Fluid Structure Interaction Simulation on the F/A-18 Vertical Tail

Abstract

For the Swiss F/A-18 Aircraft, the Boeing Company performed an Aircraft Structural Integrity Study (ASIP) to analyze the structural integrity of the entire airframe based on the Swiss design spectrum. To validate this study a full scale fatigue test was carried out at RUAG. By setting up the test facility and preparing the fatigue test loads using data from the F/A-18 Original Equipment manufacturer (OEM) RUAG met some difficulties due to the sparse documentation. This situation pushes RUAG to search for methods to generate aerodynamic loads for the F/A-18 on its own. As a result a large investment is made in the development and implementation of Computational Fluid Dynamics (CFD). The Center Aerodynamics of RUAG employs the Navier Stokes Multi Block (NSMB) computational fluid dynamics (CFD) code which is developed in an international collaboration. The CFD code was validated by comparing results of calculations with wind tunnel results, and literature cases. The F/A-18 CFD model was validated with loads data from the Boeing flight loads data base. For selected load cases unsteady calculations are carried out. The fluctuating loads at the vertical tail due to the buffeting induced by the vortices of the leading edge extension are up to 2.5 times higher than the averaged steady state value. Using the information of the CFD calculation a Swiss dynamic design spectrum is created and compared with the Boeing spectrum. Unsteady coupled results using CFD calculations for dynamic load analysis on the F/A-18 vertical tail are presented here. The use of novel unsteady aero-elastic simulation will improve the design of modern aero structures due to buffeting and flutter problems in an early design phase.