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Session: Gust 2
Session starts: Wednesday 19 June, 11:00
Presentation starts: 11:00
Room: Room 1.4/1.5

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Arne Voß (DLR Institute of Aeroelasticity)

Abstract:
The gust encounter of a supersonic fighter aircraft is investigated with the CFD code SU2 and the aerodynamic panel methods VLM and ZONA51. The interaction of the elastic aircraft, the flight controller and the gust is captured in a closed-loop time domain simulation. The comparisons show a moderate agreement between aerodynamic panel methods and CFD in terms of section loads, which has multiple reasons: first, the two aerodynamic methods yield different pitching moment characteristics, which have an influence on the flight mechanical reaction of the aircraft and the reaction of the flight controller. Second, due to the increase of the effective angle of attack during the gust encounter, vortices develop, which are not present in the horizontal level flight condition. Because of the large suction peaks due to the vortices, the surface pressure distribution changes significantly, an effect that is missed completely by the aerodynamic panel methods. The section loads predicted by the CFD based approach are higher, which eventually influences the structural sizing of the aircraft. Also, there is a significant structural dynamic reaction, which shows that for fighter aircraft, a transient gust analysis including structural elasticity is essential for the aircraft design. The comparisons show a moderate agreement between aerodynamic panel methods and CFD, which has multiple reasons: first, the two aerodynamic methods yield different longitudinal characteristics, which have an influence on the flight mechanical reaction of the aircraft and the reaction of the flight controller. Second, due to the increase of the effective angle of attack during the gust encounter, vortices develop, which were not present in the horizontal level flight condition. Because of the large suction peaks due to the vortices, the topology of the surface pressure distribution changes significantly as shown in Figure 1 - an effect that is missed completely by the aerodynamic panel methods. The section loads are higher using CFD, which possibly influences the structural sizing of the aircraft. Also, there is a significant structural dynamic reaction, which shows that for fighter aircraft, a transient gust analysis including structural elasticity is necessary. The final version of this paper will present the underlying aeroelastic models, extended by a longitudinal flight controller. The findings described above will be substantiated by inspecting the flight mechanical reaction of the aircraft and the differences due to the non-linearities in the CFD aerodynamic. The section loads are be quantified in terms of bending and torsional moments and at the wing root. Large parts of the results have been prepared already, so that the author is confident to finish the final paper in time.