High Reynolds Number Aerostructural Dynamics (HIRENASD)

With funding by the German Research Foundation (DFG), the collaborative research center "Flow Modulation and Fluid-Structure Interaction at Airplane Wings" (SFB 401) at RWTH Aachen University has prepared aeroelastic experiments with an elastic wing model in the transonic regime, which were performed in November 2006 in the European Transonic Windtunnel (ETW). DLR was engaged concerning aeroelastic data acquisition. Financial support was provided from Airbus for a new piezo balance for dynamic force measurements in ETW, and ETW prepared the accommodation for the new balance.
The transonic regime is characterised by strong non-linearities with shocks and phenomena which strongly depend on the Reynolds number such as shock-induced steady and unsteady flow separation, and possible shock-buffeting with unsteady fluid-structure interaction. Besides the necessity of a thorough understanding of the aeroelastic phenomena, wind tunnel experiments with elastic wings at Mach and Reynolds numbers of real transport aircrafts are necessary for the validation of methods for computational aeroelastic simulation (CAES).
Under cryogenic conditions in the ETW it is possible to achieve in half model testing Reynolds numbers of up to 80 million at high transonic Mach numbers, similar to the conditions of high capacity passenger aircrafts in cruise flight. A further advantage of ETW is that the parameters Mach number, Reynolds number, and dynamic pressure, which are influencing the areoelastic behaviour of the wing, can be varied independently.
The experiments included steady and unsteady measurements with the wind tunnel model of the SFB 401 clean wing reference configuration, which has the supercritical profile BAC 3-11 reported in AGARD-AR-303 and a planview typical for large passenger aircraft wings. The span of the wing model is approximately 1.3 meter, the sweep angle is 34°. The model has been equipped with about 250 miniature pressure sensors, 11 accelerometers, 22 strain gauge arrangements, and surface markers for optical deformation measurements.
In different sub-projects of SFB 401, the elastic wind tunnel model has been designed to meet required aeroelastic properties in consideration of the multidisciplinary aspects. The dynamic dimensioning mainly focusses on clearly separated eigenshapes and eigenfrequencies. In each design step the structural properties of the wing model have been computed using computational structural dynamics (CSD) methods, while a Navier-Stokes solver delivered the aerodynamic design loads. The CAE package SOFIA (Solid-Fluid Interaction) which has been developed in SFB 401 was applied to predict the steady and unsteady aeroelastic behaviour of the model under wind tunnel conditions.

Before the SFB 401 ended after the admissible maximum funding time of twelve years at the end of 2008 the HIRENASD research programm has been continued in a so-called tranfer project ASDMAD (Aero-Structural Dynamics Methods for Airplane Design) with funding from the German Research Foundation (DFG), Airbus Germany and RWTH Aachen University. The new project includes two other series of Aero-Structural Dynamics (ASD) experiments in ETW with HIRENASD wing model modified at wing tip by two types of winglets, one with fixed geometry and another equipped wit a movable flap. The first test series (ASDMAD-1, fixed winglet geometry) was held in February 2010, the second series of tests is performed 2011th.