Fluid Dynamics Analysis Protects Astronauts

Computer simulation is helping to protect astronauts in the International Space Station (ISS), from carbon dioxide buildup when the crew quarters ventilation system is out of service. Astronauts in the space station sleep in small compartments or crew quarters that are equipped with doors and ventilated with fans. The concern exists that if the fans were to stop operating, carbon dioxide could build up to potentially dangerous levels.

In the past, engineers addressed this type of environmental issue using single-node simulation software. Boeing engineers are now using computational fluid dynamics (CFD) to predict carbon dioxide concentration in every area of the cabin. One of the lessons they learned from the simulation: When the fan was turned off for a certain period, dangerous levels of carbon dioxide indeed occurred in the crew quarters.

In the past, engineers have used single-node codes to model the ISS environment. But, says Boeing Principal Engineer Chang H. Son, one basic limitation of these codes is that they cannot model airflow within a cavity, so they must assume uniform temperature and species concentration. "This simplification was not acceptable in this application because high concentrations of carbon dioxide near the crew members can be dangerous even if average levels within the crew quarters are acceptable."

As part of a CFD analysis, Son says, a researcher can change the system geometry or the boundary conditions and view the effect on fluid flow patterns, temperatures, or the distributions of other variables. Boeing engineers used FLUENT CFD software from Fluent Inc.

Son built the CFD model to represent the ventilation configuration within one of the crew quarters. The region was modeled as an enclosed cubic volume with an inlet for air at one end and an outlet at the other end. The FLUENT model had over 500,000 tetrahedral cells.

The CFD results showed that approximately 22 percent of the volume of the crew quarters had an air velocity in the range of 15 to 40 fpm.

(Top): CO2 Concentration Results--concentration contour plot at 10 min. (Bottom): Analysis Location--three locations observed (unit in feet per minute).