Dynamic stability and response analysis using a small-disturbance CFD method

In the last decades, the aerodynamic tools used for aeroelasticity have been strongly developed. Nevertheless, because of its robustness and its high computational efficiency, the potential theory (e.g. Doublet Lattice Method) is still the standard tool in the Industry. A flaw of most of the CFD tools is that they do not fit properly for a multidisciplinary analysis as needed for aeroelasticity computations, for example because of high computational costs or because of a lack of robustness. However, these CFD tools could also provide important improvements for the correct prediction of the aerodynamics forces in aeroelastic computations, especially for complex airplane configurations and also at the control surfaces, where the Doublet Lattice Method is known to be of less quality and needing some tuning. Such improvements can lead to higher fidelity results, and therefore they can help improve the performance of the airframe and reduce certification issues due to aeroelastic uncertainties. In a cooperation between Cassidian and the Technische Universität München, it was decided to assess the robustness and the quality of the small-disturbance CFD tools that are provided by the Technische Universität München, in order to enhance Cassidian's prediction capabilities for aeroelastic problems. Previous studies of both partners have already proven that small-disturbance CFD tools are well fitted for aeroelastic analyses and also for multidisciplinary design optimisation (MDO), thus it was decided to use them for a more complex configuration: a generic medium-high altitude-long endurance UAV with high aspect-ratio wings and T-tail. The Ttail is also a very attractive feature for this study, because it is known to be more sensitive to the aerodynamic interactions and to the steady flight state as other conventional empennage configurations. This study presents flutter results for such a configuration for different Mach numbers and angles of attack in order to assess the prediction improvements using the small-disturbance CFD Method (in this case the small-disturbance Euler Method) compared to results obtained with the classical Doublet-Lattice Method.