Research On Experimental Method And Optimization Design Of The Propeller Propulsion System Of Near Space Airships

The electric propeller propulsion is the primary source of power for low-speed near-space vehicles,and its performance directly affects the ability of long-term area hover,cruising,and maneuvering for near-space vehicles.However,some important issues still exist with respect to the testing and design of near-space electric propeller propulsion system.First,as the nearspace electric propeller propulsion system works under the low-density,low-temperature,and low-pressure environment,the testing techniques for system efficiency,reliability and environmental adaptability are rather different from those under the ground environment.In particular,the conventional ground experiments cannot fully reflect the actual performance of the propulsion system at the near-space conditions due to the large difference of air density between high-altitude and low-altitude atmosphere.Second,it is of vital importance to develop a lightweight and energy-efficient propulsion system in order to guarantee the long-endurance capability of the near-space vehicle.Nonetheless,most of the current research has primarily focused on the propulsion system itself while paid less attention on the design of different schemes for the multi-propeller propulsion system.To address these challenges,this research is wrapped around two aspects of electric propeller propulsion system of the near-space vehicle,which are the experimental testing framework and design optimisation methodology,respectively.This work is detailed as follows.(1)An experimental system of the near-space propulsion system based on several specific experimental platform was formulated to address the existing difficulties.Firstly,the testing items were identified for the near-space electric propeller propulsion system,and the testing difficulties were analysed in detail with respect to the high-altitude,low-density atmospheric environment,and the operating conditions with wide variations of wind speed and height.Secondly,a testing approach for the performance of the near-space electric propeller propulsion system was proposed.It was built on a vehicle-mounted dynamic testing system with altitude variability for full-size and scaled models of propellers,a general ground load simulator for permanent-magnet DC motors,and a near-space airship equipped with the experimental platform for integral propulsion systems.Thirdly,the testing framework for the overall system was completed by integrating other testing capabilities such as structural tests,environmental tests and so on.Not only can the testing framework provide experimental data to validate the design methods of the propulsion system,but also it easily fits into engineering applications.The experimental system has been recognized by many participants in the specific industry,and it has also been successfully applied to the development of the propulsion system of near-space vehicle.(2)In order to obtain the aerodynamic performance of the high-altitude propellers at both high and low altitudes,the hardware system of the vehicle-mounted dynamic testing system was established for both full-size and scaled models of propellers.Firstly,the functions,characteristics and principles of the three constitutive parts including a carrier vehicle,a test platform,and a measurement and control system are introduced.Secondly,the interference factors of the dynamic testing system were identified.Thus,two new balances were designed and calibrated for the measurements of propeller aerodynamic forces and torque,minimizing the impact the vibration of the dynamic platform.Thirdly,the devices,and equipment of the three components were selected and designed individually.The measurement requirements were satisfied by selecting appropriate I/O modules based on the Compact DAQ-9188 measurement and control terminal.Finally,The hardware condition of the dynamic testing system and measure methods of the experimental parameters are presented through the system structure diagrams.(3)The software environment of the vehicle-mounted dynamic testing system is studied and established under the environment of virtual instrument Lab VIEW.First,the architecture of vehicle-mounted measurement and control software was proposed based on the producer/customer design pattern,fulfilling the requirements of motor control and data collection.The programming was performed individually for the modules of motor-servocontrol,multi-channel data collection,and real-time data processing and storage.Then,the running process of the software was designed according to the produce of vehicle-mounted experiments,and the user interface was also designed accordingly.Finally,a set of data processing methods were developed for the dynamic testing experiments,including interception of effective data segments,rejection of coarse error,and calculation of aerodynamic coefficients,etc.The software architecture and design was completed based on the event-driven mode.(4)The full-size and scaled models of propeller testing system were verified by numerical simulations and wind tunnel experiments.Then the proposed testing system was also applied to the electric propeller propulsion system of a near-space airship.Specifically,the performance of the whole propulsion system at low-altitude conditions were obtained through the full-size model dynamic testing;whereas the performance at high-altitude conditions were obtained by combining the scaled model dynamic testing system and the motor simulator of ground loading.The experimental results show that the developed testing system meets the requirements of performance testing of a near-space propeller propulsion system,and can facilitate the design of the near-space electric propeller propulsion system by providing data support.(5)Based on the response surface methodology,an optimization design method was developed to achieve the optimum power unit for the propulsion systems of high altitude airships(HAA).First,the aerodynamic optimization design and analysis of the high altitude propeller is accomplished via the vortex theory,while the structural analysis and lamination optimum design via the commercial finite element software Msc.Patran/ Nastran.Then,for both motor and propeller,a responding surface model of the efficiency and weight with respect to the important design variables was established respectively through the optimal Latin hypercube design(Opt LHD)method.Next,an optimization model of the propulsion systems was constructed,and the design is subject to various constraints including the balance among weight and buoyancy forces,and the energy balance of the whole airship.Finally,the multiisland genetic algorithm is used to find the optimum power unit for a typical HAA.The influence of design variables including the number of propulsion systems,diameter of the propeller,and the rotational speed on the incidence of weight and efficiency of the propulsion are evaluated.It was found that the total weight of the energy storage system and propulsion system reduces by 7.2%,which increases the load capacity of the airship and hence the overall efficiency of the propulsion system.