Dispersion of Particle-laden Jet in Supersonic Crossflow(PJSC)is an essential process in many applications,experimental study on which,however,has rarely been reported.In order to gain physical insights into PJSC,a sp...Dispersion of Particle-laden Jet in Supersonic Crossflow(PJSC)is an essential process in many applications,experimental study on which,however,has rarely been reported.In order to gain physical insights into PJSC,a specialized experimental setup capable of producing a supersonic crossflow at Mach 2.6 and a particle-laden jet with particle mass loading up to 60%is developed.Visualization of the particles motion is achieved with the help of high-speed planar laser scattering technology.The dispersion characteristics of PJSC within a supersonic channel structured by cavity are systematically analyzed through six experimental cases.The results indicate that the vortices have a significant influence on particle dispersion,leading to preferential concentration of particles.i.e.particle clusters.The particle dispersion is summarized as the"scale dispersion"pattern.The primary pathways for particles entering the cavity are identified as the shear layer above the cavity and collisions at the cavity rear edge.Among the studied factors,the momentum flux ratio exerts the most substantial influence on the dispersion process.Importantly,a reduction in the injection distance is correlated with less particles entering the cavity.The insights gained from this research provide essential references for furthering understanding particle dispersion mechanisms in supersonic flows and developing highly accurate numerical models.展开更多
Plasma Synthetic Jet(PSJ) actuators have shown wide and promising application prospects in high-speed flow control, due to their advantages including high exhaust speed, wide frequency band, rapid response, and non-mo...Plasma Synthetic Jet(PSJ) actuators have shown wide and promising application prospects in high-speed flow control, due to their advantages including high exhaust speed, wide frequency band, rapid response, and non-moving components. Although previous studies on PSJ actuators are abundant, most of them have focused on the performance of a single actuator. However, in practice, an actuator array is very necessary for large-scale aerodynamic actuation on account of the small affected area of a single PSJ. In this paper, the characteristics of a twoelectrode plasma synthetic jet actuator array in serial are investigated experimentally. Compared to a parallel actuator array, the serial actuator array requires simpler power supply design and is much easier to realize. High-speed photography of the discharge evolution, voltage-current measurement, and shadowgraphy visualization are used in the investigation. Experimental results show that, for the serial actuator array, weak discharges happen firstly between energized and suspending electrodes, and then a strong pulse arc discharge is triggered. The breakdown voltage in serial is irrelevant to such factors as the number of actuators, the maximum or minimum gap in serial,the connection sequence, etc. It is mainly determined by the sum of gaps. For serial actuators with the same anode-to-cathode spacing, the energy deposition is the same, and the jet is synchronous and similar. Because of the entrainment and merging of adjacent jet vortices, the jet front speed of an aligned synchronous jet array increases as the orifice distance decreases. To achieve the highest jet front velocity, the orifice of the actuator has an optimal diameter.展开更多
The solid-fueled Scramjet is an interesting option for supersonic combustion ramjet.It shows significant advantages such as simple fuel supply and compactness,avoiding the complex system of tanks and pipelines that en...The solid-fueled Scramjet is an interesting option for supersonic combustion ramjet.It shows significant advantages such as simple fuel supply and compactness,avoiding the complex system of tanks and pipelines that encountered in liquid-fueled Scramjets.The solid-fueled Scramjet could be the simplest air-breathing engine for the hypersonic flight regime.This paper presents a comprehensive and systematic review of the research progress on solid-fueled Scramjet in various institutes and universities.It summarizes a progress overview of three types of the solid-fueled Scramjet,which covers a wealth of landmark numerical and experimental results.Based on this,several relevant key technologies are proposed.Several inherent scientific issues are refined,such as the mixing mechanism of multi-phase flow and supersonic airflow,ignition and combustion mechanism of the condensed phase in a supersonic airflow,and coupling mechanism of gas and solid phase in a supersonic flow.Finally,the historical development trend is clarified,and some recommendations are provided for future solid-fueled Scramjet.展开更多
