To investigate the influences of co-flowand counter-flowmodes of reactant flowarrangement on a proton exchange membrane fuel cell(PEMFC)during start-up,unsteady physical and mathematical models fully coupling the flow...To investigate the influences of co-flowand counter-flowmodes of reactant flowarrangement on a proton exchange membrane fuel cell(PEMFC)during start-up,unsteady physical and mathematical models fully coupling the flow,heat,and electrochemical reactions in a PEMFC are established.The continuity equation and momentum equation are solved by handling pressure-velocity coupling using the SIMPLE algorithm.The electrochemical reaction rates in the catalyst layers(CLs)of the cathode and anode are calculated using the Butler-Volmer equation.The multiphase mixture model describes the multiphase transport process of gas mixtures and liquid water in the fuel cell.After validation,the influences of co-flow and counter-flow modes on the PEMFC performance are investigated,including the evolution of the current density,flow field,temperature field,and reactant concentration field during start-up,as well as the steady distribution of the current density,reactant concentration,andmembrane water content when the start-up stabilizes.Co-flow and counter-flow modes influence the current density distribution and temperature distribution.On the one hand,the co-flow mode accelerates the start-up process of the PEMFC and leads to a more evenly distributed current density than the counter-flow mode.On the other hand,the temperature difference between the inlet and outlet sections of the cell is up to 10.1℃ under the co-flow mode,much larger than the 5.0℃ observed in the counter-flow mode.Accordingly,the counter-flowmode results in a more evenly distributed temperature and a lower maximum temperature than the co-flow case.Therefore,in the flow field design of a PEMFC,the reactant flow arrangements can be considered to weigh between better heat management and higher current density distribution of the cell.展开更多
The design objectives of modern aircraft engines include high load capacity,efficiency,and stability.With increasing loads,the phenomenon of corner separation in compressors intensifies,affecting engine performance an...The design objectives of modern aircraft engines include high load capacity,efficiency,and stability.With increasing loads,the phenomenon of corner separation in compressors intensifies,affecting engine performance and stability.Therefore,the adoption of appropriate flow control technology holds significant academic and engineering significance.This study employs the Reynolds-averaged Navier-Stokes(RANS)method to investigate the effects and mechanisms of active/passive Co-flow Jet(CFJ)control,implemented by introducing full-height and partial height jet slots between the suction surface and end wall of a compressor cascade.The results indicate that passive CFJ control significantly reduces the impact of corner separation at small incidence,with partial-height control further enhancing the effectiveness.The introduction of active CFJ enables separation control at large incidence,improving blade performance under different operating conditions.Active control achieves this by reducing the scale of corner separation vortices,effectively reducing the size of the separation region and enhancing blade performance.展开更多
The decrease in aerodynamic performance caused by the shock-induced dynamic stall of an advancing blade and the dynamic stall of a retreating blade at low speed and high angles of attack limits the flight speed of a h...The decrease in aerodynamic performance caused by the shock-induced dynamic stall of an advancing blade and the dynamic stall of a retreating blade at low speed and high angles of attack limits the flight speed of a helicopter.However,little research has been carried on the flow control methods employed to suppress both the dynamic stall induced by a shock wave and the dynamic stall occurring at high angles of attack.The dynamic stall suppression of a rotor airfoil by Co-Flow Jet(CFJ)is numerically investigated in this work.The flowfield of the airfoil is simulated by solving Reynolds Averaged Navier-Stokes equations based on the sliding mesh technique.Firstly,to improve the effect of a traditional CFJ on suppressing rotor airfoil shock-induced dynamic stall,an improved CFJ—a CFJ-sloping slot is proposed.Research shows that the CFJsloping slot suppresses the shock-induced dynamic stall more effectively than a traditional CFJ.Moreover,the improved CFJ can also suppress the dynamic stall of rotor airfoil at low speed and high angles of attack.The improved CFJ proposed in this paper is an effective flow control method that simultaneously suppresses the dynamic stall of the advancing and retreating blades.The mechanism of the improved CFJ in suppressing the dynamic stall of the rotor airfoil is studied,and a comparison is made between the improved CFJ and the traditional CFJ in terms of dynamic stall suppression at high and low speed.Finally,the effect of improved CFJ parameters(the jet momentum coefficient,the position of the injection/suction slot,and the size of the injection/suction slot)on shock-induced dynamic stall suppression is analyzed.展开更多
