Enabling off-design linearised aerodynamics analysis using Krylov subspace recycling technique

The major computational challenge, when using frequency domain linearised computational fluid dynamics in the analysis of aeroelastic problems such as aircraft flutter, gust response or shock buffet, are the excessive memory and CPU time requirements to solve the large sparse linear systems of equations. To address these issues found with the generalised minimal residual linear equation solver, the generalised conjugate residual solver with deflated restarting is adopted here in which an invariant Krylov subspace is recycled both between restarts when solving a single linear frequency domain problem and for a sequence of equations when varying the system matrix and forcing terms. The proposed method is implemented in an industrial code and applied to three test cases including the forced excitation and buffet onset of a pitch-plunge aerofoil, a realistic passenger aircraft in inviscid transonic flow and a generic half wing-body model at a pre-buffet condition. The memory requirements for the problems investigated are reduced by up to an order of magnitude, while the CPU times are reduced by up to a factor of three.