Spray Model Research Articles

Three-dimensional numerical simulations of the particle loading effect on gas flow features for low pressure cold spray applications

This paper reports numerical investigations to develop a high quality simulation model for the Cold Spray (CS) process as part of the project, Supersonic Spray Advanced Modelling (SSAM). Cold spray is a process in which unmelted solid particles are accelerated through a De Laval nozzle toward a target surface and deposited, which avoids or minimises the detrimental effects that arise from melting. The gas flow injected allows the particles to achieve velocities up to 1000 m/s until they impact onto a substrate, bonding with plastic deformation. Analytical and numerical tools were used in the recent years to study the most important parameters of the fluid dynamic of the process. These parameters are often overestimated or non-validated, as many authors tend to neglect inter-phase couplings. The interactions between the gas flow features and particulate phase are important for the present multiphase flows, and many of the connected phenomena lack physical comprehension. For this purpose, a detailed 3D model for RANS simulations has been realised and the gas and particle dynamics in the nozzle and jet were analysed. Advancements for future computational methods are derived from this study, in order to build a comprehensive and coherent numerical model for cold spray applications.

Experimental investigations of spray generated by a pressure swirl atomizer

This paper has focused on the droplets behavior of kerosene RP-3 spray produced by a pressure swirl atomizers in terms of spray pattern, droplet size spatial distribution, mean droplet size, and distribution index with variations of pressure differential. The analyses have been carried out experimentally with the aid of optical diagnostic methods. The spray pattern, such as spray cone angle and fuel spatial distribution, has been measured by the technique of planar laser induced fluorescence of kerosene. A method for correction of fuel distribution measurement error induced by laser attenuation in spray is proposed and validated. The droplet size spatial distribution in central axis plane of the spray has been measured by a planar droplet sizing method which combining laser induced fluorescence and Mie scattering. The spray pattern in axial center plane and cross-sectional plane perpendicular to axis of the atomizer indicate that the droplets in spray concentrate around the outer periphery and in a narrow annular zone at the near-field of fuel injector exit, and then disperse to produce a solid spray at downstream of the spray. The analyses of droplet size spatial distribution, Sauter mean diameter, and distribution index with pressure differential clearly show the presence of droplets collision and its adverse effects on droplet size uniformity. The spray outline, droplet mass spatial distribution, and droplet size spatial distribution, droplets dispersion and collision in the process of atomization provide a great insight into the processes of atomization and spray development, which are key information for fuel injector design and quality control. The visualizations of spray pattern and droplet size spatial distribution with variations of pressure differential for pressure swirl atomizer are key issues in swirl cup or internally staged airblast fuel injectors because pressure swirl atomizer provides primary atomization or pilot spray which affects the quality of air/fuel mixing in lean-burn combustion. Moreover, a well-defined and complete database regarding the isothermal hollow cone spray is provided for validation of spray model.

An analysis of the convergence of stochastic Lagrangian/Eulerian spray simulations

This work derives how the convergence of stochastic Lagrangian/Eulerian simulations depends on the number of computational parcels, particularly for the case of spray modeling. A new, simple, formula is derived that can be used for managing the numerical error in two or three dimensional computational studies. For example, keeping the number of parcels per cell constant as the mesh is refined yields an order one-half convergence rate in transient spray simulations. First order convergence would require a doubling of the number of parcels per cell when the cell size is halved. Second order convergence would require increasing the number of parcels per cell by a factor of eight. The results show that controlling statistical error requires dramatically larger numbers of parcels than have typically been used, which explains why convergence has been so elusive.

WAVE-MTAB モデルの切り替え手法の改良および 相似則を用いたディーゼル噴霧の LES 解析

WAVE-MTAB モデルの切り替え手法の改良および 相似則を用いたディーゼル噴霧の LES 解析

Modeling of Spray Combustion with a Steady Laminar Flamelet Model in an Aeroengine Combustion Chamber Based on OpenFOAM

The development of high-performance aeroengine combustion chambers strongly depends on the accuracy and reliability of efficient numerical models. In the present work, a reacting solver with a steady laminar flamelet model and spray model has been developed in OpenFOAM and the solver details are presented. The solver is firstly validated by Sandia/ETH-Zurich flames. Furthermore, it is used to simulate nonpremixed kerosene/air spray combustion in an aeroengine combustion chamber with the RANS method. A comparison with available experimental data shows good agreement and validates the capability of the new developed solver in OpenFOAM.

