In the 12 years since the Belt and Road Initiative was first proposed,many Chinese enterprises have made fruitful achievements in the participating countries of the Belt and Road Initiative.
Stall flutter poses great challenges to flight safety.To alleviate this problem,a steady blowing control considering the perturbation and wake-induced vibration at a large angle of attack is developed in this paper,wh...Stall flutter poses great challenges to flight safety.To alleviate this problem,a steady blowing control considering the perturbation and wake-induced vibration at a large angle of attack is developed in this paper,where two blowings are configured on upper and lower tail surfaces to suppress the stall flutter.The stall flutter with one-degree-of-freedom is first evaluated by numerical simulation.The equation of motion for stall flutter is solved by the Newmark-β method.Then,the stall flutter responses for five blowing speeds,i.e.,0,4,12,20,and 28 m/s under the airspeed range of 3–9 m/s,are studied in detail.The stall flutter suppression mechanism can be summarized as follows:a large blowing speed can inject energy into the boundary layer and enhance the high-pressure zone,which delays the flow separation on the suction surface.In this way,the formation of the leading-edge separation vortex is suppressed.Thus,the dynamic stall vortex is weakened and accelerates shedding.In addition,the driving moment is reduced,which leads to a decrement in the stall flutter amplitude.When the blowing speed is 28 m/s(stall flutter amplitude=0.1357 rad),compared with uncontrolled case(stall flutter amplitude=0.6002 rad),the amplitude can decrease by 77.39%,which demonstrates the effectiveness of the proposed steady blowing based active control strategy.展开更多
Small modular reactors have received widespread attention owing to their inherent safety,low investment,and flexibility.Small pressurized water reactors(SPWRs)have become important candidates for SMRs owing to their h...Small modular reactors have received widespread attention owing to their inherent safety,low investment,and flexibility.Small pressurized water reactors(SPWRs)have become important candidates for SMRs owing to their high technological maturity.Since the Fukushima accident,research on accident-tolerant fuels(ATFs),which are more resistant to serious accidents than conventional fuels,has gradually increased.This study analyzes the neutronics and thermal hydraulics of an SPWR(ACPR50S)for different ATFs,BeO+UO_(2)−SiC,BeO+UO_(2)−FeCrAl,U_(3)Si_(2)−SiC,and U_(3)Si_(2)−FeCrAl,based on a PWR fuel management code,the Bamboo-C deterministic code.In the steady state,the burnup calculations,reactivity coefficients,power and temperature distributions,and control rod reactivity worth were studied.The transients of the control rod ejection accident for the two control rods with the maximum and minimum reactivity worth were analyzed.The results showed that 5%B-10 enrichment in the wet annular burnable absorbers assembly can effectively reduce the initial reactivity and end-of-life reactivity penalty.The BeO+UO2−SiC core exhibited superior neutronic characteristics in terms of burnup and negative temperature reactivity compared with the other three cases owing to the strong moderation ability of BeO+UO_(2)and low neutron absorption of SiC.However,the U_(3)Si_(2)core had a marginally better power-flattening effect than BeO+UO_(2),and the differential worth of each control rod group was similar between different ATFs.During the transient of a control rod ejection,the changes in the fuel temperature,coolant temperature,and coolant density were similar.The maximum difference was less than 10℃ for the fuel temperature and 2℃ for the coolant temperature.展开更多
Understanding the steady mechanism of biomass smoldering plays a great role in the utilization of smoldering technology.In this study numerical analysis of steady smoldering of biomass rods was performed.A two-dimensi...Understanding the steady mechanism of biomass smoldering plays a great role in the utilization of smoldering technology.In this study numerical analysis of steady smoldering of biomass rods was performed.A two-dimensional(2D)steady model taking into account both char oxidation and pyrolysis was developed on the basis of a calculated propagation velocity according to empirical correlation.The model was validated against the smoldering experiment of biomass rods under natural conditions,and the maximum error was smaller than 31%.Parameter sensitivity analysis found that propagation velocity decreases significantly while oxidation area and pyrolysis zone increase significantly with the increasing diameter of rod fuel.展开更多
The close-coupled selective catalytic reduction(cc-SCR)catalyst is an effective technology to reduce tailpipe NOx emission during cold start.This paper investigated the optimal ammonia storage under steady and transie...The close-coupled selective catalytic reduction(cc-SCR)catalyst is an effective technology to reduce tailpipe NOx emission during cold start.This paper investigated the optimal ammonia storage under steady and transient state in the cc-SCR.The study showed that a trade-off between NOx conversion efficiency and ammonia slip is observed on the pareto solutions under steady state,and the optimal ammonia storage is calculated with ammonia slip less than 10μL/L based on the ChinaⅥemission legislation.The rapid temperature increase will lead to severe ammonia slip in the transient test cycle.A simplified 0-D calculation method on ammonia slip under transient state is proposed based on kinetic model of ammonia adsorption and desorption.In addition,the effect of ammonia storage,catalyst temperature and temperature increasing rate on ammonia slip are analyzed.The optimal ammonia storage is calculated with maximum ammonia slip less than 100μL/L according to the oxidation efficiency of ammonia slip catalyst(ASC)downstream cc-SCR.It was found that the optimal ammonia storage under transient state is much lower than that under steady state in cc-SCR at lower temperature,and a phase diagram is established to analyze the influence of temperature and temperature increasing rate on optimal ammonia storage.展开更多
