applications Te air entering an aeroplane is usually


supplied from the engine compressor and is processed in an air conditioning unit before it enters the fuselage compartments. Te air conditioning and distribution systems must provide a homogenous environment that adheres to stringent health and safety regulations to maintain suitable thermo-acoustic insulation and temperature levels in the cabin and cockpit. In recent commercial aircraſt developments,


there has been a trend towards electronic systems integration characterised by higher heat densities and a more frequent use of composite primary structures. Pierpaolo Borrelli, senior specialist ECS and Ice Protection Systems at Finmeccanica Aircraſt division, explained: ‘Te overall aeroplane thermal efficiency is becoming increasingly important, since it affects several high level aeroplane requirements such as the fuel consumption, the direct operating costs and noxious gas emissions.’ Borrelli added: ‘Te passengers’ comfort


requirements are a crucial aspect of current commercial aeroplane top level aircraſt requirements. All these factors require robust aeroplane thermal management and thermal architecture design already at the preliminary design stages.’ ECS and Ice protection system engineers


at Finmeccanica Aircraſt Division used multidisciplinary optimisation methods and tools, coupled with CFD, to optimise airplane conditioned air distribution network and air outlets. Tis was done in order to achieve high levels of passenger comfort, both in terms of airflow distribution in the passenger cabin and low noise, while increasing the pneumatic efficiency of the network. Aſter comparing two alternative architectures,


the engineers built a model for the selected architecture and its subsystems using Esteco’s LMS Virtual.Lab node, and the workflow for the air nozzles shape optimisation was built with Esteco’s modeFRONTIER soſtware. Gaetano Mirra, senior specialist ECS and Ice Protection Systems at Finmeccanica Aircraſt division, said: ‘Te optimisation methods and tools of modeFRONTIER have helped us to achieve the best possible compromise between noise generation in the outlets, flow uniformity on the passenger and pneumatic efficiency of the air distribution network.’ Te cabin must not just provide a comfortable


environment for passengers, but a safe one. Last decade’s SARS outbreak led the Federal Aviation Administration to set up a consortium to investigate the spread of disease in an aircraſt environment. ANSYS formed part of that consortium and ran simulations to optimise the Environmental Control System (ECS) for the aircraſt’s cabin.


www.scientific-computing.com l High fidelity 2D and 3D physics-based


simulations were used to design several components of the ECS, as well as low fidelity 0D and 1D simulations at the system level, and these were validated against experimental data. Ideally, high fidelity simulations should be


done at the system level, but this is not always practical given the real-time responses required and computational power available, as Robert Harwood, global industry director at ANSYS, said: ‘Different scenarios require different levels of detail. If you think of the ductwork behind the panels in the aircraſt cabin, for example, you don’t really need to model them in 3D.’


THESE TIME SAVINGS ARE ESPECIALLY IMPORTANT WHEN SIMULATING THE INTERIOR AIRCRAFT ENVIRONMENT


Mark Walker, application engineering


manager at MathWorks, added: ‘Tis is where having a simplified model, with an appropriate level of simplification for a problem, means I can conduct a lot simulations within a lot of scenarios without having to wait an unreasonable amount of time to find the answer.’ A system level simulation that couples reduced


order models (ROMs) derived from high fidelity simulations of key components with lower fidelity simulations, where appropriate, is a viable solution for simulating the performance of an ECS system over a given flight. As Harwood explained: ‘We have added to our portfolio multi- fidelity aspects of simulation, so you can choose the right model for the right scenario and you can stitch these things together seamlessly.’


Economy cabin One of the major outcomes of the consortium


was the development of best practices when simulating inside an aircraſt. Te necessity for such best practices is clear, in part because such interior simulations are still a relatively new area compared with exterior aircraſt simulations, as Rittenberg added: ‘When organisations move into new applications of CFD in their design process, the main challenge is lack of institutional knowledge and best practices. Unlike external aerodynamics, where most organisations have decades of experience, application of CFD to underhood cooling problems [for example] requires a different set of skills.’ Yet the exterior of an aircraſt does have an


impact on the interior environment. Engine noise is a clear example here. A computational aeroacoustics (CAA) model of a flow duct was used in COMSOL Multiphysics soſtware to model the engine’s acoustical field, in order to optimise the shape of certain engine duct parts and the lining properties to reduce sound emission outside and inside the aircraſt. Noise transfer into the plane’s interior was


simulated by COMSOL using an inverse Finite Element (FE) method to identify noise sources in the aircraſt cabin. If all sound sources are located at the cabin boundary, then the equation system resulting from a matching FE model can be altered to extrapolate the unknown boundary data, based on measurement data taken in the cavity. Aeroacoustic and noise source identification


analyses are just two examples where the ability to couple several physics and work with an accurate geometry representation is necessary. Detailed meshing and using measured data are also vital to provide accurate simulations, as Valerio Marra, technical marketing manager at COMSOL, said: ‘With aircraſt design you really need to use an approach where you are not discounting ➤


Diffuser Seats


Air outlet Simulation-based assessment of passenger comfort in an aircraft @scwmagazine APRIL//MAY 2016 31


ANSYS


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