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lagrangian view of time irreversibility of fluid turbulence

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Science China(Physics,Mechanics & Astronomy) 2016年第1期59卷 7-15页

作者： HaiTao Xu Center for Combustion Energy and Department of Thermal Engineering Tsinghua UniversityBeijing 100084China Max Planck Institute for Dynamics&Self-Organization(MPIDS) Gottingen D-37077Germany Ecole Normale Superieure de Lyon Lyon F-69007France Institute for Nonlinear Dynamics University of Gottingen GSttingen D-37077Germany Laboratory of Atomic and Solid State Physics and Sibley School of Mechanical and Aerospace Engineering Cornell UniversityIthaca NY 14853USA

A turbulent flow is maintained by an external supply of kinetic gradients. The scale at which energy is supplied greatly differs energy, which is eventually dissipated into heat at steep velocity from the scale at which energy is dissipated, the more so as the turbulent intensity （the Reynolds number） is larger. The resulting energy flux over the range of scales, intermediate between energy injection and dissipation, acts as a source of time irreversibility. As it is now possible to follow accurately fluid particles in a turbulent flow field, both from laboratory experiments and from numerical simulations, a natural question arises： how do we detect time irreversibility from these lagrangian data？ Here we discuss recent results concerning this problem. For lagrangian statistics involving more than one fluid particle, the distance between fluid particles introduces an intrinsic length scale into the problem. The evolution of quantities dependent on the relative motion between these fluid particles, including the kinetic energy in the relative motion, or the configuration of an initially isotropic structure can be related to the equal-time correlation functions of the velocity field, and is therefore sensitive to the energy flux through scales, hence to the irreversibility of the flow. In contrast, for single- particle lagrangian statistics, the most often studied velocity structure functions cannot distinguish the ＂arrow of time＂. Recent observations from experimental and numerical simulation data, however, show that the change of kinetic energy following the particle motion, is sensitive to time-reversal. We end the survey with a brief discussion of the implication of this line of work.

关键词： fluid turbulence time irreversibility energy cascade lagrangian description

The least square particle finite element method for simulating large amplitude sloshing flows

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Acta Mechanica Sinica 2008年第3期24卷 317-323页

作者： Bo Tang Junfeng Li Tianshu Wang School of Aerospace Tsinghua University Beijing 100084 China

Large amplitude sloshing in tanks is simulated by the least square particle finite element method （LSPFEM） in this paper. The least square finite element method （LSFEM） is employed to spatially discrete the Navier-Stokes equations, and to avoid the stabilization issues due to the incompressibility condition for equal-order interpolation of the velocity and the pressure, as usually used in Galerkin method to satisfy the well-known LBB condition. The LSPFEM also uses the lagrangian description to model the motion of nodes （particles）. A mesh which connects these nodes is constructed by a triangulation algorithm to avoid the mesh distortion. A quasi a-shapes algorithm is used to identify the free surface boundary. The nodes are viewed as particles which can freely move and even separate from the main fluid domain. Finally this method is used to study the large amplitude sloshing evolution in two dimensional tanks. The results are compared with those obtained by Flow-3d with good agreement.

关键词： Incompressible fluid Least square finiteelement method lagrangian description Boundaryrecognition Collapse Impact

Viscous flow with free surface motion by least square finite element method

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Applied Mathematics and Mechanics(English Edition) 2008年第7期29卷 943-952页

作者：汤波李俊峰王天舒 School of Aerospace Tsinghua University

A method for simulation of free surface problems is presented. Based on the viscous incompressible Navier-Stokes equations, space discretization of the flow is obtained by the least square finite element method. The time evolution is obtained by the finite difference method. lagrangian description is used to track the free surface. The results are compared with the experimental dam break results, including water collapse in a 2D rectangular section and in a 3D cylinder section. A good agreement is achieved for the distance of surge front as well as the height of the residual column.

