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Li, Fei, Zhenguo Wang, Peibo Li, Mingbo Sun i Hongbo Wang. "The spray distribution of a liquid jet in supersonic crossflow in the near-wall region". Physics of Fluids 34, nr 6 (czerwiec 2022): 063301. http://dx.doi.org/10.1063/5.0091985.
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The gas–liquid mixing process of a liquid jet in supersonic crossflow with a gas–liquid momentum ratio of 7.67 in the near-wall region is investigated numerically. The two-phase flow large eddy simulation is based on the Eulerian–Lagrangian approach and considers the droplet–wall interaction. The results indicate the penetration depth and the lateral extension width, which are in good agreement with the experimental data. The [Formula: see text] shape, especially the spray foot structure of spray in the cross-sectional plane, is captured well. The transport process of spray toward the wall and the formation of spray foot are systematically studied. Under the influence of the upper CVP (counter-rotating vortex pair), partial droplets in the center region of the spray are transported to the near-wall region and move toward both sides when encountering the wall CVP. Under the current gas–liquid momentum ratio, droplets collide with the wall mainly in the central region at the bottom, which will produce splashed droplets. Affected by the horseshoe vortex, the instantaneous distribution of droplets on both sides near the wall shows stripes shape. The spray foot structure forms the shape that is narrow on the top and wide on the bottom and is mainly formed by splashed droplets. Some splashed droplets in the low-speed boundary layer constitute the lower half of the spray foot; meanwhile, some splashed droplets enter mainstream and constitute the upper half of the spray foot. Moreover, the spray is mainly distributed in the core region, and the spray concentration is very sparse in the spray foot region.
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WANG, JIANGFENG, CHEN LIU i YIZHAO WU. "NUMERICAL SIMULATION OF SPRAY ATOMIZATION IN SUPERSONIC FLOWS". Modern Physics Letters B 24, nr 13 (30.05.2010): 1299–302. http://dx.doi.org/10.1142/s0217984910023475.
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With the rapid development of the air-breathing hypersonic vehicle design, an accurate description of the combustion properties becomes more and more important, where one of the key techniques is the procedure of the liquid fuel mixing, atomizing and burning coupled with the supersonic crossflow in the combustion chamber. The movement and distribution of the liquid fuel droplets in the combustion chamber will influence greatly the combustion properties, as well as the propulsion performance of the ramjet/scramjet engine. In this paper, numerical simulation methods on unstructured hybrid meshes were carried out for liquid spray atomization in supersonic crossflows. The Kelvin-Helmholtz/Rayleigh-Taylor hybrid model was used to simulate the breakup process of the liquid spray in a supersonic crossflow with Mach number 1.94. Various spray properties, including spray penetration height, droplet size distribution, were quantitatively compared with experimental results. In addition, numerical results of the complex shock wave structure induced by the presence of liquid spray were illustrated and discussed.
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Li, Chenyang, Chun Li, Feng Xiao, Qinglian Li i Yuanhao Zhu. "Experimental study of spray characteristics of liquid jets in supersonic crossflow". Aerospace Science and Technology 95 (grudzień 2019): 105426. http://dx.doi.org/10.1016/j.ast.2019.105426.
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Wang, Yu-Qi, Feng Xiao, Sen Lin i Yao-Zhi Zhou. "Numerical Investigation of Droplet Properties of a Liquid Jet in Supersonic Crossflow". International Journal of Aerospace Engineering 2021 (9.07.2021): 1–17. http://dx.doi.org/10.1155/2021/8828015.
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The atomization process of a liquid jet in supersonic crossflow with a Mach number of 1.94 was investigated numerically under the Eulerian-Lagrangian scheme. The droplet stripping process was calculated by the KH (Kelvin-Helmholtz) breakup model, and the secondary breakup due to the acceleration of shed droplets was calculated by the combination of the KH breakup model and the RT (Rayleigh-Taylor) breakup model. In our research, the existing KH-RT model was modified by optimizing the empirical constants incorporated in this model. Moreover, it was also found that the modified KH-RT breakup model is applied better to turbulent inflow of a liquid jet than laminar inflow concluded from the comparisons with experimental results. To validate the modified breakup model, three-dimensional spatial distribution and downstream distribution profiles of droplet properties of the liquid spray in the Ma = 1.94 airflow were successfully predicted in our simulations. Eventually, abundant numerical cases under different operational conditions were launched to investigate the correlations of SMD (Sauter Mean Diameter) with the nozzle diameter as well as the airflow Mach number, and at the same time, modified multivariate power functions were developed to describe the correlations.
