Liquid metal droplets are accelerated by electrostatic forces in a process known as field emission.In this study,we simulate the emission of charged indium droplets on a needle in 2D cylindrical coordinates.The bounda...Liquid metal droplets are accelerated by electrostatic forces in a process known as field emission.In this study,we simulate the emission of charged indium droplets on a needle in 2D cylindrical coordinates.The boundary element method is used to rapidly and accurately calculate the electric field on the fluid surface,which is then advected forward in time using level sets.This is the first time these methods have been combined,and this combination addresses difficult detachable surface tracking issues successfully.A histogram of droplet charge-to-mass ratio is generated in which it is predicted that smaller satellite droplets are more densely charged.In addition,our model is compared with independent pre-and post-snap off data and produces good agreement with the result.展开更多
A new criterion is presented to detect global convergence to steady state,and to identify local transient characteristics,during rarefied gas flow simulations performed using the direct simulation Monte Carlo(DSMC)met...A new criterion is presented to detect global convergence to steady state,and to identify local transient characteristics,during rarefied gas flow simulations performed using the direct simulation Monte Carlo(DSMC)method.Unlike deterministic computational fluid dynamics(CFD)schemes,DSMC is generally subject to large statistical scatter in instantaneous flow property evaluations,which prevents the use of residual tracking procedures as are often employed in CFD simulations.However,reliable prediction of the time to reach steady state is necessary for initialization of DSMC sampling operations.Techniques currently used in DSMC to identify steady state convergence are usually insensitive to weak transient behavior in small regions of relatively low density or recirculating flow.The proposed convergence criterion is developed with the goal of properly identifying such weak transient behavior,while adding negligible computational expense and allowing simple implementation in any existing DSMC code.Benefits of the proposed technique over existing convergence detection methods are demonstrated for representative nozzle/plume expansion flow,hypersonic blunt body flow and driven cavity flow problems.展开更多
基金supported in part by the NSF under contract DMS 0108672Christlieb’s work supported in part by the Air Force Office of Scientific Research(AFOSR)under Grant FA9550-05-1-0199.
文摘Liquid metal droplets are accelerated by electrostatic forces in a process known as field emission.In this study,we simulate the emission of charged indium droplets on a needle in 2D cylindrical coordinates.The boundary element method is used to rapidly and accurately calculate the electric field on the fluid surface,which is then advected forward in time using level sets.This is the first time these methods have been combined,and this combination addresses difficult detachable surface tracking issues successfully.A histogram of droplet charge-to-mass ratio is generated in which it is predicted that smaller satellite droplets are more densely charged.In addition,our model is compared with independent pre-and post-snap off data and produces good agreement with the result.
基金NASA for financial support of this work,through grant NNX08AD02A.
文摘A new criterion is presented to detect global convergence to steady state,and to identify local transient characteristics,during rarefied gas flow simulations performed using the direct simulation Monte Carlo(DSMC)method.Unlike deterministic computational fluid dynamics(CFD)schemes,DSMC is generally subject to large statistical scatter in instantaneous flow property evaluations,which prevents the use of residual tracking procedures as are often employed in CFD simulations.However,reliable prediction of the time to reach steady state is necessary for initialization of DSMC sampling operations.Techniques currently used in DSMC to identify steady state convergence are usually insensitive to weak transient behavior in small regions of relatively low density or recirculating flow.The proposed convergence criterion is developed with the goal of properly identifying such weak transient behavior,while adding negligible computational expense and allowing simple implementation in any existing DSMC code.Benefits of the proposed technique over existing convergence detection methods are demonstrated for representative nozzle/plume expansion flow,hypersonic blunt body flow and driven cavity flow problems.
