During the cruise phase of flight, the flow around the fuselage and wings is transonic, i.e. there are areas where the Mach number is higher than 1 and others where it is lower.
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Computing of the Transonic Flow around Fuselage and Wings
for the Cat3D project
(elsA Computation by Vincent Brunet - DAAP)
This type of flow implies a recompression shock, characterized by a sharp pressure rise on the wing. Manoeuvring in such conditions might increase the shock, causing the rise of pressure gradient and the separation of the boundary layer. A zone of recirculation appears downstream from the shock. This zone, strongly unstable, is likely to cause important lateral instability on the plane, and thus its buffeting, which limits the flight envelope.
The prediction of this type of complex flow remains difficult since it is necessary to calculate the whole plane. The improvements of numerical methods and turbulence models will increase precision in the simulations.