Introducing active flow control into the design of flapping wing is an effective way to enhance its aerodynamic performance.In this paper,a novel active flow control technology called Co-Flow Jet(CFJ)is applied to fla...Introducing active flow control into the design of flapping wing is an effective way to enhance its aerodynamic performance.In this paper,a novel active flow control technology called Co-Flow Jet(CFJ)is applied to flapping airfoils.The effect of CFJ on aerodynamic performance of flapping airfoils at low Reynolds number is numerically investigated using Unsteady Reynolds Averaged Navier-Stokes(URANS)simulation with Spalart-Allmaras(SA)turbulence model.Numerical methods are validated by a NACA6415-based CFJ airfoil case and a S809 pitching airfoil case.Then NACA6415 baseline airfoil and NACA6415-based CFJ airfoil with jet-off and jet-on are simulated in flapping motion,with Reynolds number 70,000 and reduced frequency 0.2.As a result,CFJ airfoils with jet-on generally have better lift and thrust characteristics than baseline airfoils and jet-off airfoil when Cμgreater than 0.04,which results from the CFJ effect of reducing flow separation by injecting high-energy fluid into boundary layer.Besides,typical kinematic and geometric parameters,including the reduced frequency and the positions of the suction and injection slot,are systematically studied to figure out their influence on aerodynamic performance of the CFJ airfoil.And a variable Cμjet control strategy is proposed to further improve effective propulsive efficiency.Compared with using constant Cμ,an increase of effective propulsive efficiency by22.6%has been achieved by using prescribed variable CμNACA6415-based CFJ airfoil at frequency 0.2.This study may provide some guidance to performance enhancement for Flapping wing Micro Air Vehicles(FMAV).展开更多
The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet(CFJ)airfoil with simple high-lift device configuration,with a specific goal to examine the feasibility and ...The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet(CFJ)airfoil with simple high-lift device configuration,with a specific goal to examine the feasibility and capability of the proposed configuration for low-speed take-off and landing.Computations have been accomplished by an in-house-programmed Reynoldsaveraged Navier-Stokes solver enclosed by k-ωshear stress transport turbulence model.Three crucial geometric parameters,viz.,injection slot location,suction slot location and its angle were selected for the sake of revealing their effects on aerodynamic lift,drag,power consumption and equivalent lift-to-drag ratio.Results show that using simple high-lift devices on CFJ airfoil can significantly augment the aerodynamic associated lift and efficiency which evidences the feasibility of CFJ for short take-off and landing with small angle of attack.The injection and suction slot locations are more influential with respect to the aerodynamic performance of CFJ airfoil compared with the suction slot angle.The injection location is preferable to be located in the downstream of the pressure suction peak on leading edge to reduce the power expenditure of the pumping system for a relative higher equivalent lift-to-drag ratio.Another concluded criterion is that the suction slot should be oriented on the trailing edge flap for achieving more aerodynamic gain,meanwhile,carefully selecting this location is crucial in determining the aerodynamic enhancement of CFJ airfoil with deflected flaps.展开更多
Numerical investigations are conducted to explore the aerodynamic characteristics of three-dimensional Co-Flow Jet(CFJ) wing with simple high-lift devices during low-speed takeoff and landing. Effects of three crucial...Numerical investigations are conducted to explore the aerodynamic characteristics of three-dimensional Co-Flow Jet(CFJ) wing with simple high-lift devices during low-speed takeoff and landing. Effects of three crucial parameters of CFJ wing, i.e., angle of attack, jet momentum and swept angle, are comprehensively examined. Additionally, the aerodynamic characteristics of two CFJ configurations, i.e., using open and discrete slots for injection, are compared. The results show that applying CFJ technique to a wing with simple high-lift device is able to generate more lift,reduce drag and enlarge stall margin with lower energy expenditure due to the super-circulation effect. Increasing the jet intensity can reduce the drag significantly, which is mainly contributed by the reaction jet force. The Oswald efficiency factor is, in some circumstances, larger than one,which indicates the potential of CFJ in reducing induced drag. Compared with clean wing configuration, using CFJ technique allows the aerodynamic force variation less sensitive to the swept angle, and such phenomenon is better observed for small swept angle region. Eventually, it is interesting to know that the discrete slotted CFJ configuration demonstrates a promising enhancement in aerodynamic performance in terms of high lift, low drag and efficiency.展开更多
