COMPUTATIONAL MODELING OF AN 8-GHz MICROWAVE ELECTROTHERMAL THRUSTER

Open Access
Author:
DeForce Jr. , Christopher Allen
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 28, 2011
Committee Members:
  • Michael Matthew Micci, Thesis Advisor
  • Sven G Bilen, Thesis Advisor
Keywords:
  • microwave electrothermal thruster
  • MET
  • computational modeling
  • COMSOL
  • Chris DeForce
  • electromagnetics
  • fluid mechanics
  • plasma
  • electric propulsion
  • deforce
Abstract:
The design of an 8-GHz Microwave Electrothermal Thruster was studied and optimized via numerical modeling. The electromagnetics of the thruster was modeled in an effort to develop and optimize a thruster design that would produce a robust electric field and resonate at the mode shape. The fluid dynamics of the MET propellant injection system were modeled in two and three dimensions. The electromagnetics study investigated multiple designs and configurations in an effort obtain a robust mode shape with an intense electric field concentration at the nozzle end of the thruster cavity. Models using both coaxial and waveguide ports for microwave energy inputs were investigated and optimized. It was found that though the coaxial input provided a stable mode, a much stronger electric field could be obtained by coupling a waveguide to a coaxial port. Also, using a waveguide short, the result could be fine-tuned. The design was optimized through testing different waveguide sizes and varying the antenna depth in the chamber. It was also found that the electric field intensity varied based upon the amount of dielectric in the cavity. Also, the resonant frequency increased when using a dielectric with a higher dielectric constant, but had little effect on the electric field intensity. In the fluid dynamic analysis, three-dimensional models were developed for the propellant injection system using incompressible and weakly compressible fluid flow assumptions. A viscous compressible flow model was being developed using the governing equations: mass, momentum, and energy. Both two- and three-dimensional compressible flow models were developed; however, a three-dimensional compressible flow model was not completed. Future recommendations are made for future modeling efforts in completing the three-dimensional compressible flow modeling, as well as moving forward toward developing a numerical model that encapsulates the coalesced plasma characteristics that a physical prototype demonstrates.