Gas-phase polyethylene(PE)processes are among the most important methods for PE production.A deeper understanding of the process characteristics and dynamic behavior,such as properties of PE and reactor stability,hold...Gas-phase polyethylene(PE)processes are among the most important methods for PE production.A deeper understanding of the process characteristics and dynamic behavior,such as properties of PE and reactor stability,holds substantial interest for both academic researchers and industries.In this study,both steady-state and dynamic models for a gas-phase polyethylene process are established as a simulation platform,which can be used to study a variety of operation tasks for commercial solution polyethylene processes,such as new product development,process control and real-time optimization.The copolymerization kinetic parameters are fitted by industrial data.Additionally,a multi-reactor series model is developed to characterize the temperature distribution within the fluidized bed reactor.The accuracy in predicting melt index and density of the polymer,and the dynamic behavior of the developed models are verified by real plant data.Moreover,the dynamic simulation platform is applied to compare four practical control schemes for reactor temperature by a series of simulation experiments,since temperature control is important in industrial production.The results reveal that all four schemes effectively track the setpoint temperature.However,only the demineralized water temperature cascade control demonstrates excellent performance in handling disturbances from both the recycle gas subsystem and the heat exchange subsystem.展开更多
Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings ...Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings which are termed as sparse,moderate and dense are considered,and the induced vortex system and shock structures are compared.A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation,reducing the separation region.The dense jet spacing configuration creates a larger momentum deficit region,reducing the friction downstream of the corner.Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock.The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation.Furthermore,the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods,revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.展开更多
The rheological properties and limited flow velocities of solvent-free nanofluids are crucial for their technologically significant applications.In particular,the flow in a solvent-free nanofluid system is steady only...The rheological properties and limited flow velocities of solvent-free nanofluids are crucial for their technologically significant applications.In particular,the flow in a solvent-free nanofluid system is steady only when the flow velocity is lower than a critical value.In this paper,we establish a rigid-flexible dynamic model to investigate the existence of the upper bound on the steady flow velocities for three solvent-free nanofluid systems.Then,the effects of the structural parameters on the upper bound on the steady flow velocities are examined with the proposed structure-preserving method.It is found that each of these solvent-free nanofluid systems has an upper bound on the steady flow velocity,which exhibits distinct dependence on their structural parameters,such as the graft density of branch chains and the size of the cores.In addition,among the three types of solvent-free nanofluids,the magnetic solvent-free nanofluid poses the largest upper bound on the steady flow velocity,demonstrating that it is a better choice when a large flow velocity is required in real applications.展开更多
The reduction of oxygen consumption is a key factor to improve the energy density of underwater Stirling engine.A series of fundamental experiments are carried out to elucidate the spray characteristics of soybean oil...The reduction of oxygen consumption is a key factor to improve the energy density of underwater Stirling engine.A series of fundamental experiments are carried out to elucidate the spray characteristics of soybean oil/2,5-dimethylfuran(DMF)blended fuel in an underwater Stirling engine.Spray characteristics such as spray penetration,spray angle,spray area,and light intensity level under low injection and ambient pressures are obtained using image post-processing method.The results show that the effects of injection pressure,ambient pressure,and nozzle diameter on the transient spray characteristics of underwater Stirling engine are similar to those of diesel engine.However,in the steady spray process,the injection pressure has little effect on spray near angle,and the spray far angle increases with the increase of the injection pressure.Compared with the spray far angle at injection pressure of 3 MPa,the spray far angle at 5 MPa and 7 MPa increased by 11.38%and 18.14%respectively.The addition of DMF can obviously improve the atomization of soybean oil/DMF blended fuel.The spray angle of blended fuel in transient process increases with the increase of the DMF concentration.The spray near angle has exceeded that of diesel(46.21°)when the DMF volume fraction exceeds 25%.The spray far angle is equivalent to that of diesel when the DMF volume fraction reaches 75%.Moreover,the spray with gas ejection no longer keeps conical,the droplet diameter distribution is more dispersed,and the droplet diameter is smaller.展开更多