Both the Active Flow Control(AFC)and the variable-camber technology are considered as efficient ways to enhance the aerodynamic performance of an aircraft.The present study investigated the feasibility of the combinat...Both the Active Flow Control(AFC)and the variable-camber technology are considered as efficient ways to enhance the aerodynamic performance of an aircraft.The present study investigated the feasibility of the combination of a Co-Flow Jet(CFJ)airfoil and a parabolic flap,where the Reynolds Average Navier-Stokes(RANS)equations and the Spalart-Allmaras(S-A)turbulence model were exploited for the numerical simulation.Several significant geometric parameters,including the injection slot location,the suction slot location,the injection slot angle,the suction slot angle and the airfoil Suction Surface Translation(SST),were selected to study their effects on the aerodynamics of the proposed configuration.Then,an optimized design was created and compared with the baseline airfoil.The results show that the CFJ airfoil combined with the parabolic flap is more beneficial to the aerodynamic performance enhancement at small angles of attack.It is preferable to locate the injection slot at a 2%chord-wise location and the suction slot at a 75%chord-wise location.Both the decrease of the injection slot angle and the augmentation of the suction slot angle could reduce the drag.Furthermore,the SST of 0.5%chord is selected due to its high gain in the corrected aerodynamic efficiency at small angles of attack.Compared with the baseline,the optimized design could increase the lift coefficient and the corrected lift-to-drag ratio by 32.1%and 93.8%respectively at the angle of attack a=4°.展开更多
A novel method was presented to create composite micelles of amphiphilic copolymers and Ag nanoparticles(NPs) in a three-dimensional co-flow focusing microfluidic device(3D CFMD). Self-assembly of the copolymers was i...A novel method was presented to create composite micelles of amphiphilic copolymers and Ag nanoparticles(NPs) in a three-dimensional co-flow focusing microfluidic device(3D CFMD). Self-assembly of the copolymers was initiated by the fast mixing of water and a blend dispersion of hydrophobic Ag NPs and amphiphilic copolymers. At the same time, the hydrophobic Ag NPs enter the core of copolymer micelles, based on the hydrophobic interaction. The copolymer-Ag NPs composite micelles have a core-shell structure with copolymer shell and Ag NPs core. COMSOL Multiphysics is used to simulate the concentration distribution of copolymers and Ag NPs under different flow rates. Co-assembly microfluidic conditions are determined based on simulation results. Under suitable microfluidic conditions, both block copolymers and gradient copolymers can co-assemble with hydrophobic Ag NPs to form composite micelles, respectively. This microfluidic coassembly method will have a good prospect in the preparation of composite micelles of amphiphilic copolymers and metal nanoparticles.展开更多
The jet co-flow packing tray(JCPT) with three different types of perforation in equal opening fraction was tested in two rectangular columns with 0.12m in width and 0.27m in length operated with air-water system. The ...The jet co-flow packing tray(JCPT) with three different types of perforation in equal opening fraction was tested in two rectangular columns with 0.12m in width and 0.27m in length operated with air-water system. The influences of gas phase orifice F-factor and clear liquid height Hc on the amount of liquid lifted, Q, were examined. The corresponding correlation between Q with F-factor and equivalent diameter of perforated holes as well as Hc was obtained. Furthermore, the non-steady state mass transfer performance of JCPT was tested by the humidification of air with water. Finally, by the analysis of data and comparison, it was found that the JCPT tray with single cap and two holes exhibited the highest mass transfer efficiency and best performance.展开更多
The effects of a co-flow on a spreading and entrainment rate of turbulent round jets have been studied numerically. The first and second order closure models are used and have been comp- ared with existing experimenta...The effects of a co-flow on a spreading and entrainment rate of turbulent round jets have been studied numerically. The first and second order closure models are used and have been comp- ared with existing experimental data. The influence of theses models on the dynamic fields is examined. The results of the models in general agree well with the trends observed experiment- tally. The co-flowing imposed noticeable restri- ctions on the spreading and the turbulent mixing. Finally, an entrainment hypothesis has been introduced to describe the development of turbulent jets issuing into a stagnant or co-flowing air. It relates the mass flow rate of the surround- ing fluid entrained into the jet to the characteristic velocity difference between the jet and the co-flow. It is obvious that the co-flow decreases considerably the entrainment of air.展开更多
Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was c...Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was conducted to test the validity of the two models.Results show that the different range of predicted reaction rates is mainly responsible for their different performances in large eddy simulation(LES)studies.In this paper,beta PDF was used to model the mixture fraction distribution,while two different shapes of PDF,delta function and beta function,were applied for the reaction progress.Compared to the FPV model,the AI model combined with beta function for reaction progress could capture the auto-ignition process and predict the exact lifted height.Also the results indicate that the variance of reaction progress plays an important role in predicting the flame lifted height.展开更多
基金supported by the Projects of Talents Recruitment of Guangdong University of Petrochemical Technology(No.2018rc14)Maoming City Science and Technology Plan Project(Nos.210427094551264 and 220415004552411).
