The mixing phenomena of a two-layer density-stratified fluid induced by a jet in a tank are experimentally investigated. The upper and lower fluids are water and a NaCl-water solution, respectively, with the lower flu...The mixing phenomena of a two-layer density-stratified fluid induced by a jet in a tank are experimentally investigated. The upper and lower fluids are water and a NaCl-water solution, respectively, with the lower fluid issued vertically upward from a nozzle at the bottom of the tank. The jet Reynolds number Re, defined by the jet velocity and the water kinematic viscosity, ranges from 90 to 4,200. The mass concentration of the NaCl-water solution Co is less than 0.08. The flow visualization makes clear the jet behavior relative to the density interface between the upper and lower fluids. The measurement of the concentration distribution of the water paint issued with the jet highlights the effects of Re and Co on the mixing between the jet and the ambient fluid. The measurement of the fluid velocity distribution with a PIV （particle image velocimetry） system successfully elucidates the relationship between the velocity field and the resultant mixing.展开更多
The characteristics of single and multiple tandem jets(n=2,3,4) in crossflow have been investigated using the realizable k-ε model.The results of this model agree well with experimental measurements using PIV(Particl...The characteristics of single and multiple tandem jets(n=2,3,4) in crossflow have been investigated using the realizable k-ε model.The results of this model agree well with experimental measurements using PIV(Particle Image Velocimetry) or LIF(Laser Induced Fluorescence).We analyzed the calculated results and obtained detailed properties of velocity and concentration of the multiple jets in the pre-merging and post-merging regions.When the velocity ratio is identical,the bending degree of the leading jet is greater than that of the rear jets.The last jet penetrates deeper as the jet number increases,and the shielding effect of the front jet declines with jet spacing increase.Interaction of the jet and crossflow induces formation and development of a counter-rotating vortex pair(CVP).CVP makes the distribution of concentration appear kidney-shaped(except in the merging region),and maximum concentration is at the center of the counter-rotating vortex.Concentration at the CVP center is 1.03-1.4 times that of the local jet trajectory.Post-merging velocity and concentration characteristics differ from those of the single jet because of the shielding effect and mixing of all jets.This paper presents a unified formula of trajectory,concentration half-width and trajectory dilution,by introducing a reduction factor.展开更多
When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obsta...When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obstacle and so on. This oscillation is related with the noise problems of aeronautical and other industrial engineering so that the characteristic and the mechanism of self-induced flow oscillation have to be cleared to control the various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of oscillation have to be more clear to control the oscillation. This paper aims to clarify the effect of the plate position and the width for the self-induced flow oscillation of an underexpanded supersonic jet impinging on the perpendicular plate by the experiment and the numerical analysis. From the results, it is clear that the occurring domain of the self-induced flow oscillation and its dimension strongly depend on the plate position and the width.展开更多
Flow-induced preordering or precursor(FIP) has been studied in a series of lightly cross-linked high-density polyethylene with a combination of extensional rheology and in situ synchrotron radiation small-angle X-ray ...Flow-induced preordering or precursor(FIP) has been studied in a series of lightly cross-linked high-density polyethylene with a combination of extensional rheology and in situ synchrotron radiation small-angle X-ray scattering(SAXS) and wide-angle X-ray diffraction(WAXD) measurements. Based on the incipient strains of SAXS and WAXD signals during extension in a large temperature range, strain-temperature diagrams for flow-induced preordering and nucleation were constructed and revealed that flow-induced crystallization(FIC) undergoes two stages: melt-precursor transition(MPT) and precursor-nuclei transition(PNT). At different temperatures, FIP with different inner structures and morphologies can be induced by strain; these embryos have shape and structure that are related to those of the corresponding critical nuclei. With the strain-temperature diagrams, the thermodynamic properties of FIP are deduced, which shows that compared with the relative nuclei the FIP always has a lower bulk free energy(?H) and a much lower surface free energy(?e). In extreme cases(high temperature), the ?e of FIP can be negligible. The quantitative estimation of the thermodynamic parameters suggests the existence of variant FIPs, which plays a vital role for the subsequent progress of PNT and the whole process of FIC.展开更多
文摘The mixing phenomena of a two-layer density-stratified fluid induced by a jet in a tank are experimentally investigated. The upper and lower fluids are water and a NaCl-water solution, respectively, with the lower fluid issued vertically upward from a nozzle at the bottom of the tank. The jet Reynolds number Re, defined by the jet velocity and the water kinematic viscosity, ranges from 90 to 4,200. The mass concentration of the NaCl-water solution Co is less than 0.08. The flow visualization makes clear the jet behavior relative to the density interface between the upper and lower fluids. The measurement of the concentration distribution of the water paint issued with the jet highlights the effects of Re and Co on the mixing between the jet and the ambient fluid. The measurement of the fluid velocity distribution with a PIV （particle image velocimetry） system successfully elucidates the relationship between the velocity field and the resultant mixing.
