Swirl recovery vanes（SRVs） are a set of stationary vanes located downstream from a propeller, which may recover some of the residual swirl from the propeller, hoping for an improvement in both thrust and efficiency....Swirl recovery vanes（SRVs） are a set of stationary vanes located downstream from a propeller, which may recover some of the residual swirl from the propeller, hoping for an improvement in both thrust and efficiency. The SRV concept design for a scaled version representing the Fokker 29 propeller is performed in this paper, which may give rise to a promotion in propulsive performance of this traditional propeller. Firstly the numerical strategy is validated from two aspects of global quantities and the local flow field of the propeller compared with experimental data, and then the exit flow together with the development of propeller wake is analyzed in detail.Three kinds of SRV are designed with multiple circular airfoils. The numerical results show that the swirl behind the propeller is recovered significantly with Model V3, which is characterized by the highest solidity along spanwise, for various working conditions, and the combination of rotor and vane produced 5.76% extra thrust at the design point. However, a lower efficiency is observed asking for a better vane design and the choice of a working point. The vane position is studied which shows that there is an optimum range for higher thrust and efficiency.展开更多
A new hybrid control scheme is presented with a robust multiple model fusion control（RMMFC） law for a UH-60 helicopter and an active disturbance rejection control（ADRC） controller for its engines.This scheme is a ...A new hybrid control scheme is presented with a robust multiple model fusion control（RMMFC） law for a UH-60 helicopter and an active disturbance rejection control（ADRC） controller for its engines.This scheme is a control design method with every subsystem designed separately but fully considering the couplings between them.With three subspaces with respect to forward flight velocity,a RMMFC is proposed to devise a four-loop reference signal tracing control for the helicopter,which escapes the closed-loop system from unstable state due to the extreme complexity of this integrated nonlinear system.The engines are controlled by the proposed ADRC decoupling controller,which fully takes advantage of a good compensation ability for unmodeled dynamics and extra disturbances,so as to compensate torque disturbance in power turbine speed loop.By simulating a forward acceleration flight task,the RMMFC for the helicopter is validated.It is apparent that the integrated helicopter and engine system（IHES） has much better dynamic performance under the new control scheme.Especially in the switching process,the large transient is significantly weakened,and smooth transition among candidate controllers is achieved.Over the entire simulation task,the droop of power turbine speed with the proposed ADRC controller is significantly slighter than with the conventional PID controller,and the response time of the former is much faster than the latter.By simulating a rapid climb and descent flight task,the results also show the feasibility for the application of the proposed multiple model fusion control.Although there is aggressive power demand in this maneuver,the droop of power turbine speed with an ADRC controller is smaller than using a PID controller.The control performance for helicopter and engine is enhanced by adopting this hybrid control scheme,and simulation results in other envelope state give proofs of robustness for this new scheme.展开更多
Multiple degenerate band engineering has been established as an effective approach to maximize electrical transport in thermoelectric materials.A series of polycrystalline samples of chalcopyrite Cu_(1-x-δ)Ag_(x)InTe...Multiple degenerate band engineering has been established as an effective approach to maximize electrical transport in thermoelectric materials.A series of polycrystalline samples of chalcopyrite Cu_(1-x-δ)Ag_(x)InTe_(2)(x=0-0.5,δ=0.02-0.05)was synthesized,to achieve multiple degenerate bands.A pseudocubic structure is realized when x is around 0.2.As a result,the degenerate valence bands influence electrical transport significantly.In addition,the lattice thermal conductivity is significantly depressed in the solid solution due to the strong phonon scattering by strain-field fluctuations,since Ag substitution brings significant anharmonicity to the crystal structure.The highest ZT of 1.24 was obtained at the composition Cu_(0.75)Ag_(0.2)InTe_(2).This study provides an example how the pseudocubic crystal structure is applied to design and evaluate the TE properties in diamond-like compounds.展开更多
基金supported by the National Natural Science Foundation of China (No. 51376150)
文摘Swirl recovery vanes（SRVs） are a set of stationary vanes located downstream from a propeller, which may recover some of the residual swirl from the propeller, hoping for an improvement in both thrust and efficiency. The SRV concept design for a scaled version representing the Fokker 29 propeller is performed in this paper, which may give rise to a promotion in propulsive performance of this traditional propeller. Firstly the numerical strategy is validated from two aspects of global quantities and the local flow field of the propeller compared with experimental data, and then the exit flow together with the development of propeller wake is analyzed in detail.Three kinds of SRV are designed with multiple circular airfoils. The numerical results show that the swirl behind the propeller is recovered significantly with Model V3, which is characterized by the highest solidity along spanwise, for various working conditions, and the combination of rotor and vane produced 5.76% extra thrust at the design point. However, a lower efficiency is observed asking for a better vane design and the choice of a working point. The vane position is studied which shows that there is an optimum range for higher thrust and efficiency.
基金Funding of Jiangsu Innovation Program for Graduate Education (CXLX11_0213)Aeronautical Science Foundation of China (2010ZB52011)
文摘A new hybrid control scheme is presented with a robust multiple model fusion control（RMMFC） law for a UH-60 helicopter and an active disturbance rejection control（ADRC） controller for its engines.This scheme is a control design method with every subsystem designed separately but fully considering the couplings between them.With three subspaces with respect to forward flight velocity,a RMMFC is proposed to devise a four-loop reference signal tracing control for the helicopter,which escapes the closed-loop system from unstable state due to the extreme complexity of this integrated nonlinear system.The engines are controlled by the proposed ADRC decoupling controller,which fully takes advantage of a good compensation ability for unmodeled dynamics and extra disturbances,so as to compensate torque disturbance in power turbine speed loop.By simulating a forward acceleration flight task,the RMMFC for the helicopter is validated.It is apparent that the integrated helicopter and engine system（IHES） has much better dynamic performance under the new control scheme.Especially in the switching process,the large transient is significantly weakened,and smooth transition among candidate controllers is achieved.Over the entire simulation task,the droop of power turbine speed with the proposed ADRC controller is significantly slighter than with the conventional PID controller,and the response time of the former is much faster than the latter.By simulating a rapid climb and descent flight task,the results also show the feasibility for the application of the proposed multiple model fusion control.Although there is aggressive power demand in this maneuver,the droop of power turbine speed with an ADRC controller is smaller than using a PID controller.The control performance for helicopter and engine is enhanced by adopting this hybrid control scheme,and simulation results in other envelope state give proofs of robustness for this new scheme.
基金supported by the National Basic Research Program of China(973-program)under Project No.2013CB632501the National Natural Science Foundation of China(NSFC)under No.11234012 and 51302300+1 种基金the Key Research Program of Chinese Academy of Sciences(Grant No.KGZD-EW-T06)the International S&T Cooperation Program of China(2015DFA51050).
文摘Multiple degenerate band engineering has been established as an effective approach to maximize electrical transport in thermoelectric materials.A series of polycrystalline samples of chalcopyrite Cu_(1-x-δ)Ag_(x)InTe_(2)(x=0-0.5,δ=0.02-0.05)was synthesized,to achieve multiple degenerate bands.A pseudocubic structure is realized when x is around 0.2.As a result,the degenerate valence bands influence electrical transport significantly.In addition,the lattice thermal conductivity is significantly depressed in the solid solution due to the strong phonon scattering by strain-field fluctuations,since Ag substitution brings significant anharmonicity to the crystal structure.The highest ZT of 1.24 was obtained at the composition Cu_(0.75)Ag_(0.2)InTe_(2).This study provides an example how the pseudocubic crystal structure is applied to design and evaluate the TE properties in diamond-like compounds.
