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Modelling: AerospAce
Aerospace modelling
is taking off
can weed out unacceptable ones
Aircraft are enormously sophisticated systems – and
before going to the time and
the expense of building a wind
expensive, as well, so effective prototyping becomes
tunnel model and testing it.
a matter of survival. Paul Schreier investigates how
Almost a flying wing
CFD and other engineering software tools have become And that’s if you have access to
indispensable in optimising aircraft and for developing
a wind tunnel, which wasn’t the
case for the start-up Propulsive
completely new concepts
Wing LLC. That firm initially
used what company president
Joe Kummer refers to as the
In the early days of aerospace conflicting, requirements. In made a significant improvement ‘poor man’s infinite wind
design, most CFD analysis was the case of a wing, the trade-off in a wing’s cruise efficiency. tunnel’ – strapping an early
done with in-house codes, is usually drag versus weight. Unfortunately, adds Ball, three-foot prototype to the roof
but the situation is changing. You can always reduce a designers still ended up testing of a minivan and driving down
For example, Doug Ball, chief transonic wing’s drag by making many, many wings. While it’s country roads. In those tests,
engineer of aero characteristics it thinner – but it will then be necessary for a wing to have empirical data showed good
and flight performance at much heavier, resulting in an good cruise performance, correlation with pitch stability
Boeing, estimates that these airplane whose performance the lift/drag ratio is not the from CFD results. In this way,
days about 20 per cent of his is not as good. Structural only factor affecting wing they had confidence that the
company’s utilisation is with weight is driven by how much acceptance. Wings must actual craft would be stable in
proprietary codes, 30 per cent depth you have as well as the have acceptable off-design the air, dramatically cutting
NASA-originated codes and 50 load’s magnitude. And as any characteristics, particularly in down the cost for trial and error.
per cent commercial software. passenger can see through an the longitudinal axis. Improved The company is now flying
airplane window, wings often CFD tools that model separated prototypes of what looks like a
A universal tool move in response to gusts; flows allow engineers to assess flying wing with a small fuselage.
As the image (right) indicates, these are elastic structures. But various designs throughout the This new class of aircraft uses
CFD is contributing to many as a wing bends and deflects, flight envelope – especially the a cross-flow fan built into the
facets of aerospace design and the loads change. In order off-design areas, so that they trailing edge of the wing; the
development, going far beyond to accurately predict both a
the traditional aspects of flow wing’s performance as well as its
analysis around the wings weight, you must know how the
and fuselage. Of these areas, structure will react to expected
Ball points to two as being loads. Boeing’s processes in this
particularly interesting and regard have been dramatically
where CFD has made a major improved to the extent that the
contribution. first loads database for the 747-
One such area is aeroelastic 8F now in development was
load prediction. The ‘best’ produced by computer.
airplane, comments Ball, A similar aspect deals with
rarely has the ‘best’ individual the edges of the flight envelope
components; it becomes and wing design. The advent
the best by having the right of Euler solvers with coupled
cFd is being used in a wide range of application areas in the design of
balance across many, often boundary layers around 1980
the Boeing 787 dreamliner (image courtesy of Boeing).
scienTiFic coMpUTing World october/november 2009
SCWoct09 pp44-47 aerospace.indd 44 10/1/09 12:50:57 PM
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