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Aerial electrostatic spray technology for agriculture is the integration of precision agricultural aviation and electrostatic spray technology. It is one of the research topics that have been paid close attention to by scholars in the field of agricultural aviation. This study summarizes the development of airborne electrostatic spray technology for agricultural use in China, including the early research and exploration of Chinese institutions and researchers in the aspects of nozzle structure design optimization and theoretical simulation. The research progress of UAV-based aerial electrostatic spray technology for agricultural use in China was expounded from the aspects of nozzle modification, technical feasibility study, influencing mechanism of various factors, and field efficiency tests. According to the current development of agricultural UAVs and the characteristics of the farmland environment in China, the UAV-based aerial electrostatic spray technology, which carries the airborne electrostatic spray system on the plant protection UAVs, has a wide potential in the future. At present, the application of UAV-based aerial electrostatic spray technology has yet to be further improved due to several factors, such as the optimization of the test technology for charged droplets, the impact of UAV rotor wind field, comparison study on charging modes, and the lack of technical accumulation in the research of aerial electrostatic spray technology. With the continuous improvement of the research system of agricultural aviation electrostatic spray technology, UAV-based electrostatic spray technology will give play to the advantages in increasing the droplets deposition on the target and reducing environmental pollution from the application of pesticides. This study is capable of providing a reference for the development of the UAV-based agricultural electrostatic spray technology and the spray equipment.

Infrared radiation signatures of gas turbine engine exhaust are suppressed markedly when equipped with a serpentine nozzle compared to an axisymmetric nozzle. The aim of this paper is to research more detailed flow characteristics of the serpentine nozzle, and to this end a double serpentine nozzle cold fluid test was conducted in this paper, static pressures on the nozzle walls surface were measured, and schlieren flow visualizations downstream of the nozzle exit were observed. Then numerical simulations of the experimental model were carried out using CFD software with k-ɛ turbulence model adopted. And the effects of geometric design parameters (the length ratio of first S length to second S length and the centerline distributions) on serpentine nozzle performance were investigated numerically. Detailed flow characteristics were presented including the distributions of static pressure, Ma number (streamlines), wall shear stress (limited streamlines), and the total pressure. Results show good agreement between the experimental data and computation. Static pressure distributions on the upper and down walls surface of double serpentine nozzle are completely different compared to the traditional axisymmetric nozzle. The rapid turning and steep passage slope of the serpentine nozzle would result in high friction loss and strong secondary flow loss, hence the value of the length ratio of first S passage to second S passage is recommended to be chosen from 2:5 to 2:3. The centerline distributions are crucial to the nozzle design for its influence on air acceleration inside the nozzle. The centerlines with a rapid turning at the exit would result in a high Ma number, which brings on high friction loss and secondary loss at the turnings. For maximum efficiency of centerline distributions, it is recommended that curves with a gentle turning at each serpentine passage exit should be chosen.

A study on the radial-mode abrasive waterjet turning (AWJT) process is presented and discussed. An experimental investigation is carried out to explore the influence of process parameters on the depth of turning and material removal rate (MRR) when turning 96% alumina ceramics. The experiment is designed by the multifactor orthogonal experiment methods. The effect of feed speed, water pressure, abrasive mass flow rate, nozzle tilted angle and surface speed are investigated by the range analysis and variance analysis. The results show that the feed speed is the most significant variables affecting the depth of turning. Based on the test conditions, it is found that the most efficient conditions to maximize depth of turning are at a jet angle of 105 degree, a water pressure of 310MPa, an abrasive mass flow rate of 11.5 g/s, a surface speed of 5.5m/s and a feed speed of 0.05mm/s. At last, the effect mechanism of process variables on the depth of turning is analyzed qualitatively.

Abrasive water jet (AWJ) technology, due to its potential advantages, is a promising machining method for precision machining brittle materials. In this research, the AlN ceramics was polished using an AWJ machining system. A considerable processing quality has been achieved and a reduction up to 62% of the surface roughness has been obtained. Effects of different process parameters on the surface roughness of the polished workpiece were analyzed. Under the current conditions of the experiments, using a lower impact angle, smaller abrasives and a lower nozzle traverse speed may be appropriate for polishing AlN ceramics.

