Numerous investigations have been conducted to understand the wall effects on rotors.The purpose of this study is to further investigate the aerodynamic performance of revolving wings,especially when it is very close ...Numerous investigations have been conducted to understand the wall effects on rotors.The purpose of this study is to further investigate the aerodynamic performance of revolving wings,especially when it is very close to the ground and ceiling(i.e.,less than half the wingspan)at low Reynolds numbers.Hence,the ground and ceiling effect for hovering micro revolving wings at low Reynolds numbers are investigated by improving the theoretical models.The theoretical model for the ground effect is established based on the wall-jet assumption,and that for the ceiling effect is improved by considering the uneven spanwise distribution of induced velocity.These two models are validated by comparing the results of experiments and CFD simulations with the Lattice-Boltzmann Method(LBM).Both ground and ceiling effects are found helpful to enhance the thrust,especially with small wing-wall distances,by making a difference to the induced velocity and the pressure distribution.By comparing the thrust generation and aerodynamic efficiency between the ground and ceiling effects,the former is found more helpful to the thrust augmentation,and the latter is more beneficial for the aerodynamic efficiency promotion.展开更多
Based on the investigation data of social position of national women in the third phase by National Women's Federation and National Bureau of Statistics in 2010,regression analysis on sex wage difference is conduc...Based on the investigation data of social position of national women in the third phase by National Women's Federation and National Bureau of Statistics in 2010,regression analysis on sex wage difference is conducted. It is divided into two parts. The first part is the impact on wage by sex,and it is divided into whole country,eastern,central and western regions. The second part is the impact on wage by different education backgrounds. It tries to explore sex wage difference situation at different positions of wage distribution,study if there exists " ceiling effect" or " floor effect" in population's wage distribution situation,sex wage difference situation in eastern,central and western regions and the education's impact on future income situations of men and women.展开更多
Ducted-fan drones are expected to become the main drone configuration in the future due to their high efficiency and minimal noise.When drones operate in confined spaces,significant proximity effects may interfere wit...Ducted-fan drones are expected to become the main drone configuration in the future due to their high efficiency and minimal noise.When drones operate in confined spaces,significant proximity effects may interfere with the aerodynamic performance and pose challenges to flight safety.This study utilizes computational fluid dynam-ics simulation with the Unsteady Reynolds-averaged Navier–Stokes(URANS)method to estimate the proximity effects.Through experimental validation,our computational results show that the influence range of proximity effects lies within four rotor radii.The ground effect and the ceiling effect mainly affect thrust properties,while the wall effect mainly affects the lateral force and the pitching moment.In ground effect,the rotor thrust increases exponentially by up to 26%with ground distance compared with that in open space.Minimum duct thrust and total thrust are observed at one rotor radius above the ground.In ceiling effect,all the thrusts rise as the drone approaches the ceiling,and total thrust increases by up to 19%.In wall effect,all the thrusts stay constant.The pitching moment and lateral force rise exponentially with the wall distance.Changes in blade angle of attack and duct pressure distributions can account for the performance change.The results are of great importance to the path planning and flight controller design of ducted-fan drones for safe and effi-cient operations in confined environments.展开更多
基金supported by the National Natural Science Foundation of China(No.11902017)the China Postdoctoral Science Foundation(Nos.2020T130043,2019M650418).
文摘Numerous investigations have been conducted to understand the wall effects on rotors.The purpose of this study is to further investigate the aerodynamic performance of revolving wings,especially when it is very close to the ground and ceiling(i.e.,less than half the wingspan)at low Reynolds numbers.Hence,the ground and ceiling effect for hovering micro revolving wings at low Reynolds numbers are investigated by improving the theoretical models.The theoretical model for the ground effect is established based on the wall-jet assumption,and that for the ceiling effect is improved by considering the uneven spanwise distribution of induced velocity.These two models are validated by comparing the results of experiments and CFD simulations with the Lattice-Boltzmann Method(LBM).Both ground and ceiling effects are found helpful to enhance the thrust,especially with small wing-wall distances,by making a difference to the induced velocity and the pressure distribution.By comparing the thrust generation and aerodynamic efficiency between the ground and ceiling effects,the former is found more helpful to the thrust augmentation,and the latter is more beneficial for the aerodynamic efficiency promotion.
文摘Based on the investigation data of social position of national women in the third phase by National Women's Federation and National Bureau of Statistics in 2010,regression analysis on sex wage difference is conducted. It is divided into two parts. The first part is the impact on wage by sex,and it is divided into whole country,eastern,central and western regions. The second part is the impact on wage by different education backgrounds. It tries to explore sex wage difference situation at different positions of wage distribution,study if there exists " ceiling effect" or " floor effect" in population's wage distribution situation,sex wage difference situation in eastern,central and western regions and the education's impact on future income situations of men and women.
文摘Ducted-fan drones are expected to become the main drone configuration in the future due to their high efficiency and minimal noise.When drones operate in confined spaces,significant proximity effects may interfere with the aerodynamic performance and pose challenges to flight safety.This study utilizes computational fluid dynam-ics simulation with the Unsteady Reynolds-averaged Navier–Stokes(URANS)method to estimate the proximity effects.Through experimental validation,our computational results show that the influence range of proximity effects lies within four rotor radii.The ground effect and the ceiling effect mainly affect thrust properties,while the wall effect mainly affects the lateral force and the pitching moment.In ground effect,the rotor thrust increases exponentially by up to 26%with ground distance compared with that in open space.Minimum duct thrust and total thrust are observed at one rotor radius above the ground.In ceiling effect,all the thrusts rise as the drone approaches the ceiling,and total thrust increases by up to 19%.In wall effect,all the thrusts stay constant.The pitching moment and lateral force rise exponentially with the wall distance.Changes in blade angle of attack and duct pressure distributions can account for the performance change.The results are of great importance to the path planning and flight controller design of ducted-fan drones for safe and effi-cient operations in confined environments.