Identification of steady state and transient state plays an important role in modeling,control,optimiza-tion,and fault detection of industrial processes.Many existing methods for state identification are not satisfact...Identification of steady state and transient state plays an important role in modeling,control,optimiza-tion,and fault detection of industrial processes.Many existing methods for state identification are not satisfactory in practical applications due to problems of ideal hypothesis,too many parameters,and poor robustness.In this paper,a novel state identification approach is proposed.The problem of state identification is transformed into finding the noise band of differential signal.For practical application,automatic selection of noise band amplitude is proposed to make the method convenient to be used.Problems of gross errors,low signal-to-noise ratio and online identification are considered.And comparison with other two methods shows that the proposed method has better identification performance.Simulations and experiments also prove the effectiveness and practicability of the proposed method.展开更多
In recent years, metallurgical slags have been increasingly used as materials for the manufacture of cement, pavement and filling material. The transport of the molten slag to the receiving pots is carried out through...In recent years, metallurgical slags have been increasingly used as materials for the manufacture of cement, pavement and filling material. The transport of the molten slag to the receiving pots is carried out through open channels. The transient and steady-state flow of a molten slag in a rectangular open channel is numerically analyzed here. For the transient flow, the Saint-Venant equations were numerically solved. For the steady-state flow, the derivatives in time and space in the Saint-Venant equations were set equal to zero and a polynomial of degree 3 is obtained whose roots are the slag height values. It was assumed that the viscosity of the slag has an Arrhenius-type behavior with temperature. Four values of temperature values, namely 1723.15, 1773.15, 1823.15, 18873.15 ˚K, and five values of the angle of inclination of the channel, namely 1, 2, 3, 4, 5 degrees, are considered. Numerical results show that the steady-state values of the height and velocity of the molten slag depend strongly on the temperature of the slag and the angle of inclination of the channel. As the slag temperature and channel angle increase, the value of the steady-state slag height decreases. The value of the steady-state slag velocity increases as the slag temperature and channel inclination angle increase.展开更多
The energy equilibrium equation and discrete ordinate methods are combined to establish the one-dimensional steady heat transfer mathematical model of multi-layer thermal insulations （MTIs） in metallic thermal prote...The energy equilibrium equation and discrete ordinate methods are combined to establish the one-dimensional steady heat transfer mathematical model of multi-layer thermal insulations （MTIs） in metallic thermal protection systems. The inverse problem of heat transfer is solved by the genetic algorithm and data from the steady heat transfer experiment of fibrous thermal insulations. The density radiation attenuation coefficient, the albedo of fibrous thermal insulations and the surface emissivity of reflective screens are optimized. Finally, the one-dimensional steady heat transfer model of MTIs with optimized thermal physical parameters is verified by experimental data of the effective MTI conductivity.展开更多
A mathematical model has been presented for describing single droplet unsteady processes of vaporization, ignition and combustion in a hot quiescent air environment. The arbitrary Lagrangian Eulerian numerical method...A mathematical model has been presented for describing single droplet unsteady processes of vaporization, ignition and combustion in a hot quiescent air environment. The arbitrary Lagrangian Eulerian numerical method, incorporated with an effective adaptive mesh method, is applied. From the obtained time space distributions of gas temperature and species densities, the characteristics of droplet ignition and combustion process are clarified. It is also demonstrated that, due to the strong damping of the high temperature flame region around the droplet, the ambient conditions have little effects on the properties of the drop's surface; and that, due to the unsteady prediction of droplet heating time being much less than the corresponding quasi steady prediction under burning condition, the differences between unsteady and quasi steady results are much greater than those under pure vaporization.展开更多
A numerical analysis of the steady and pulsatile, macromolecular(such as low density lipopotein (LDL), Albumin) transport in T-bifurcation was proposed. The influence of Reynolds number and mass flow ratio etc. parame...A numerical analysis of the steady and pulsatile, macromolecular(such as low density lipopotein (LDL), Albumin) transport in T-bifurcation was proposed. The influence of Reynolds number and mass flow ratio etc. parameters on the velocity field and mass transport were calculated. The computational results predict that the blood flow factors affect the macromolecular distribution and the transport across the wall, it shows that hemodynamic play an important role in the process of atherosclerosis. The LDL and Albumin concentration on the wall varies most greatly in flow bifurcation area where the wall shear stress varies greatly at the branching vessel and the atherosclerosis often appears there.展开更多