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Kartanas, T., Z. Toprakcioglu, T. A. Hakala, A. Levin, T. W. Herling, R. Daly, J. Charmet i T. P. J. Knowles. "Mechanism of droplet-formation in a supersonic microfluidic spray device". Applied Physics Letters 116, nr 15 (13.04.2020): 153702. http://dx.doi.org/10.1063/1.5145109.
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Salewski, Mirko, Dragan Stankovic i Laszlo Fuchs. "A Comparison of Single and Multiphase Jets in a Crossflow Using Large Eddy Simulations". Journal of Engineering for Gas Turbines and Power 129, nr 1 (28.09.2005): 61–68. http://dx.doi.org/10.1115/1.2180810.
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Large eddy simulations (LES) are performed for single and multiphase jets in crossflow (JICF). The multiphase JICF are compared to the single-phase case for the same momentum and mass flow ratios but with droplets of different sizes. Multiphase JICF have stronger counterrotating vortex pairs (CVPs) than a corresponding single-phase JICF. Moreover, their trajectories are higher and their induced wakes weaker. The smaller the Stokes number of the droplets, the more the solution approaches the solution for single-phase flow. The computed results show the formation of a CVP and horseshoe vortices, which are convected downstream. LES also reveals the intermittent formation of upright wake vortices from the horseshoe vortices on the ground toward the CVP. The dispersion of polydisperse spray droplets is computed using the stochastic parcel method. Atomization and droplet breakup are modeled by a combination of the breakup model by Reitz and the Taylor analogy breakup model (see Caraeni, D., Bergström, C., and Fuchs, L., 2000, Flow, Turbul. Combust., 65(2), pp. 223–244). Evaporation and droplet collision are also modeled. The flow solver uses two-way coupling. Averages of the velocity and gaseous fuel mass fraction are computed. The single-phase JICF is validated against experimental data obtained by PIV. Additionally, the PDFs and frequency spectra are presented.
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Shaha, Sugrib Kumar, i Hamid Jahed. "Characterization of Nanolayer Intermetallics Formed in Cold Sprayed Al Powder on Mg Substrate". Materials 12, nr 8 (23.04.2019): 1317. http://dx.doi.org/10.3390/ma12081317.
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Supersonic impact of particles in their solid state with substrate at a low temperature creates a complex bonding mechanism and surface modification in cold spray coating. Here, we report the formation of a layer of 200 to 300 nm intermetallic at the interface of cold spray coated AZ31B-type Mg alloy with AA7075-type Al alloy powder. XRD, SAED, and FFT analysis confirmed the layer possessed BBC crystal structure of Mg17Al12 intermetallic. The HR-TEM image analysis at the interface identified the BBC crystal structure with interplanar spacing of 0.745 nm for (110) planes, suggesting the Mg17Al12 phase. The nanoindentation tests showed that the hardness at the interface was ~3 times higher than the substrate. It was also noticed that Young’s modulus at the interface was 117GPa. The combined action of impact energy and carrier gas temperature, along with the multiple passes during coating, caused the formation of intermetallic.
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Shen, Mingguang, Ben Q. Li i Yu Bai. "Modeling Microstructure Formation in Yttria-Stabilized Zirconia (YSZ) Droplet with High Impact Velocity in Supersonic Plasma Spray". Journal of Thermal Spray Technology 29, nr 7 (11.06.2020): 1695–707. http://dx.doi.org/10.1007/s11666-020-01060-3.
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Borisov, Sergey, Julia Gloukhovskaya, Sergey Dobrovolskiy, Alexander Myakochin i Igor Podporin. "Mechanism of heterogeneous flow—solid substrate interaction on the formation of coatings of different thicknesses using different types of spray accelerators". MATEC Web of Conferences 362 (2022): 01004. http://dx.doi.org/10.1051/matecconf/202236201004.
