in this research, their effects on the flight of airplanes were investigated. The study area is the country of Iran, and the flight routes of Kermanshah, Ahvaz and BandarAbbas to Tehran. The research data includes maps of the Vertical Transect (profile) of the jet stream, the daily average of the Zonal wind (U-Wind) and meridional wind (V-Wind) components for the winter period of 2018 through NOAA/NCEP environmental databases. Also, flight route information was received from FlightRadar24 and Flightaware systems. First, by using Vertical Transect maps, the days containing strong U-Wind were extracted, and the average position of the core of the Jet Streams in the Zonal and meridional wind components, the Tropospheric level of 200 HP was detected. The list of flights was prepared, and the Zonal Wind maps were produced. Finally, the height of the flights was compared with the level of the currents of the Jet Streams, and the influence or lack of influence of the Jet Streams on the flights was studied. According to the results of the research, all the Jet Streams caused turbulence for all flights, and they caused a decrease in the speed of flights between Ahvaz and BandarAbbas to Tehran and an increase in the speed of flights between Kermanshah and Tehran according to the direction and type of Jet Streams. It was also found that all the Jet Streams had a speed of more than 90 knots, so the capacity to create tension and turbulence such as CAT was seen in them

The pantograph is a critical instrument that significantly affects the aerodynamics of high-speed trains, posing a considerable challenge to the energy conservation and environmental protection of trains. This study explores the feasibility and efficiency of a jet-flow control technique in optimising the aerodynamic characteristics of the pantograph. A numerical method was adopted to investigate the effects of various jet-flow parameters, such as the jet positions, velocities and jet-slot widths, on the flow changes around the pantograph and subsequent reduction in aerodynamic drag of the pantograph. The results show that the impact of the jet position is negligible when the jet velocity is lower than the train speed. The aerodynamic drag reduction rate decreased with increasing distance from the pantograph as the jet velocity increased. When the distance between the jet slot and pantograph is less than 0.6 times the height of the pantograph, the aerodynamic drag reduction rate continuously increased with the jet velocity. As the jet slot moved away from the pantograph, the aerodynamic drag reduction rate initially increased rapidly with the jet velocity and then gradually decreased when the velocity surpassed 1.2 times the train speed. In addition, the aerodynamic drag of the pantograph decreased as the width of the jet slot decreased. However, the energy of the whole train can be only saved when the jet velocity is below 0.6 times the train speed. Findings in this study verified the effectiveness of the jet-flow method in reducing the aerodynamic drag of pantographs and provide important engineering guidance for the energy-saving of high-speed trains.

A new and effective electrospinning method has been developed for producing aligned polymer nanofibers. The conventional electrospinning technique has been modified to fabricate nanofibers as uniaxially aligned array. The key to the success of this technique is the creation of a rotating jet by using a cylindrical collector in which the needle tip is located at its center. The unique advantage of this method among the current methods is the ability of apparatus to weave continuously nanofibers in uniaxially aligned form. Fibers produced by this method are well- ligned, with several meters in length, and can be spread over a large area. Wehave employed a voltage range of (6-16 kV), a collector diameter in the range of 20-50 cm and various concentrations of PAN solutions ranging from 15 wt% to 19 wt %. The electrospun nanofibers could be conveniently formed onto the surface of any thin substrate such as glass sampling plate for subsequent treatments and other applications. Therefore, the linear speed of electrospinning process is determined experimentally as a function of cylindrical collector diameter, polymer concentration and field potential difference.

