Today, virtually all commercial aircraft possess sophisticated systems that contribute to a comfortable—not to mention safe and healthy—environment for passengers. These systems mostly operate in the background and often go unnoticed. However, some systems, like individual air nozzles, have an interface that passengers can personally control. By increasing or decreasing airflow from the overhead nozzles, passengers can affect their thermal environment; a must-have feature during crowded flights, especially during extended waiting periods while the aircraft is on the tarmac. But individual air nozzles have a high pressure loss that also contributes to in-cabin flow noise.
Recently, engineers at Airbus investigated the individual air distribution system and found that the system could be simplified significantly once the pressure loss of the nozzle was reduced. This simplification could result in system-wide weight reduction and contribute to tertiary efficiencies in aircraft fuel economy, production, and maintenance.
The objective of Airbus’ optimization work was to minimize the pressure loss of an individual air distribution nozzle while maintaining the cooling effect perceived by the passenger. “The shapes of the cone and the inside of the housing are what we specifically tried to optimize,” said Airbus Systems Engineer, Andreas Ruch at the 2017 STAR Global Conference in Berlin.
Air nozzles historically don’t receive much critical design attention. Running an analysis on various designs in search of the optimal design would have been a very time intensive process. However, Airbus engineers utilized Dassault Systèmes CATIA and Siemens' STAR-CCM+ and Optimate+ CFD tools to perform the simulation and design exploration in a relatively short period of time.
The STAR-CCM+ application allows engineers to input fluid flow problems via a personal computer or laptop, while a remote machine calculates the computationally expensive math. This client-server architecture reduces the need for in-house computer rigs or separate solving applications coupled together (a complicated and time-consuming process that degrades accuracy).
“It only took four days for the optimization itself. For every CFD simulation, the biggest part is the preprocessing. Once we identified the proper parameters, it took three or four days for the creation of the various design geometries. But the actual time for the calculation of 175 different designs, took four days," said Ruch.
Of the 175 designs, he said about 20% would feasibly reduce pressure losses in the passenger air system. “In the past, when we did this manually, we would have needed at least one day for one design. And these were calculated and post processed without any human interaction. And that is the biggest benefit of this way of working.”
Since the development of a new, clean sheet aircraft occurs every 10 or 15 years, Airbus’ daily focus is to constantly improve the aircraft it already produces. The first A320 entered service nearly 30 years ago and the A320neo program centered on updating the aircraft’s engines (to the CFM International LEAP-1A and the Pratt & Whitney PW1100G-JM) began in 2010. Apart from new engines, the -neo versions have been enhanced with numerous aerodynamic refinements and systems upgrades. However, the motivation behind the air nozzle exploration is only a small piece of Airbus’ parallel strategy of incremental development.
Since 2014, Airbus has made a multitude of incremental improvements to the A320 platform. Some of these include changes to lavatories to increase available passenger seating, LED lighting to reduce maintenance costs, and the fitting of a Wi-Fi connected in-flight entertainment (IFE) systems. But incremental development goes far beyond passenger comfort.
“We are always looking for weight improvements and reduction in complexity, so we can produce our aircraft faster. For example, when the A320 program started, each airframe spent roughly 40 days in the final assembly line. Today it’s 26 days. Optimization is everywhere,” said Ruch.
The air nozzle optimization is still only in the feasibility study stage. Since it is a component visible to the passenger, the design change requires analysis and buy-in from acoustic and industrial designers. Aesthetics also comes into consideration.
“We still have to start and invest and highlight the potential of such improvements,” says Ruch. “Pressure loss is always killing efficiency. These are not huge parts of course, but we are looking as secondary effects. If we can cut out extra duct from the aircraft, that might be 10 or 15 kilos of weight. That’s a major benefit. And then there’s also the complexity and efficiency in production and maintenance. Simple is always better.”
Over the next few years, further incremental improvements for the A320 line include an optimized cabin layout, outfitting cockpits with WiFi networks to improve pilot operations, and the development of a long-range A321LR model.