Modeling of Diesel Spray Impinging Behavior in Lubricating Oil Film

Modeling of Diesel Spray Impinging Behavior in Lubricating Oil Film

Modeling of Diesel Spray Impinging Behavior in Lubricating Oil Film

Modeling of Diesel Spray Impinging Behavior in Lubricating Oil Film

Precision Spraying Model Based on Kinect Sensor for Orchard Applications

ABSTRACT. This study describes the use of an integrated Kinect video sensor in a spray system to capture color and depth information to improve the efficiency of spraying in an orchard. Equations for calculating the optimal spray distance and pattern based on data collected by the video sensor are proposed, in conjunction with the leaf wall area density, to address the difficulty in estimating the dose of sprayed chemicals. First, to estimate the optimal distance and route, this study designs a spray system using the Kinect integrated video sensor and proposes an equation for calculating the leaf wall distance of fruit trees for spraying. Second, to control the dose of sprayed chemicals by adjusting the nozzle angle and rate of flow, this study proposes the concept of leaf wall area density and analyzes the leaf area shapes of peach, apricot and grapevine, which are fan shaped, round and square, respectively. Finally, the results of the experiment on peach trees, apricot trees and grapevines demonstrated that the intelligent orchard chemical precision spray model established based on the spray distance and the leaf wall area density can adjust the system to the optimal spray distance and dose, which can improve efficiency in spraying chemicals, increasing the economic benefits for fruit farmers. Keywords: Integrated sensor, Kinect, Leaf wall area density, Optimal spray distance.

Numerical investigation of the transient spray cooling process for quenching applications

Water spray quenching distinguished itself as a promising method for industry production, especially for the parts which require good mechanical strength while simultaneously retaining the initial toughness. Studies have shown that the heat transfer process during the spray quenching is mostly influenced by the spray impingement density, particle velocities and sizes. The application of advanced numerical methods still plays insufficient role in the development of the production process, in spite of the fact that industry today is facing major challenges that can be met only by development of new and more efficient systems using advanced tools for product development, one of which is CFD. Taking the above stated, the object of this research is numerical simulation of spray quenching process in order to determine validity of mathematical models implemented within the commercial CFD code Fire, especially droplet evaporation/condensation and droplet-wall heat transfer model. After review of the relevant literature suitable benchmark case was selected and simulated by employing discrete droplet method for the spray treatment and Eulerian approach for the gas phase description. Simulation results indicated that existing droplet/wall heat transfer model is not able to reproduce heat transfer of dense water spray. Thus, Lagrangian spray model was improved by implementing experimental correlation for heat transfer coefficient during spray quenching. Finally, verification of the implemented model was assessed based on the conducted simulations and recommendations for further improvements were given.

Investigation of effect of nozzle geometry on spray with a 3-D Eulerian-Lagrangian spray model coupled with the nozzle cavitating flow

A 3D Eulerian-Lagrangian spray model coupled with the nozzle cavitating flow was proposed to simulate the atomization and secondary break-up. The nozzle flow and near-field spray were simulated with the Volume Of Fluid (VOF) multiphase model. At a certain downstream location, where the spray is diluted, the Eulerian spray approach was switched to the conventional Lagrangian approach. This entire methodology was validated through the experimental data of liquid spray penetration under non-evaporating chamber conditions. The numerical simulations based on multi-scheme were implemented by this model to investigate the effects of nozzle geometry and configuration on the subsequent spray development.

Numerical analysis of downwash flow field from quad-rotor unmanned aerial vehicles

Abstract: Agricultural drones, also known as Unmanned Aerial Vehicles(UAV), have attracted increasing attention because of their advantages of small size, convenient handling, and the ability to function without a runway, and they are particularly suitable for small farmlands in Asia, especially in China. The downwash flow field caused by the rotors of agricultural drone is one of main characteristics and affects the droplet deposition and drift law. Studying the distribution characteristics and development law of the downwash flow field is the basis for improving the application performance of spray technology applied on agricultural drones. With the development of computational fluid dynamics, agricultural aerial spray modeling has become an area of academic interest. In this study, the numerical simulation method was used to calculate the downwash flow field model of the quad-rotor UAV, to analyze its distribution characteristics and development law over time at different flight speeds. The accuracy of the numerical simulation was verified by field test. The simulation results show that the average velocities of airflow under1.6m from rotors at 2, 4 and6m/s are 2.33 m/s,1.90m/s and1.03m/s, respectively, which are high enough to disturb most of plant canopy and enhance the penetration rate of droplets. The flight velocity of drone has a significant effect on the downwash flow field. With the increase of the flight velocity, the wake of drones is gradually raised, and the concentration of wingtip vortices increases. When the flight velocity is increased to6m/s, the wingtip vortex velocity reaches3.3m/s, which has a strong entrainment effect on the droplets and greatly increases the risk of droplet drift. Keywords: quad-rotor UAV for plant protection, agricultural drones, downwash flow field, flight velocity DOI: 10.33440/j.ijpaa.20200304.138 Citation: Zhang H Y, Lan Y B, Shen N W, Wu J Y, Wang T, Han J, Wen S. Numerical analysis of downwash flow field from quad-rotor unmanned aerial vehicles. Int J Precis Agric Aviat, 2020; 3(4): 1–7.