关键词： incompressible viscous fluid lagrangian description least square finite element method dam break experiment

Investigations on High-Speed Flash Boiling Atomization of Fuel Based on Numerical Simulations

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Computer Modeling in Engineering & Sciences 2024年第5期139卷 1427-1453页

作者： Wei Zhong Zhenfang Xin Lihua Wang Haiping Liu School of Aerospace Engineering and Applied Mechanics Tongji UniversityShanghai200092China Beijing Mechanical Equipment Research Institute Beijing100854China

Flash boiling atomization(FBA)is a promising approach for enhancing spray atomization,which can generate a fine and more evenly distributed spray by increasing the fuel injection temperature or reducing the ambient ***,when the outlet speed of the nozzle exceeds 400 m/s,investigating high-speed flash boiling atomization(HFBA)becomes quite *** difficulty arises fromthe involvement ofmany complex physical processes and the requirement for a very fine mesh in numerical *** this study,an HFBA model for gasoline direct injection(GDI)is *** model incorporates primary and secondary atomization,as well as vaporization and boilingmodels,to describe the development process of the flash boiling *** to lowspeed FBA,these physical processes significantly impact *** this model,the Eulerian description is utilized for modeling the gas,and the lagrangian description is applied to model the droplets,which effectively captures the movement of the droplets and avoids excessive mesh in the Eulerian *** various conditions,numerical solutions of the Sauter mean diameter(SMD)for GDI show good agreement with experimental data,validating the proposed model’s *** based on this HFBA model investigate the influences of fuel injection temperature and ambient pressure on the atomization *** analyses of the velocity field,temperature field,vapor mass fraction distribution,particle size distribution,and spray penetration length under different superheat degrees reveal that high injection temperature or low ambient pressure significantly affects the formation of small and dispersed droplet *** effect is conducive to the refinement of spray particles and enhances atomization.

关键词： High-speed flash boiling atomization numerical simulations Eulerian description lagrangian description gasoline direct injection

FAST SIMULATION OF FLOWS IN SHOCK TUBE WITH AREA CHANGE

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Transactions of Nanjing University of Aeronautics and Astronautics 2013年第3期30卷 260-263页

作者：朱浩沈清宫建 China Academy of Aerospace Aerodynamics

The shock tubes with area change are used in the free piston shock tunnels,owing to its higher driver *** optimized operation of this kind of shock tube,a computer program for fast simulation of transient hypersonic flow is *** numerical modeling embodied within this code is based on a quasi-one-dimensional lagrangian description of the gas *** this code,a mass-loss model is also applied by using Mirels′theory of shock *** simulation of particular condition for T4 free piston shock tunnel is conducted and compared with experimental measurements and numerical *** results provide good estimate for shock speed and pressure obtained after shock reflection.

关键词： shock tube with area change lagrangian description Riemann solver mass-loss model

Generation and Deformation of Solitary Waves

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China Ocean Engineering 1996年第4期11卷 419-432页

作者： Chou Chung-Ren Shih Ruey-Syan Professor, Dept. of Harbor and River Engineering, National Taiwan Ocean University . Graduate Student, Dept. of Harbor and River Engineering, National Taiwan Ocean University Dept. of Harbor and River Eng. National Taiwan Ocean University

Base on the lagrangian description and finite differencing of the time step, the generation, propagation and deformation of solitary waves are simulated numerically by means of boundary element method. An algorithm to generate waves with any prescribed form is also implanted in the scheme, but in this research, solitary waves are studied. The numerical model is first verified by studying the case of a solitary wave impinging against a vertical wall. Time histories of evolution of a soliton running up on a sloping beach, as well as over a submerged obstacle are then presented. Applications to scattering problems due to solitary waves progressing over a slope onto a shelf are also shown.

关键词： lagrangian description solitary wave boundary element method time histories

lagrangian block hydrodynamics for environmental fluid mechanics simulations

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Lagrangian block hydrodynamics for environmental fluid mecha...

Shallow Water Flow Computation Using the Unified Coordinates

第九届国际水动力学会议

作者： Vincent H.Chu Department of Civil Engineering and Applied Mechanics McGill University

The lagrangian block hydrodynamics is formulated based on the block advection of *** enforcing the mass and momentum conservations on the lagrangian mesh,the numerical oscillation problem encountered in the classical Eulerian computational methods is circumvented.A large number of the previously computationally difficult problems in environmental fluid mechanics are successfully simulated using the *** of these simulations are described in this paper.

关键词： lagrangian description computational hydrodynamics block advection shallow-water waves turbulence simulations.

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Shallow Water Flow Computation Using the Unified Coordinates