Parabolic through concentrators and parabolic dish concentrators followed by a PVR （pressurized volumetric receiver） are proposed, studying the performance behavior of a RCBC （regenerative closed Brayton cycle） op...Parabolic through concentrators and parabolic dish concentrators followed by a PVR （pressurized volumetric receiver） are proposed, studying the performance behavior of a RCBC （regenerative closed Brayton cycle） operating with helium or hydrogen. A pressurized gas such as helium circulates along the volumetric receiver, capturing the concentrated thermal solar energy to be further converted into electric power via a thermal cycle. The overall efficiency of the plant has been computed under variable parameters to determine the operating conditions for which efficiency and specific power are acceptable. As consequence of the proposed analysis, it is concluded that direct coupling between volumetric receivers and thermal engines renders high efficiency while avoiding an intermediate heat transfer medium.展开更多
One of the crucial factors affecting the carrying capacity of the cryogenic liquid launch vehicle is the effective volume of the tank.Theoretical and experimental investigations on vortex breaker mechanisms have propo...One of the crucial factors affecting the carrying capacity of the cryogenic liquid launch vehicle is the effective volume of the tank.Theoretical and experimental investigations on vortex breaker mechanisms have proposed promising schemes applied in the oxygen tank of the liquid-propellant launch vehicle to ensure the normal operation of the engine.In this paper,the liquid surface profile functions of the laminar core when the vortex generates were derived based on the Rankine vortex model.The dimensionless residual volume V/d3 and the Froude number were applied to compare the theoretical prediction of critical height with the actual simulation data of liquid oxygen.This comparison method can improve the model’s accuracy.The efficiency of different basic shapes of vortex breakers was tested by conducting CFD modelling on a non-vertical outflow tank under a specific operating condition.Simulation results suggest negligible effects of heat transfer and surface tension.A circular plate is considered the optimal vortex breaker shape in traditional vertical outflow tanks,while a higher optimize efficiency was discovered in the half baffle basic shape in a non-vertical outflow tank by comparing the dimensionless residual volume and flow coefficient.A 34.26%reduction in flow resistance of half baffle breaker can be reached when applying a twenty-degree outlet pipe chamfering setting compared to a zero-degree chamfer.Considering practical operating limitations,it is concluded that a vortex breaker mechanism in a half baffle basic shape with a radius of 2.5d and a height of 4/d is the optimal scheme,which is suitable for all types of tanks.Its optimization efficiency of the residual volume reduction is about 56.68%compared to a nobreaker installation case.Lastly,a general equation based on CFD simulation for predicting the residual volume under a certain outflow velocity was proposed:V=d3yaFr0:3,which trend is consistent with that of mathematical prediction V=d3yaFr1=3.This consistency proves the accuracy and applicability of optimization strategy in this paper.展开更多
This paper focuses on the experimental investigation of the time-averaged and time-accurate aero- thermodynamics of a second stator tested in a 1.5 stage high-pressure turbine. The effect of clocking on aerodynamic an...This paper focuses on the experimental investigation of the time-averaged and time-accurate aero- thermodynamics of a second stator tested in a 1.5 stage high-pressure turbine. The effect of clocking on aerodynamic and heat transfer are investigated. Tests are performed under engine representative conditions in the VKI compression tube CT3. The test program includes four different clocking positions, i.e. relative pitch-wise positions between the fh-st and the second stator. Probes located upstream and downstream of the second stator provide the thermodynamic conditions of the flow field. On the second stator airfoil, measurements are taken around the blade profile at 15, 50 and 85% span with pressure sensors and thin-film gauges. Both time-averaged and time-resolved aspects of the flow field are addressed. Regarding the time-averaged results, clocking effects are mainly observed within the leading edge region of the second stator, the largest effects being observed at 15% span. The surface static pressure distribution is changed locally, hence affecting the overall airfoil performance. For one clocking position, the thermal load of the airfoil is noticeably reduced. Pressure fluctuations are attributed to the passage of the up- stream transonic rotor and its associated pressure gradients. The pattern of these fluctuations changes noticeably as a function of docking. The time-resolved variations of heat flux and static pressure are analyzed together showing that the major effect is due to a potential interaction. The time-resolved pressure distribution integrated along the second stator surface yields the unsteady forces on the vane. The magnitude of the unsteady force is very dependent on the clocking position.展开更多
