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As we move into the summer months, I am ever thankful that modern commercial aircraft systems have been developed to provide a safe and comfortable passenger experience. The Environmental Control System (ECS) is responsible for keeping the cabin at a comfortable temperature, pressure and humidity throughout the flight profile. This is done through a complex system of ducting, pressure regulators, heat exchangers and air conditioning components. Before the FAA can certify a new aircraft for commercial flight, the manufacturer has to be able to provide proof that the system can respond to situations where things go wrong.

One such scenario is when one of the ECS packs malfunctions mid-flight and the aircraft is left with one less ECS unit to control the cabin environment. Given there are 100-plus passengers in a cabin, the temperature and humidity in the cabin can become very uncomfortable without the aid of a full complement of cooling systems.

To this end, modern engineering groups have leveraged low fidelity system simulation to model the response of the system to ECS pack failure, which has helped ensure the overall system can continue to cool the cabin. The challenge with this approach alone is it can often neglect 3D effects which can be significant in such a scenario. We recently partnered with the AMEsim group in Lyon, France, to evaluate a coupled approach leveraging 1D system simulation coupled with 3D CFD to improve 3D prediction and 1D system performance.

With the help of AMEsim’s Olivier Broca and STAR-CCM+ expert Matthieu Stasia, we decided to look at several operating conditions, including various system failures. The strength of 1D system simulation is in modeling the complete flight profile from takeoff to landing, which is both fast and efficient but requires engineers to ignore 3D effects. Although it would be possible to model the complete profile with 3D CFD, it would likely be very expensive computationally as it would almost certainly require several weeks or more of wall clock time. Our approach was to couple AMEsim for the ECS system behavior, and STAR-CCM+ for the cabin environment, which could provide temperature pressure and humidity back to the system.

Once the concept was validated, we evaluated cabin environment during an ECS pack failure. The animation below shows the 3D cabin response when the system loses the cooling power of one of the units. You can see the rapid rise in temperature followed by a normalization of the cabin. In figure 1 below, you can see the 1D system response during the failure event. The conclusion of the study was that the combination of 1D system simulation and 3D CFD simulation is a powerful design tool that allows engineering groups to design more robust and comfortable cabins faster. 

 Figure 1: 1D system response results



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