A fatal accident in July 2000 involving an Air France Concorde near the Charles De Gaulle Airport in Paris led to the temporary grounding of the entire fleet of these supersonic passenger planes.
An investigation revealed that a metal strip had fallen from another plane onto to the runway. When the Concorde taxied over the shard, its tyres burst, sending pieces of rubber flying into the air.
One piece struck the left wing fuel tank of the airplane, rupturing it. The leaking fuel ignited near the left engine, causing a huge flame to erupt behind the aircraft. The altered aerodynamics made it impossible for the pilot to control the plane as it took off. Tragically, the Concorde crashed near the airport, killing all people on board and some on the ground.
As part of the accident investigation, researchers from the University of Leeds looked into why the fire stabilised on the wing.
They used the VOF model in Fluent to understand the flow characteristics of the leaking fuel that gave rise to the observed flame formation.
A CFD model of the delta wing of the Concorde, minus the fuselage, was created. The fuselage was judged to have little or no impact on the development of the leaking fuel jet. Several simulations were performed using an estimated take-off speed of 100m/s (224 mph) and a range of attack angles that matched amateur photos of the incident.
In each model, a steady stream of fuel was discharged into the CFD domain from a small hole on the underside of the aircraft wing. Both the k-e and Spalart-Allmaras turbulence models were used in the study, and both led to similar results.
Fluent’s predictions indicated that a complex, recirculating flow structure developed under the wing as the aircraft lifted off, particularly inside the wheel bay.
This suggested that large recirculating air cells in the landing gear bay provided a suitably stable attachment point for the flame once it was ignited, probably by an electrical spark. The predicted fuel trajectory was mainly confined to a small area under the wing that closely matched the observed flame in the amateur footage of the crash.
This was a qualitative verification of the conclusions drawn by the model. The CFD study, plus other recent studies on how to improve fuel tanks for the Concorde fleet, has led to modifications that should prevent a similar incident from happening in the future.
The modified Concorde airliners were reintroduced to commercial service in October 2001, and the operational fleet is now fully functional.