Turbine noise would be one of the dominant noise sources especially in future UHBR (Ultra High Bypass-Ratio) aeroengine, but its currently far from being studied enough. Acoustic mode is crucial for duct propagation b...Turbine noise would be one of the dominant noise sources especially in future UHBR (Ultra High Bypass-Ratio) aeroengine, but its currently far from being studied enough. Acoustic mode is crucial for duct propagation but little study about the relation between serration and mode. Thus, taking axial single-turbine test bench NPU-Turb as object, the effect of Stator with Serrated Trailing-edge (Bionic S) and Rotor with Serrated Leading-edge (Bionic R) on duct acoustic modes of turbine turbulence interac-tion noise were studied in detail using DDES/AA hybrid model validated by acoustic experiment of NPU-Turb. Serval conclusions can be made here. First, for broadband noise, the effect of serrations on duct modes (increased or reduced of PWL<sub>mn</sub>) with the increasing frequency is more prominent. Second, the changing trend of ?PWL<sub>mn</sub> is something like Chinese character “人” with circumferential mode m and alternating with radial mode. Such distribution is more obvious at higher frequency. More theoretical and mechanistic research work needs to be carried out in depth in the future. .展开更多
Exohiss are broadband,structureless whistler-mode waves outside the plasmapause.In our work,using the data sets detected by the EMFISIS suite aboard Van Allen Probe A,from 1st January 2013 to 30th June 2017,the exohis...Exohiss are broadband,structureless whistler-mode waves outside the plasmapause.In our work,using the data sets detected by the EMFISIS suite aboard Van Allen Probe A,from 1st January 2013 to 30th June 2017,the exohiss waves are categorized among two types based on the direction of Poynting flux:unidirectional exohiss,and bidirectional exohiss waves.It seems that most exohiss waves are bidirectional,which are mainly distributed on the dayside.Compared to the hiss waves within the plasmasphere,the amplitude of bidirectional exohiss waves on the prenoon side increase very little with the enhancement of geomagnetic activity.Through the analysis of suprathermal electron flux associated with geomagnetic activity,this suggests that the waves may undergo very strong Landau damping during intense geomagnetic activity.On the other hand,the unidirectional exohiss waves are mainly distributed on the afternoon side,and the largest unidirectional exohiss waves are observed during the highest levels of substorm activity.展开更多
E-learning platforms support education systems worldwide, transferring theoretical knowledge as well as soft skills. In the present study high-school pupils’, and adult students’ opinions were evaluated through a mo...E-learning platforms support education systems worldwide, transferring theoretical knowledge as well as soft skills. In the present study high-school pupils’, and adult students’ opinions were evaluated through a modern structured MOODLE interactive course, designed for the needs of the laboratory course “Automotive Systems”. The study concerns Greek secondary vocational education pupils aged 18 and vocational training adult students aged 20 to 50 years. The multistage, equal size simple random cluster sample was used as a sampling method. Pupils and adult students of each cluster completed structured 10-question questionnaires both before and after attending the course. A total of 120 questionnaires were collected. In general, our findings disclosed that the majority of pupils and adult students had significantly improved their knowledge and skills from using MOODLE. They reported strengthening conventional teaching, using the new MOODLE technology. The satisfaction indices improved quite, with the differences in their mean values being statistically significant.展开更多
文摘Turbine noise would be one of the dominant noise sources especially in future UHBR (Ultra High Bypass-Ratio) aeroengine, but its currently far from being studied enough. Acoustic mode is crucial for duct propagation but little study about the relation between serration and mode. Thus, taking axial single-turbine test bench NPU-Turb as object, the effect of Stator with Serrated Trailing-edge (Bionic S) and Rotor with Serrated Leading-edge (Bionic R) on duct acoustic modes of turbine turbulence interac-tion noise were studied in detail using DDES/AA hybrid model validated by acoustic experiment of NPU-Turb. Serval conclusions can be made here. First, for broadband noise, the effect of serrations on duct modes (increased or reduced of PWL<sub>mn</sub>) with the increasing frequency is more prominent. Second, the changing trend of ?PWL<sub>mn</sub> is something like Chinese character “人” with circumferential mode m and alternating with radial mode. Such distribution is more obvious at higher frequency. More theoretical and mechanistic research work needs to be carried out in depth in the future. .
基金supported by National Natural Science Foundation of China under Grants 42374201,42274206,42374187Natural Science Foundation of Jiangxi Province under grants 20243BCE51,20243BCE51151 and 20232BAB213078.
文摘Exohiss are broadband,structureless whistler-mode waves outside the plasmapause.In our work,using the data sets detected by the EMFISIS suite aboard Van Allen Probe A,from 1st January 2013 to 30th June 2017,the exohiss waves are categorized among two types based on the direction of Poynting flux:unidirectional exohiss,and bidirectional exohiss waves.It seems that most exohiss waves are bidirectional,which are mainly distributed on the dayside.Compared to the hiss waves within the plasmasphere,the amplitude of bidirectional exohiss waves on the prenoon side increase very little with the enhancement of geomagnetic activity.Through the analysis of suprathermal electron flux associated with geomagnetic activity,this suggests that the waves may undergo very strong Landau damping during intense geomagnetic activity.On the other hand,the unidirectional exohiss waves are mainly distributed on the afternoon side,and the largest unidirectional exohiss waves are observed during the highest levels of substorm activity.
文摘E-learning platforms support education systems worldwide, transferring theoretical knowledge as well as soft skills. In the present study high-school pupils’, and adult students’ opinions were evaluated through a modern structured MOODLE interactive course, designed for the needs of the laboratory course “Automotive Systems”. The study concerns Greek secondary vocational education pupils aged 18 and vocational training adult students aged 20 to 50 years. The multistage, equal size simple random cluster sample was used as a sampling method. Pupils and adult students of each cluster completed structured 10-question questionnaires both before and after attending the course. A total of 120 questionnaires were collected. In general, our findings disclosed that the majority of pupils and adult students had significantly improved their knowledge and skills from using MOODLE. They reported strengthening conventional teaching, using the new MOODLE technology. The satisfaction indices improved quite, with the differences in their mean values being statistically significant.