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Physical processes of the inleakage of a supersonic heterogeneous flow of air-powder mixture to a solid substrate, tested on the experimental setup designed for applying protective coatings by a cold spray method, are considered. The interaction of a particle with a flat plane and cylindrical solid substrates, the multilayer coatings and the application of coatings using spray accelerators of different configurations are considered. A mathematical model is demonstrated based on the equation of energy balance in the impact area intended to estimate the interaction between a particle and a solid substrate during impact, as well as examples of results calculated using this model. Methods for calculation of the thickness of the coating applied to flat plane and cylindrical substrates are described. The features of one-step and multi-step coating applications with and without additional exposures are described. As an example, the results of testing the coating for porosity are given. A list of factors and additional exposures affecting the strength of the coating is given.
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Garmeh, Saeed, Mehdi Jadidi i Ali Dolatabadi. "Cold Spray for Additive Manufacturing: Possibilities and Challenges". Key Engineering Materials 813 (lipiec 2019): 423–28. http://dx.doi.org/10.4028/www.scientific.net/kem.813.423.
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Cold spray (CS) is a deposition technique to form a coating from the particles with temperature lower than their melting point. In this technique, particles are accelerated by a supersonic flow of a carrier gas such as air or nitrogen. Upon impact, particles undergo significant plastic deformation that bonds them to the substrate. Since the particles are not molten, this deposition method does not apply a lot of heat to the substrate and this makes CS the best candidate for temperature sensitive and oxygen sensitive materials. CS can be adapted to form 3D objects following layer-by-layer approach. This is called cold gas dynamic manufacturing (CGDM) or cold spray as additive manufacturing. Developing complex shapes by CGDM may result in formation of inclined surfaces, corners and sharp edges. Deposition in those regions is often accompanied with challenges that affect the accuracy and efficiency of the manufacturing. In this study, CGDM for two typical shapes such as cylinder and frustum on a flat substrate has been simulated to represent the additively manufactured parts. Particle trajectories and impact conditions i.e. velocity and size distributions have been compared. The results of numerical modelling provided useful information for understanding the limitations and challenges associated with CGDM that can help us to improve the quality and precision of particle deposition.
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Li, Zhijie, Jie Pan, Wei Li, Xiangting Wang, Haiqiao Wei i Jiaying Pan. "New Insights into Abnormal Combustion Phenomena Induced by Diesel Spray-Wall Impingement under Engine-Relevant Conditions". Energies 15, nr 8 (17.04.2022): 2941. http://dx.doi.org/10.3390/en15082941.
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High altitude and low temperature is the common extreme environment for internal combustion engines. Under such operating conditions, heavy-duty diesel engines often suffer from serious abnormal combustion, such as knocking combustion, which results in piston crown breakdown and cylinder head erosion. Spray-wall impingement and pool fires are considered potential causes; however, the detailed mechanism remains poorly understood owing to the lack of research data. In this study, for the first time, the destructive abnormal combustion induced by diesel spray-wall impingement was identified using an optical rapid compression machine under engine-relevant conditions at high altitudes. Combining instantaneous pressure and temperature measurements with simultaneously recorded high-speed photography gives useful insights into understanding the detailed combustion processes. The experimental results show that depending on the extent of diesel spray-wall impingement, supersonic detonation-like reaction fronts featuring bright luminosity can be observed. The propagation of these reaction fronts in-cylinder results in severe pressure oscillations with an amplitude approaching hundreds of atmospheres, which is like the super-knock events in boosted direct-injection spark-ignition engines. Further parametric analysis indicates that the interplay between the diffusion combustion controlled by diesel spray and the premixed combustion dominated by attached film evaporation results in the formation of abnormal combustion. Destructive reaction fronts tend to occur at a prolonged ignition delay time, which facilitates the mixing between diesel evaporation and hot air.
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Wang, Xiangting, Haiqiao Wei, Jiaying Pan, Zhen Hu, Zeyuan Zheng i Mingzhang Pan. "Analysis of Diesel Knock for High-Altitude Heavy-Duty Engines Using Optical Rapid Compression Machines". Energies 13, nr 12 (14.06.2020): 3080. http://dx.doi.org/10.3390/en13123080.
