شبيه سازي هيدروديناميكي برخورد قطره در مقياس مزو با سطح جامد به روش DPD

چكيده انگليسي :

Mesoscopic Hydrodynamic Simulation of Drop Impact on a Solid Surface Using DPD Method Najmeh Ghorbani Ghorbani2400@yahoo com April 6 2011 Department of Mechanical Engineering Isfahan university of technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Dr Ahmad Reza Pishevar apishe@cc iut ac ir Abstract Drop impact on solid surface has many industrial applications such as surface coating steam turbines spray cooling erosion of soils fuel injection in engines forensic medicine blood splatter ink jet printing and many other applications in chemical processes Limitations in experimental and analytical methods for exploiting behavior of mesoscale drops during the impact to the rigid surfaces conduct us to use numerical simulation for this study Methods like Monte carlo and molecular dynamics have been used to analyze the statics and dynamics of drop on solid surface but these methods are limited to small time and length scales To solve these problems a three dimensional coarse grained and particle based method called Many body Dissipative Particle Dynamics MDPD which can be used at meso level simulations is selected and used in this project MDPD is a short range method thus each particle can only interact with particles that are within its certain cut off distance At present work link cells LC algorithm is used for fast search and finding the location of these interacting neighbor particles In MDPD soft core potential is used and dissipative random and conservative forces are the three forces that act on any particle according to Newton s second and third laws Velocity verlet algorithm for integrating the equation of motion has been adapted and the determination of time step depends on the stability of the global density Like standard DPD method dissipative and random forces are used to produce viscous effects and account for the lost degrees of freedom because of coarse graining respectively MDPD differs from its predecessor DPD method in the definition of conservative forces acting between particles In DPD conservative force is added to account for non ideality of the system and only contains a repulsive term In MDPD rather than assuming the dependence of the force on the interparticle separation repulsive term is made additionally dependent on the instantaneous local particle density and an attractive term is added to the conservative force that acts on a longer range than repulsive term for each particle Solid surface contains freezing particles which don t move but interact with liquid particles Hydrophobic and hydrophilic surfaces can be modeled by changing the liquid solid conservative force amplitude and color function is used for measuring the drop static contact angle on the solid surface In this project the influence of patterned substrates on the static contact angle is also exploited by simulating surfaces in various surface fractions and their results are compared with Cassie Baxter s law Dynamic wetting is studied by simulating the drop impact on horizontal and homogeneous surface in this work Drop spreading occurs after drop impact on solid surface This step is consist of drop diameter increase and drop height decrease Drop recoil phenomenon happens after drop quietness and continues to reach the equilibrium In this work dimensionless drop diameter change and dimensionless drop height change versus dimensionless time are compared with experimental results at three static contact angles For searching the influence of surface energy on drop spreading process drop impact in various We numbers are simulated and their dimensionless drop height change and dimensionless drop diameter change diagrams are compared Key words Many body Dissipative Particle Dynamics Nanodrop Hydrophobic surface Hydrophilic surface Wettability Drop impact Drop spreadPDF created with FinePrint pdfFactory trial version www pdffactory com

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شبيه سازي هيدروديناميكي برخورد قطره در مقياس مزو با سطح جامد به روش DPD

ديناميك استهلاكي ذره , سطح آب گريز , سطح آبدوست , ترشوندگي , پخش قطره