This paper theoretically analyzed the jet field of laser spraying method of coaxial type.The results that were got by means of analyzing the model of axisymmetric turbulent jet field showed that jet field consists of ...This paper theoretically analyzed the jet field of laser spraying method of coaxial type.The results that were got by means of analyzing the model of axisymmetric turbulent jet field showed that jet field consists of two parts,flow developing region and fully developed flow region.In flow develop- ing region exists a potential core region of a constant initial jet velocity.Using π theorem,we have got the relations of u_m∝C(1/x)and b∝x,and the form that velo city distribution has series solution of Tollmien type.This paper provides theo- retical basis for nozzle design,choice of spraying conditions and explanation of spraying phenomena of laser spraying method.展开更多
Stabilities of supersonic jets are examined with different velocities, momentum thicknesses, and core temperatures. Amplification rates of instability waves at inlet are evaluated by linear stability theory （LST）. I...Stabilities of supersonic jets are examined with different velocities, momentum thicknesses, and core temperatures. Amplification rates of instability waves at inlet are evaluated by linear stability theory （LST）. It is found that increased velocity and core temperature would increase amplification rates substantially and such influence varies for different azimuthal wavenumbers. The most unstable modes in thin momentum thickness cases usually have higher frequencies and azimuthal wavenumbers. Mode switching is observed for low azimuthal wavenumbers, but it appears merely in high velocity cases. In addition, the results provided by linear parabolized stability equations show that the mean-flow divergence affects the spatial evolution of instability waves greatly. The most amplified instability waves globally are sometimes found to be different from that given by LST.展开更多
This paper is devoted to the study of the shape of the free boundary for a threedimensional axisymmetric incompressible impinging jet.To be more precise,we will show that the free boundary is convex to the fluid,provi...This paper is devoted to the study of the shape of the free boundary for a threedimensional axisymmetric incompressible impinging jet.To be more precise,we will show that the free boundary is convex to the fluid,provided that the uneven ground is concave to the fluid.展开更多
It is of great practical and theoretical importance to study the properties and flow behavior of laminar jet,because it tightly links the physical phenomena of nonlinerity such as flow stability and transition and so ...It is of great practical and theoretical importance to study the properties and flow behavior of laminar jet,because it tightly links the physical phenomena of nonlinerity such as flow stability and transition and so forth.However,many problems and differences exist in ba- sic concepts and in understanding of stable and transitional properties and flow patterns of ax- isymmetric laminar jet.Therefore,a further study on this subject is needed to evaluate the exist- ing understandings and to find out the mechanism governing the behavior of actual axisymmetric laminar jet flow. In this thesis,the flow behavior of axisymmetric laminar jet issuing from nozzles of several diameters in the direction of gravity was studied experimentally using flow visualization tech- nique in the range of Reynolds number from tens to thousands.The unstable and transitional processes in the laminar jet were observed.The influence on the jet flow of different geometry contours of jet chamber boundary was investigated.Some new flow phenomena were discovered which gave deeper understanding of flow patterns and their dependent factors in low Reynolds number axisymmetric laminar jet.A theoretical model to describe the variation of the axisym- metric laminar jet length influenced by the weak density difference is proposed based on the ex- perimental observation,which will be helpful in recognizing the flow behavior of axisymmetric laminar jet of low Reynolds numbers.展开更多
文摘This paper theoretically analyzed the jet field of laser spraying method of coaxial type.The results that were got by means of analyzing the model of axisymmetric turbulent jet field showed that jet field consists of two parts,flow developing region and fully developed flow region.In flow develop- ing region exists a potential core region of a constant initial jet velocity.Using π theorem,we have got the relations of u_m∝C(1/x)and b∝x,and the form that velo city distribution has series solution of Tollmien type.This paper provides theo- retical basis for nozzle design,choice of spraying conditions and explanation of spraying phenomena of laser spraying method.
基金supported by the National Natural Science Foundation of China(11232011 and 11402262)China Postdoctral Science Foundation Funded Project(2014M561833)111 Project(B07033)
文摘Stabilities of supersonic jets are examined with different velocities, momentum thicknesses, and core temperatures. Amplification rates of instability waves at inlet are evaluated by linear stability theory （LST）. It is found that increased velocity and core temperature would increase amplification rates substantially and such influence varies for different azimuthal wavenumbers. The most unstable modes in thin momentum thickness cases usually have higher frequencies and azimuthal wavenumbers. Mode switching is observed for low azimuthal wavenumbers, but it appears merely in high velocity cases. In addition, the results provided by linear parabolized stability equations show that the mean-flow divergence affects the spatial evolution of instability waves greatly. The most amplified instability waves globally are sometimes found to be different from that given by LST.
基金supported in part by the National Natural Science Foundation of China(12101088)the Natural Science Foundation of Sichuan Province(2022NSFSC1858)。
文摘This paper is devoted to the study of the shape of the free boundary for a threedimensional axisymmetric incompressible impinging jet.To be more precise,we will show that the free boundary is convex to the fluid,provided that the uneven ground is concave to the fluid.
文摘It is of great practical and theoretical importance to study the properties and flow behavior of laminar jet,because it tightly links the physical phenomena of nonlinerity such as flow stability and transition and so forth.However,many problems and differences exist in ba- sic concepts and in understanding of stable and transitional properties and flow patterns of ax- isymmetric laminar jet.Therefore,a further study on this subject is needed to evaluate the exist- ing understandings and to find out the mechanism governing the behavior of actual axisymmetric laminar jet flow. In this thesis,the flow behavior of axisymmetric laminar jet issuing from nozzles of several diameters in the direction of gravity was studied experimentally using flow visualization tech- nique in the range of Reynolds number from tens to thousands.The unstable and transitional processes in the laminar jet were observed.The influence on the jet flow of different geometry contours of jet chamber boundary was investigated.Some new flow phenomena were discovered which gave deeper understanding of flow patterns and their dependent factors in low Reynolds number axisymmetric laminar jet.A theoretical model to describe the variation of the axisym- metric laminar jet length influenced by the weak density difference is proposed based on the ex- perimental observation,which will be helpful in recognizing the flow behavior of axisymmetric laminar jet of low Reynolds numbers.
