Simplifying simulation


Robert Roe investigates the use of simulation within


the aerospace industry and the steps taken to reduce the complexity of software for engineers


soſtware vendors to create packages that can take more of the work off the users by streamlining or even automating processes. Soſtware that is easier to use allows engineers


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more time to focus on simulation and analysis of the data rather than trying to adapt to new soſtware, learn proprietary coding languages, or the worrying about how to map algorithms to the latest GPU or accelerator technology. At one level, the move to more user-friendly


soſtware can be as straightforward as migrating legacy code from Fortran to newer, more intuitive languages such as Matlab. In complex aerospace design problems, on the other hand, sophisticated soſtware that can automate much of the process of optimising designs can shorten development times and make design engineers more productive. Sometimes, the benefits in aerospace engineering come not solely from the soſtware alone but by coupling the package to novel manufacturing techniques such as 3D printing. Aircraſt noise has become a major concern


and in some cases is an obstacle to growth in air transport as numbers of airports place restrictions on the amount of noise that can be generated by an aircraſt. Designers and engineers must work hard to reduce the noise of jet engines by placing acoustic


32 SCIENTIFIC COMPUTING WORLD


t all stages of aerospace design, engineers find themselves using models of increasing complexity. In turn, this generates a requirement on


Airbus: Nacelle liner acoustic simulation


liners in the nacelle, a housing that holds engines, fuel, or equipment on an aircraſt, to minimise the fan noise radiated from the engine. One example of the use of MSC soſtware


for acoustic simulation looked at the use of nacelle liners on Airbus aircraſt. Te company evaluated several different shapes and materials to understand the best performance. Airbus found that it could dramatically reduce


the time required to design and evaluate acoustic liners by moving to a simulation-based process using Actran acoustic simulation soſtware developed by Free Field Technologies (FFT), a subsidiary of MSC. Diego Copiello, MSC product marketing


manager and senior application engineer, said: ‘Liners are absolutely fundamental to the aircraſt design. If you want to reduce the noise generated by the engine, the only technology that you can apply in the nacelle is to use the liners.’ Te design of the nacelle itself is made more


difficult by several factors, first of which is that the final geometry of the nacelle may not yet be finalised, so any design may have to accommodate changes in the shape of the nacelle in which it is housed. Another restraint is the materials that can be


used for the nacelle liner, as Copiello explained: ‘You cannot use a porous material on a nacelle for


secures soaring success


example, because porous materials absorb and keep the water or kerosene so there is a risk of ice formation or there is a fire hazard.’ Copiello went on to highlight how this restricts


the potential design options available to engineers looking to optimise the design of these liners for commercial aircraſt, as they have no choice but to innovate when designing the geometry of the liner to allow for the greatest increase in performance. Even a small part of an aircraſt, which at first


glance may seem insignificant, oſten requires several simulations and a delicate balance must be struck between performance, cost and weight. Another oſten overlooked layer of complexity is in the combination of different disciplines or different types of data that need to be integrated to provide a clear picture of the overall behaviour of the system. Tis could take the form of FEA, CFD, or thermal analysis as well as acoustic. To combat increasing complexity, soſtware


developers abstract complexity or completely automate features that traditionally would have required many man-hours’ work in repeating experiments or simulations. In the case of Airbus, the engineers found they could automate the optimisation process when designing the nacelle liners. Copiello said: ‘So the automated liner


optimisation chain basically gives Airbus the possibility to run everything automatically.’ Te team at Airbus developed an integrated


numerical chain for Actran in order to streamline its use by acoustics engineers who are not numerical experts. Te chain, called the Automated Liner Optimization Chain for Nacelles Air Inlets and Exhausts (ANaNax), automated the simulation process from engine geometry to results. A typical optimisation loop for the nacelle


liner requires evaluation of 80 liner iterations and three flight conditions at a frequency range from 125Hz to 5650Hz, which means several thousand different iterations.


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