Breathe easy: Clean Sky’s ADVENT brings innovation to aircraft cabin ventilation

Entrance to the new long-range cabin mock-up with active temperature control allowing the study of different flight phases
Entrance to the new long-range cabin mock-up with active temperature control allowing the study of different flight phases

Higher seating densities and more personal electronic equipment being used onboard by travellers means cabin ventilation systems have to work overtime to maintain air quality standards and meet passenger comfort requirements. Clean Sky’s ADVENT project is exploring advanced ventilation techniques with enhanced heat removal and local ventilation efficiencies. This is achieved through experimental simulations of operational conditions as well as  implementation of numerical simulations.

’Increased thermal loads in aircraft cabins brought about by higher seating densities and more personal electronic equipment, as well as the demand for industrial modular design, are pushing state-of-the-art mixing ventilation to its limits,’ says Dr. Daniel Schmeling, Team Leader of Vehicle Ventilation and Air- Conditioning at the German Aerospace Center (DLR) in Göttingen.

’Alternative ventilation concepts with enhanced heat removal efficiency and local ventilation efficiency require reconsidering the air fraction [the ratio between fresh air and recycled air] in modern passenger aircraft cabins in order to save bleed air [drawn off the main aircraft engines] so as to conserve energy in the future.’

Clean Sky’s ADVENT project, which is supported by the EU’s Horizon 2020 programme in collaboration with the aviation industry and runs until 2021, is taking on the challenge of improving cabin ventilation standards with a project that has set itself three interconnected objectives:

Firstly, to identify and benchmark a ventilation concept for long-range cabins with enhanced heat removal efficiency, increased local ventilation efficiency and improved thermal passenger comfort. The novel ventilation concept is intended to exhibit at least the same or better performance under dynamic conditions compared to mixing ventilation.

Secondly, a ground-based, full-sized mockup of a widebody aircraft cabin is in the final stage of construction at DLR, to facilitate experimental simulations and studies of future long-range cabin ventilation concepts. This is a milestone for Clean Sky systems demonstrators as the mock-up will be able to realistically replicate the thermodynamic boundary conditions and exceptionally homogeneous inflow conditions for unprecedented validation of Computational Fluid Dynamics (CFD) methods in subsequent projects. The facility will be used to simulate the different flight phases (i.e. push-back, take off, climb, cruise, etc.) under static and dynamic conditions.

Thirdly, the project provides an experimental reference database of velocity and temperature distributions, CO2 distributions and local ventilation efficiencies in the cabin for different ventilation systems.

Numerical thermal comfort evaluation for a novel ventilation concept presenting operative temperature
Numerical thermal comfort evaluation for a novel ventilation concept presenting operative temperature

’The design and set-up of the mock-up is part of the project and special attention will be given to the possibility to precisely define the thermal and fluid dynamical boundary conditions,’ says Dr. Schmeling. ’This allows for experimental simulations of operational conditions using temperature-controlled surfaces on the one hand and precise implementation in numerical simulations by appropriate idealisation of the inflow velocity profiles on the other hand.’

In terms of what Clean Sky’s ADVENT project brings to European aviation, Dr. Schmeling points first to the mock-up that provides thermodynamically realistic boundary conditions for static and dynamic investigation of different flight phases.

’To our best knowledge, this new mock-up will be the largest highly modular dual-aisle cabin mock-up allowing the investigation of ventilation concepts regarding their energy efficiency, thermal comfort and capability of integration under precise boundary conditions.’ He adds that the ’new hybrid ventilation concepts revealed their advantages regarding heat removal efficiency, spatial homogeneity of temperature and velocity and thermal comfort (i.e. predicted mean vote, predicted percentage of dissatisfied passengers and equivalent temperature distribution) in numerical simulations’. Patents have been applied for in cooperation with Airbus.

Design study for new mock-up
Design study for new mock-up

’The capability to integrate the new system in the aircraft itself and in the industrial production process is an additional evaluation parameter,’ says Dr. Schmeling. ’Further, the deployment of a groundbased full-scale test facility for experimental simulations of future long-range cabins will be highly relevant for the European aircraft industry. This mock-up will be very flexible in terms of integrating novel ventilation concepts. Also, an experimental and numerical database for different ventilation systems will be compiled comprising velocity, temperature and CO2 distributions as well as ventilation efficiencies.’

New cabin mock-up fully equipped with thermal mannequins simulating the blockage and heat release of real passengers
New cabin mock-up fully equipped with thermal mannequins simulating the blockage and heat release of real passengers

Implementing innovative and efficient ventilation concepts in ’twin aisle’ cabins will impact the aircraft systems by reducing the required cooling demands of the cabin air conditioning system. Several components of the electric environmental control system (E-ECS) will benefit from these new concepts resulting in smaller and lighter components. Furthermore, novel ventilation systems will provide the opportunity to redesign the whole ducting system and save weight. The capability of the deduced ventilation systems to modify the local Air Change Efficiency (ACE) offers the possibility to improve the air quality and thus the passenger well-being with the actual fresh air fraction.

Though the ADVENT project is just past the half-way stage, DLR is already able to make some estimations of the eventual outcomes: ’With respect to the current value of already about 50% of recirculated air, a further reduction of bleed air by e.g. 25% would result in fuel savings of about 0.25%. If we assume that a 25% reduction of bleed air results in the same relative weight reduction of the environmental control system (ECS) – bearing in mind that the novel ventilation systems potentially allow for a reduction of the ECS tubing and a reduced cooling demand – further fuel savings of 0.125 to 0.25% can be achieved,’ indicates Dr. Schmeling.

’Taking the predicted global aviation fuel consumption into account, our estimation corresponds to annual savings of up to 5.3 Mio. tons/yr. of CO2 in 2020. All of this aligns, of course with the European sustainability objectives for “a transport system that is fit for a modern, competitive Europe”.’

’The ADVENT project is addressing this ambition in a way that the new ventilation concepts will help to reduce the fuel consumption and further will allow to promote future energy management systems for modern long-range passenger aircraft,’ concludes Dr. Schmeling. ’Additionally, the innovation action of Clean Sky’s ADVENT project in terms of developing and operating a new ground-based, full-scale test facility will be a contribution to the EU Horizon 2020 ambition of world-class infrastructure.’

View from outside new cabin mock-up, located below original rebuilding of the Lilienthal glider
View from outside new cabin mock-up, located below original rebuilding of the Lilienthal glider

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