STAR-CCM+ enables ICON to develop a complete-cabin CFD simulation process for Airbus
Article by ICON - Simon Weston, Thomas Schumacher.
ICON would like to thank Airbus-Deutschland for kindly allowing this work to be presented.

A long-standing co-operation with Airbus has seen ICON working on the design and improvement of ventilation systems for a number of different aircraft programmes such as the A380, A380-F, A340/330, A400M, A350XWB.

In the case of the A380, Airbus’ next generation full double-deck passenger aircraft, simulation engineers faced many new challenges. In its standard version the A380 holds 555 passengers in three classes, on two decks. In theory, a layout holding more than 800 economy class passengers is also possible. It is well documented that Airbus wants to offer airlines and passengers an improved level of cabin comfort and as a result significant demands are placed on the cabin ventilation system.

The ventilation system has to fulfil not only the requirements imposed by the authorities, like minimum air exchange rates or maximum pollutant concentrations, but also Airbus’ self imposed limits like maximum velocity, minimum humidity, etc.
In addition, the nature of the cabin flow field has to be designed to ensure the risk for spreading airborne transmitted
diseases is kept to a minimum. Public concern over the spread of Severe Acute Respiratory Syndrome (SARS) during 2003, ensured that aircraft cabin ventilation systems became the focus of public interest.

The fast turn-around times required in the early design stages of large cabin models are often not feasible due to the high
amount of cells required to resolve small features like air inlets. In the past, the hardware resources and software
capabilities were not always available to run extensive cabin models, which resulted in the problem of “boundary condition
closure”. Simulating just a slice of the cabin leaves two major boundaries (front & back) in the open. This problem can be
addressed by using no-slip walls, symmetry planes, prescribed in- and outflow or cyclic boundary conditions. However, each solution comes with certain compromises on either the accuracy and/or comparability of results. This is especially true if the area of interest is close to a cabin feature such as the galley, lavatory or, in the special case of the A380, stairhouses. The availability of low-cost CPU power and the release of STAR-CCM+ allowed ICON to approach the problem by creating a complete cabin model for a double deck aircraft seating 484 passengers in three classes.

The intention of this work was to:

• investigate the practicality of handling models for very
  
• develop an efficient work process including testing the
  suitability of CD-adapco’s new STAR-CCM+ solver
  
• investigate the cabin flow field in a complete “closed”
  domain by erasing the problems associated with additional
  unknown boundary conditions
  
• investigate the flow in the stairhouses and its effect on the
  adjacent cabin areas

Due to asymmetric geometry features in some galley areas and most notably the rear stairhouse, it was not possible to model just half of the aircraft. Only hex-dominant meshes were considered suitable to meet the required refinement levels near inlets and outlets and keep the overall mesh size within reasonable limits. The final mesh consisted of 75 million cells with over 90% being hexahedral cells (with aspect ratio equal to 1).

Using CD-adapco’s next generation software STAR-CCM+ and exploiting its new approach to parallel processing, ICON was able to use modest hardware to perform a detailed CFD study of the flow field in the whole cabin. This included assessment of comfort related parameters such as PMV (Predicted Mean Vote), PPD (Percentage People Dissatisfied), Age of Air etc. These results helped ICON to understand the special flow phenomena existing in complex cabin geometries such as the A380. It can also be seen as a “worst” case scenario in terms of domain size, since the only similar sized aircraft in the foreseeable future will be -900 stretch version of the A380. Finally, as CPU power becomes cheaper and more readily available, models of complete aircraft cabins will become even more detailed and/or quicker to run.