CTSP (Contamination Transport Simulation Program)

CTSP (Contamination Transport Simulation Program) is a PIC-C developed program for modeling molecular and particulate contamination transport. The need to model contamination is commonly encountered in vacuum and aerospace industries. Plastics and other organic materials exposed to low pressures outgas unspent hydrocarbons which then deposit onto sensitive surfaces such as camera lenses or radiators. Other components may be sensitive to particulates. These are tiny dust particles arising from air pollution, garments, or flaking off paints. Particulates are present on all surfaces but can redistribute during vibrational events such as spacecraft launch or on-orbit deployments.

CTSP models the transport of molecular and particulate contaminants from their sources to the eventual target settling locations in order to estimate the end of life cleanliness levels. The code utilizes a kinetic method in which the contaminants are represented by simulation particles. Particle positions are advanced through small time steps. This allows the code to take into account aerodynamic, gravitational, or electrostatic forces. Unlike Monte Carlo ray tracing tools, CTSP concurrently simulates the entire contaminant population. This allows the end user to visualize the contaminant plume partial pressures and bulk streaming velocities. It also allows the code to simulate the transition regime (such as chamber repress) in which inter-molecular collisions become important. CTSP supports highly detailed, multi-million element surface meshes to represent the test geometry. The code also implements multiple contamination-specific material sources, including a detailed model for molecular outgassing and particulate generation. Molecular surface adhesion and desorption physics is governed by surface temperature and material activation energy.

Features

  • Supports highly complex geometries loaded from surface mesh files in common formats such as OBJ, STL, Nastran, UNV, and TSS
  • Detailed model for molecular outgassing, which takes into account surface desorption and adsorption from the gas phase
  • Particulate generation per IEST-STD-1246D and ISO-14644-1 industry standards
  • Material activation energy and time-dependent surface temperature used to compute sticking probability
  • Drifting Maxwellian and effusion sources can be included to model venting of internal cavities
  • Multiple simulation particles traced concurrently, allowing visualization of contaminant plume densities
  • Support for external gravitational, aerodynamic, and electrostatic forces
  • Intermolecular collisions can be included via DSMC
  • Simulation results saved in VTK or Tecplot format. Support for saving surface, volume, and particle data.
  • Support for multithreading and parallel processing with MPI

Examples


Figure 1. Molecular contaminant plume and surface deposition on a generic satellite. Thanks to John Chowner from Pointwise for tracking down the CAD file and generating the mesh.
Figure 2. Steady state equilibrium in a closed system. Contaminant initially present only inside the small sphere redistributes until concentration gradients vanish.

Figure 3. Simulation of a QCM being used to monitor a bakeout of a test article. By comparing QCM deposition rate before and after a scavenger plate activation, we can obtain the QCM view factor and thus compute the article outgassing rate. The scavenger was activated dynamically by specifying a time-dependent surface temperature.

Figure 4. Simulation of a gaseous purge being used to prevent infiltration of particulates onto a detector. The detector percent area coverage (PAC) scales inversely with purge gas flow rate.
vacuum chamber water flash off simulation frame 1 vacuum chamber water flash off simulation frame 2 vacuum chamber water flash off simulation frame 3 vacuum chamber water flash off simulation frame 4
Figure 5. Time evolution of surface water flash off in a vacuum chamber with warm (left image in each plot) and cold (right image) thermal shroud. Cold shroud leads to lower chamber pressure.
Figure 6. Use of CTSP’s MPI ensemble averaging to improve resolution. Log-scale result with 1, 6, and 60 processes.

System Requirements

CTSP is a command line program for Microsoft Windows and Linux Ubuntu or CentOS distros. A CAD/FEM meshing package (such as FreeCAD, Salome, or Pointwise) is needed to generate the surface geometry model. A data visualization program (such as Paraview, Visit, or Tecplot) is needed to visualize the results.

Licensing

Seat licenses are available to US customers. Please contact us for pricing information.

A handout is available here: CTSP-flyer.pdf

References

  1. L. Brieda, “Numerical Model for Molecular and Particulate Contamination Transport”, AIAA J. Spacecraft & Rockets, published online, October 2018 (link)
  2. L. Brieda, “Molecular Contamination Modeling with CTSP”, Proceedings of 30th International Symposium on Rarefied Gas Dynamics, Vol. 1786, No. 01, 2016, http://doi.org/10.1063/1.4967536 (pdf)
  3. L. Brieda, “Molecular Outgassing and Deposition in EP Applications”, 34th International Electric Propulsion Conference (IEPC), Kobe, Japan, 2015 (pdf)