Based on the basic facts that the martensitic transformation is a physical phenomenon which occurs in non equilibrium conditions and there exists the feedback mechanism in the martensitic transformation, the dynamical...Based on the basic facts that the martensitic transformation is a physical phenomenon which occurs in non equilibrium conditions and there exists the feedback mechanism in the martensitic transformation, the dynamical processes of the isothermal and athermal martensitic transformations were analyzed by using nonlinear theory and a bifurcation theory model was established. It is shown that a multiple steady state phenomenon can take place as austenite is cooled, and the transitions of the steady state temperature between the branches of stable steady states can be considered the transformation from austenite to martensite. This model can estimate the starting temperature of the martensitic transformation and explain some experimental features of the martensitic transformation such as the effects of cooling rate, fluctuation and austenitic grain size on the martensitic transformation. [展开更多
A simple strategy for capturing unstable steady solution is proposed in this paper. By enlarging the real time step, the unstable high frequency modes of the unsteady flow can be effectively suppressed because of the ...A simple strategy for capturing unstable steady solution is proposed in this paper. By enlarging the real time step, the unstable high frequency modes of the unsteady flow can be effectively suppressed because of the damping action on the real time level. The steady component will not be changed during real time marching. When the unsteady flow solution converges to a steady state, the partial derivatives of real time in unsteady governing equations will disappear automatically. The steady solution is the exacted unstable steady solution. The method is validated by the laminar flow past a circular cylinder and a transonic buffet of NACA0012 airfoil. This approach can acquire high-precision unstable steady solutions quickly and effectively without reducing the spatial discretization accuracy. This work provides the basis for unstable flow modeling and analysis.展开更多
Taking wall-flow diesel particulate filter(DPF) as the research objective and separately assuming its filtering wall to be composed of numerous spherical or cylindrical elements, two different mathematical models of s...Taking wall-flow diesel particulate filter(DPF) as the research objective and separately assuming its filtering wall to be composed of numerous spherical or cylindrical elements, two different mathematical models of steady filtration for wall-flow diesel particulate filter were developed and verified by experiments as well as numerically solved. Furthermore, the effects of the macroand micro-structural parameters of filtering wall and exhaust-flow characteristic parameters on trapping efficiency were also analyzed and researched. The results show that: 1) The two developed mathematical models are consistent with the prediction of variation of particulate size; the influence of various factors on the steady trapping efficiency is exactly the same. Compared to model 2, model 1 is more suitable for describing the steady filtration process of wall-flow diesel particulate filter; 2)The major influencing factors on steady trapping efficiency of wall-flow diesel particulate filter are the macro-and micro-structural parameters of filtering wall; and the secondary influencing factors are the exhaust-flow characteristic parameters and macro-structural parameters of filter; 3)The steady trapping efficiency will be improved by increasing filter body volume, pore density as well as wall thickness and by decreasing exhaust-flow, but effects will be weakened when particulate size exceeds a certain critical value; 4) The steady trapping efficiency will be significantly improved by increasing exhaust-flow temperature and filtering wall thickness, but effects will be also weakened when particulate size exceeds a certain critical value; 5) The steady trapping efficiency will approximately linearly increase with reducing porosity, micropore aperture and pore width.展开更多
The multi-piped freezing method is usually applied in artificial ground freezing （AGF） projects to fulfill special construction requirements, such as two-, three-, or four-piped freezing. Based on potential superpos...The multi-piped freezing method is usually applied in artificial ground freezing （AGF） projects to fulfill special construction requirements, such as two-, three-, or four-piped freezing. Based on potential superposition theory, this paper gives analytical solutions to steady-state frozen temperature for two, three, and four freezing pipes with different temperatures and arranged at random. Specific solutions are derived for some particular arrangements, such as three freezing pipes in a linear arrangement with equal or unequal spacing, right and isosceles triangle arrangements, four freezing pipes in a linear arrangement with equal spacing, and rhombus and rectangle arrangements. A comparison between the analytical solutions and numerical thermal analysis shows that the analytical solutions are sufficiently precise. As a part of the theory of AGF, the analytical solutions of temperature fields for multi-piped freezing with arbitrary layouts and different temperatures of freezing pipes are approached for the first time.展开更多
文摘In the 12 years since the Belt and Road Initiative was first proposed,many Chinese enterprises have made fruitful achievements in the participating countries of the Belt and Road Initiative.
