Ensuring damage-free emergency water landing of airplanes and helicopters

by Amaury Bannier, Product Manager at Nextflow Software
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Aircraft, such as airplanes and helicopters, are often required to fly overseas and must therefore be able to ditch (i.e. land on water) in case of emergency. Manufacturers are required to guarantee the integrity of the aircraft and the safety of passengers and crew during ditching and the subsequent flotation. To meet this ambitious challenge, appropriate structural sizing is essential.

The proper prediction of the stress endured by an aircraft during ditching is crucial to guarantee its resistance and ensure safety of passengers and crew. Unfortunately, due to the extreme violence and briefness of this stress and to the numerous physical phenomena involved, experimental testing is particularly complex and probably too expensive. Subject to time and financial constraints, numerical simulation is therefore essential.

Ditching of the US Airways Flight 1549 in the Hudson River, New York, USA on 15 January 2009Ditching of the US Airways Flight 1549 in the Hudson River, New York, USA on 15 January 2009 (by Greg L, cropped, Some rights reserved).

The physical phenomena involved in ditching are not only varied, involving simultaneously aerodynamics, hydrodynamics and structural analysis, but may also be extremely complex: 6-degrees-of-freedom aircraft, ground effect, pilot maneuvering, air cushion and ventilation, swell, impact-induced water jet, fluid-structure interaction, cavitation, hydrostatic load…

To properly account for all relevant phenomena when simulating aircraft ditching, engineers must resort to CFD software able to model each of those physical phenomena: multiphase flow (air and water), large distortion of free surface, swell generation and propagation, fluid-structure interaction, etc.

Validating the relevancy of such simulation is not an easy task, due to the wide range of physics. However, reference data have been made available thanks to the qualitative experimental campaigns conducted by the LHEEA laboratory of Ecole #CentraleNantes #CNRS and the #CNR-INM research institute, as part of the #SARAH #H2020 European project, with the help of #BureauVeritas, #Airbus and #DassaultAviation.

In upcoming articles, we will present the step-by-step approach adopted by Nextflow Software to assess and improve its numerical simulation capabilities, starting from a bi-dimensional academic test cases to a realistic business-jet ditching simulation as illustrated below.

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