Simulation of Aircraft Ditching
On Jan. 15th 2009 an Airbus A320 of the US Airways landed on the Hudson River in New York after a failure of both engines. All 155 people on board did survive this event (aka. aircraft ditching) with minor injuries. The present research is concerned with a seemingly marginal area of an aircraft's design, i.e. its ditching capabilities.
The topic is of relevance for the certification of commercial aircraft. This is evident, since a significant portion of an average air travel is above an ocean or a lake. Accordingly, simulation methods for the investigation of aircraft ditching are developed and continuously improved in cooperation with Airbus Germany.
The research effort is concerned with the prediction of the impact and landing phase of the ditching event (cf. Fig. 1). Emphasis is given to a fast ditching-simulation method "Ditch", which is based on an extension of the momentum theories initially reported by von-Karman (1929) and Wagner (1932). The numerical approach considers
- modelled hydrodynamic effects of cavitation and ventilation
- potential loss of appendages like engines and flaps
- motion of the aircraft (restricted to 3 degrees of freedom - thus, only the vertical plane is investigated)
- calm-water surface, periodic waves, natural long-crested seaway or shallow-water waves
- elastic beam models for the wing and the fuselage
Principal results are the time records of the aircraft motion supplemented by the computed forces and pressures on the aircraft components.
Fig 1: Four phases of the ditching event, i.e approach, impact, landing and floatation phase (from left to right).
Analysis and Validation
Intensive model tests - primarily based upon guided motion - are carried out to assess the predictive quality of the approach. Moreover, validation against full-scale and model-scale, 3D-multiphase RANS-simulations are performed next to an intensive analysis of accidents.
Fig. 2: Example for a guided motion test (left) and ditching investigation triangle (right).
Results displayed in figures 3 and 4 indicate that the ditching simulation tool returns a fair predictive accuracy even for complex situations, where cavitation and ventilation occurs.
Fig. 3: Experimentally observed water lines (left) vs. computed ditching footprints (right).
Fig. 4: Surface pressure distribution for full-scale simulations using 3D RANS-CFD with (left bottom) and without (left top) cavitation and comparison of predicted section forces (right).
The work is supported by the AIRBUS Operations GmbH, Germany.