基金supported by the National Natural Science Foundation of China (Grant No. 11172218)academic award for excellent Ph.D.Candidates funded by the Ministry of Education of China
文摘The characteristics of single and multiple tandem jets(n=2,3,4) in crossflow have been investigated using the realizable k-ε model.The results of this model agree well with experimental measurements using PIV(Particle Image Velocimetry) or LIF(Laser Induced Fluorescence).We analyzed the calculated results and obtained detailed properties of velocity and concentration of the multiple jets in the pre-merging and post-merging regions.When the velocity ratio is identical,the bending degree of the leading jet is greater than that of the rear jets.The last jet penetrates deeper as the jet number increases,and the shielding effect of the front jet declines with jet spacing increase.Interaction of the jet and crossflow induces formation and development of a counter-rotating vortex pair(CVP).CVP makes the distribution of concentration appear kidney-shaped(except in the merging region),and maximum concentration is at the center of the counter-rotating vortex.Concentration at the CVP center is 1.03-1.4 times that of the local jet trajectory.Post-merging velocity and concentration characteristics differ from those of the single jet because of the shielding effect and mixing of all jets.This paper presents a unified formula of trajectory,concentration half-width and trajectory dilution,by introducing a reduction factor.
文摘When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs at the specific condition of the pressure ratio in the flowfield, the position of an obstacle and so on. This oscillation is related with the noise problems of aeronautical and other industrial engineering so that the characteristic and the mechanism of self-induced flow oscillation have to be cleared to control the various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of oscillation have to be more clear to control the oscillation. This paper aims to clarify the effect of the plate position and the width for the self-induced flow oscillation of an underexpanded supersonic jet impinging on the perpendicular plate by the experiment and the numerical analysis. From the results, it is clear that the occurring domain of the self-induced flow oscillation and its dimension strongly depend on the plate position and the width.
基金supported by the National Natural Science Foundation of China(51325301,51033004,51120135002,51227801)the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics(U1330202)+1 种基金Project 2013BB05 supported by the Key Laboratory of Neutron Physics,China Academy of Engineering Physicsin part supported by"Ludo Frevel Crystallography Scholarships"from the International Centre for Diffraction Data
文摘Flow-induced preordering or precursor(FIP) has been studied in a series of lightly cross-linked high-density polyethylene with a combination of extensional rheology and in situ synchrotron radiation small-angle X-ray scattering(SAXS) and wide-angle X-ray diffraction(WAXD) measurements. Based on the incipient strains of SAXS and WAXD signals during extension in a large temperature range, strain-temperature diagrams for flow-induced preordering and nucleation were constructed and revealed that flow-induced crystallization(FIC) undergoes two stages: melt-precursor transition(MPT) and precursor-nuclei transition(PNT). At different temperatures, FIP with different inner structures and morphologies can be induced by strain; these embryos have shape and structure that are related to those of the corresponding critical nuclei. With the strain-temperature diagrams, the thermodynamic properties of FIP are deduced, which shows that compared with the relative nuclei the FIP always has a lower bulk free energy(?H) and a much lower surface free energy(?e). In extreme cases(high temperature), the ?e of FIP can be negligible. The quantitative estimation of the thermodynamic parameters suggests the existence of variant FIPs, which plays a vital role for the subsequent progress of PNT and the whole process of FIC.