A comparison of computational fluid dynamics predicted initial liquid penetration using rate of injection profiles generated using two different measurement techniques

The rate of injection profile is a key parameter describing the fuel injection process for diesel injection. It is also an essential input parameter for computational fluid dynamics simulations of spray flows. In the present work, rate of injection profiles of a multi-hole diesel injector were measured using the Zeuch method and the momentum flux method. The rate of injection profiles measured by the momentum flux method had a faster rise in rate of injection during the initial ramp-up phase than with the Zeuch method. The measured rate of injection profiles were applied in three-dimensional computational fluid dynamics simulations of diesel sprays under non-vaporizing and vaporizing conditions with sweeps in injection pressure, bulk charge gas density, and bulk charge gas temperature. Analytical results were compared against experimental data for liquid penetration generated under those conditions. Computational fluid dynamics results with the rate of injection profile measured by the Zeuch method under-predict liquid penetration during the initial ramp-up phase, while computational fluid dynamics results with the rate of injection profiles measured by the momentum flux method showed much better agreement with the experimental data of liquid length and penetration. This suggests that current computational fluid dynamics spray models may be able to more accurately model transient liquid penetration when using the velocity profile developed from momentum flux measurements. Further study is needed to evaluate how computational fluid dynamics predictions of combustion and emissions of affected when using these two rate of injection profiles.

An equilibrium phase spray model for high-pressure fuel injection and engine combustion simulations

High-pressure fuel injection impacts mixture preparation, ignition and combustion in engines and other applications. Experimental studies have revealed the mixing-controlled and local phase equilibrium characteristics of liquid vaporization in high injection pressure diesel engine sprays. However, most computational fluid dynamics models for engine simulations spend much effort in solving for non-equilibrium spray processes. In this study, an equilibrium phase spray model is explored. The model is developed based on jet theory and a phase equilibrium assumption, without modeling drop breakup, collision and finite-rate interfacial vaporization processes. The proposed equilibrium phase spray model is validated extensively against experimental data in simulations of the engine combustion network Spray A and in an optical diesel engine. Predictions of liquid/vapor penetration, fuel mass fraction distribution, heat release rate and emission formation are all in good agreement with experimental data. In addition, good computational efficiency and grid-independency are also seen with the present equilibrium phase model. The examined operating conditions cover wide ranges that are relevant to internal combustion engines, which include ambient temperatures from 700 to 1400 K, ambient densities from 7.6 to 22.8 kg/m3 and injection pressures from 1200 to 1500 bar for diesel sprays.

Separate and combined effects of hydrogen and nitrogen additions on diesel engine combustion

Shortage of non-renewable energies, increase in fossil fuel prices and stricter emissions regulations due to high NOx and soot emissions emitted from combustion of heavy diesel fuels by compression ignition engines, has led consumers to use renewable, cleaner and cheap fuels. An investigation has been computationally carried out to explore the influences of hydrogen and nitrogen addition on engine performance such as indicated power and indicated specific energy consumption and amounts of pollutant emissions like NOx, soot, and CO in an HSDI (High-Speed Direct Injection) diesel engine. Optimized sub-models, such as turbulence model, spray model, combustion model and emissions models have selected for the main CFD code. Meanwhile, HF (Homogeneity Factor) has been employed for analysing in-cylinder air-fuel mixing quality under various addition conditions. After validations with experimental data of diesel combustion with a single addition of 4% hydrogen and combined addition of 6% hydrogen + 6% nitrogen, investigations have conducted for modeling mixing and combustion processes with additions of hydrogen and nitrogen by ranges of 2–8% (v/v). Results showed that a single addition of H2 increased NOx and decreased CO and soot and improved ISEC and IP. In the case of nitrogen addition, NOx decreased, both CO and soot emission increased and ISEC and IP considerably ruined compared with NDC operation. Based on the results obtained for simultaneous addition of N2 (8% of v/v) and H2 (8% of v/v), NOx and soot emissions decreased by 11.5% and 42.5% respectively, and ISEC and IP improved 25.7% and 13%, respectively. But amount of CO emissions had an increase of 52% should be paid necessary attention as a main disadvantage.

CFD studies on effects of SCR mixers on the performance of urea conversion and mixing of the reducing agent

A numerical model of spray and its interaction with the gas exhaust flow and static mixer are developed to investigate the effects of the mixer on the selective catalytic reduction (SCR). The residence time of spray droplets in straight pipes with and without mixers and the interaction between spray droplets and the blades of mixers are investigated. The numerical results show that due to the improvement of evaporation rates of sprays and the ability to break droplets into smaller ones, static mixers can help SCR systems achieve better urea conversion efficiency. Furthermore, the using of mixers significantly improves the uniformity of the reducing agent in a pipe.