A numerical model for aluminum cloud combustion which includes the effects of interphase heat transfer,phase change,heterogeneous surface reactions,homogeneous combustion,oxide cap growth and radiation within the Eule...A numerical model for aluminum cloud combustion which includes the effects of interphase heat transfer,phase change,heterogeneous surface reactions,homogeneous combustion,oxide cap growth and radiation within the Euler–Lagrange framework is proposed.The model is validated in single particle configurations with varying particle diameters.The combustion process of a single aluminum particle is analyzed in detail and the particle consumption rates as well as the heat release rates due to the various physical/chemical sub-models are presented.The combustion time of single aluminum particles predicted by the model are in very good agreement with empirical correlations for particles with diameters larger than 10μm.The prediction error for smaller particles is noticeably reduced when using a heat transfer model that is capable of capturing the transition regime between continuum mechanics and molecular dynamics.The predictive capabilities of the proposed model framework are further evaluated by simulating the aluminum/air Bunsen flames of Mc Gill University for the first time.Results show that the predicted temperature distribution of the flame is consistent with the experimental data and the double-front structure of the Bunsen flame is reproduced well.The burning rates of aluminum in both single particle and particle cloud configurations are calculated and compared with empirical correlations.Results show that the burning rates obtained from the present model are more reasonable,while the correlations,when embedded in the Euler–Lagrange context,tend to underestimate the burning rate in the combustion stage,particularly for the considered fuel-rich flames.展开更多
In this paper,the Eulerian Stochastic Field(ESF)model in the Transported Probability Density Function(TPDF)class model is combined with the Flamelet Generated Manifolds(FGM)model.This method solves the joint probabili...In this paper,the Eulerian Stochastic Field(ESF)model in the Transported Probability Density Function(TPDF)class model is combined with the Flamelet Generated Manifolds(FGM)model.This method solves the joint probability density function transport equation by ESF method that considers the interaction mechanism between flame and turbulence with high precision.At the same time,by making use of the advantage of the FGM model,this model is able to incorporate the detailed chemical reaction mechanism(GRI 3.0)with acceptable computational cost.The new model has been implemented in the open source CFD suite-Open FOAM.Validation of the model has been carried out by simulating the Sandia flame series(three turbulent piloted methane jet flames)issued by the National Laboratory of the United States.The accuracy and advancement of the ESF/FGM turbulent combustion model are verified by comparing the LES results of the new model with the rich experimental data as well as the RANS results.The results demonstrate that the model has a strong ability in capturing combustion phenomena such as extinction and re-ignition in turbulent flame,which is essential in the accurate prediction of the combustion process in real combustion devices,for example,aircraft engines.展开更多
In ramjet combustion chambers,carbon dioxide(CO_(2))produced by the combustion of carbonaceous fuel enters the chamber together with boron agglomerates.In order to investigate the effect of CO_(2)concentration present...In ramjet combustion chambers,carbon dioxide(CO_(2))produced by the combustion of carbonaceous fuel enters the chamber together with boron agglomerates.In order to investigate the effect of CO_(2)concentration present in an oxygen-containing atmosphere on the combustion characteristics and oxidation mechanisms of boron agglomerates,we used a laser ignition system,an X-ray diffractometer(XRD),and a thermogravimetric-differential scanning calorimetry(TG-DSC)combined thermal analysis system.Single-particle boron was tested in the laser-ignition experiments as the control group.The ignition experiment results showed that with a fixed O2 concentration of 20%,when the particle temperature reaches the melting point of boron,increasing CO_(2)content causes the combustion process of boron agglomerates to transition from single-particle molten droplet combustion to porous-particle combustion.Furthermore,XRD analysis results indicated that the condensed-phase combustion products(CCPs)of boron particles in a mixed atmosphere of O2 and CO_(2)contained B4C,which is responsible for the porous structure of the particles.At temperatures below 1200℃,the addition of CO_(2)has no obvious promotion effect on boron exothermic reaction.However,in the laser-ignition experiment,when the oxygen concentration was fixed at 20%while the CO_(2)concentration increased from 0%to 80%,the maximum temperature of boron agglomerates rose from 2434 to 2573 K,the self-sustaining combustion time of single-particle boron decreased from 396 to 169 ms,and the self-sustaining combustion time of boron agglomerates decreased from 198 to 40 ms.This study conclusively showed that adding CO_(2)to an oxygen-containing atmosphere facilitates boron reaction and consumption pathways,which is beneficial to promoting exothermic reaction of boron agglomerates at relatively high temperatures.展开更多
The supersonic gas-particle two-phase transverse jet is a typical flow process in many applications,such as solid rocket scramjet.This study carried out experimental tests as well as Large Eddy Simulation(LES)to inves...The supersonic gas-particle two-phase transverse jet is a typical flow process in many applications,such as solid rocket scramjet.This study carried out experimental tests as well as Large Eddy Simulation(LES)to investigate the evolution process of transverse gas-particle two-phase jets in supersonic crossflow,especially focusing on the phenomena called preferential concentration.The simulation is based on the Eulerian-Lagrangian method,which successfully reproduces the characteristic phenomena observed in experiments.The particle cloud forms three different characteristic distribution patterns:tooth-like waves near the jet port,quasi-ordered structures near counter-rotating vortex pairs(CVP),and filamentous clouds in the upper part.The turbulence and small unstable shock play a suppressing role in mixing small-diameter particles,which tend to aggregate in regions of high density and low vorticity.Furthermore,it is found that there exists a specific range of particle sizes,as particles'sizes approach this specific range,the influence of compressibility of the airflow on particle distribution becomes increasingly prominent.Overall,this study shed some light on the understanding of the complex and intricate nature of the supersonic gas-particle two-phase transverse jet.展开更多
