A new vibration mechanism of balancing machine for satellite-borne spinning rotors

The centrifugal force and overturning moment generated by satellite-borne rotating payload have a significant impact on the stability of on-orbit satellite attitude, which must be controlled to the qualified range. For the satellite-borne rotors＇ low working revs and large centroidal deviation and height, and that the horizontal vibration produced by centrifugal force is not of the same magnitude as the torsional vibration by overturning moment, the balancing machine＇s measurement accuracy is low. Analysis shows that the mixture of horizontal vibration and torsional vibration of the vibrational mechanism contribute mainly to the machine＇s performance, as well as the instability of vibration center position. A vibrational mechanism was put forward, in which the horizontal and torsional vibration get separated effectively by way of fixing the vibration center. From experimental results, the separation between the weak centrifugal force signal and the strong moment signal was realized, errors caused by unstable vibration center are avoided, and the balancing machine based on this vibration structure is able to meet the requirements of dynamic balancing for the satellite＇s rotating payloads in terms of accuracy and stability.

Performance characterization on downwash flow and spray drift of multirotor unmanned agricultural aircraft system based on CFD

In recent years,multi-rotor Unmanned Aerial Vehicles(UAVs)have been employed in the field of plant protection in China.Spray drift has been considered a major impact in agriculture aerial spraying,and spray quality in the application of plant protection products.The downwash including wake vortices and downward wind field plays a major role in the dispersal and deposition of pesticide spray released by nozzle(s)equipped in aircraft.Differ from the fixed-wing UAV,the downwash flow of multi-rotor UAV was result from the rotation of rotor.Therefore,a study on off-target drift and ground deposit concerning the rotor rotation was simulated through a series of Computational Fluid Dynamics(CFD)simulations to obtain the influence of downwash.The discrete Phase Model(DPM)was taken to simulate the motion of droplet particles since it is an appropriate way to simulate discrete phases in flow field and can track particle trajectory.In this study,the parameters of CFD simulations were acquired by three kinds of actual replicated experiment.The simulation analysis mainly obtains the droplet drift and deposition rule,the influence of eddy current,and downwash flow caused by the rotor rotation.The results showed that the downwash distribution below different rotors was different owing to the flight angle of inclination,“behind”is the greatest,“middle”is secondly,and“forward”is smallest in value(behind,middle,and forward represent three regions below rotors along flight direction).According to the simulation results,two methods of reducing droplet drift were put forward and specific simulations were carried out to prove their feasibility.The results of this study can provide theoretical support for improving the spray quality of UAV and reducing the drift of droplets.