A metastableβTi alloy was additively manufactured by laser powder bed fusion(LPBF).Tensile testing along the build direction of the as-LPBF material(LPBF-0°)revealed signifcant work softening immediately followi...A metastableβTi alloy was additively manufactured by laser powder bed fusion(LPBF).Tensile testing along the build direction of the as-LPBF material(LPBF-0°)revealed signifcant work softening immediately following yielding with no uniform deformation.By contrast,substantial work hardening and uniform elongation well over 10%were achieved perpendicular to the build direction(LPBF-90°).Similar effects were obtained in the build direction after super transus heat treatment(LPBF-0°+HT)although the strength was slightly lowered.In addition,the yield drop phenomenon observed in both orientations of the as-LPBF materials disappeared after HT.The enhanced work hardening ability,and thus ductility,can be attributed to increased interactions of slip bands/slip bands owing to additional{112}<111>slip systems becoming operative in LPBF-0°+HT and LPBF-90°while LPBF-0°was dominated by{110}<111>only.The other variations after HT may be related to the coarsening of grain structure and removal of specifc substructures in the as-LPBF microstructure.展开更多
In this paper, we review some recent studies on compressible turbulence conducted by the authors＇ group, which include fundamental studies on compressible isotropic turbulence （CIT） and applied studies on developin...In this paper, we review some recent studies on compressible turbulence conducted by the authors＇ group, which include fundamental studies on compressible isotropic turbulence （CIT） and applied studies on developing a con- strained large eddy simulation （CLES） for wall-bounded turbulence. In the first part, we begin with a newly pro- posed hybrid compact-weighted essentially nonoscillatory （WENO） scheme for a CIT simulation that has been used to construct a systematic database of CIT. Using this database various fundamental properties of compressible turbulence have been examined, including the statistics and scaling of compressible modes, the shocklet-turbulence interac- tion, the effect of local compressibility on small scales, the kinetic energy cascade, and some preliminary results from a Lagrangian point of view. In the second part, the idea and for- mulas of the CLES are reviewed, followed by the validations of CLES and some applications in compressible engineering problems.展开更多
This paper presents a deep reflection on the advective wave equations for velocity vector and dilatation discovered in the past decade.We show that these equations can form the theoretical basis of modern gas dynamics...This paper presents a deep reflection on the advective wave equations for velocity vector and dilatation discovered in the past decade.We show that these equations can form the theoretical basis of modern gas dynamics,because they dominate not only various complex viscous and heat-conducting gas flows but also their associated longitudinal waves,including aero-generated sound.Current aeroacoustics theory has been developing in a manner quite independently of gas dynamics;it is based on the advective wave equations for thermodynamic variables,say the exact Phillips equation of relative disturbance pressure as a representative one.However,these equations do not cover the fluid flow that generates and propagates sound waves.In using them,one has to assume simplified base-flow models,which we argue is the main theoretical obstacle to identifying sound source and achieving effective noise control.Instead,we show that the Phillips equation and alike is nothing but the first integral of the dilatation equation that also governs the longitudinal part of the flow field.Therefore,we conclude that modern aeroacoustics should merge back into the general unsteady gas dynamics as a special branch of it,with dilatation of multiple sources being a new additional and sharper sound variable.展开更多