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In high altitude regions, affected by the low-pressure and low-temperature atmosphere, diesel knock is likely to be encountered in heavy-duty engines operating at low-speed and high-load conditions. Pressure oscillations during diesel knock are commonly captured by pressure transducers, while there is a lack of direct evidence and visualization images, such that its fundamental formation mechanism is still unclear. In this study, optical experiments on diesel knock with destructive pressure oscillations were investigated in an optical rapid compression machine. High-speed direct photography and simultaneous pressure acquisition were synchronically performed, and different injection pressures and ambient pressures were considered. The results show that for the given ambient temperature and pressure, diesel knock becomes prevalent at higher injection pressures where fuel spray impingement becomes enhanced. Higher ambient pressure can reduce the tendency to diesel knock under critical conditions. For the given injection pressure satisfying knocking combustion, knock intensity is decreased as ambient pressure is increased. Further analysis of visualization images shows diesel knock is closely associated with the prolonged ignition delay time due to diesel spray impingement. High-frequency pressure oscillation is caused by the propagation of supersonic reaction-front originating from the second-stage autoignition of mixture. In addition, the oscillation frequencies are obtained through the fast Fourier transform (FFT) analysis.
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Шорінов, Олександр Володимирович, Андрій Олегович Волков, Сергій Євгенійович Маркович i Анатолій Іванович Долматов. "РОЗРАХУНОК ТЕМПЕРАТУРНО-ШВИДКІСНИХ ПАРАМЕТРІВ ЧАСТИНОК ПРИ ХОЛОДНОМУ ГАЗОДИНАМІЧНОМУ НАПИЛЮВАННІ". Aerospace technic and technology, nr 7 (31.08.2019): 139–44. http://dx.doi.org/10.32620/aktt.2019.7.20.
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The method of computational fluid dynamics (CFD) for the supersonic nozzle SK-20 of the low-pressure cold gas-dynamic spraying equipment DYMET-405 was applied for calculation of particles impact temperature and velocity. The application of the CFD method is the one-dimensional isentropic gas-dynamic model considers the flow only along the nozzle axis, without taking into account the heat exchange with the nozzle and the friction losses on the internal walls, which leads to obtaining overestimated results of calculations. Previously it was found out that the difference in the values obtained by numerical simulation and the results of calculations of a one-dimensional isentropic model was less than 10%. Numerical simulation of the two-phase flow of the cold spray process has been performed using the Ansys Fluent Academic software package. The influence of the initial cold spray process parameters such as temperature and pressure at the nozzle inlet on the change in temperature and velocity of aluminum particles with a diameter of 25 μm at the moment of impact with the substrate has been studied. Also, the influence of the particle size on the above-mentioned parameters has been obtained. The numerical simulation results of the particle impact temperature with the substrate have been used to calculate the critical velocity of aluminum powder – the velocity needed for coating formation. It is known that the formation of cold spray coatings depends on the velocity of the powder particles. For each material, there is a critical velocity at which the process of forming the coating begins. At particle velocities above the critical one, their adhesion to the substrate and the formation of the coating, due to the plastic deformation of the particles, occurs, while at lower velocities the surface erosion or deposition with low efficiency under certain conditions is observed. As a result of simulation and calculations of the critical velocity, the window of spraying was developed, that is the region of values of velocities and temperatures of the particles of aluminum powder, depending on the temperature and pressure of the air at the nozzle inlet, at which the formation of coatings is possible.
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Шоринов, Александр Владимирович. "ПЕРСПЕКТИВЫ ПРИМЕНЕНИЯ ТЕХНОЛОГИИ ХОЛОДНОГО ГАЗОДИНАМИЧЕСКОГО НАПЫЛЕНИЯ ДЛЯ ЗАЩИТЫ И ВОССТАНОВЛЕНИЯ ДЕТАЛЕЙ ИЗ МАГНИЕВЫХ СПЛАВОВ". Aerospace technic and technology, nr 2 (26.04.2018): 20–27. http://dx.doi.org/10.32620/aktt.2018.2.03.