文摘To investigate the influences of co-flowand counter-flowmodes of reactant flowarrangement on a proton exchange membrane fuel cell(PEMFC)during start-up,unsteady physical and mathematical models fully coupling the flow,heat,and electrochemical reactions in a PEMFC are established.The continuity equation and momentum equation are solved by handling pressure-velocity coupling using the SIMPLE algorithm.The electrochemical reaction rates in the catalyst layers(CLs)of the cathode and anode are calculated using the Butler-Volmer equation.The multiphase mixture model describes the multiphase transport process of gas mixtures and liquid water in the fuel cell.After validation,the influences of co-flow and counter-flow modes on the PEMFC performance are investigated,including the evolution of the current density,flow field,temperature field,and reactant concentration field during start-up,as well as the steady distribution of the current density,reactant concentration,andmembrane water content when the start-up stabilizes.Co-flow and counter-flow modes influence the current density distribution and temperature distribution.On the one hand,the co-flow mode accelerates the start-up process of the PEMFC and leads to a more evenly distributed current density than the counter-flow mode.On the other hand,the temperature difference between the inlet and outlet sections of the cell is up to 10.1℃ under the co-flow mode,much larger than the 5.0℃ observed in the counter-flow mode.Accordingly,the counter-flowmode results in a more evenly distributed temperature and a lower maximum temperature than the co-flow case.Therefore,in the flow field design of a PEMFC,the reactant flow arrangements can be considered to weigh between better heat management and higher current density distribution of the cell.
基金National Science&Technology Major Project(Grant No.2017-II-0004-0016)National Nature Science Foundation of China(Grant No.52176044)。
文摘The design objectives of modern aircraft engines include high load capacity,efficiency,and stability.With increasing loads,the phenomenon of corner separation in compressors intensifies,affecting engine performance and stability.Therefore,the adoption of appropriate flow control technology holds significant academic and engineering significance.This study employs the Reynolds-averaged Navier-Stokes(RANS)method to investigate the effects and mechanisms of active/passive Co-flow Jet(CFJ)control,implemented by introducing full-height and partial height jet slots between the suction surface and end wall of a compressor cascade.The results indicate that passive CFJ control significantly reduces the impact of corner separation at small incidence,with partial-height control further enhancing the effectiveness.The introduction of active CFJ enables separation control at large incidence,improving blade performance under different operating conditions.Active control achieves this by reducing the scale of corner separation vortices,effectively reducing the size of the separation region and enhancing blade performance.
基金supported by the National Natural Science Foundation of China(No.12072305)Equipment Field Preresearch Fund,China(No.61402060205)+1 种基金the Open Fund from Rotor Aerodynamics Key Laboratory of China Aerodynamics Research and Development Center,China(No.RAL20190303)the Aeronautics Power Foundation,China(No.6141B09050347)。
文摘The decrease in aerodynamic performance caused by the shock-induced dynamic stall of an advancing blade and the dynamic stall of a retreating blade at low speed and high angles of attack limits the flight speed of a helicopter.However,little research has been carried on the flow control methods employed to suppress both the dynamic stall induced by a shock wave and the dynamic stall occurring at high angles of attack.The dynamic stall suppression of a rotor airfoil by Co-Flow Jet(CFJ)is numerically investigated in this work.The flowfield of the airfoil is simulated by solving Reynolds Averaged Navier-Stokes equations based on the sliding mesh technique.Firstly,to improve the effect of a traditional CFJ on suppressing rotor airfoil shock-induced dynamic stall,an improved CFJ—a CFJ-sloping slot is proposed.Research shows that the CFJsloping slot suppresses the shock-induced dynamic stall more effectively than a traditional CFJ.Moreover,the improved CFJ can also suppress the dynamic stall of rotor airfoil at low speed and high angles of attack.The improved CFJ proposed in this paper is an effective flow control method that simultaneously suppresses the dynamic stall of the advancing and retreating blades.The mechanism of the improved CFJ in suppressing the dynamic stall of the rotor airfoil is studied,and a comparison is made between the improved CFJ and the traditional CFJ in terms of dynamic stall suppression at high and low speed.Finally,the effect of improved CFJ parameters(the jet momentum coefficient,the position of the injection/suction slot,and the size of the injection/suction slot)on shock-induced dynamic stall suppression is analyzed.