Functionalized monodisperse microbubbles have the potential to boost the sensitivity and efficacy of molecular ultrasound imaging and targeted drug delivery using bubbles and ultrasound.Monodisperse bubbles can be pro...Functionalized monodisperse microbubbles have the potential to boost the sensitivity and efficacy of molecular ultrasound imaging and targeted drug delivery using bubbles and ultrasound.Monodisperse bubbles can be produced in a microfluidic flow focusing device.However,their functionalization and sequential use require removal of the excess lipids from the bubble suspension to minimize the use of expensive ligands and to avoid competitive binding and blocking of the receptor molecules.To date,excess lipid removal is performed by centrifugation,which is labor intensive and challenging to automate.More importantly,as we show,the increased hydrostatic pressure during centrifugation can reduce bubble monodispersity.Here,we introduce a novel automated microfluidic’washing’method.First,bubbles are injected in a microfluidic chamber 1mm in height where they are left to float against the top wall.Second,lipid-free medium is pumped through the chamber to remove excess lipids while the bubbles remain located at the top wall.Third,the washed bubbles are resuspended and removed from the device into a collection vial.We demonstrate that the present method can(i)reduce the excess lipid concentration by 4 orders of magnitude,(ii)be fully automated,and(iii)be performed in minutes while the size distribution,functionality,and acoustic response of the bubbles remain unaffected.Thus,the presented method is a gateway to the fully automated production of functionalized monodisperse microbubbles.展开更多
We report a robust fabrication method for patterning freestanding Pt nanowires for use as thermal anemometry probes for small-scale turbulence measurements.Using e-beam lithography,high aspect ratio Pt nanowires(~300 ...We report a robust fabrication method for patterning freestanding Pt nanowires for use as thermal anemometry probes for small-scale turbulence measurements.Using e-beam lithography,high aspect ratio Pt nanowires(~300 nm width,~70µm length,~100 nm thickness)were patterned on the surface of oxidized silicon(Si)wafers.Combining wet etching processes with dry etching processes,these Pt nanowires were successfully released,rendering them freestanding between two silicon dioxide(SiO2)beams supported on Si cantilevers.Moreover,the unique design of the bridge holding the device allowed gentle release of the device without damaging the Pt nanowires.The total fabrication time was minimized by restricting the use of e-beam lithography to the patterning of the Pt nanowires,while standard photolithography was employed for other parts of the devices.We demonstrate that the fabricated sensors are suitable for turbulence measurements when operated in constant-current mode.A robust calibration between the output voltage and the fluid velocity was established over the velocity range from 0.5 to 5 m s−1 in a SF6 atmosphere at a pressure of 2 bar and a temperature of 21°C.The sensing signal from the nanowires showed negligible drift over a period of several hours.Moreover,we confirmed that the nanowires can withstand high dynamic pressures by testing them in air at room temperature for velocities up to 55 m s−1.展开更多
In this paper, we apply a scaling analysis of the maximum of the probability density function（pdf） of velocity increments, i.e., max（） = max（）up p u, for a velocity field of turbulent Rayleigh-Bénard convec...In this paper, we apply a scaling analysis of the maximum of the probability density function（pdf） of velocity increments, i.e., max（） = max（）up p u, for a velocity field of turbulent Rayleigh-Bénard convection obtained at the Taylor-microscale Reynolds number Re60. The scaling exponent is comparable with that of the first-order velocity structure function, （1）, in which the large-scale effect might be constrained, showing the background fluctuations of the velocity field. It is found that the integral time T（x/ D） scales as T（x/ D）（x/ D）, with a scaling exponent =0.25 0.01, suggesting the large-scale inhomogeneity of the flow. Moreover, the pdf scaling exponent （x, z） is strongly inhomogeneous in the x（horizontal） direction. The vertical-direction-averaged pdf scaling exponent （x） obeys a logarithm law with respect to x, the distance from the cell sidewall, with a scaling exponent 0.22 within the velocity boundary layer and 0.28 near the cell sidewall. In the cell＇s central region, （x, z） fluctuates around 0.37, which agrees well with （1） obtained in high-Reynolds-number turbulent flows, implying the same intermittent correction. Moreover, the length of the inertial range represented in decade（）IT x is found to be linearly increasing with the wall distance x with an exponent 0.65 0.05.展开更多
