Consideration of ROM interpolation for aeroelastic design using structural modification

Accurate aeroelastic simulations are an important part of the design process, but full nonlinear CFD codes are computationally expensive and therefore difficult to include. Significant progress has been made with the development of reduced order models (ROM) of CFD codes, which capture the dominant characteristics of the flow, but at a much lower cost. These compact models are constructed on the basis that the dynamic behaviour of the fluid is assumed to be approximately linear about a nonlinear mean solution. However, when computing the flutter boundary of an aircraft wing, many ROMs must be constructed to account for varying parameters such as angle of attack and mass distribution which change the appropriate mean solution. In particular, this paper is concerned with the effect a change in structural mass can have on an aeroelastic ROM, as it is created using pulse responses to structural modal inputs. A modal modification method is suggested as a way of solving this problem, and is tested successfully for a range of different wing mass cases. The eventual aim of this research is to use the modal modification so that ROMs for particular mass cases may be interpolated from two or three other ROMs.