Breathing space

Ventilation systems work efficiently on earth, but in space the rules change dramatically. Computational fluid dynamics helped Boeing engineers solve a tricky design challenge.

Boeing engineers have made a simulation breakthrough that will enable them to make vital changes to the ventilation system of the International Space Station’s cupola.

Using computational fluid dynamics (CFD) software to simulate the airflow and temperature within the cupola – a pressurised observation area – the team claims it can improve the air breathed by the crew member manning it.

The cupola, not due to be attached to the ISS for several years, will house a robotic workstation (RWS) that will control the station’s robotic arm.

Boeing’s Jorge Zapata explained that because using the robotic arm is such a delicate operation, it is essential to keep the operator comfortable and relaxed with fresh air and a cool environment.

Although CFD is commonly used in the heating, ventilation and air conditioning industry, it is being used in a slightly different way for the ISS programme said Zapata. He explained that while inhaling our own exhaled air isn’t a worry on Earth, the rules change considerably in space.

‘In our environment the gases in the air mix naturally due to differences in density. Onboard the ISS, the lack of gravity means natural convection is not present and therefore forced convection is required to mix the gases,’ he said.

The crux of the problem was the effect of the robotic workstation on the cupola’s ventilation system. Using CFD software, the team modelled the airflow within the cupola with and without the RWS operating.

The CFD tests indicated that the required air velocity of 15-40 ft a minute was met when the RWS was switched off. However, as soon as the computer was switched on, the increased flow rate created by its fans seriously affected the ventilation system.Zapata explained why this happens. ‘the cupola obtains fresh air through tiny slits located around its edge. Without a modification to the RWS and with its fans running, the high-velocity air overpowers the air coming out of the slits and prevents it from reaching the crew member using the RWS.

‘The high-velocity air coming out of the RWS causes a cyclone-like air pattern within the cupola, so there is high velocity near the walls and low velocity near the crew member.’

The team also noted that this reduced air mixing made temperatures uncomfortable.

Test results showed that a laterally located vent on the RWS is responsible for the vortex air pattern. CFD was used to resolve the problem. A deflector was placed over the vent to bring the ventilation closer to specification, improve the air mixture, and lower the temperature around the astronaut.

The results of these simulations show that the deflector works by diverting the air from the laterally-located vent directly out of the cupola hatch, thereby hindering the formation of the vortex. This, in turn, results in lower air velocities, improved air, and more comfortable temperatures.

With the cupola not due to join the ISS for several years, and the RWS already onboard, these modifications will have to be carried out in space. How that challenge will be dealt with has not yet been decided said Zapata.

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