格子Boltzmann(LBM)方法已成为处理介于宏观与微观之间介观流体问题的有效数值方法对LBM方法的数值计算结果进行可视化,实时绘制成流体动画,以便从形象直观的角度进一步进行数据分析。针对二维LBM可视化方法,基于LBGK方程和D2Q9模型设...格子Boltzmann(LBM)方法已成为处理介于宏观与微观之间介观流体问题的有效数值方法对LBM方法的数值计算结果进行可视化,实时绘制成流体动画,以便从形象直观的角度进一步进行数据分析。针对二维LBM可视化方法,基于LBGK方程和D2Q9模型设计算法模型,提出了一种通过指标标准化,将浮点型流体速度值进行归一化处理,转化为RGBA颜色模式的强度值的速度场绘制方法。针对三维可视化方法,引入粒子水平集方法(Particle Level Set Method,PLSM)对LBM流体的液面进行追踪,并设计了LBM与PLSM间的耦合算法。结果表明,所提出的流体可视化仿真方法正确有效,流体动画效果清晰、准确。展开更多
This article reports recent developments and advances in the simulation of the CO2-formation fluid displacement behaviour at the pore scale of subsurface porous media. Roughly, there are three effective visualization ...This article reports recent developments and advances in the simulation of the CO2-formation fluid displacement behaviour at the pore scale of subsurface porous media. Roughly, there are three effective visualization approaches to detect and observe the CO2-formation fluid displacement mechanism at the micro-scale, namely, magnetic resonance imaging, X-ray computed tomography and fabricated micromodels, but they are not capable of investigating the dis- placement process at the nano-scale. Though a lab-on-chip approach for the direct visualization of the fluid flow behaviour in nanoscale channels has been developed using an advanced epi-fluorescence microscopy method combined with a nanofluidic chip, it is still a qualitative analysis method. The lattice Boltzmann method （LBM） can simulate the CO2 displacement processes in a two-dimensional or three-dimensional （3D） pore structure, but until now, the CO2 displace- ment mechanisms had not been thoroughly investigated and the 3D pore structure of real rock had not been directly taken into account in the simulation of the CO2 displacement process. The status of research on the applications of CO2 displacement to enhance shale gas recovery is also analyzed in this paper. The coupling of molecular dynamics and LBM in tandem is proposed to simulate the CO2-shale gas displacement process based on the 3D digital model of shale obtained from focused ion beams and scanning electron microscopy.展开更多
A three-dimensional large eddy simulation （LES） of a spatially developing round jet is carried out in cylindrical coordinates using a dynamic subgrid model with strong inflow instability. Evolutions of large-scale v...A three-dimensional large eddy simulation （LES） of a spatially developing round jet is carried out in cylindrical coordinates using a dynamic subgrid model with strong inflow instability. Evolutions of large-scale vortex structures represented by tangential vortices are obtained and compared with flow visualization. Also presented are three-dimensional spatial evolutions of coherent structure, which are of quasi two-dimensional Kelvin-Helmholtz instability and vortex rings as well as breaking up of the vortex rings with fully three-dimensional characteristics. Predicted results of mean velocity and turbulent intensity agree well with experiments. They are also compared with the results predicted by LES using standard Smagorinsky model and show good self-similarity. Turbulence spectrum of the predicted velocity shows the -5/3 decay for higher wave number, as expected for turbulent round jet flows. In addition, fl-test and y-test are carded out for the instantaneous velocity, showing that the present LES method can successfully predict the hierarchical structure of round jet.展开更多
An experimental investigation is carded out to study fluid flow and heat transfer characteristics on the endwall fitted with arrays （ 7 × 7 ） of short rectangular plate fins of different pattern （co-angular an...An experimental investigation is carded out to study fluid flow and heat transfer characteristics on the endwall fitted with arrays （ 7 × 7 ） of short rectangular plate fins of different pattern （co-angular and zigzag） for different pitch ratio. Experiments were conducted in a rectangular duct of 50 mm height for an air flow of Reynolds number ranged from 18750 to 62500 based on the equivalent diameter and air velocity of the duct. Infrared image analysis technique was employed to make clear the characteristics of local heat transfer coefficients on fin base, endwall and overall surface. Flow pattern around the short rectangular plates were visualized by inducing fluorescent dye in a water channel and longitudinal vortices were observed. Increasing the distance between plates in flow direction causes heat transfer enhancement for co-angular pattern, while decreasing the distance causes heat transfer enhancement for zigzag pattern. Zigzag pattern with pitch ratio 2 is found to be more effective in heat transfer enhancement than any other cases investigated.展开更多
The objective of this study is to apply the shock wave for control in a micro channel. The shock wave was generated by a laser focusing of pulsed laser beam in the channel. Using a pulse laser to generate a shock wave...The objective of this study is to apply the shock wave for control in a micro channel. The shock wave was generated by a laser focusing of pulsed laser beam in the channel. Using a pulse laser to generate a shock wave, a non-stationary flow was induced in the small space between the parallel plates. The spherical and cylindrical shock propagations were observed with schlieren method. The shock Mach number decreases with time and approaches to unity. As reported in the previous investigations, the shock speed was attenuated in a short distance and time. In the present experiment, It was not found a remarkable difference in the shock speed between the spherical and cylindrical shock experiments. Subsequently, the flow induced by the cylindrical shock wave was studied using PIV technique. A smoke tracer was used in the experiment and its velocity was measured within 100 μs. A numerical simulation was carried out to investigate the momentum relaxation between the gas and smoke particle. A suitable shock initiation model was introduced in the simulation. The experimental results show that a wide acceleration and deceleration zone exist behind the shock wave. Also, the relaxation distance in the experimental data is much longer than that in numerical simulation.展开更多
文摘格子Boltzmann(LBM)方法已成为处理介于宏观与微观之间介观流体问题的有效数值方法对LBM方法的数值计算结果进行可视化,实时绘制成流体动画,以便从形象直观的角度进一步进行数据分析。针对二维LBM可视化方法,基于LBGK方程和D2Q9模型设计算法模型,提出了一种通过指标标准化,将浮点型流体速度值进行归一化处理,转化为RGBA颜色模式的强度值的速度场绘制方法。针对三维可视化方法,引入粒子水平集方法(Particle Level Set Method,PLSM)对LBM流体的液面进行追踪,并设计了LBM与PLSM间的耦合算法。结果表明,所提出的流体可视化仿真方法正确有效,流体动画效果清晰、准确。
基金The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China （Grant Nos. 51374213 and 51674251）, the State Key Research Development Program of China （Grant No. 2016YFC0600705）, the National Natural Science Fund for Distinguished Young Scholars of China （Grant No. 51125017）, the Fund for Innovative Research and Development Group Program of Jiangsu Province （Grant No. 2014- 27）, the Science Fund for Creative Research Groups of the National Natural Science Foundation of China （Grant No. 51421003）, and the Priority Academic Program Development of the Jiangsu Higher Education Institutions （PAPD 2014）.
