Ducted fans have been widely used in VTOL aircraft due to the high propulsion efficiency and safety.The efficiency and stability of ducted fans deteriorate in some flight conditions such as hovering in crosswinds or g...Ducted fans have been widely used in VTOL aircraft due to the high propulsion efficiency and safety.The efficiency and stability of ducted fans deteriorate in some flight conditions such as hovering in crosswinds or ground effect.It is necessary to optimize the ducted fan’s structures or apply flow control methods for better adaptions to the typical conditions.This paper presents a detailed review on the ducted fan technology for VTOL applications,especially the methods for improving its efficiency and stability.We first simplified the classification categories based on boundary conditions instead of flight conditions,since the new classification method covers more situations and is easier to distinguish flow field characteristics.The flow characteristics,thrust properties and the optimal structures under different boundary conditions were summarized and discussed.Finally,new configurations and flow control methods for increasing the efficiency and stability were introduced.The newly proposed integration design between the ducted fan and the motor was emphasized for increasing the power density of the ducted fans.This review would be helpful to improve our understanding of the relationship between the structures,flow characteristics and thrust properties of ducted fans under different flight conditions,and inspires scientists to design high-efficiency and high-stability propulsion systems with ducted fans.展开更多
Nanowires （NWs） are ideal nanostructures for exploring the effects of low dimensionality and thermal conductivity suppression on thermoelectric behavior. However, it is challenging to accurately measure temperature ...Nanowires （NWs） are ideal nanostructures for exploring the effects of low dimensionality and thermal conductivity suppression on thermoelectric behavior. However, it is challenging to accurately measure temperature gradients and heat flow in such systems. Here, using a combination of spatially resolved Raman spectroscopy and transport measurements, we determine all the thermoelectric properties of single Se-doped InSb NWs and quantify the figure of merit ZT. The measured laser-induced heating in the NWs and associated electrical response are well described by a 1D heat equation model. Our method allows the determination of the thermal contact resistances at the source and drain electrodes of the NW, which are negligible in our system. The measured thermoelectric parameters of InSb NWs agree well with those obtained based on field-effect transistor Seebeck measurements.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2020YFC1512500)the Advanced Aviation Power Innovation Institution,the Aero Engine Academy of ChinaTsinghua University Initiative Scientific Research Program。
文摘Ducted fans have been widely used in VTOL aircraft due to the high propulsion efficiency and safety.The efficiency and stability of ducted fans deteriorate in some flight conditions such as hovering in crosswinds or ground effect.It is necessary to optimize the ducted fan’s structures or apply flow control methods for better adaptions to the typical conditions.This paper presents a detailed review on the ducted fan technology for VTOL applications,especially the methods for improving its efficiency and stability.We first simplified the classification categories based on boundary conditions instead of flight conditions,since the new classification method covers more situations and is easier to distinguish flow field characteristics.The flow characteristics,thrust properties and the optimal structures under different boundary conditions were summarized and discussed.Finally,new configurations and flow control methods for increasing the efficiency and stability were introduced.The newly proposed integration design between the ducted fan and the motor was emphasized for increasing the power density of the ducted fans.This review would be helpful to improve our understanding of the relationship between the structures,flow characteristics and thrust properties of ducted fans under different flight conditions,and inspires scientists to design high-efficiency and high-stability propulsion systems with ducted fans.
文摘Nanowires （NWs） are ideal nanostructures for exploring the effects of low dimensionality and thermal conductivity suppression on thermoelectric behavior. However, it is challenging to accurately measure temperature gradients and heat flow in such systems. Here, using a combination of spatially resolved Raman spectroscopy and transport measurements, we determine all the thermoelectric properties of single Se-doped InSb NWs and quantify the figure of merit ZT. The measured laser-induced heating in the NWs and associated electrical response are well described by a 1D heat equation model. Our method allows the determination of the thermal contact resistances at the source and drain electrodes of the NW, which are negligible in our system. The measured thermoelectric parameters of InSb NWs agree well with those obtained based on field-effect transistor Seebeck measurements.
