Transient Thrust Analysis of Rigid Rotors in Forward Flight

The purpose of this study was to investigate and quantify the transient thrust response of two small rigid rotors in forward flight. This was accomplished using a distributed doublet-based potential flow method, which was validated against wind-tunnel experimentation and a transient CFD analysis. The investigation showed that for both rotors, advancing and retreating blade effects were predicted to contribute to transient thrust amplitudes of 5–30% of the mean rotor thrust. The thrust output amplitudes of individual rotors blades were observed to be 15–45% of the mean rotor thrust, indicating that it is not uncommon for the thrust output variation of an individual rotor blade to approach the same value as the mean thrust output of the rotor itself. In addition to this, the theoretical analysis also illustrated that higher blade thrust oscillations resulted in pronounced asymmetric rotor wake structures.

SOME ASPECTS OF PRACTICAL BALANCING RIGID ROTORS IN OWN SUPPORTS

The balancing of rotors of fans, pumps, smoke exhausters, blowers (with a capacity of 50...500 kW, with a rotational speed of 950...3000 rpm) in their own supports is carried out most often at industrial enterprises. The effectiveness of this operation is ensured by the implementation of a number of rules, confirmed by practical experience. Some stages of balancing of rotors are considered in the work. A preliminary examination of the mechanism provides an accurate diagnosis and an informed decision for balancing. Correct determination of the angle of installation of the test cargo at various places of installation of the vibration and photo sensor allows reducing the level of vibration and additional loads on the elements of the mechanism during the test run. Controlling the values of the dynamic coefficient of influence during the balancing process allows you to control the change in the stiffness of the base, loosening of threaded connections, which are often the cause of unsuccessful balancing. The above provisions are confirmed by the results of research and practical application.

Flexible Flaps Inspired by Avian Feathers Can Enhance Aerodynamic Robustness in low Reynolds Number Airfoils

Unlike rigid rotors of drones, bird wings are composed of flexible feathers that can passively deform while achieving remarkable aerodynamic robustness in response to wind gusts. In this study, we conduct an experimental study on the effects of the flexible flaps inspired by the covert of bird wings on aerodynamic characteristics of fixed-wings in disturbances. Through force measurements and flow visualization in a low-speed wind tunnel, it is found that the flexible flaps can suppress the large-scale vortex shedding and hence reduce the fluctuations of aerodynamic forces in a disturbed flow behind an oscillating plate. Our results demonstrate that the stiffness of the flaps strongly affects the aerodynamic performance, and the force fluctuations are observed to be reduced when the deformation synchronizes with the strong vortex generation. The results point out that the simple attachment of the flexible flaps on the upper surface of the wing is an effective method, providing a novel biomimetic design to improve the aerodynamic robustness of small-scale drones with fixed-wings operating in unpredictable aerial environments.

Stability analysis of rigid rotors supported by gas foil bearings coupled with electromagnetic actuators

Rotors supported on gas foil bearings have low damping characteristics, which limits its application. A possible solution could be an integration of a gas foil bearing with an electromagnetic actuator. This paper discusses the effect of electromagnetic actuators on the stability of a rotor supported on gas foil bearings. A coupled dynamic model combining the dynamics of gas foil bearing and electromagnetic actuator has been developed. The fluid film forces from the gas foil bearings and the electromagnetic forces from the electromagnetic actuators are integrated into the equations of motion of the rotor. The sub-synchronous vibration present in case of conventional gas foil bearings is reduced and the stability band of the rotor is increased due to the implementation of electromagnetic actuator.