基金co-supported by the National Key Research and Development Program of China(No.:2017YFB1300102)the National Natural Science Foundation of China(No.:11872314)。
文摘Introducing active flow control into the design of flapping wing is an effective way to enhance its aerodynamic performance.In this paper,a novel active flow control technology called Co-Flow Jet(CFJ)is applied to flapping airfoils.The effect of CFJ on aerodynamic performance of flapping airfoils at low Reynolds number is numerically investigated using Unsteady Reynolds Averaged Navier-Stokes(URANS)simulation with Spalart-Allmaras(SA)turbulence model.Numerical methods are validated by a NACA6415-based CFJ airfoil case and a S809 pitching airfoil case.Then NACA6415 baseline airfoil and NACA6415-based CFJ airfoil with jet-off and jet-on are simulated in flapping motion,with Reynolds number 70,000 and reduced frequency 0.2.As a result,CFJ airfoils with jet-on generally have better lift and thrust characteristics than baseline airfoils and jet-off airfoil when Cμgreater than 0.04,which results from the CFJ effect of reducing flow separation by injecting high-energy fluid into boundary layer.Besides,typical kinematic and geometric parameters,including the reduced frequency and the positions of the suction and injection slot,are systematically studied to figure out their influence on aerodynamic performance of the CFJ airfoil.And a variable Cμjet control strategy is proposed to further improve effective propulsive efficiency.Compared with using constant Cμ,an increase of effective propulsive efficiency by22.6%has been achieved by using prescribed variable CμNACA6415-based CFJ airfoil at frequency 0.2.This study may provide some guidance to performance enhancement for Flapping wing Micro Air Vehicles(FMAV).
基金supported by the National Natural Science Foundation of China(No.11672133)the Research Funds for Central Universities(No.kfjj20180104)support from Rotor Aerodynamics Key Laboratory(No.RAL20190202-2)。
文摘The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet(CFJ)airfoil with simple high-lift device configuration,with a specific goal to examine the feasibility and capability of the proposed configuration for low-speed take-off and landing.Computations have been accomplished by an in-house-programmed Reynoldsaveraged Navier-Stokes solver enclosed by k-ωshear stress transport turbulence model.Three crucial geometric parameters,viz.,injection slot location,suction slot location and its angle were selected for the sake of revealing their effects on aerodynamic lift,drag,power consumption and equivalent lift-to-drag ratio.Results show that using simple high-lift devices on CFJ airfoil can significantly augment the aerodynamic associated lift and efficiency which evidences the feasibility of CFJ for short take-off and landing with small angle of attack.The injection and suction slot locations are more influential with respect to the aerodynamic performance of CFJ airfoil compared with the suction slot angle.The injection location is preferable to be located in the downstream of the pressure suction peak on leading edge to reduce the power expenditure of the pumping system for a relative higher equivalent lift-to-drag ratio.Another concluded criterion is that the suction slot should be oriented on the trailing edge flap for achieving more aerodynamic gain,meanwhile,carefully selecting this location is crucial in determining the aerodynamic enhancement of CFJ airfoil with deflected flaps.
基金the National Natural Science Foundation of China (No. 11672133)the Fundamental Research Funds for the Central Universities, China (No. kfjj20180104)support from Rotor Aerodynamics Key Laboratory, China (No. RAL20190202-2/RAL20190101-1)
文摘Numerical investigations are conducted to explore the aerodynamic characteristics of three-dimensional Co-Flow Jet(CFJ) wing with simple high-lift devices during low-speed takeoff and landing. Effects of three crucial parameters of CFJ wing, i.e., angle of attack, jet momentum and swept angle, are comprehensively examined. Additionally, the aerodynamic characteristics of two CFJ configurations, i.e., using open and discrete slots for injection, are compared. The results show that applying CFJ technique to a wing with simple high-lift device is able to generate more lift,reduce drag and enlarge stall margin with lower energy expenditure due to the super-circulation effect. Increasing the jet intensity can reduce the drag significantly, which is mainly contributed by the reaction jet force. The Oswald efficiency factor is, in some circumstances, larger than one,which indicates the potential of CFJ in reducing induced drag. Compared with clean wing configuration, using CFJ technique allows the aerodynamic force variation less sensitive to the swept angle, and such phenomenon is better observed for small swept angle region. Eventually, it is interesting to know that the discrete slotted CFJ configuration demonstrates a promising enhancement in aerodynamic performance in terms of high lift, low drag and efficiency.