In this study,boron–magnesium agglomerates with varying mass ratios were prepared by drying a micron-sized boron–magnesium mixed suspension,and the combustion process of these agglomerates under different oxygen-ric...In this study,boron–magnesium agglomerates with varying mass ratios were prepared by drying a micron-sized boron–magnesium mixed suspension,and the combustion process of these agglomerates under different oxygen-rich concentrations were investigated using a laser ignition system.The test results showed that when the mass fraction of magnesium powder in boron-magnesium agglomerates exceeded a certain threshold(between 2%and 5%),flame extinction and reignition occurred after a significant reduction in the agglomerate volume during combustion.This process is referred to as the transient flameout process,which is affected by the magnesium content of the agglomerate and the oxygen concentration in the ambient atmosphere.An increase in the magnesium content or oxygen concentration makes this phenomenon more pronounced.During weakening of the flame intensity,a dark film gradually covered the particle surfaces.X-ray diffraction and elemental analyses of the cross-section and outer surface of the condensed combustion product suggested that the dark film is primarily composed of Mg-B-O ternary oxides.This film prevents direct contact between boron and oxygen,thereby inhibiting surface and gas-phase reactions and leading to the occurrence of the transient flameout phenomenon.展开更多
基金co-supported by the National Natural Science Foundation of China (No. 12272409)the Scientific Research and Innovation Project of Hunan Province, China (Nos. CX20230058, kq2107001, 2022RC1233 and QL20230015)
文摘Dispersion of Particle-laden Jet in Supersonic Crossflow(PJSC)is an essential process in many applications,experimental study on which,however,has rarely been reported.In order to gain physical insights into PJSC,a specialized experimental setup capable of producing a supersonic crossflow at Mach 2.6 and a particle-laden jet with particle mass loading up to 60%is developed.Visualization of the particles motion is achieved with the help of high-speed planar laser scattering technology.The dispersion characteristics of PJSC within a supersonic channel structured by cavity are systematically analyzed through six experimental cases.The results indicate that the vortices have a significant influence on particle dispersion,leading to preferential concentration of particles.i.e.particle clusters.The particle dispersion is summarized as the"scale dispersion"pattern.The primary pathways for particles entering the cavity are identified as the shear layer above the cavity and collisions at the cavity rear edge.Among the studied factors,the momentum flux ratio exerts the most substantial influence on the dispersion process.Importantly,a reduction in the injection distance is correlated with less particles entering the cavity.The insights gained from this research provide essential references for furthering understanding particle dispersion mechanisms in supersonic flows and developing highly accurate numerical models.
基金supported by the National Natural Science Foundation of China(Nos.11372349,11502295,and11572349)
文摘Plasma Synthetic Jet(PSJ) actuators have shown wide and promising application prospects in high-speed flow control, due to their advantages including high exhaust speed, wide frequency band, rapid response, and non-moving components. Although previous studies on PSJ actuators are abundant, most of them have focused on the performance of a single actuator. However, in practice, an actuator array is very necessary for large-scale aerodynamic actuation on account of the small affected area of a single PSJ. In this paper, the characteristics of a twoelectrode plasma synthetic jet actuator array in serial are investigated experimentally. Compared to a parallel actuator array, the serial actuator array requires simpler power supply design and is much easier to realize. High-speed photography of the discharge evolution, voltage-current measurement, and shadowgraphy visualization are used in the investigation. Experimental results show that, for the serial actuator array, weak discharges happen firstly between energized and suspending electrodes, and then a strong pulse arc discharge is triggered. The breakdown voltage in serial is irrelevant to such factors as the number of actuators, the maximum or minimum gap in serial,the connection sequence, etc. It is mainly determined by the sum of gaps. For serial actuators with the same anode-to-cathode spacing, the energy deposition is the same, and the jet is synchronous and similar. Because of the entrainment and merging of adjacent jet vortices, the jet front speed of an aligned synchronous jet array increases as the orifice distance decreases. To achieve the highest jet front velocity, the orifice of the actuator has an optimal diameter.
