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 transport is commonly encountered in vacuum and aerospace industries. Plastics and other organic materials exposed to low pressures outgas unspent hydrocarbon molecules which can deposit on 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 acting on the particles. Unlike Monte Carlo ray tracing tools, CTSP concurrently simulates the entire contaminant population. The transition regime can thus be considered by including inter-particle collisions via the DSMC method. It also allows the end user to visualize the contaminant plume partial pressures or bulk streaming velocities. CTSP supports highly detailed, multi-million mesh 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

  • Support for complex geometry defined in common mesh formats, including OBJ, STL, Nastran, UNV, and TSS
  • Utilizes methods found in DSMC / PIC to account for external forces and inter-particle interactions
  • Simulation results saved in VTK or Tecplot format. Output options include surface, volume, and particle data
  • Implements a detailed model for outgassing which takes into account surface desorption and adsorption from gas phase
  • Surface temperature and material activation energy used to compute sticking probability
  • Drifting Maxwellian and effusion sources can be included to model venting of internal cavities
  • Particulates generated according to the IEST-STD-1246D distribution coupled with a release model of Klavins and Lee

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. Simulated QCM is 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. This then allows us to compute the article outgassing rate from the QCM deposition rate. The scavenger was activated dynamically by changing the temperature of the corresponding surface mesh elements.

Figure 4. Gaseous purge is 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.

System Requirements

CTSP is a command line program for Microsoft Windows and Linux Ubuntu or CentOS distros. A COTS CAD/FEM meshing package is needed to generate the surface geometry model. A plotting program such as Tecplot or Paraview is needed to visualize the results.

Availability

Seat licenses are available to US customers. Please contact us for more 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, accepted for publication July 2018
  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)