Moving Mesh CFD-CSD Aeroservoelastic Modelling of BACT Wing with Autonomous Flap Control

Abstract

Initial results produced by aeroservoelastic simulations of the BACT (Benchmark Active Control Technology) wing are presented. This is a low aspect ratio wing with large trailing edge ap. A fully time-synchronised aeroelastic simulation tool has previously been developed at the University of Bristol, by coupling a 3D central-dierence, nite-v olume, muliblock structured, unsteady CFD code with a linear computational structural dynamics code, in the time-domain. This has recently been extended to account for control surface representation and igh t control system integration, and various aspects of aeroservoelastic simulation have been analysed. All control surface motion is driven through control laws acting on the structure, allowing both commanded and un-commanded deections and distortions in the body modelled. The simulated response of the BACT wing and mount to aerodynamic perturbations and ap angle demands are presented, and a number of key issues relating to the modelling of surface motion are identied, the most signican t of which being the need for consideration of structural and aerodynamic grid behaviour at hinge lines. I. Introduction The accurate prediction of various types of non-linear aeroelastic behaviour is an important area of aircraft design. Whilst utter is the most spectacular example of the dangers posed by unpredicted and uncontrolled oscillations, other phenomena, whilst posing a less immediate threat to vehicle integrity, can have serious eects in the long term due to structural fatigue. Such phenomena would include, for example, Limit Cycle Oscillations (LCO’s) of control surfaces. Methods currently common in industry for aeroelastic analysis involve the use of linear techniques, allowing uncoupling of the aerodynamic and structural equations. However, these methods are not applicable in the most demanding design areas, i.e. non-linear regimes such as transonic utter, control surface LCO’s, and buzz. This can lead to the need for signican t safety margins, creating over-sti and hence high mass designs. More signican tly, it is likely that any errors in design will only be picked up during either ground vibration, or more likely igh t testing. This extends the length of the igh t test program (typically at a cost of thousands of dollars an hour), as a lack of condence in the prediction means that the initial tests must be carried out well below the expected onset of the non-linear behaviour, and speed increased only gradually. Further, the cost of xing any errors encountered at this stage is considerably greater than would be the case if they were to be identied before prototype manufacture through accurate modelling. Prediction methods proven to be of greater accuracy will therefore lead directly to signican t cost savings, without requiring any advances in the underlying aerodynamic or structural design methodologies. For this reason, non-linear techniques are under widespread development (e.g. references 1{22) consisting of time-accurate CFD (Computational Fluid Dynamics) analysis of the o w, coupled to a Computational Structural Dynamics (CSD) structural model. This oers the potential for modelling both the structure and aerodynamics in a non-linear fashion, although admittedly at a far higher cost in terms of CPU time. These methods can also be used to obtain high delit y o w data in regions of particular interest. At the