基金supported by the China Scholarship Council and the National Natural Science Foundation of China(Nos.2020JJ4665,51706241).
文摘The solid-fueled Scramjet is an interesting option for supersonic combustion ramjet.It shows significant advantages such as simple fuel supply and compactness,avoiding the complex system of tanks and pipelines that encountered in liquid-fueled Scramjets.The solid-fueled Scramjet could be the simplest air-breathing engine for the hypersonic flight regime.This paper presents a comprehensive and systematic review of the research progress on solid-fueled Scramjet in various institutes and universities.It summarizes a progress overview of three types of the solid-fueled Scramjet,which covers a wealth of landmark numerical and experimental results.Based on this,several relevant key technologies are proposed.Several inherent scientific issues are refined,such as the mixing mechanism of multi-phase flow and supersonic airflow,ignition and combustion mechanism of the condensed phase in a supersonic airflow,and coupling mechanism of gas and solid phase in a supersonic flow.Finally,the historical development trend is clarified,and some recommendations are provided for future solid-fueled Scramjet.
基金supported by the National Natural Science Foundation of China(No.51706241)Hunan Provincial Natural Science Foundation of China(Nos.2020JJ4665 and 2021JJ30775)+1 种基金Hunan Provincial Innovation Foundation for Postgraduate,China(No.CX2019-0050)support provided by China Scholarship Council(No.201903170201)。
文摘A numerical model for aluminum cloud combustion which includes the effects of interphase heat transfer,phase change,heterogeneous surface reactions,homogeneous combustion,oxide cap growth and radiation within the Euler–Lagrange framework is proposed.The model is validated in single particle configurations with varying particle diameters.The combustion process of a single aluminum particle is analyzed in detail and the particle consumption rates as well as the heat release rates due to the various physical/chemical sub-models are presented.The combustion time of single aluminum particles predicted by the model are in very good agreement with empirical correlations for particles with diameters larger than 10μm.The prediction error for smaller particles is noticeably reduced when using a heat transfer model that is capable of capturing the transition regime between continuum mechanics and molecular dynamics.The predictive capabilities of the proposed model framework are further evaluated by simulating the aluminum/air Bunsen flames of Mc Gill University for the first time.Results show that the predicted temperature distribution of the flame is consistent with the experimental data and the double-front structure of the Bunsen flame is reproduced well.The burning rates of aluminum in both single particle and particle cloud configurations are calculated and compared with empirical correlations.Results show that the burning rates obtained from the present model are more reasonable,while the correlations,when embedded in the Euler–Lagrange context,tend to underestimate the burning rate in the combustion stage,particularly for the considered fuel-rich flames.
基金supported by the National Natural Science Foundation of China(No.51706241).
文摘In this paper,the Eulerian Stochastic Field(ESF)model in the Transported Probability Density Function(TPDF)class model is combined with the Flamelet Generated Manifolds(FGM)model.This method solves the joint probability density function transport equation by ESF method that considers the interaction mechanism between flame and turbulence with high precision.At the same time,by making use of the advantage of the FGM model,this model is able to incorporate the detailed chemical reaction mechanism(GRI 3.0)with acceptable computational cost.The new model has been implemented in the open source CFD suite-Open FOAM.Validation of the model has been carried out by simulating the Sandia flame series(three turbulent piloted methane jet flames)issued by the National Laboratory of the United States.The accuracy and advancement of the ESF/FGM turbulent combustion model are verified by comparing the LES results of the new model with the rich experimental data as well as the RANS results.The results demonstrate that the model has a strong ability in capturing combustion phenomena such as extinction and re-ignition in turbulent flame,which is essential in the accurate prediction of the combustion process in real combustion devices,for example,aircraft engines.