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Magnesium alloys are widely used in modern technology, especially in the aviation and automotive industries, primarily due to low density, which allows reducing the weight of products and structures significantly. However, one of the main disadvantages of magnesium alloys is low corrosion resistance, which limits the possibilities of their wide application. A large number of magnesium parts of helicopters are prone to corrosion in places of contact with parts made of other metals forming a galvanic couple. Moreover, magnesium alloys are also susceptible to surface damage due to impact, which often occurs in the manufacture, repair and maintenance of aviation equipment. Scratches and damage can lead to local corrosion. It is shown that energy- and resource-saving cold spraying technology is effective and advanced technology for repairing and recovering of magnesium parts against corrosion. The cold gas-dynamic spraying technology is a relatively new industry among the processes of thermal spraying. The cold spray process is based on accelerating the metal powder particles with a supersonic gas stream in the Laval nozzle followed by an impact on the substrate and the formation of a coating. The process is characterized in that the powder material used in the spraying process does not melt and therefore the oxidation of the coating decreases; there are no phase changes in the material and no considerable heating of the substrate. The results of the analysis of the current state of cold spraying of protective and restorative coatings as well as the analysis of the aviation engines magnesium parts manufactured by «MOTOR SICH», their damages, in particular corrosion, causes of occurrence and current protection methods are accomplished. The works aimed to deposition of cold spray corrosion-resistant coatings and its application for restoration and protection of magnesium parts against corrosion are analyzed. The previous work in the field of cold spraying of anticorrosive coatings was mainly aimed to achieving maximum density of coatings, since the absence of through porosity provides reliable protection of the base material. Coatings with a minimum porosity were obtained using the high-pressure cold spray systems. The analysis showed that the issue of using low-pressure cold-spray equipment remains open and confirms the urgency of further research
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Волков, Андрій Олегович, Олександр Володимирович Шорінов, Анатолій Іванович Долматов i Сергій Євгенійович Маркович. "МОДЕЛЮВАННЯ ДВОФАЗНОГО ПОТОКУ ПРИ ХОЛОДНОМУ ГАЗОДИНАМІЧНОМУ НАПИЛЮВАННІ". Aerospace technic and technology, nr 8 (31.08.2020): 153–59. http://dx.doi.org/10.32620/aktt.2020.8.20.
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The one-dimensional gas-dynamic model for calculation of acceleration and heating of particles which takes into account space from the nozzle outlet to the substrate has been improved. One cycle of particle acceleration by a gas flow can be divided into three parts: mixing a gas flow with powder; particle movement and acceleration in the divergent part of the nozzle; the movement of gas-powder flow from nozzle outlet to substrate. It is known that cold spray coating formation depends on the normal component of particle velocity towards the surface to be sprayed. Each material obtains its value of the critical velocity when the coating formation process starts. At particle velocities above critical, they adhere to the substrate and form coating due to plastic deformation of particles, and at velocities below critical value surface erosion or spraying with low efficiency is observed. One of the features of the process of cold gas-dynamic spraying is a relatively small distance between the nozzle outlet and the deposited surface, which leads to the occurrence of the reverse flow of the gas stream (bow shock) reflected from the substrate. The reflected flow significantly inhibits the trajectory of particles of sprayed powder which need to be investigated. Impact temperature and velocity of aluminum and nickel particles with size 25 microns with a substrate for SK-20 supersonic nozzle of DIMET-405 low-pressure cold spraying machine has been calculated. Although the one-dimensional isentropic gas-dynamic model, which is usually used to calculate flow parameters, describes flow only along the axis of the nozzle, excluding heat transfer with nozzle and friction loss on the inner walls, which leads to overestimated results of calculations, its utilization allows to optimize the geometry of the nozzle channel and develop a technological process of the spraying process. Mathematical modeling of two-phase flow dynamics of the cold spraying process was performed using the MATLAB software. Comparison of simulation results with experimental data to determine the flow velocity and temperature showed that the theoretical calculations differ from the experimental ones by no more than 10 %.
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Sohi, M. Heydarzadeh, Shahin Khameneh Asl, Kazuyuki Hokamoto i M. Rezvani. "A DTA Study on HVOF Thermally Sprayed WC–M Coatings". Materials Science Forum 566 (listopad 2007): 155–60. http://dx.doi.org/10.4028/www.scientific.net/msf.566.155.
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Five types of tungsten carbide based powders with different chemical compositions (WC-12Co, WC-17Co, WC-10Ni, WC-10Co-4Cr and WC- 20Cr-7Ni) were deposited onto ST37 mild steel substrate using high velocity oxy fuel (HVOF) spray technique. The feedstock powders and sprayed coatings were studied by using X-ray diffraction (XRD), and differential thermal analyzing (DTA). The results were shown during HVOF thermal spraying, WC-M powders become partially melted before being sprayed on the surface of the substrate with supersonic speed. In these types of coatings, the crystallographic structures are normally non equilibrium, because the cooling rates of the deposited splats are very high due to the cold substrate acting as a thermal sink. These partially melted powders are then rapidly solidified to an amorphous phase. XRD analysis showed that the amorphous phase was existed in all of the as sprayed coatings. The amorphous phase in WC-12Co, WC-17Co and WC-10Ni coatings was transformed to crystalline phases by heat treatment at high temperature. Heat treatment of these coatings at high temperature also resulted in partially dissolution of WC particles and formation of new crystalline phases. In cobalt base coatings, the new phases were eta carbide phases like Co6W6C and Co3W3C but in WC-10Ni coating a NiW intermetallic phase was formed. Heat treatment of WC-10Co-4Cr and WC-20Cr-7Ni coatings did not change the amorphous phases in these coatings. Differential thermal analysis of cobalt containing coatings revealed an exothermic reaction at approximately 880°C. This exothermic reaction may be related to the transformation of the amorphous phase to eta phases. On the contrary, DTA analysis of feedstock powders of these coatings showed an endothermic reaction at approximately 1000°C. DTA analyses of nickel containing cermets also showed similar results. Differential thermal analysis of chromium containing cermets did not show any noticeable exothermic or endothermic reactions.
