Advanced Fluid-Structure Interaction Modelling and Simulation for Aerospace Applications

Licentiate thesis, 2022

Numerical fluid-structure interaction (FSI) methods for the prediction of aeroelastic phenomena are important within aerospace. The continuous development of computer technologies has enabled the use of more advanced FSI methods. The use of advanced methods has the potential to provide more accurate predictions. It also enables simulation of applications for which engineers traditionally have relied upon wind tunnel testing and flight testing, and still do to a large extent. Hence, the use of more advanced FSI methods would limit the need for wind tunnel testing and flight testing, and in extension reduce the lead time and cost of aircraft development.
High Reynolds number flows, involving separated flow, are very challenging to simulate. Hybrid Reynolds-averaged Navier-Stokes (RANS)-large-eddy simulation (LES) techniques provide the possibility to simulate such flows for industrial purposes. Hybrid RANS-LES methods are employed in this thesis for two applications which require turbulence-resolving techniques.
First, the effects of elastic walls on the aeroacoustics in transonic cavity flow are investigated. The prediction of structural vibrations is also important since vibrations may endanger the structural integrity, additionally, vibrations may negatively affect other apparatuses. The features of cavity flow appear in weapon bays and landing gear bays in an aircraft. In a deep cavity, the flow constitutes of broadband and tonal noise, referred to as Rossiter modes. The cavity structure is simulated with a modal-based approach and with a non-modal approach where the equation of motion is solved for all degrees-of-freedom of a reduced order finite element model. The results evince that the aeroacoustic field is altered by the elastic walls. For the investigated case, the energy of the 4th Rossiter mode is depleted and a strong tone is induced at a frequency below the 4th Rossiter mode, which is absent in the rigid cavity; these observations are made with both the structural simulation methods. However, with the non-modal approach, a second strong tone is induced at a frequency above the 4th Rossiter frequency.
The second investigated application is the aeroelastic prediction of a wing at Mach numbers ranging from subsonic to supersonic speeds. The viscous effects become significant at transonic speeds and may provoke shock induced flow separation. It is shown that the viscous effects play an important role under such circumstances and that both static and dynamic structural responses differ significantly depending on whether hybrid RANS-LES or unsteady RANS is employed for the flow simulation.