A Hybrid CFD-DSMC Model Designed to Simulate Rapidly Rarefying Flow Fields and its Application to Physical Vapor Deposition

Open Access
Author:
Gott, Kevin Nathaniel
Graduate Program:
Mechanical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 05, 2015
Committee Members:
  • Anil Kamalakant Kulkarni, Dissertation Advisor
  • Jogender Singh, Committee Member
  • Daniel Connell Haworth, Committee Member
  • Savas Yavuzkurt, Committee Member
Keywords:
  • Physical Vapor Deposition
  • CFD
  • DSMC
  • Multi-physics Modeling
  • Vacuum
  • Coatings
Abstract:
This research endeavors to better understand the physical vapor deposition (PVD) vapor transport process by determining the most appropriate fluidic model to design PVD coating manufacturing. An initial analysis was completed based on the calculation of Knudsen number from titanium vapor properties. The results show a dense Navier-Stokes solver best describes flow near the evaporative source, but the material properties suggest expansion into the chamber may result in a strong drop in density and a rarefied flow close to the substrate. A hybrid CFD-DSMC solver is constructed in OpenFOAM for rapidly rarefying flow fields such as PVD vapor transport. The models are patched together combined using a new patching methodology designed to take advantage of the one-way motion of vapor from the CFD region to the DSMC region. Particles do not return to the dense CFD region, therefore the temperature and velocity can be solved independently in each domain. This novel technique allows a hybrid method to be applied to rapidly rarefying PVD flow fields in a stable manner. Parameter studies are performed on a CFD, Navier-Stokes continuum based compressible solver, a Direct Simulation Monte Carlo (DSMC) rarefied particle solver, a collisionless free molecular solver and the hybrid CFD-DSMC solver. The radial momentum at the inlet and radial diffusion characteristics in the flow field are shown to be the most important to achieve an accurate deposition profile. The hybrid model also shows sensitivity to the shape of the CFD region and rarefied regions shows sensitivity to the Knudsen number. The models are also compared to each other and appropriate experimental data to determine which model is most likely to accurately describe PVD coating deposition processes. The Navier-Stokes solvers are expected to yield backflow across the majority of realistic inlet conditions, making their physics unrealistic for PVD flow fields. A DSMC with improved collision model may yield an accurate model, but additional research will first need to be completed to accurately describe the complex intermolecular forces of metals and ceramics. Overall, a hybrid CFD-DSMC solver with an improved equation of state for evaporated PVD materials is recommended to model PVD flow.