基金co-supported by the National Natural Science Foundation of China(Nos.52472394,52425211,52201327,52272360)。
文摘Stall flutter poses great challenges to flight safety.To alleviate this problem,a steady blowing control considering the perturbation and wake-induced vibration at a large angle of attack is developed in this paper,where two blowings are configured on upper and lower tail surfaces to suppress the stall flutter.The stall flutter with one-degree-of-freedom is first evaluated by numerical simulation.The equation of motion for stall flutter is solved by the Newmark-β method.Then,the stall flutter responses for five blowing speeds,i.e.,0,4,12,20,and 28 m/s under the airspeed range of 3–9 m/s,are studied in detail.The stall flutter suppression mechanism can be summarized as follows:a large blowing speed can inject energy into the boundary layer and enhance the high-pressure zone,which delays the flow separation on the suction surface.In this way,the formation of the leading-edge separation vortex is suppressed.Thus,the dynamic stall vortex is weakened and accelerates shedding.In addition,the driving moment is reduced,which leads to a decrement in the stall flutter amplitude.When the blowing speed is 28 m/s(stall flutter amplitude=0.1357 rad),compared with uncontrolled case(stall flutter amplitude=0.6002 rad),the amplitude can decrease by 77.39%,which demonstrates the effectiveness of the proposed steady blowing based active control strategy.
基金supported by the National Natural Science Foundation of China (No. 12205150)Natural Science Foundation of Jiangsu Province (No. BK20210304)+1 种基金China Postdoctoral Science Foundation (Nos. 2020M681594 and 2019TQ0148)Jiangsu Province Postdoctoral Science Foundation (Nos. 2020Z231)
文摘Small modular reactors have received widespread attention owing to their inherent safety,low investment,and flexibility.Small pressurized water reactors(SPWRs)have become important candidates for SMRs owing to their high technological maturity.Since the Fukushima accident,research on accident-tolerant fuels(ATFs),which are more resistant to serious accidents than conventional fuels,has gradually increased.This study analyzes the neutronics and thermal hydraulics of an SPWR(ACPR50S)for different ATFs,BeO+UO_(2)−SiC,BeO+UO_(2)−FeCrAl,U_(3)Si_(2)−SiC,and U_(3)Si_(2)−FeCrAl,based on a PWR fuel management code,the Bamboo-C deterministic code.In the steady state,the burnup calculations,reactivity coefficients,power and temperature distributions,and control rod reactivity worth were studied.The transients of the control rod ejection accident for the two control rods with the maximum and minimum reactivity worth were analyzed.The results showed that 5%B-10 enrichment in the wet annular burnable absorbers assembly can effectively reduce the initial reactivity and end-of-life reactivity penalty.The BeO+UO2−SiC core exhibited superior neutronic characteristics in terms of burnup and negative temperature reactivity compared with the other three cases owing to the strong moderation ability of BeO+UO_(2)and low neutron absorption of SiC.However,the U_(3)Si_(2)core had a marginally better power-flattening effect than BeO+UO_(2),and the differential worth of each control rod group was similar between different ATFs.During the transient of a control rod ejection,the changes in the fuel temperature,coolant temperature,and coolant density were similar.The maximum difference was less than 10℃ for the fuel temperature and 2℃ for the coolant temperature.
文摘Understanding the steady mechanism of biomass smoldering plays a great role in the utilization of smoldering technology.In this study numerical analysis of steady smoldering of biomass rods was performed.A two-dimensional(2D)steady model taking into account both char oxidation and pyrolysis was developed on the basis of a calculated propagation velocity according to empirical correlation.The model was validated against the smoldering experiment of biomass rods under natural conditions,and the maximum error was smaller than 31%.Parameter sensitivity analysis found that propagation velocity decreases significantly while oxidation area and pyrolysis zone increase significantly with the increasing diameter of rod fuel.
基金supported by the National Natural Science Foundation of China(No.51976100)the co-founding of FAW Jiefang Automobile Co.,Ltd.Wuxi Diesel Engine Factory,Saudi Aramco Technologies CompanyShandong Chambroad Petrochemicals Co.,Ltd.with the project“Fuel and Engine Co-optimization for high Efficiency and Net-Zero Emission Heavy-duty Engine”。
文摘The close-coupled selective catalytic reduction(cc-SCR)catalyst is an effective technology to reduce tailpipe NOx emission during cold start.This paper investigated the optimal ammonia storage under steady and transient state in the cc-SCR.The study showed that a trade-off between NOx conversion efficiency and ammonia slip is observed on the pareto solutions under steady state,and the optimal ammonia storage is calculated with ammonia slip less than 10μL/L based on the ChinaⅥemission legislation.The rapid temperature increase will lead to severe ammonia slip in the transient test cycle.A simplified 0-D calculation method on ammonia slip under transient state is proposed based on kinetic model of ammonia adsorption and desorption.In addition,the effect of ammonia storage,catalyst temperature and temperature increasing rate on ammonia slip are analyzed.The optimal ammonia storage is calculated with maximum ammonia slip less than 100μL/L according to the oxidation efficiency of ammonia slip catalyst(ASC)downstream cc-SCR.It was found that the optimal ammonia storage under transient state is much lower than that under steady state in cc-SCR at lower temperature,and a phase diagram is established to analyze the influence of temperature and temperature increasing rate on optimal ammonia storage.
