The inhomogeneity is introduced by a nonzero density gradient which separates the plasma into two different regions where plasma density are constant.The Alfvén waves,the phase mixing and the fast magnetosonic wa...The inhomogeneity is introduced by a nonzero density gradient which separates the plasma into two different regions where plasma density are constant.The Alfvén waves,the phase mixing and the fast magnetosonic wave are excited by the boundary condition in inhomogeneous magnetized plasma.By using the Hall–magnetohydrodynamics(MHD)model,it is found that there are Alfvén waves in the homogeneous regions,while the phase mixing appears in the inhomogeneous region.The interesting result is that a fast magnetosonic wave is excited in a different direction which has a nonzero angle between the wave propagation direction and the direction of the background magnetic field.The dependence of the propagation direction of the excited fast magnetosonic wave and its strength of the magnetic field on the plasma parameters are given numerically.The results show that increasing both the driving frequency and the ratio of magnetic pressure to thermal pressure will increase the acceleration of the electrons.The electron acceleration also depends on the inhomogeneity parameters.展开更多
The attenuation of spatially evolving instability Tollmien-Schlichting(T-S)waves in the boundary layer of a flat plate with zero pressure gradients using an active feedback control scheme is theoretically and numerica...The attenuation of spatially evolving instability Tollmien-Schlichting(T-S)waves in the boundary layer of a flat plate with zero pressure gradients using an active feedback control scheme is theoretically and numerically investigated.The boundary layer is excited artificially by various perturbations to create a three-dimensional field of instability waves.Arrays of actuators and sensors are distributed locally at the wall surface and connected together via a feedback controller.The key elements of this feedback control are the determination of the dynamic model of the flat plate boundary layer between the actuators and the sensors,and the design of the model-based feedback controller.The dynamic model is established based on the linear stability calculation which simulates the three-dimensional input-output behaviour of the boundary layer.To simplify the control problem,an uncoupled control mode of the dynamic model is made to capture only those dynamics that have greatest influences on the input-output behaviour.A Proportional-Integral-Derivative(PID)controller,i.e.a lead-lag compensator,combining with a standard Smith predictor is designed based on the system stability criterion and the specifications using frequency-response methods.Good performance of the feedback control with the uncoupled control mode is demonstrated by the large reduction of the three-dimensional disturbances in the boundary layer.This simple feedback control is realistic and competitive in a practical implementation of T-S wave cancellation using a limited number of localised sensors and actuators.展开更多
The rapid deployment of solar and wind technology produces significant amount of low-quality electricity that calls for a better storage or usage instead of being discarded by the grid.Instead of electrochemical CO2 r...The rapid deployment of solar and wind technology produces significant amount of low-quality electricity that calls for a better storage or usage instead of being discarded by the grid.Instead of electrochemical CO2 reduction and/or NH3 production,here we propose that non-thermal plasma oxidation of N2 into nitrate or other valuable nitrogen containing compounds deserve more research attention because it uses free air as the reactant and avoids the solubility difficulty,and also because its energy consumption is merely 0.2 MJ/mol,even lower than the industrially very successful Haber-Bosch process（0.48 MJ/mol）for NH3 production.We advocate that researchers from the plasma community and chemistry community should work together to build energy efficient non-thermal plasma setup,identify robust,active and low-cost catalyst,and understand the catalyzing mechanism in a plasma environment.We are confident that free production of nitrate with zero C02 emission will come true in the near future.展开更多
基金supported by National Natural Science Foundation of China(Nos.11965019,42004131 and 61863032)。
文摘The inhomogeneity is introduced by a nonzero density gradient which separates the plasma into two different regions where plasma density are constant.The Alfvén waves,the phase mixing and the fast magnetosonic wave are excited by the boundary condition in inhomogeneous magnetized plasma.By using the Hall–magnetohydrodynamics(MHD)model,it is found that there are Alfvén waves in the homogeneous regions,while the phase mixing appears in the inhomogeneous region.The interesting result is that a fast magnetosonic wave is excited in a different direction which has a nonzero angle between the wave propagation direction and the direction of the background magnetic field.The dependence of the propagation direction of the excited fast magnetosonic wave and its strength of the magnetic field on the plasma parameters are given numerically.The results show that increasing both the driving frequency and the ratio of magnetic pressure to thermal pressure will increase the acceleration of the electrons.The electron acceleration also depends on the inhomogeneity parameters.
基金supported by the Foundation of the State Key Laboratory of Aerodynamics(Grant No.SKLA2019040302)the National Natural Science Foundation of China(Grant No.11872038).
基金the support provided by the Open Fund of Key Laboratory of Aerodynamic Noise Control of China(No:1901ANCL20190105)。
文摘The attenuation of spatially evolving instability Tollmien-Schlichting(T-S)waves in the boundary layer of a flat plate with zero pressure gradients using an active feedback control scheme is theoretically and numerically investigated.The boundary layer is excited artificially by various perturbations to create a three-dimensional field of instability waves.Arrays of actuators and sensors are distributed locally at the wall surface and connected together via a feedback controller.The key elements of this feedback control are the determination of the dynamic model of the flat plate boundary layer between the actuators and the sensors,and the design of the model-based feedback controller.The dynamic model is established based on the linear stability calculation which simulates the three-dimensional input-output behaviour of the boundary layer.To simplify the control problem,an uncoupled control mode of the dynamic model is made to capture only those dynamics that have greatest influences on the input-output behaviour.A Proportional-Integral-Derivative(PID)controller,i.e.a lead-lag compensator,combining with a standard Smith predictor is designed based on the system stability criterion and the specifications using frequency-response methods.Good performance of the feedback control with the uncoupled control mode is demonstrated by the large reduction of the three-dimensional disturbances in the boundary layer.This simple feedback control is realistic and competitive in a practical implementation of T-S wave cancellation using a limited number of localised sensors and actuators.
基金This work was financially supported by the National Natural Science Foundation of China （Grant No. 61725401 ） and the National Key R＆D Program of China （No. 2016YFA0204000）. We also thank Junye Zhang from School of Optical and Electronic Information, Huazhong University of Science and Technology, and Sai Tu from College of Chemistry and Molecular Science, Wuhan University for helpful discussions.
文摘The rapid deployment of solar and wind technology produces significant amount of low-quality electricity that calls for a better storage or usage instead of being discarded by the grid.Instead of electrochemical CO2 reduction and/or NH3 production,here we propose that non-thermal plasma oxidation of N2 into nitrate or other valuable nitrogen containing compounds deserve more research attention because it uses free air as the reactant and avoids the solubility difficulty,and also because its energy consumption is merely 0.2 MJ/mol,even lower than the industrially very successful Haber-Bosch process（0.48 MJ/mol）for NH3 production.We advocate that researchers from the plasma community and chemistry community should work together to build energy efficient non-thermal plasma setup,identify robust,active and low-cost catalyst,and understand the catalyzing mechanism in a plasma environment.We are confident that free production of nitrate with zero C02 emission will come true in the near future.