Influence of the Guide Blade Angle to the Airflow Velocity Inside the Spray Drying Chamber: A Numerical Study

In the present study, a three-dimensional model of spray drying chamber was established. The velocity magnitudes inside the chamber under different guide blade angles are analyzed by using Fluent. The velocity fields inside the spray drying chamber are then simulated under different airflow guide blade angles. It is concluded according to the simulation results that the guide blades cause a rotating airflow field inside the chamber. 3D model is required for numerical simulation due to the asymmetrical flow field. Uniform distribution of velocity field inside the spray drying chamber is beneficial to the drying quality. Too large airflow speed would decrease the contact time inside the chamber, and too small airflow speed would weaken the mix of the hot airflow and feed material, which are both not beneficial to the dry quality. The guide blade angle would lead to beneficial airflow velocity filed inside the spray drying chamber when it is among the range of 20° to 40°.

Optimization of cylinder liner plasma spraying mode

At present one of the most promising methods to remanufacture worn-out machine parts is plasma spraying. The paper describes the selection of the optimum plasma spraying technique to coat the worn-out wall surface of the diesel engine cylinder liners. All the data have been MathCad processed and the regression models equivalent to the algoristic-type model of plasma spraying have been developed. The experiments have resulted in achieving the optimization parameters, the mean value of which is presented in the paper. The given plasma spraying mode allows one not only to remanufacture the worn-out wall surface of the diesel engine cylinder liners but also to obtain the best coating properties.

Numerical investigation towards HiTAC conditions in laboratory-scale ethanol spray combustion

In the past 25years high temperature air combustion (HiTAC) technology has been proved and utilized in industry as a promising way to increase thermal efficiency, create a relatively uniform temperature distribution, and reduce emissions of harmful pollutants such as NOX and CO. However, due to the complexity of fuel-oil combustion, to date HiTAC is mainly applied to gaseous fuel or coal, and little is known about spray combustion under HiTAC condition. In the present study, we numerically investigate the Delft Spray-in-Hot-Coflow (DSHC) using ethanol in high temperature diluted combustion air, and extend it to more co-flow conditions. We employ different temperatures and oxygen concentrations of the co-flow in order to dilute the oxidizer/fuel before it reacts with the fuel/ oxidizer. The pressure-swirl atomizer model with an Eulerian-Lagrangian approach was implemented for the spray modeling. Collision, coalescence, secondary breakup and evaporation of the drops were taken into account. The steady laminar flamelet model for the combustion of ethanol, the Discrete Ordinate model for radiation and the k-ε model for the turbulence with enhanced wall treatment were validated by the simulation of the NIST flame under conventional conditions and then used in the current study.The results indicate that the decreased peak temperature in many HiTAC applications with high temperature combustion air is mainly due to the reduced oxygen concentration by entraining flue gas.In the present study, a low oxygen concentration slows the evaporation process of droplets. It results in an enlarged combustion zone, a lowered peak temperature and minor NOX emission. However, decreasing the oxygen concentration may lead to problems of cracking, soot formation and flame extinction, especially for heavy oils. The optimization needs to be carried out based on the analysis of a specific fuel in order to create a HiTAC-like condition.Based on the results of the current study, the 1500K and 6%vol oxygen concentration case is considered as a HiTAC condition.

Engineering Fluid Dynamics

Over the last few decades, the use of computational fluid dynamics (CFD) and experimental fluid dynamics (EFD) methods has penetrated into all fields of engineering. [...]

Assessment of the wet area of a heat exchanger exposed to a water spray

Evaporative spray cooling is widely used to increase heat transfer of air exchangers and improve their efficiency. However, exchanges inside the spray mixture are difficult to express as combined mass and heat are transferred between phases, resulting in difficulties for the design of spraying systems. In this paper, a model describing the 3D distribution of temperature and liquid content during the dispersion of a thermal spray was developed. A spray model was used to describe the first stage of water fragmentation. A Gaussian model including sedimentation of particles and wall effects was added to handle the dispersion process of the total water content. The microphysical part of the model results from energy and mass balances of water and air allowing local splitting between vapor and liquid content. Simulation results, comparing with temperature and humidity measurements for spray dispersion in a wind tunnel are in good agreement in various conditions of air temperature, humidity, velocity and water flow rate. Further analysis shows that the cooling is higher when the spray radius is close to the wind tunnel dimensions. The model was then used to compute the optimal distance between nozzle and exchanger in order to reach the highest efficiency. This position depends upon the nozzle hole and water-and-air flow rates. As evaporation is slow down when air becomes wetter, the remaining liquid droplets are deposited on the exchanger surface. The wet area was defined assuming a threshold value beyond which liquid flux clogs exchanger fins. Results showed that this area is sensitive not only to the dispersion radius, but also to the evaporation rate.