The vibration characteristics of transverse oscillation of an axially moving beam with high velocity is in- vestigated. The vibration equation and boundary conditions of the free-free axially moving beam are derived u...The vibration characteristics of transverse oscillation of an axially moving beam with high velocity is in- vestigated. The vibration equation and boundary conditions of the free-free axially moving beam are derived using Hamilton＇s principle. Furthermore, the linearized equations are set up based on Galerkinl s method for the ap- proximation solution. Finally, three influencing factors on the vibration frequency of the beam are considered： （1） The axially moving speed. The first order natural frequency decreases as the axial velocity increases, so there is a critical velocity of the axially moving beam. （2） The mass loss. The changing of the mass density of some part of the beam increases the beam natural frequencies. （3） The thermal effect.＇ The temperature increase will decrease the beam elastic modulus and induce the vibration frequencies descending.展开更多
Under the guidance of the major two-period research program of the National Natural Science Foundation of China,the hypersonic technique has steadily matured.Further development of its core component-the airbreathing ...Under the guidance of the major two-period research program of the National Natural Science Foundation of China,the hypersonic technique has steadily matured.Further development of its core component-the airbreathing hypersonic propulsion system,and of some novel concepts of the combined cycle engine,is needed urgently to meet the power requirements of single/two-stage-to-orbit manned spacecraft and hypersonic aircraft,such as the SR-72(Fig.1).However,the resident time of the high-speed flow in the scramjet combustor is very limited,only a few milliseconds,and the generation of useful thrust through additional heat at such high speeds is still a challenging task(Huang et al.,2019).Therefore,many mixing augmentation devices have been proposed and investigated,as well as flame propagation and stabilization mechanisms in the supersonic or hypersonic flow(Huang et al.,2018).Fig.2 shows the operational process in an airbreathing hypersonic propulsion system.The developed computational fluid dynamics(CFD)approaches,such as the efficient WENOCU4 developed by Li et al.(2020),have contributed greatly to ground experimental testing,especially of approaches with high-order accuracy.展开更多
This paper reports the direct numerical simulation (DNS) for hypersonic turbulent boundary layer over a flat-plate at Ma∞ =8 with the ratio of wall-to-freestream temperature equal to 1.9, which indicates an extremely...This paper reports the direct numerical simulation (DNS) for hypersonic turbulent boundary layer over a flat-plate at Ma∞ =8 with the ratio of wall-to-freestream temperature equal to 1.9, which indicates an extremely cold wall condition. It is primarily used to assess the wall temperature effects on the mean velocity profile, Walz equation, turbulent intensity, strong Reynolds analogy (SRA), and compressibility. The present high Mach number with cold wall condition induces strong compressibility effects. As a result, the Morkovin's hypothesis is not fully valid and so the classical SRA is also not fully consistent. However, some modified SRA is still valid at the far-wall region. It is also verified that the semi-local wall coordinate y* is better than conventional y+ in analysis of statistics features in turbulent boundary layer (TBL) in hypersonic flow.展开更多
In this study, comparative heat flux measurements for a sharp cone model were conducted by utilizing a high enthalpy shock tunnel JF-10 and a large-scale shock tunnel JF-12, responsible for providing nonequilibrium an...In this study, comparative heat flux measurements for a sharp cone model were conducted by utilizing a high enthalpy shock tunnel JF-10 and a large-scale shock tunnel JF-12, responsible for providing nonequilibrium and perfect gas flows, respectively. Experiments were performed at the Key Laboratory of High Temperature Gas Dynamics(LHD), Institute of Mechanics, Chinese Academy of Sciences. Corresponding numerical simulations were also conducted in effort to better understand the phenomena accompanying in these experiments. By assessing the consistency and accuracy of all the data gathered during this study, a detailed comparison of sharp cone heat transfer under a totally different kind of freestream conditions was build and analyzed. One specific parameter, defined as the product of the Stanton number and the square root of the Reynold number, was found to be more characteristic for the aerodynamic heating phenomena encountered in hypersonic flight. Adequate use of said parameter practically eliminates the variability caused by the deferent flow conditions, regardless of whether the flow is in dissociation or the boundary condition is catalytic. Essentially, the parameter identified in this study reduces the amount of ground experimental data necessary and eases data extrapolation to flight.展开更多