基金the National Natural Science Foundation of China(No.52006240)the Hunan Provincial Natural Science Foundation of China(Nos.2020JJ4665 and 2021JJ30775).
文摘In ramjet combustion chambers,carbon dioxide(CO_(2))produced by the combustion of carbonaceous fuel enters the chamber together with boron agglomerates.In order to investigate the effect of CO_(2)concentration present in an oxygen-containing atmosphere on the combustion characteristics and oxidation mechanisms of boron agglomerates,we used a laser ignition system,an X-ray diffractometer(XRD),and a thermogravimetric-differential scanning calorimetry(TG-DSC)combined thermal analysis system.Single-particle boron was tested in the laser-ignition experiments as the control group.The ignition experiment results showed that with a fixed O2 concentration of 20%,when the particle temperature reaches the melting point of boron,increasing CO_(2)content causes the combustion process of boron agglomerates to transition from single-particle molten droplet combustion to porous-particle combustion.Furthermore,XRD analysis results indicated that the condensed-phase combustion products(CCPs)of boron particles in a mixed atmosphere of O2 and CO_(2)contained B4C,which is responsible for the porous structure of the particles.At temperatures below 1200℃,the addition of CO_(2)has no obvious promotion effect on boron exothermic reaction.However,in the laser-ignition experiment,when the oxygen concentration was fixed at 20%while the CO_(2)concentration increased from 0%to 80%,the maximum temperature of boron agglomerates rose from 2434 to 2573 K,the self-sustaining combustion time of single-particle boron decreased from 396 to 169 ms,and the self-sustaining combustion time of boron agglomerates decreased from 198 to 40 ms.This study conclusively showed that adding CO_(2)to an oxygen-containing atmosphere facilitates boron reaction and consumption pathways,which is beneficial to promoting exothermic reaction of boron agglomerates at relatively high temperatures.
基金supported by the National Natural Science Foundation of China(grant Nos.12272409,T2221002)Changsha Science and Technology Project(grant No.kq2107001)+1 种基金the Science and Technology Innovation Program of Hunan Province(grant No.2022RC1233)Hunan Provincial Innovation Foundation for Postgraduate(grant No.QL20230015).
文摘The supersonic gas-particle two-phase transverse jet is a typical flow process in many applications,such as solid rocket scramjet.This study carried out experimental tests as well as Large Eddy Simulation(LES)to investigate the evolution process of transverse gas-particle two-phase jets in supersonic crossflow,especially focusing on the phenomena called preferential concentration.The simulation is based on the Eulerian-Lagrangian method,which successfully reproduces the characteristic phenomena observed in experiments.The particle cloud forms three different characteristic distribution patterns:tooth-like waves near the jet port,quasi-ordered structures near counter-rotating vortex pairs(CVP),and filamentous clouds in the upper part.The turbulence and small unstable shock play a suppressing role in mixing small-diameter particles,which tend to aggregate in regions of high density and low vorticity.Furthermore,it is found that there exists a specific range of particle sizes,as particles'sizes approach this specific range,the influence of compressibility of the airflow on particle distribution becomes increasingly prominent.Overall,this study shed some light on the understanding of the complex and intricate nature of the supersonic gas-particle two-phase transverse jet.
基金financial support provided by the National Natural Science Foundation of China(grant No.52006240)supported by Hunan Provincial Natural Science Foundation of China(grant No.2020JJ4665 and No.2021JJ30775).
文摘In this study,boron–magnesium agglomerates with varying mass ratios were prepared by drying a micron-sized boron–magnesium mixed suspension,and the combustion process of these agglomerates under different oxygen-rich concentrations were investigated using a laser ignition system.The test results showed that when the mass fraction of magnesium powder in boron-magnesium agglomerates exceeded a certain threshold(between 2%and 5%),flame extinction and reignition occurred after a significant reduction in the agglomerate volume during combustion.This process is referred to as the transient flameout process,which is affected by the magnesium content of the agglomerate and the oxygen concentration in the ambient atmosphere.An increase in the magnesium content or oxygen concentration makes this phenomenon more pronounced.During weakening of the flame intensity,a dark film gradually covered the particle surfaces.X-ray diffraction and elemental analyses of the cross-section and outer surface of the condensed combustion product suggested that the dark film is primarily composed of Mg-B-O ternary oxides.This film prevents direct contact between boron and oxygen,thereby inhibiting surface and gas-phase reactions and leading to the occurrence of the transient flameout phenomenon.