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Li, Fei, Peibo Li, Xu Liu, Hongbo Wang, Mingbo Sun, Zhenguo Wang, Fan Li, Jincheng Zhang i Xiaolong Yang. "Numerical study on spray characteristics of liquid jets in supersonic crossflow". Aerospace Science and Technology, sierpień 2023, 108543. http://dx.doi.org/10.1016/j.ast.2023.108543.
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ZHOU, Yaozhi, Zun CAI, Qinglian LI, Chenyang LI, Mingbo SUN, Peibo LI i Hongbo WANG. "Review of atomization mechanism and spray characteristics of a liquid jet in supersonic crossflow". Chinese Journal of Aeronautics, marzec 2023. http://dx.doi.org/10.1016/j.cja.2023.03.010.
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Lubarsky, Eugene, Jonathan R. Reichel, Ben T. Zinn i Rob McAmis. "Spray in Crossflow: Dependence on Weber Number". Journal of Engineering for Gas Turbines and Power 132, nr 2 (15.10.2009). http://dx.doi.org/10.1115/1.2904892.
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This paper describes an experimental investigation of the spray created by Jet A fuel injection from a plate containing sharp edged orifice 0.018in.(457μm) in diameter and L∕D ratio of 10 into the crossflow of preheated air (555K) at elevated pressure in the test section (4atm) and liquid to air momentum flux ratio of 40. A two component phase Doppler particle analyzer was used for measuring the characteristics of the spray. The Weber number of the spray in crossflow was varied between 33 and 2020 and the effect of Weber number on spray properties was investigated. It was seen that the shear breakup mechanism dominates at Weber number greater than about 300. Droplets’ diameters were found to be in the range of 15–30μm for higher values of Weber numbers, while larger droplets (100–200μm) were observed at Weber number of 33. Larger droplets were observed at the periphery of the spray. The droplet velocities and diameters were measured in a plane 30mm downstream of the orifice along the centerline of the spray at an incoming airflow Mach number of 0.2. The droplets reach a maximum of 90% of the flow velocity at this location. The velocity of the droplets in the directions perpendicular to the airflow direction is higher at the periphery of the spray possibly due to the presence of larger droplets there. The rms values of the droplet velocities are highest slightly off the centerline of the spray due to the presence of vortices and shear layers around the liquid jet. The data presented here improve the understanding of spray formation processes, and provide benchmark data for computational fluid dynamics (CFD) code validation.
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Obenauf, Dayna, James Braun, Terrence Meyer, Guillermo Paniagua, Paul Sojka i Francois Falempin. "Characterization of the steady and unsteady spray structures of a liquid jet in supersonic crossflow". International Conference on Liquid Atomization and Spray Systems (ICLASS) 1, nr 1 (30.08.2021). http://dx.doi.org/10.2218/iclass.2021.6157.
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Tang, Tao, Guoyan Zhao, Hongbo Wang, Mingbo Sun i Zhenguo Wang. "Effects of cavity parameters on flame flashback phenomenon in a supersonic crossflow with a cavity flameholder". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, 19.10.2022, 095441002211334. http://dx.doi.org/10.1177/09544100221133423.