基金financial support provided by the Project of the National Key Research and Development Program of China(2018YFA0704601)the National Natural Science Foundation of China(U22A20415,22308314)+1 种基金the Natural Science Foundation of Zhejiang Province,China(LQ24B060001)the“Pioneer”and“Leading Goose”Research and Development Program of Zhejiang,China(2022C01SA442617)are gratefully acknowledged.
文摘Gas-phase polyethylene(PE)processes are among the most important methods for PE production.A deeper understanding of the process characteristics and dynamic behavior,such as properties of PE and reactor stability,holds substantial interest for both academic researchers and industries.In this study,both steady-state and dynamic models for a gas-phase polyethylene process are established as a simulation platform,which can be used to study a variety of operation tasks for commercial solution polyethylene processes,such as new product development,process control and real-time optimization.The copolymerization kinetic parameters are fitted by industrial data.Additionally,a multi-reactor series model is developed to characterize the temperature distribution within the fluidized bed reactor.The accuracy in predicting melt index and density of the polymer,and the dynamic behavior of the developed models are verified by real plant data.Moreover,the dynamic simulation platform is applied to compare four practical control schemes for reactor temperature by a series of simulation experiments,since temperature control is important in industrial production.The results reveal that all four schemes effectively track the setpoint temperature.However,only the demineralized water temperature cascade control demonstrates excellent performance in handling disturbances from both the recycle gas subsystem and the heat exchange subsystem.
基金Supported by the National Natural Science Foundation of China(Nos.11972064,92052104)the Key Laboratory of Computational Aerodynamics,AVIC Aerodynamics Research Institute,China(No.YL2022XFX0405)the Fundamental Research Funds for the Central Universities,China.
文摘Shock wave/boundary layer interaction in a 24°turning angle of the compression ramp at Mach number 2.9 controlled by steady microjet is investigated using direct numerical simulation.Three different jet spacings which are termed as sparse,moderate and dense are considered,and the induced vortex system and shock structures are compared.A moderate jet spacing configuration is found to generate counter-rotating vortex pairs that transport high-momentum fluid towards the vicinity of wall and strengthen the boundary layer to resist separation,reducing the separation region.The dense jet spacing configuration creates a larger momentum deficit region,reducing the friction downstream of the corner.Analysis of pressure and pressure gradient reveals that dense jet spacing configuration reduces the intensity of separation shock.The impact of varying jet spacings on the turbulent kinetic energy transport mechanism is also investigated by decomposing the budget terms in the transport equation.Furthermore,the spectral characteristics of the separation region are studied using power spectral density and dynamic mode decomposition methods,revealing that moderate jet spacing configuration suppresses low-frequency fluctuations in the separation region.
基金Project supported by the National Natural Science Foundation of China(No.12172281)the Fund of the Science and Technology Innovation Team of Shaanxi Province of China(No.2022TD-61)+2 种基金the Open Project of State Key Laboratory of Performance Monitoring and Protecting of Rail Transit InfrastructureEast China Jiaotong University(No.HJGZ2023102)the Shaanxi Province Key Research and Development Project(No.2024SFYBXM-531)。
文摘The rheological properties and limited flow velocities of solvent-free nanofluids are crucial for their technologically significant applications.In particular,the flow in a solvent-free nanofluid system is steady only when the flow velocity is lower than a critical value.In this paper,we establish a rigid-flexible dynamic model to investigate the existence of the upper bound on the steady flow velocities for three solvent-free nanofluid systems.Then,the effects of the structural parameters on the upper bound on the steady flow velocities are examined with the proposed structure-preserving method.It is found that each of these solvent-free nanofluid systems has an upper bound on the steady flow velocity,which exhibits distinct dependence on their structural parameters,such as the graft density of branch chains and the size of the cores.In addition,among the three types of solvent-free nanofluids,the magnetic solvent-free nanofluid poses the largest upper bound on the steady flow velocity,demonstrating that it is a better choice when a large flow velocity is required in real applications.