We show that the lattice Boltzmann method(LBM)based color-gradient model with a central moments formulation(CG-CM)is capable of accurately simulating the droplet-on-demand inkjetting process on a micrometer length sca...We show that the lattice Boltzmann method(LBM)based color-gradient model with a central moments formulation(CG-CM)is capable of accurately simulating the droplet-on-demand inkjetting process on a micrometer length scale by comparing it to the Arbitrary Lagrangian Eulerian Finite Element Method(ALE-FEM).A full jetting cycle is simulated using both CG-CM and ALE-FEMand results are quantitatively compared by measuring the ejected ink velocity,volume and contraction rate.We also show that the individual relevant physical phenomena are accurately captured by considering three test-cases;droplet oscillation,ligament contraction and capillary rise.The first two cases test accuracy for a dynamic system where surface tension is the driving force and the third case is designed to test wetting boundary conditions.For the first two cases we also compare the CG-CM and ALE-FEM results to Volume of Fluid(VOF)simulations.Comparison of the three methods shows close agreement when compared to each other and analytical solutions,where available.Finally we demonstrate that asymmetric jetting is achievable using 3D CG-CM simulations utilizing asymmetric wetting conditions inside the jet-nozzle.This allows for systematic investigation into the physics of asymmetric jetting,e.g.due to jet-nozzle manufacturing imperfections or due to other disturbances.展开更多
The current progress of system miniaturization relies extensively on the development of 3D machining techniques to increase the areal structure density.In this work,a wafer-scale out-of-plane 3D silicon(Si)shaping tec...The current progress of system miniaturization relies extensively on the development of 3D machining techniques to increase the areal structure density.In this work,a wafer-scale out-of-plane 3D silicon(Si)shaping technology is reported,which combines a multistep plasma etching process with corner lithography.The multistep plasma etching procedure results in high aspect ratio structures with stacked semicircles etched deep into the sidewall and thereby introduces corners with a proper geometry for the subsequent corner lithography.Due to the geometrical contrast between the gaps and sidewall,residues are left only inside the gaps and form an inversion mask inside the semicircles.Using this mask,octahedra and donuts can be etched in a repeated manner into Si over the full wafer area,which demonstrates the potential of this technology for constructing high-density 3D structures with good dimensional control in the bulk of Si wafers.展开更多
基金supported by the Australian Research Council(No.DP190103557)the University of Melbourne(No.ECRG20)。
文摘A metastableβTi alloy was additively manufactured by laser powder bed fusion(LPBF).Tensile testing along the build direction of the as-LPBF material(LPBF-0°)revealed signifcant work softening immediately following yielding with no uniform deformation.By contrast,substantial work hardening and uniform elongation well over 10%were achieved perpendicular to the build direction(LPBF-90°).Similar effects were obtained in the build direction after super transus heat treatment(LPBF-0°+HT)although the strength was slightly lowered.In addition,the yield drop phenomenon observed in both orientations of the as-LPBF materials disappeared after HT.The enhanced work hardening ability,and thus ductility,can be attributed to increased interactions of slip bands/slip bands owing to additional{112}<111>slip systems becoming operative in LPBF-0°+HT and LPBF-90°while LPBF-0°was dominated by{110}<111>only.The other variations after HT may be related to the coarsening of grain structure and removal of specifc substructures in the as-LPBF microstructure.
基金supported by the National Natural Science Foundation of China (Grants 11221061, 91130001, and 11302006)the National Science Foundation for Postdoctoral Scientists of China (Grants 2011M500194 and 2012M520109)
文摘In this paper, we review some recent studies on compressible turbulence conducted by the authors＇ group, which include fundamental studies on compressible isotropic turbulence （CIT） and applied studies on developing a con- strained large eddy simulation （CLES） for wall-bounded turbulence. In the first part, we begin with a newly pro- posed hybrid compact-weighted essentially nonoscillatory （WENO） scheme for a CIT simulation that has been used to construct a systematic database of CIT. Using this database various fundamental properties of compressible turbulence have been examined, including the statistics and scaling of compressible modes, the shocklet-turbulence interac- tion, the effect of local compressibility on small scales, the kinetic energy cascade, and some preliminary results from a Lagrangian point of view. In the second part, the idea and for- mulas of the CLES are reviewed, followed by the validations of CLES and some applications in compressible engineering problems.