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In this paper, the cavity parameters of length-to-depth ratio, aft ramp angle, and nitrogen throttling positions are numerically studied by a Large Eddy Simulation (LES) combined with the Flamelet/Progress Variable (FPV) model, to investigate the inducing factors and formation mechanism of flame flashback. These numerical studies are validated and compared to our previous experiments. It can be observed from both the calculated and experimental flow field that the larger length-to-depth ratio, sharper aft ramp angle, and nitrogen throttling closer to the cavity strengthen the mixing of fuel wake and promote the jet penetration depth. Meanwhile, the separation of the boundary layer downstream of the cavity can be induced by the shear layer, acoustic oscillation, as well as nitrogen throttling. And the above favorable prerequisites enhance the heat release nearby, while the reverse pressure gradient causes the enlargement of the boundary layer separation in turn. Under this positive feedback, thermal choking is formed and drives the reverse propagation of the high-temperature flame. It is concluded that the downstream boundary layer separation induced by the changes of the cavity parameters is a prerequisite for the flame flashback, and the formation of the thermal choking is the main reason for the flame flashback.
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Samareh, B., i A. Dolatabadi. "Dense Particulate Flow in a Cold Gas Dynamic Spray System". Journal of Fluids Engineering 130, nr 8 (30.07.2008). http://dx.doi.org/10.1115/1.2957914.
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The effect of particle-gas and particle-particle interactions in a cold spray process is studied when the particle loading is high. To examine the effect of the presence of a dense particulate flow on the supersonic gas, an Eulerian-Eulerian approach is used. It is found that when the volume fraction of the injected particles is increased, the turbulence of the gas phase will be augmented by the motion of particles and consequently, the shape, the strength, and the location of the compression and expansion waves will be altered. Shock-particle interactions are demonstrated for various volume fractions. Another important parameter, which will affect the spraying deposition efficiency, is the substrate stand-off distance. It is found that the stagnation pressure alternates for different stand-off distances because of the formation of compression and expansion waves outside the nozzle exit. The particle normal velocity on impact is a strong function of the stagnation pressure on the substrate as particles must pierce through the bow shock formed on that region. The effect of the particle size and number density are also studied for different loading conditions. It is found that small and large particles behave differently as they pass through shock diamonds and the bow shock, i.e., in the case of very small particles, as the loading increases, the impact velocity increases, while, for the large particles, the trend is reversed.
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Liu, Cunxi, Fuqiang Liu, Jinhu Yang, Yong Mu, Chunyan Hu i Gang Xu. "Experimental Investigation of Spray and Combustion Performances of a Fuel-Staged Low Emission Combustor: Effects of Main Swirl Angle". Journal of Engineering for Gas Turbines and Power 139, nr 12 (23.08.2017). http://dx.doi.org/10.1115/1.4037451.
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In order to reduce NOx emissions, modern gas turbines are often equipped with lean-burn combustion systems, where the high-velocity fuel-lean conditions that limit NOx formation in combustors also inhibit the ability of ignition, high altitude relight, and lean combustion stability. To face these issues, internally staged scheme of fuel injection is proposed. Primary and main fuel staging enable fuel distribution control, and multi-injections of main fuel lead to a fast and efficient mixing. A fuel-staged low emission combustor in the framework of lean-burn combustion is developed in the present study, i.e., the central pilot stage for low power conditions is swirl-cup prefilming atomization, the main stage is jet-in-crossflow multi-injection, and a combination of primary and main stage injection is provided for higher power output conditions. In lean-burn combustors, the swirling main air naturally tends to entrain the pilot flame and quench it at low power conditions, which is adverse to the operability specifications, such as ignition, lean blow-out (LBO), and high-altitude relight. In order to investigate the effects of the main swirl angle on combustion performances, the ignition and LBO performances were evaluated in a single dome rectangular combustor. Furthermore, the spray patterns and flow field are characterized by kerosene-planar laser induced fluorescence and particle image velocimetry (PIV) to provide insight into spray and combustion performances. Flow–flow interactions between pilot and main air streams, spray–flow interactions between pilot spray and main air streams, and flame–flow interactions between pilot flame and main air streams are comprehensively analyzed. The entrainment of recirculating main air streams on pilot air streams enhances with the increase of main swirl angle, because of the upward motion and increasing width of main recirculation zone. A small part of droplets are entrained by the recirculating main air streams at periphery of combustor and a majority of droplets concentrate near the centerline of combustor, making that entrainment of recirculating main air streams on pilot spray and quenching effects of recirculating main air streams on pilot flame are slight, and the extinguishing effects can be ignored. The contributions of main swirl strength to improvement of ignition and LBO performances are due to enhancement of air/fuel mixing by strengthening turbulence level in pilot zone.