基金the Natural Science Foundation of Jiangsu Province(No.BK20220588)the Initial Scientific Research Fund of Yangzhou University(No.137012553)and the Public Welfare Technology Research Program of Zhejiang Province(Nos.LGG19E060001 and LGG 21E090001)。
文摘The reduction of oxygen consumption is a key factor to improve the energy density of underwater Stirling engine.A series of fundamental experiments are carried out to elucidate the spray characteristics of soybean oil/2,5-dimethylfuran(DMF)blended fuel in an underwater Stirling engine.Spray characteristics such as spray penetration,spray angle,spray area,and light intensity level under low injection and ambient pressures are obtained using image post-processing method.The results show that the effects of injection pressure,ambient pressure,and nozzle diameter on the transient spray characteristics of underwater Stirling engine are similar to those of diesel engine.However,in the steady spray process,the injection pressure has little effect on spray near angle,and the spray far angle increases with the increase of the injection pressure.Compared with the spray far angle at injection pressure of 3 MPa,the spray far angle at 5 MPa and 7 MPa increased by 11.38%and 18.14%respectively.The addition of DMF can obviously improve the atomization of soybean oil/DMF blended fuel.The spray angle of blended fuel in transient process increases with the increase of the DMF concentration.The spray near angle has exceeded that of diesel(46.21°)when the DMF volume fraction exceeds 25%.The spray far angle is equivalent to that of diesel when the DMF volume fraction reaches 75%.Moreover,the spray with gas ejection no longer keeps conical,the droplet diameter distribution is more dispersed,and the droplet diameter is smaller.
文摘Identification of steady state and transient state plays an important role in modeling,control,optimiza-tion,and fault detection of industrial processes.Many existing methods for state identification are not satisfactory in practical applications due to problems of ideal hypothesis,too many parameters,and poor robustness.In this paper,a novel state identification approach is proposed.The problem of state identification is transformed into finding the noise band of differential signal.For practical application,automatic selection of noise band amplitude is proposed to make the method convenient to be used.Problems of gross errors,low signal-to-noise ratio and online identification are considered.And comparison with other two methods shows that the proposed method has better identification performance.Simulations and experiments also prove the effectiveness and practicability of the proposed method.
文摘In recent years, metallurgical slags have been increasingly used as materials for the manufacture of cement, pavement and filling material. The transport of the molten slag to the receiving pots is carried out through open channels. The transient and steady-state flow of a molten slag in a rectangular open channel is numerically analyzed here. For the transient flow, the Saint-Venant equations were numerically solved. For the steady-state flow, the derivatives in time and space in the Saint-Venant equations were set equal to zero and a polynomial of degree 3 is obtained whose roots are the slag height values. It was assumed that the viscosity of the slag has an Arrhenius-type behavior with temperature. Four values of temperature values, namely 1723.15, 1773.15, 1823.15, 18873.15 ˚K, and five values of the angle of inclination of the channel, namely 1, 2, 3, 4, 5 degrees, are considered. Numerical results show that the steady-state values of the height and velocity of the molten slag depend strongly on the temperature of the slag and the angle of inclination of the channel. As the slag temperature and channel angle increase, the value of the steady-state slag height decreases. The value of the steady-state slag velocity increases as the slag temperature and channel inclination angle increase.
文摘The energy equilibrium equation and discrete ordinate methods are combined to establish the one-dimensional steady heat transfer mathematical model of multi-layer thermal insulations （MTIs） in metallic thermal protection systems. The inverse problem of heat transfer is solved by the genetic algorithm and data from the steady heat transfer experiment of fibrous thermal insulations. The density radiation attenuation coefficient, the albedo of fibrous thermal insulations and the surface emissivity of reflective screens are optimized. Finally, the one-dimensional steady heat transfer model of MTIs with optimized thermal physical parameters is verified by experimental data of the effective MTI conductivity.
文摘A mathematical model has been presented for describing single droplet unsteady processes of vaporization, ignition and combustion in a hot quiescent air environment. The arbitrary Lagrangian Eulerian numerical method, incorporated with an effective adaptive mesh method, is applied. From the obtained time space distributions of gas temperature and species densities, the characteristics of droplet ignition and combustion process are clarified. It is also demonstrated that, due to the strong damping of the high temperature flame region around the droplet, the ambient conditions have little effects on the properties of the drop's surface; and that, due to the unsteady prediction of droplet heating time being much less than the corresponding quasi steady prediction under burning condition, the differences between unsteady and quasi steady results are much greater than those under pure vaporization.