Rolling contact fatigue(RCF)issues,such as pitting,might occur on bevel gears because load fluctuation induces considerable subsurface stress amplitudes.Such issues can dramatically affect the service life of associat...Rolling contact fatigue(RCF)issues,such as pitting,might occur on bevel gears because load fluctuation induces considerable subsurface stress amplitudes.Such issues can dramatically affect the service life of associated machines.An accurate geometry model of a hypoid gear utilized in the main reducer of a heavy-duty vehicle is developed in this study with the commercial gear design software MASTA.Multiaxial stress–strain states are simulated with the finite element method,and the RCF life is predicted using the Brown–Miller–Morrow fatigue criterion.The patterns of fatigue life on the tooth surface are simulated under various loading levels,and the RCF S–N curve is numerically generated.Moreover,a typical torque–time history on the driven axle is described,followed by the construction of program load spectrum with the rain flow method and the Goodman mean stress equation.The effects of various fatigue damage accumulation rules on fatigue life are compared and discussed in detail.Predicted results reveal that the Miner linear rule provides the most optimistic result among the three selected rules,and the Manson bilinear rule produces the most conservative result.展开更多
A similitude method to model the tip clearance flow in a high-speed compressor with a low-speed model is presented in this paper.The first step of this method is the derivation of similarity criteria for tip clearance...A similitude method to model the tip clearance flow in a high-speed compressor with a low-speed model is presented in this paper.The first step of this method is the derivation of similarity criteria for tip clearance flow,on the basis of an inviscid model of tip clearance flow.The aerodynamic parameters needed for the model design are then obtained from a numerical simulation of the target high-speed compressor rotor.According to the aerodynamic and geometric parameters of the target compressor rotor,a large-scale low-speed rotor blade is designed with an inverse blade design program.In order to validate the similitude method,the features of tip clearance flow in the low-speed model compressor are compared with the ones in the high-speed compressor at both design and small flow rate points.It is found that not only the trajectory of the tip leakage vortex but also the interface between the tip leakage flow and the incoming main flow in the high-speed compressor match well with that of its low speed model.These results validate the effectiveness of the similitude method for the tip clearance flow proposed in this paper.展开更多
This paper reports on an experimental and numerical study at low Reynolds number in order to evaluate the influence of the Coriolis forces on the flow in radial rotating channels. Operating conditions correspond to th...This paper reports on an experimental and numerical study at low Reynolds number in order to evaluate the influence of the Coriolis forces on the flow in radial rotating channels. Operating conditions correspond to the flow in radial impellers for micro gasturbine applications. A comparison of detailed flow measurements with CFD resuits indicates that Navier Stokes solvers with standard k-ω and SST turbulence models predict the flow surprisingly well and that no extra corrections for Coriolis forces are required at these operating conditions展开更多
Reducing the influence of back-sputtering effect can effectively improve the accuracy of the measurement of the Hall thruster plume effect.Quartz crystal microbalance(QCM)was used to measure the deposition and sputter...Reducing the influence of back-sputtering effect can effectively improve the accuracy of the measurement of the Hall thruster plume effect.Quartz crystal microbalance(QCM)was used to measure the deposition and sputtering distribution of HET-40 thruster plume on two different experimental conditions:case1,using liquid nitrogen heat sinks and case 2,without using liquid nitrogen heat sinks.Meanwhile,X-ray photoelectron spectroscopy(XPS)was used to analyze the composition of the QCM surface after two experiments.The results of the two experiments showed that the sputtering rate under the condition of case 1 was slightly higher than case 2.Especially within the range of 90°to 110°relative to the thruster axis,case 1 experiment result showed sputtering effect,while case 2 experiment showed deposition effect.Through analysis of the experimental results,it can be found that using liquid nitrogen heat sink to reduce the temperature of the inner wall surface of vacuum chamber can effectively adsorb the particles sputtered by the plume and reduce the concentration of back-sputtering particles,leading to the above phenomenon.展开更多
文摘Parabolic through concentrators and parabolic dish concentrators followed by a PVR （pressurized volumetric receiver） are proposed, studying the performance behavior of a RCBC （regenerative closed Brayton cycle） operating with helium or hydrogen. A pressurized gas such as helium circulates along the volumetric receiver, capturing the concentrated thermal solar energy to be further converted into electric power via a thermal cycle. The overall efficiency of the plant has been computed under variable parameters to determine the operating conditions for which efficiency and specific power are acceptable. As consequence of the proposed analysis, it is concluded that direct coupling between volumetric receivers and thermal engines renders high efficiency while avoiding an intermediate heat transfer medium.