文摘This article reports recent developments and advances in the simulation of the CO2-formation fluid displacement behaviour at the pore scale of subsurface porous media. Roughly, there are three effective visualization approaches to detect and observe the CO2-formation fluid displacement mechanism at the micro-scale, namely, magnetic resonance imaging, X-ray computed tomography and fabricated micromodels, but they are not capable of investigating the dis- placement process at the nano-scale. Though a lab-on-chip approach for the direct visualization of the fluid flow behaviour in nanoscale channels has been developed using an advanced epi-fluorescence microscopy method combined with a nanofluidic chip, it is still a qualitative analysis method. The lattice Boltzmann method （LBM） can simulate the CO2 displacement processes in a two-dimensional or three-dimensional （3D） pore structure, but until now, the CO2 displace- ment mechanisms had not been thoroughly investigated and the 3D pore structure of real rock had not been directly taken into account in the simulation of the CO2 displacement process. The status of research on the applications of CO2 displacement to enhance shale gas recovery is also analyzed in this paper. The coupling of molecular dynamics and LBM in tandem is proposed to simulate the CO2-shale gas displacement process based on the 3D digital model of shale obtained from focused ion beams and scanning electron microscopy.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50176027 and 50706021)a grant from the Research Committee of The Hong Kong Polytechnic University (Grant No.G-U294)
文摘A three-dimensional large eddy simulation （LES） of a spatially developing round jet is carried out in cylindrical coordinates using a dynamic subgrid model with strong inflow instability. Evolutions of large-scale vortex structures represented by tangential vortices are obtained and compared with flow visualization. Also presented are three-dimensional spatial evolutions of coherent structure, which are of quasi two-dimensional Kelvin-Helmholtz instability and vortex rings as well as breaking up of the vortex rings with fully three-dimensional characteristics. Predicted results of mean velocity and turbulent intensity agree well with experiments. They are also compared with the results predicted by LES using standard Smagorinsky model and show good self-similarity. Turbulence spectrum of the predicted velocity shows the -5/3 decay for higher wave number, as expected for turbulent round jet flows. In addition, fl-test and y-test are carded out for the instantaneous velocity, showing that the present LES method can successfully predict the hierarchical structure of round jet.
文摘An experimental investigation is carded out to study fluid flow and heat transfer characteristics on the endwall fitted with arrays （ 7 × 7 ） of short rectangular plate fins of different pattern （co-angular and zigzag） for different pitch ratio. Experiments were conducted in a rectangular duct of 50 mm height for an air flow of Reynolds number ranged from 18750 to 62500 based on the equivalent diameter and air velocity of the duct. Infrared image analysis technique was employed to make clear the characteristics of local heat transfer coefficients on fin base, endwall and overall surface. Flow pattern around the short rectangular plates were visualized by inducing fluorescent dye in a water channel and longitudinal vortices were observed. Increasing the distance between plates in flow direction causes heat transfer enhancement for co-angular pattern, while decreasing the distance causes heat transfer enhancement for zigzag pattern. Zigzag pattern with pitch ratio 2 is found to be more effective in heat transfer enhancement than any other cases investigated.
文摘The objective of this study is to apply the shock wave for control in a micro channel. The shock wave was generated by a laser focusing of pulsed laser beam in the channel. Using a pulse laser to generate a shock wave, a non-stationary flow was induced in the small space between the parallel plates. The spherical and cylindrical shock propagations were observed with schlieren method. The shock Mach number decreases with time and approaches to unity. As reported in the previous investigations, the shock speed was attenuated in a short distance and time. In the present experiment, It was not found a remarkable difference in the shock speed between the spherical and cylindrical shock experiments. Subsequently, the flow induced by the cylindrical shock wave was studied using PIV technique. A smoke tracer was used in the experiment and its velocity was measured within 100 μs. A numerical simulation was carried out to investigate the momentum relaxation between the gas and smoke particle. A suitable shock initiation model was introduced in the simulation. The experimental results show that a wide acceleration and deceleration zone exist behind the shock wave. Also, the relaxation distance in the experimental data is much longer than that in numerical simulation.