文摘A numerical analysis of the steady and pulsatile, macromolecular(such as low density lipopotein (LDL), Albumin) transport in T-bifurcation was proposed. The influence of Reynolds number and mass flow ratio etc. parameters on the velocity field and mass transport were calculated. The computational results predict that the blood flow factors affect the macromolecular distribution and the transport across the wall, it shows that hemodynamic play an important role in the process of atherosclerosis. The LDL and Albumin concentration on the wall varies most greatly in flow bifurcation area where the wall shear stress varies greatly at the branching vessel and the atherosclerosis often appears there.
文摘Based on the basic facts that the martensitic transformation is a physical phenomenon which occurs in non equilibrium conditions and there exists the feedback mechanism in the martensitic transformation, the dynamical processes of the isothermal and athermal martensitic transformations were analyzed by using nonlinear theory and a bifurcation theory model was established. It is shown that a multiple steady state phenomenon can take place as austenite is cooled, and the transitions of the steady state temperature between the branches of stable steady states can be considered the transformation from austenite to martensite. This model can estimate the starting temperature of the martensitic transformation and explain some experimental features of the martensitic transformation such as the effects of cooling rate, fluctuation and austenitic grain size on the martensitic transformation. [
文摘A simple strategy for capturing unstable steady solution is proposed in this paper. By enlarging the real time step, the unstable high frequency modes of the unsteady flow can be effectively suppressed because of the damping action on the real time level. The steady component will not be changed during real time marching. When the unsteady flow solution converges to a steady state, the partial derivatives of real time in unsteady governing equations will disappear automatically. The steady solution is the exacted unstable steady solution. The method is validated by the laminar flow past a circular cylinder and a transonic buffet of NACA0012 airfoil. This approach can acquire high-precision unstable steady solutions quickly and effectively without reducing the spatial discretization accuracy. This work provides the basis for unstable flow modeling and analysis.
基金Projects(5117604551276056)supported by the National Natural Science Foundation of China+1 种基金Projects(201208430262201306130031)supported by the National Studying Abroad Foundation of the China Scholarship Council
文摘Taking wall-flow diesel particulate filter(DPF) as the research objective and separately assuming its filtering wall to be composed of numerous spherical or cylindrical elements, two different mathematical models of steady filtration for wall-flow diesel particulate filter were developed and verified by experiments as well as numerically solved. Furthermore, the effects of the macroand micro-structural parameters of filtering wall and exhaust-flow characteristic parameters on trapping efficiency were also analyzed and researched. The results show that: 1) The two developed mathematical models are consistent with the prediction of variation of particulate size; the influence of various factors on the steady trapping efficiency is exactly the same. Compared to model 2, model 1 is more suitable for describing the steady filtration process of wall-flow diesel particulate filter; 2)The major influencing factors on steady trapping efficiency of wall-flow diesel particulate filter are the macro-and micro-structural parameters of filtering wall; and the secondary influencing factors are the exhaust-flow characteristic parameters and macro-structural parameters of filter; 3)The steady trapping efficiency will be improved by increasing filter body volume, pore density as well as wall thickness and by decreasing exhaust-flow, but effects will be weakened when particulate size exceeds a certain critical value; 4) The steady trapping efficiency will be significantly improved by increasing exhaust-flow temperature and filtering wall thickness, but effects will be also weakened when particulate size exceeds a certain critical value; 5) The steady trapping efficiency will approximately linearly increase with reducing porosity, micropore aperture and pore width.
基金Project supported by the National Natural Science Foundation of China （Nos. 51178336 and 51478340）, the Natural Science Foundation of Zhejiang Province, China （No. LZ13E080002）, and the China Ministry of Communications Construction Science ＆ Technology Projects （No. 2013318R11300）
文摘The multi-piped freezing method is usually applied in artificial ground freezing （AGF） projects to fulfill special construction requirements, such as two-, three-, or four-piped freezing. Based on potential superposition theory, this paper gives analytical solutions to steady-state frozen temperature for two, three, and four freezing pipes with different temperatures and arranged at random. Specific solutions are derived for some particular arrangements, such as three freezing pipes in a linear arrangement with equal or unequal spacing, right and isosceles triangle arrangements, four freezing pipes in a linear arrangement with equal spacing, and rhombus and rectangle arrangements. A comparison between the analytical solutions and numerical thermal analysis shows that the analytical solutions are sufficiently precise. As a part of the theory of AGF, the analytical solutions of temperature fields for multi-piped freezing with arbitrary layouts and different temperatures of freezing pipes are approached for the first time.