Narrow, rapidly flowing currents of air located near the tropopause are known as jet streams. These jets, often found nearly girdling the globe while exhibiting large meridional meanders, are among the most ubiquitous structural characteristics of Earth’s atmosphere and are known to play a substantial role in the production of sensible weather in the mid-latitudes. Jet streams are classified into two different types subtropical jet and polar-front jet streams. Subtropical jets are driven by angular momentum transport from the tropics and are centered at the poleward boundaries of the Hadley cell and polar-front jets are driven by baroclinic eddies and are associated with weather and climate events, such as precipitation and cold wave processes.To study whether jet streams have been changing in the past decades, we used the historical data of NCEP/NCAR from the National Centers for Environmental Protection and the National Center for Atmospheric Research, covering 1948 to 2023.We have used the daily means of u, v components, temperature and geopotential height, at 6 levels from 400 to 100 hPa and daily means temperature at 4 levels from 1000 to 700 hPa.In this paper, we firstly calculated the wind speed index, pressure index and latitude index that were defined by Archer and Caldeira (2008) to characterize the strength, the pressure level, and the latitudinal position of a jet stream, respectively. Then after that the variability of the characteristics of jet streams of both hemispheres in warm and cold seasons were investigated.In addition, the temperature trend in the upper and lower troposphere was determined by calculating the average seasonal temperatures over latitudinal zones 0°-15°, 15°-30°, 30°-45°, 45°-60°, 60°-75°, 75°-90° in northern and southern hemisphere at upper levels of 400, 300, 250, 200, 150, 100 hPa and lower levels of 1000, 925, 850, 700 hPa.We found that, in general, the jet streams have moved poleward in both hemispheres so that the shift of subtropical jets in the northern hemisphere was 0.061 (0.019) °/decade in DJF poleward (JJA) and in the southern hemisphere was 0.307 (0.223) °/decade in DJF (JJA) for 1948-2023. Also in the southern hemisphere, the subtropical jet in winter and summer is weakening but the polar front jet is strengthening. In the northern hemisphere, in both warm and cold seasons the trend of wind speed is increasing in the poleward side of the jet axis, and is decreasing in the southern side of its axis, while the trend of the maximum wind speed is upward. One of the important factors of these changes can be related to the upward temperature trend in the tropical and subtropical regions of both hemispheres.In this statistical period, the smallness of the slope of the zonal mean of seasonal temperature trend of the lower levels of the tropical region, compared to the slope of the average temperature trend of the upper levels of the subtropical region, has caused strengthening of the Hadley cell convection which is less than the weakening of its meridional circulation range. This could be one of the factors that lowered the trend of the jet streams speed in both hemispheres. Also, the results show that the mass-flux weighted pressure in the DJF season is minimum around the equator and is minimum in the JJA season around the orbit of 12°N from the west of Mauritania to the southeast of China.

The interior noise caused by the pantograph area is greater than that caused by other areas, and the impact of this pantograph area becomes more significant as the speed of high-speed trains increases, especially above 350 km/h. This study proposes an active jet method for pantograph cavities to control noise at the source. First, a predictive model for the interior noise of pantograph carriages was established by jointly adopting large eddy simulation–statistical energy analysis methods. Then, numerical simulations were conducted to determine the external noise sources and interior sound pressure level at different speeds (300, 350, 400, and 450 km/h). Finally, active jets at different speeds (97.2, 111.1, 125, and 140 m/s) were used to analyze the reduction in interior noise. Results showed that the active jet method decreased the average overall sound pressure level of the acoustic cavity in the horizontal plane. When the train speed reached 450 km/h, the optimal reduction in interior noise was approximately 7.5 dB in the horizontal plane for both the standing and sitting postures. The proposed method can efficiently reduce interior noise in the pantograph area.

Synthetic jet has been confirmed as a novel flow control technology. However, the existing application research on synthetic jet in axial flow compressor is still confined to cascade or low-speed axial flow compressors, and rarely high-speed axial flow compressor. The effects of three vital parameters (i. e., the action position, frequency, peak velocity) on the aerodynamic performance and stability margin are systematically studied, with a high-speed compressor rotor as the object of numerical simulation. An optimal excitation position is determined, corresponding to the core position of the compressor top blockage, as indicated by the results, which increases the stability margin and efficiency of the compressor by 13. 2% and 1. 15% respectively. The excitation frequency has a threshold ranging from 300Hz to 600Hz. Only when the frequency of synthetic jet exceeds this threshold can it suppress the tip leakage flow. Besides, the jet peak velocity may not have a threshold. However, the higher the peak velocity, the greater the mixing loss between the jet and the mainstream of the compressor rotor will be, thus limiting the further increase of the compressor efficiency.

This paper investigates the influence of a weak-jet on the development of a turbulent axisymmetric strong jet. A parametric study is carried out to evaluate simultaneously the effect to the jets-spacing (S/D=3 and S/D=7. 5) and their velocity ratios in range 0≤ λ ≤ 1. The mixing phenomenon is studied numerically by the finite volume method using the 3D-RANS second-order model, which gives a good agreement with the available data. Three distinct regions of this type of jets interaction are evidenced. This study confirms that the jets spacing affects strongly the converging region and has a minor effect on the combining region. It is found that the weak jet attracts the strong jet and the combining region extends from 30D to 40D where the self-similarity of a single jet is obtained. The jet width decreases when velocity ratio and jets spacing augment. In the combining region, in comparison with the free jet, it is found that the addition of a weak-jet increases the decay rate of the centerline velocity.