摘要
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.
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.
