propulsion system. In the open propeller system, the thrust level decreased according to the parallel to the flow, but the thrust level increased as the free flow velocity increased under the cross flow. This unexpected result confirms the correctness of the output when examining the relationship between propeller velocity vectors and free flow. The toroidal design provides the best impulse contribution to static thrust and the lowest level of flow cross flow; but the toroidal channel structure also created a large drag force due to the size of the perpendicular cross-sectional area of ​​the flow, and due to this drag force, it couldn't not give the desired expectation in the static flow and in the cross flows. On the other hand, the leading edge is designed to provide the fastest reattachment under cross flow due to the very high diameter of the leading edge circle. As expected, the fan system for the slot-designed duct, which has a small cross-section perpendicular to the flow but can direct the flow with the auxiliary flow-guide aerodynamic structures, provides good cross-flow performance as well as the toroidal channel, while providing a parallel flow trajectory as low as the normal duct. it has been observed that the performance in the cross-flow motion system is considerably increased. Experiments can be conducted with larger diameter channel designs to observe the viscous effects less often during subsequent phase-in studies. Home-made studies can also be repeated with different CFD analyzes.