Serpentine nozzles are supplied in stealth bombers and unmanned aerial vehicles (UAVs) to evidently suppress the infrared radiation signatures (IRSs) emitted by engine exhausts. It is commonly known that excessive geometric parameters are included in the double serpentine nozzle design and, as a result, the aim of this paper is to study the influences of the design parameters on the performance of double serpentine nozzle. To this end, the design method of the serpentine nozzle was concisely introduced, and the qualifications to completely shield turbine were given. Simulations using six different turbulence models were conducted and compared to the experimental data in order to determine the suitable turbulence model for serpentine duct simulations. Then, the effects of geometric design parameters at the first serpentine paragraph exit (the dimensionless width of W1/D, area of A1/Ain, and offset distance of ΔY1/L1) on the flowfield, and the performance of double serpentine nozzle was investigated numerically. The validation study shows that the simulations with shear-stress transport (SST) κ–ω turbulence model adopted can accurately predict the flux rate, the axial thrust, and the static pressure of the experimental nozzle, and therefore, SST κ–ω turbulence model is the most suitable turbulence model in the selected six turbulence models to be used for the simulation of the double serpentine nozzles. The numerical results show that friction loss increases with the increment of W1/D due to the increased wetted perimeter, but small value of W1/D would lead to large secondary flow loss; even the shock loss appears because of the steep curvature of the second turning. Small area of the first serpentine duct A1/Ain induces high flow velocity in the first duct, which corresponds to large friction loss. Steep offset distance of the first serpentine duct ΔY1/L1 induces high local losses. As the geometric design parameters of the double serpentine nozzle interact mutually with the qualifications to completely shield the turbine, the range of design parameters should be synthetically chosen during the design progress. Thus, the width of the first serpentine duct W1/D is recommended to be from 1.0 to 1.3. The area of the first serpentine duct A1/Ain should be as large as possible, and the offset distance of the first serpentine ΔY1/L1 should be small in the permission range of the design parameters.

Micro abrasive air jet (MAAJ) cutting technology is being increasingly used in the precision machining of hard and brittle materials, due to its distinct advantages of negligible heat effect zone and small cutting force. In this paper, an experimental study on the kerf characteristics, especially for the effect of cutting parameters on the top edge definition, is presented. It shows that the top kerf edge is straight but not sharp. The top edge definition of the kerf improves with a decrease in the air pressure, while the effect of abrasive flow rate and nozzle traverse speed are hardly discernible. The optimum jet incidence angle for highest top edge definition of the kerf is 60°. The results of this paper may be useful for the cutting parameters optimization in the precision three-dimensional micro-structural machining.

Micro abrasive air jet machining technology is being increasingly used in the fields of micro cutting. Since the aspect ratio is a major interest characteristics of kerf in micro cutting, an experimental investigation is carried out to study the effect of cutting process parameters on the aspect ratio in this study. It is found that the aspect ratio increases with an increase in air pressure, abrasive flow rate and jet incidence angle, while decreases with an increase in nozzle traverse speed. Furthermore a predictive model for aspect ratio is developed using the dimensional analysis technique. It is shown that the model predictions are in good agreement with the experimental results. The research results may be meaningful to efficiently control the aspect ratio.

Simulation on velocity field of gas-solid flow in the abrasive air jet nozzle was studied by the computed fluid dynamics(CFD) software. The velocity field of the two-phase flow in the abrasive air jet nozzle can be obtained by means of simulation. The effect of the nozzle diameter on the velocity field shows that the velocity field in the nozzle with a smaller diameter is more well-distributed. The velocity distribution along the nozzle axis and the radial direction of the nozzle outlet was also simulated.

Based on Computational Fluid Dynamic technology, the mixing process of Rocket Based Combined Cycle (RBCC) propulsion system is researched. The idea of RBCC propulsion system means combining rocket engine with ramjet engine effectively, which can flight from sea level to high altitude in wide Mach ranges. In order to analyze how the length of the mixing part affects mixing process, different length of mixing part are researched. As it is indicated, with a constant Mach number, increasing the length of mixing part makes main flow and second flow mix more evenly. Moreover, the length of mixing part has a slight impact on the thrust. Obviously the main consequence of increasing the length of mixing part is promoting the mix of main flow and second flow. Therefore, in order to decrease the weight of aircraft, it is of importance to reduce the length. Through comparing distribution of different cases, when working in the situation of maximum power, the flow in the nozzle of rocket engine is under expansion, while that in the nozzle is fully expanded. Nevertheless, in the case of high altitude and high Mach number, there exists a vortex in the nozzle of rocket engine because of over expansion; meanwhile, the flow in the nozzle is under expansion. Therefore, it is necessary to adjust nozzle throat area in order to increase the thrust of RBCC at high altitude.

In the actual design of turbofan engine with a high thrust-weight ratio, its secondary flow comes from the engine compression parts (fan or high pressure compressor), no matter the Fluidic Thrust Vector (FTV) nozzle is based on Shock Vectoring Controlling (SVC) or Throat Shift (TS). When the turbofan engine works in the state of thrust vector, regardless of the air bleeding from fan or high pressure compressor, the secondary flow have an impact on the components matching and engine performance. Therefore, the study of FTV technology in structurally fixed nozzle cannot just focus on a single nozzle, in the meantime, nozzle should be installed in the actual environment considering the synthesis of flow loss caused by bleed air (for example, bleed air from the compressor) and mixing of the main flow and secondary flow in the nozzle expansion section as well as effect on engine cycle and performance caused by the shockwave loss. Based on this consideration, this article proposes a component-based matching technique, which is applied via numerical simulation in the real environment. The main purpose of this article is research on the effect of FTV on the engine thermodynamic cycle and performance (thrust, fuel consumption and other parameters), considering the processes both air bleeds from fan/high pressure compressor, and it injects into the nozzle expansion section through the holes / slot.