A rapid approach to hypersonic aeroheating predictions in the stagnation region and downstream is developed in the present paper.The engineering method is used to calculate inviscid hypersonic flowfields to reduce tim...A rapid approach to hypersonic aeroheating predictions in the stagnation region and downstream is developed in the present paper.The engineering method is used to calculate inviscid hypersonic flowfields to reduce time cost,and a combination of the mass flow balance technique and the axisymmetric analog is proposed to account for the entropy swallowing effects.A three-dimensional linear method is derived to fit the vehicle surface flowfields.Then a new axisymmetric analog method based on linear flowfields and linear surface equations is developed,with the complexity and computational cost reduced dramatically.In the stagnation region,an implicit surface fitting is introduced to approximate the primary curvatures and a robust aeroheating prediction method is constructed.The proposed approach is verified on a variety of configurations including spherically blunted cone,double ellipsoid and aerospace vehicle.Numerical results indicate the followings:1)The approach predicts aeroheating in about one second and the results agree well with CFD simulations and wind-tunnel measurements;2)with the help of entropy correction,the precision is further improved in the streamline diverging regions on the vehicle surface,while little improvement is found after entropy correction in the regions where the streamlines do not diverge.展开更多
Tsien summarized the similarity in hypersonic flows, and related Knudsen number to Mach number and Reynolds number. Recently, a path-based problem, aero-optical effect, arises in hypersonic flows, and it concerns abou...Tsien summarized the similarity in hypersonic flows, and related Knudsen number to Mach number and Reynolds number. Recently, a path-based problem, aero-optical effect, arises in hypersonic flows, and it concerns about the compressibility and the Knudsen number of the gas flows, which differs from the Tsien's focus to some extent. In this paper, the similarity of hypersonic aero optics is theoretically studied, and both flow fields and induced aero-optical effect after flows pass through a cylinder are predicted by a well-accepted particle-based method, direct simulation Monte-Carlo(DSMC) method. The results show that the optical distortions are inversely proportional to the Knudsen number, while the compressibility plays an important role in the optical degradations.Hence, it is confirmed that the effects of Mach number and Knudsen number on the aero-optical effect induced by hypersonic flows are of great significance. Besides, since the Knudsen number is defined straightforwardly based on the optically active region, the physics is clearer than any other similarity criteria.展开更多
基金Supported by the National Natural Science Foundation of China(10972104)~~
文摘The vibration characteristics of transverse oscillation of an axially moving beam with high velocity is in- vestigated. The vibration equation and boundary conditions of the free-free axially moving beam are derived using Hamilton＇s principle. Furthermore, the linearized equations are set up based on Galerkinl s method for the ap- proximation solution. Finally, three influencing factors on the vibration frequency of the beam are considered： （1） The axially moving speed. The first order natural frequency decreases as the axial velocity increases, so there is a critical velocity of the axially moving beam. （2） The mass loss. The changing of the mass density of some part of the beam increases the beam natural frequencies. （3） The thermal effect.＇ The temperature increase will decrease the beam elastic modulus and induce the vibration frequencies descending.
文摘Under the guidance of the major two-period research program of the National Natural Science Foundation of China,the hypersonic technique has steadily matured.Further development of its core component-the airbreathing hypersonic propulsion system,and of some novel concepts of the combined cycle engine,is needed urgently to meet the power requirements of single/two-stage-to-orbit manned spacecraft and hypersonic aircraft,such as the SR-72(Fig.1).However,the resident time of the high-speed flow in the scramjet combustor is very limited,only a few milliseconds,and the generation of useful thrust through additional heat at such high speeds is still a challenging task(Huang et al.,2019).Therefore,many mixing augmentation devices have been proposed and investigated,as well as flame propagation and stabilization mechanisms in the supersonic or hypersonic flow(Huang et al.,2018).Fig.2 shows the operational process in an airbreathing hypersonic propulsion system.The developed computational fluid dynamics(CFD)approaches,such as the efficient WENOCU4 developed by Li et al.(2020),have contributed greatly to ground experimental testing,especially of approaches with high-order accuracy.
