Small disturbance Euler simulations for delta wing unsteady flows due to harmonic oscillations

Unsteady aerodynamic forces for aeroelastic analyses may be calculated by Euler or Navier-Stokes codes. Because of the large number of parameters, the computation times and costs become very high and the iteration process for a flutter free configuration could become quite lengthy. Therefore, classical potential methods are still widely used, and advanced codes are applied punctually in critical ranges for validation or refinement only. At the Institute for Fluid Mechanics (FLM) of the Technische Universität München it was proposed since 1998 to make use of the fact that the unsteady forces required for aeroelastic stability investigations are usually related to small displacements of the aircraft structure. They are, in general, only a small fraction of the occurring steady forces. Therefore, the Euler or Navier-Stokes equations may be developed for small displacements in the frequency domain, realized for inviscid flow in the FLM small disturbance Euler code, FLM-SDEu. After a comprehensive validation, here FLM-SDEu is applied to a cropped delta wing with 53-deg leading-edge sweep, investigating rigid body, flap, and elastic harmonic motions. Compared to the full Euler solution, the accuracy of FLM-SDEu is very good, and the required computer time is reduced by an order of magnitude.