Greater use is being made of computational fluid dynamics (CFD) in the development of the Airbus A350XWB. CFD is being used to help design the external shape of components such as the wing and its elements, which are exposed to airflow in order to optimise aerodynamic performance.
The quality of CFD has improved in recent years, making predictions very reliable. Also new for the A350 programme is the early delivery of aerodynamic data, which previously had only been carried out with wind tunnel testing. Compared to the A380, CFD has reduced the amount of high speed wind tunnel testing needed for the A350â€™s development by 40 per cent, advancing its aerodynamic development time by six months or so.
One of the key advantages of CFD is its ability to begin delivering aerodynamic information as soon as the outer shape of the aircraft has been defined and is available in the form of computer-aided designs. There is no need to manufacture a complex, instrumented scale model - which is necessary for wind tunnel testing.
CFD also provides a comprehensive picture of the aircraft's aerodynamic information, whereas tunnel tests only provide local information at points where particular probes are placed. With CFD, it also is possible to simulate the aircraft's structural behaviour - for example, determining the effect of a structural deformation caused by aerodynamic forces, which in turn is needed to optimise the aircraft design.
Even with the benefits of CFD, wind tunnel testing remains an important part of the A350 design process. In particularly complex cases, the physics of air flow cannot be practically modelled on computers. In addition, wind tunnel productivity is still beyond that of CFD.
Aerodynamic tunnel testing on the A350 began in late 2006 and will run for another three years. Wind tunnel tests are performed in both low and high speed conditions to analyse the aircraft's take-off, landing, cruise behaviour and flight performance. The aerodynamic data produced from these tests is used to size the aircraft and to describe its handling qualities.
In order to meet the challenging programme milestones, most of the tunnel testing is being conducted in shifts involving trans-national teams. Within the A350 XWB aerodynamics development plan, wind tunnels are the key tools for massive data production and final design validation.