基金supported by the National Natural Science Foundation of China(Grant Nos.12102365,91752202 and 11472016)Luoqin Liu was supported by the Hundred Talents Program of the Chinese Academy of Sciences(CAS).
文摘This paper presents a deep reflection on the advective wave equations for velocity vector and dilatation discovered in the past decade.We show that these equations can form the theoretical basis of modern gas dynamics,because they dominate not only various complex viscous and heat-conducting gas flows but also their associated longitudinal waves,including aero-generated sound.Current aeroacoustics theory has been developing in a manner quite independently of gas dynamics;it is based on the advective wave equations for thermodynamic variables,say the exact Phillips equation of relative disturbance pressure as a representative one.However,these equations do not cover the fluid flow that generates and propagates sound waves.In using them,one has to assume simplified base-flow models,which we argue is the main theoretical obstacle to identifying sound source and achieving effective noise control.Instead,we show that the Phillips equation and alike is nothing but the first integral of the dilatation equation that also governs the longitudinal part of the flow field.Therefore,we conclude that modern aeroacoustics should merge back into the general unsteady gas dynamics as a special branch of it,with dilatation of multiple sources being a new additional and sharper sound variable.
文摘Functionalized monodisperse microbubbles have the potential to boost the sensitivity and efficacy of molecular ultrasound imaging and targeted drug delivery using bubbles and ultrasound.Monodisperse bubbles can be produced in a microfluidic flow focusing device.However,their functionalization and sequential use require removal of the excess lipids from the bubble suspension to minimize the use of expensive ligands and to avoid competitive binding and blocking of the receptor molecules.To date,excess lipid removal is performed by centrifugation,which is labor intensive and challenging to automate.More importantly,as we show,the increased hydrostatic pressure during centrifugation can reduce bubble monodispersity.Here,we introduce a novel automated microfluidic’washing’method.First,bubbles are injected in a microfluidic chamber 1mm in height where they are left to float against the top wall.Second,lipid-free medium is pumped through the chamber to remove excess lipids while the bubbles remain located at the top wall.Third,the washed bubbles are resuspended and removed from the device into a collection vial.We demonstrate that the present method can(i)reduce the excess lipid concentration by 4 orders of magnitude,(ii)be fully automated,and(iii)be performed in minutes while the size distribution,functionality,and acoustic response of the bubbles remain unaffected.Thus,the presented method is a gateway to the fully automated production of functionalized monodisperse microbubbles.
基金This work is supported by the Max Planck-University of Twente Center for Complex Fluid Dynamics and by the Netherlands Organisation for Scientific Research(NWO)Gravitation program funded by the Ministry of Education,Culture and Science of the government of the Netherlands.
文摘We report a robust fabrication method for patterning freestanding Pt nanowires for use as thermal anemometry probes for small-scale turbulence measurements.Using e-beam lithography,high aspect ratio Pt nanowires(~300 nm width,~70µm length,~100 nm thickness)were patterned on the surface of oxidized silicon(Si)wafers.Combining wet etching processes with dry etching processes,these Pt nanowires were successfully released,rendering them freestanding between two silicon dioxide(SiO2)beams supported on Si cantilevers.Moreover,the unique design of the bridge holding the device allowed gentle release of the device without damaging the Pt nanowires.The total fabrication time was minimized by restricting the use of e-beam lithography to the patterning of the Pt nanowires,while standard photolithography was employed for other parts of the devices.We demonstrate that the fabricated sensors are suitable for turbulence measurements when operated in constant-current mode.A robust calibration between the output voltage and the fluid velocity was established over the velocity range from 0.5 to 5 m s−1 in a SF6 atmosphere at a pressure of 2 bar and a temperature of 21°C.The sensing signal from the nanowires showed negligible drift over a period of several hours.Moreover,we confirmed that the nanowires can withstand high dynamic pressures by testing them in air at room temperature for velocities up to 55 m s−1.
