شبيه سازي قطره سيال در ميدان گريز از مركز در ابعاد نانويه به روش DPD

چكيده انگليسي :

Simulation of Nano size Drop in Centrifugal Field by DPD Method Sorush Khajepor s khajepor@me iut ac ir 28st April 2010 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Persian Ahmad Reza Pishevar apishe@cc iut ac ir Abstract A particle based analysis is carried out to simulate formation of a viscous Newtonian liquid drop from a mesoscale nozzle into an inert medium by imposing low flow rate says dripping In the case of mesoscale free surface flow thermal fluctuations become important as they can no longer be justifiable with the continuum perturbation theory On the other hand the resolution of this scale is beyond the applicability of Molecular Dynamics Therefore this category of physics problems is remarkably challenging According to mentioned conditions Dissipative Particle Dynamics DPD is an eligible method DPD is a relatively new mesoscopic simulation approach which highlights the importance of thermal fluctuations In addition it would capture hydrodynamics details on a larger length and time scale than atomistic resolution Adjusting DPD parameters to simulate a special physical problem is an area of interest since fluid properties and kinematic variables in DPD simulation are in reduced units To reach this aim we present a different approach by concept of dimensionless numbers The dripping dynamics is studied as a function of Ohnesorge number viscous surface tension force Bond number inertial surface tension force and dimensionless thermal length thermal surface tension energy Therefore a DPD simulation of dripping is planned to achieve the aforementioned dimensionless numbers The nozzle is constructed with frozen particles and its impenetrability and proper surface wettability is attained by manipulating coefficient of conservative force between wall and fluid In seeking validation of method dripping simulation is compared with macroscopic experiment This comparison is governed by matching only Ohnesorge number and bond number and leaving dimensionless thermal length unmatched Our results are in good agreement with the macroscopic experiment except near the break up time when the fluid thread that connects the primitive drop to the nozzle becomes tenuous At this point the DPD simulation comes into question by two issues thermal length of DPD fluid and the finest achievable resolution that is radius of a particle The former was much longer than corresponding value in physics of mentioned experiment Larger thermal length leads to break up which happens before expected time However this simulation could be observed in different way in fact it corresponds to physics of dripping from a nano nozzle that thermal length of both are matched Accordingly in this view fast drop break up would be intelligible A nano jet in a centrifugal field is simulated by DPD The simulation is run in a rotating reference frame that results in the addition of fictitious forces to DPD inter particle forces In seeking validation of trajectory of jet DPD simulation is comprised with continuum theory The Agreement among them concluded that the fictitious forces are correctly exerted It is shown that the occurrence of mode 1 and mode 2 which are observed in macroscopic is unlikely in nano scale Mode 3 and mode 4 of breakup is simulated by DPD Fast breakup of spiralling jet in mode 3 is justified with surface thermal fluctuations The Simulation of mode 4 of breakup is similar to that of macroscopic The breakup length of jets are measured as a function of Rossby number in nano scale and compared with

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شبيه سازي قطره سيال در ميدان گريز از مركز در ابعاد نانويه به روش DPD

نانو جت , جريان ميكرونانو , جريان دو فازي , جت چرخان