This video presents some of the results obtained with the developed model.

Particule dispersion - Biosmhars project - Copyright VTT

The micro-organisms found in confined manned spacecraft are dominantly from human (respirator tract, skin, etc.) and partially from environmental origin (equipment, food, etc.).The crew is the most significant source of microbial contamination carriedonto the ISS.

Microbes can be transmitted to humans in a variety of ways, including via exposure to airborne, water-borne, and food-borne contamination, contact with contaminated objects, and person-to-person transmission. Airborne biocontamination, i.e. bio-aerosols, is considered to be especially important in spaceflight conditions, because microgravity makes bio-aerosol dispersion in space very different from what is known in earth conditions. Due to microgravity the relative importance of various deposition and removal mechanisms is very different in space than on earth. Particles will remain much longer airborne in space than on earth; and most particles will need to be removed by air flows of the-ventilation and high efficiency filtration, because deposition rate is decreased due to the almost negligible settling of particles. As such, airborne biocontamination and bio-aerosol dispersion were selected as primary focus of the BIOSMHARS project.

The development of a reliable mathematical model to predict bio-aerosol particle dispersion and deposition in closed space habitats would significantly improve the microbial biocontamination management. Such a model then can be used to pinpoint critical locations in a certain habitat design or operation and develop adequate prevention and monitoring procedures. Simulations with validated models will help to identify the risk areas where microbial growth may occur and to focus control measures appropriately. Ideally these areas can be avoided by careful redesign so that healthy indoor environment can be ensured.

In the BIOSMHARS project a CFD model was developed to describe and predict the airborne microbial contamination in confined space habitats, taking in to account the specific characteristics ofventilation in such habitats.

The model was calibrated first in a special test room at VTT, with volume, geometry and ventilation system similar to the one of the European Columbus module on the International Space Station. It was then validated in the BIOS-3 facility in Krasnoyarsk, Siberia. Calibration and validation were both done in 2 steps: first with non biological particles and then with biological particles.

  • In the first phase, the turbulent air flow field of the confined space was simulated, which is the cornerstone for model development. Provided that the key parameters in the CFD model were correctly set,satisfactory results were achieved with more robust high-Reynolds numberturbulence model and slightly better results were achieved with low-Reynolds turbulence model which is more costly to use due to increased grid size.The key parameters in the CFD modelcomprises computational grid, turbulence model, boundary conditions and near-wall treatment.
  • In the second phase, sources of human originated pathogens were included in the model. The aim was to model the dispersion of respiratory droplets as well as pathogens released from human skin. Two different approaches were used for the biocontamination dispersion; contaminant concentration dispersion method and discrete particle tracking method.

  • In the third phase, bio-aerosol deposition on surfaces was studied. The released particles are largely removed by ventilation with high efficiency filtration, but a fraction of them may also deposit by various mechanisms. Reliable simulation of deposition requirescareful treatment of near wall regions. In general, the performance of turbulence models increases with sophistication, but at the expense of increased computational effort.