基金supported by the National Nature Science Foundation of China(Grant No. 11072248)the National Basic Research Program(Grant No. 2009CB724100)+1 种基金the National High-tech R&D Program(No.2012AA01A304)the CAS Information Project(INFO-115-B01)
文摘This paper reports the direct numerical simulation (DNS) for hypersonic turbulent boundary layer over a flat-plate at Ma∞ =8 with the ratio of wall-to-freestream temperature equal to 1.9, which indicates an extremely cold wall condition. It is primarily used to assess the wall temperature effects on the mean velocity profile, Walz equation, turbulent intensity, strong Reynolds analogy (SRA), and compressibility. The present high Mach number with cold wall condition induces strong compressibility effects. As a result, the Morkovin's hypothesis is not fully valid and so the classical SRA is also not fully consistent. However, some modified SRA is still valid at the far-wall region. It is also verified that the semi-local wall coordinate y* is better than conventional y+ in analysis of statistics features in turbulent boundary layer (TBL) in hypersonic flow.
基金the National Natural Science Foundation of China(Grant Nos.1140227511472280 and 11532014)
文摘In this study, comparative heat flux measurements for a sharp cone model were conducted by utilizing a high enthalpy shock tunnel JF-10 and a large-scale shock tunnel JF-12, responsible for providing nonequilibrium and perfect gas flows, respectively. Experiments were performed at the Key Laboratory of High Temperature Gas Dynamics(LHD), Institute of Mechanics, Chinese Academy of Sciences. Corresponding numerical simulations were also conducted in effort to better understand the phenomena accompanying in these experiments. By assessing the consistency and accuracy of all the data gathered during this study, a detailed comparison of sharp cone heat transfer under a totally different kind of freestream conditions was build and analyzed. One specific parameter, defined as the product of the Stanton number and the square root of the Reynold number, was found to be more characteristic for the aerodynamic heating phenomena encountered in hypersonic flight. Adequate use of said parameter practically eliminates the variability caused by the deferent flow conditions, regardless of whether the flow is in dissociation or the boundary condition is catalytic. Essentially, the parameter identified in this study reduces the amount of ground experimental data necessary and eases data extrapolation to flight.
基金supported by the Doctorate Creation Foundation of Northwestern Polytechnical University (Grant No. CX200902)
文摘A rapid approach to hypersonic aeroheating predictions in the stagnation region and downstream is developed in the present paper.The engineering method is used to calculate inviscid hypersonic flowfields to reduce time cost,and a combination of the mass flow balance technique and the axisymmetric analog is proposed to account for the entropy swallowing effects.A three-dimensional linear method is derived to fit the vehicle surface flowfields.Then a new axisymmetric analog method based on linear flowfields and linear surface equations is developed,with the complexity and computational cost reduced dramatically.In the stagnation region,an implicit surface fitting is introduced to approximate the primary curvatures and a robust aeroheating prediction method is constructed.The proposed approach is verified on a variety of configurations including spherically blunted cone,double ellipsoid and aerospace vehicle.Numerical results indicate the followings:1)The approach predicts aeroheating in about one second and the results agree well with CFD simulations and wind-tunnel measurements;2)with the help of entropy correction,the precision is further improved in the streamline diverging regions on the vehicle surface,while little improvement is found after entropy correction in the regions where the streamlines do not diverge.
文摘Tsien summarized the similarity in hypersonic flows, and related Knudsen number to Mach number and Reynolds number. Recently, a path-based problem, aero-optical effect, arises in hypersonic flows, and it concerns about the compressibility and the Knudsen number of the gas flows, which differs from the Tsien's focus to some extent. In this paper, the similarity of hypersonic aero optics is theoretically studied, and both flow fields and induced aero-optical effect after flows pass through a cylinder are predicted by a well-accepted particle-based method, direct simulation Monte-Carlo(DSMC) method. The results show that the optical distortions are inversely proportional to the Knudsen number, while the compressibility plays an important role in the optical degradations.Hence, it is confirmed that the effects of Mach number and Knudsen number on the aero-optical effect induced by hypersonic flows are of great significance. Besides, since the Knudsen number is defined straightforwardly based on the optically active region, the physics is clearer than any other similarity criteria.