基金supported by the National Natural Science Foundation of China(Nos.12102431,12002340,and 11902320).
文摘Both the Active Flow Control(AFC)and the variable-camber technology are considered as efficient ways to enhance the aerodynamic performance of an aircraft.The present study investigated the feasibility of the combination of a Co-Flow Jet(CFJ)airfoil and a parabolic flap,where the Reynolds Average Navier-Stokes(RANS)equations and the Spalart-Allmaras(S-A)turbulence model were exploited for the numerical simulation.Several significant geometric parameters,including the injection slot location,the suction slot location,the injection slot angle,the suction slot angle and the airfoil Suction Surface Translation(SST),were selected to study their effects on the aerodynamics of the proposed configuration.Then,an optimized design was created and compared with the baseline airfoil.The results show that the CFJ airfoil combined with the parabolic flap is more beneficial to the aerodynamic performance enhancement at small angles of attack.It is preferable to locate the injection slot at a 2%chord-wise location and the suction slot at a 75%chord-wise location.Both the decrease of the injection slot angle and the augmentation of the suction slot angle could reduce the drag.Furthermore,the SST of 0.5%chord is selected due to its high gain in the corrected aerodynamic efficiency at small angles of attack.Compared with the baseline,the optimized design could increase the lift coefficient and the corrected lift-to-drag ratio by 32.1%and 93.8%respectively at the angle of attack a=4°.
基金Funded by the National Natural Science Foundation of China(Nos.51873167 and 50803048)
文摘A novel method was presented to create composite micelles of amphiphilic copolymers and Ag nanoparticles(NPs) in a three-dimensional co-flow focusing microfluidic device(3D CFMD). Self-assembly of the copolymers was initiated by the fast mixing of water and a blend dispersion of hydrophobic Ag NPs and amphiphilic copolymers. At the same time, the hydrophobic Ag NPs enter the core of copolymer micelles, based on the hydrophobic interaction. The copolymer-Ag NPs composite micelles have a core-shell structure with copolymer shell and Ag NPs core. COMSOL Multiphysics is used to simulate the concentration distribution of copolymers and Ag NPs under different flow rates. Co-assembly microfluidic conditions are determined based on simulation results. Under suitable microfluidic conditions, both block copolymers and gradient copolymers can co-assemble with hydrophobic Ag NPs to form composite micelles, respectively. This microfluidic coassembly method will have a good prospect in the preparation of composite micelles of amphiphilic copolymers and metal nanoparticles.
文摘The jet co-flow packing tray(JCPT) with three different types of perforation in equal opening fraction was tested in two rectangular columns with 0.12m in width and 0.27m in length operated with air-water system. The influences of gas phase orifice F-factor and clear liquid height Hc on the amount of liquid lifted, Q, were examined. The corresponding correlation between Q with F-factor and equivalent diameter of perforated holes as well as Hc was obtained. Furthermore, the non-steady state mass transfer performance of JCPT was tested by the humidification of air with water. Finally, by the analysis of data and comparison, it was found that the JCPT tray with single cap and two holes exhibited the highest mass transfer efficiency and best performance.
文摘The effects of a co-flow on a spreading and entrainment rate of turbulent round jets have been studied numerically. The first and second order closure models are used and have been comp- ared with existing experimental data. The influence of theses models on the dynamic fields is examined. The results of the models in general agree well with the trends observed experiment- tally. The co-flowing imposed noticeable restri- ctions on the spreading and the turbulent mixing. Finally, an entrainment hypothesis has been introduced to describe the development of turbulent jets issuing into a stagnant or co-flowing air. It relates the mass flow rate of the surround- ing fluid entrained into the jet to the characteristic velocity difference between the jet and the co-flow. It is obvious that the co-flow decreases considerably the entrainment of air.
基金supported by the National Natural Science Foundation of China(Grant Nos.51176178 and 50936005)
文摘Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was conducted to test the validity of the two models.Results show that the different range of predicted reaction rates is mainly responsible for their different performances in large eddy simulation(LES)studies.In this paper,beta PDF was used to model the mixture fraction distribution,while two different shapes of PDF,delta function and beta function,were applied for the reaction progress.Compared to the FPV model,the AI model combined with beta function for reaction progress could capture the auto-ignition process and predict the exact lifted height.Also the results indicate that the variance of reaction progress plays an important role in predicting the flame lifted height.