文摘One of the crucial factors affecting the carrying capacity of the cryogenic liquid launch vehicle is the effective volume of the tank.Theoretical and experimental investigations on vortex breaker mechanisms have proposed promising schemes applied in the oxygen tank of the liquid-propellant launch vehicle to ensure the normal operation of the engine.In this paper,the liquid surface profile functions of the laminar core when the vortex generates were derived based on the Rankine vortex model.The dimensionless residual volume V/d3 and the Froude number were applied to compare the theoretical prediction of critical height with the actual simulation data of liquid oxygen.This comparison method can improve the model’s accuracy.The efficiency of different basic shapes of vortex breakers was tested by conducting CFD modelling on a non-vertical outflow tank under a specific operating condition.Simulation results suggest negligible effects of heat transfer and surface tension.A circular plate is considered the optimal vortex breaker shape in traditional vertical outflow tanks,while a higher optimize efficiency was discovered in the half baffle basic shape in a non-vertical outflow tank by comparing the dimensionless residual volume and flow coefficient.A 34.26%reduction in flow resistance of half baffle breaker can be reached when applying a twenty-degree outlet pipe chamfering setting compared to a zero-degree chamfer.Considering practical operating limitations,it is concluded that a vortex breaker mechanism in a half baffle basic shape with a radius of 2.5d and a height of 4/d is the optimal scheme,which is suitable for all types of tanks.Its optimization efficiency of the residual volume reduction is about 56.68%compared to a nobreaker installation case.Lastly,a general equation based on CFD simulation for predicting the residual volume under a certain outflow velocity was proposed:V=d3yaFr0:3,which trend is consistent with that of mathematical prediction V=d3yaFr1=3.This consistency proves the accuracy and applicability of optimization strategy in this paper.
基金the European Commission as part of the BRITE EuRAM Ⅲ BE97-4440 project Turbine Aero-Thermal Extermal Flowthe contributions of the industrial partners ALSTOM POWER,FIAT AVIO,ITP,SNECMA and TURBOMECA
文摘This paper focuses on the experimental investigation of the time-averaged and time-accurate aero- thermodynamics of a second stator tested in a 1.5 stage high-pressure turbine. The effect of clocking on aerodynamic and heat transfer are investigated. Tests are performed under engine representative conditions in the VKI compression tube CT3. The test program includes four different clocking positions, i.e. relative pitch-wise positions between the fh-st and the second stator. Probes located upstream and downstream of the second stator provide the thermodynamic conditions of the flow field. On the second stator airfoil, measurements are taken around the blade profile at 15, 50 and 85% span with pressure sensors and thin-film gauges. Both time-averaged and time-resolved aspects of the flow field are addressed. Regarding the time-averaged results, clocking effects are mainly observed within the leading edge region of the second stator, the largest effects being observed at 15% span. The surface static pressure distribution is changed locally, hence affecting the overall airfoil performance. For one clocking position, the thermal load of the airfoil is noticeably reduced. Pressure fluctuations are attributed to the passage of the up- stream transonic rotor and its associated pressure gradients. The pattern of these fluctuations changes noticeably as a function of docking. The time-resolved variations of heat flux and static pressure are analyzed together showing that the major effect is due to a potential interaction. The time-resolved pressure distribution integrated along the second stator surface yields the unsteady forces on the vane. The magnitude of the unsteady force is very dependent on the clocking position.