基金supported by the Natural Science Foundation of China(Grant Nos.11102114,11202122 and 11222222)the Innovation Program of Shanghai Municipal Education Commission(Grant No.13YZ008,13YZ124)+1 种基金the Shanghai Shuguang Project(Grant No.13SG40)the Program for New Century Excellent Talents in University(Grant No.NCET-13-0)
文摘In this paper, we apply a scaling analysis of the maximum of the probability density function（pdf） of velocity increments, i.e., max（） = max（）up p u, for a velocity field of turbulent Rayleigh-Bénard convection obtained at the Taylor-microscale Reynolds number Re60. The scaling exponent is comparable with that of the first-order velocity structure function, （1）, in which the large-scale effect might be constrained, showing the background fluctuations of the velocity field. It is found that the integral time T（x/ D） scales as T（x/ D）（x/ D）, with a scaling exponent =0.25 0.01, suggesting the large-scale inhomogeneity of the flow. Moreover, the pdf scaling exponent （x, z） is strongly inhomogeneous in the x（horizontal） direction. The vertical-direction-averaged pdf scaling exponent （x） obeys a logarithm law with respect to x, the distance from the cell sidewall, with a scaling exponent 0.22 within the velocity boundary layer and 0.28 near the cell sidewall. In the cell＇s central region, （x, z） fluctuates around 0.37, which agrees well with （1） obtained in high-Reynolds-number turbulent flows, implying the same intermittent correction. Moreover, the length of the inertial range represented in decade（）IT x is found to be linearly increasing with the wall distance x with an exponent 0.65 0.05.
基金the Netherlands Organization for Scientific Research(NWO)research project High Tech Systems and Materials(HTSM),with project number 13912the NWO and co-financers Canon Production Printing Holding B.V.,University of Twente and Eindhoven University of Technology for financial support.This work was carried out on the Dutch national e-infrastructure with the support of SURF Cooperative,project number 2021.035。
文摘We show that the lattice Boltzmann method(LBM)based color-gradient model with a central moments formulation(CG-CM)is capable of accurately simulating the droplet-on-demand inkjetting process on a micrometer length scale by comparing it to the Arbitrary Lagrangian Eulerian Finite Element Method(ALE-FEM).A full jetting cycle is simulated using both CG-CM and ALE-FEMand results are quantitatively compared by measuring the ejected ink velocity,volume and contraction rate.We also show that the individual relevant physical phenomena are accurately captured by considering three test-cases;droplet oscillation,ligament contraction and capillary rise.The first two cases test accuracy for a dynamic system where surface tension is the driving force and the third case is designed to test wetting boundary conditions.For the first two cases we also compare the CG-CM and ALE-FEM results to Volume of Fluid(VOF)simulations.Comparison of the three methods shows close agreement when compared to each other and analytical solutions,where available.Finally we demonstrate that asymmetric jetting is achievable using 3D CG-CM simulations utilizing asymmetric wetting conditions inside the jet-nozzle.This allows for systematic investigation into the physics of asymmetric jetting,e.g.due to jet-nozzle manufacturing imperfections or due to other disturbances.
基金Financial support for this project was provided by the Foundation for Fundamental Research on Matter(FOM,Project 13CO12-1)which is part of The Netherlands Organization for Scientific Research(NWO).
文摘The current progress of system miniaturization relies extensively on the development of 3D machining techniques to increase the areal structure density.In this work,a wafer-scale out-of-plane 3D silicon(Si)shaping technology is reported,which combines a multistep plasma etching process with corner lithography.The multistep plasma etching procedure results in high aspect ratio structures with stacked semicircles etched deep into the sidewall and thereby introduces corners with a proper geometry for the subsequent corner lithography.Due to the geometrical contrast between the gaps and sidewall,residues are left only inside the gaps and form an inversion mask inside the semicircles.Using this mask,octahedra and donuts can be etched in a repeated manner into Si over the full wafer area,which demonstrates the potential of this technology for constructing high-density 3D structures with good dimensional control in the bulk of Si wafers.