基金The work was supported by the National Natural Science Foundation of China(Grant No.U1864210)the Open Foundation of the State Key Laboratory of Mechanical Transmissions(Grant No.SKLMT-KFKT-201701)Chongqing Research Program of Basic Research and Frontier Technology(Grant No.cstc2017jcyjAX0103).
文摘Rolling contact fatigue(RCF)issues,such as pitting,might occur on bevel gears because load fluctuation induces considerable subsurface stress amplitudes.Such issues can dramatically affect the service life of associated machines.An accurate geometry model of a hypoid gear utilized in the main reducer of a heavy-duty vehicle is developed in this study with the commercial gear design software MASTA.Multiaxial stress–strain states are simulated with the finite element method,and the RCF life is predicted using the Brown–Miller–Morrow fatigue criterion.The patterns of fatigue life on the tooth surface are simulated under various loading levels,and the RCF S–N curve is numerically generated.Moreover,a typical torque–time history on the driven axle is described,followed by the construction of program load spectrum with the rain flow method and the Goodman mean stress equation.The effects of various fatigue damage accumulation rules on fatigue life are compared and discussed in detail.Predicted results reveal that the Miner linear rule provides the most optimistic result among the three selected rules,and the Manson bilinear rule produces the most conservative result.
基金supported by National Natural Science Foundation of China(No.51206164,No.51106153,No.51236001)Chinese Academy of Sciences Visiting Professorship for Senior International Scientists Grant No.2001T2G01
文摘A similitude method to model the tip clearance flow in a high-speed compressor with a low-speed model is presented in this paper.The first step of this method is the derivation of similarity criteria for tip clearance flow,on the basis of an inviscid model of tip clearance flow.The aerodynamic parameters needed for the model design are then obtained from a numerical simulation of the target high-speed compressor rotor.According to the aerodynamic and geometric parameters of the target compressor rotor,a large-scale low-speed rotor blade is designed with an inverse blade design program.In order to validate the similitude method,the features of tip clearance flow in the low-speed model compressor are compared with the ones in the high-speed compressor at both design and small flow rate points.It is found that not only the trajectory of the tip leakage vortex but also the interface between the tip leakage flow and the incoming main flow in the high-speed compressor match well with that of its low speed model.These results validate the effectiveness of the similitude method for the tip clearance flow proposed in this paper.
文摘This paper reports on an experimental and numerical study at low Reynolds number in order to evaluate the influence of the Coriolis forces on the flow in radial rotating channels. Operating conditions correspond to the flow in radial impellers for micro gasturbine applications. A comparison of detailed flow measurements with CFD resuits indicates that Navier Stokes solvers with standard k-ω and SST turbulence models predict the flow surprisingly well and that no extra corrections for Coriolis forces are required at these operating conditions
文摘Reducing the influence of back-sputtering effect can effectively improve the accuracy of the measurement of the Hall thruster plume effect.Quartz crystal microbalance(QCM)was used to measure the deposition and sputtering distribution of HET-40 thruster plume on two different experimental conditions:case1,using liquid nitrogen heat sinks and case 2,without using liquid nitrogen heat sinks.Meanwhile,X-ray photoelectron spectroscopy(XPS)was used to analyze the composition of the QCM surface after two experiments.The results of the two experiments showed that the sputtering rate under the condition of case 1 was slightly higher than case 2.Especially within the range of 90°to 110°relative to the thruster axis,case 1 experiment result showed sputtering effect,while case 2 experiment showed deposition effect.Through analysis of the experimental results,it can be found that using liquid nitrogen heat sink to reduce the temperature of the inner wall surface of vacuum chamber can effectively adsorb the particles sputtered by the plume and reduce the concentration of back-sputtering particles,leading to the above phenomenon.
