Galerkin projection of the Navier-Stokes equations on Proper Orthogonal Decomposition (POD) basis is predominantly used for model reduction in fluid dynamics. Robustness for changing operating conditions, numerical stability for long-term transient behaviour and pressure-term consideration are still major concerns of the Galerkin Reduced-Order Models (ROMs). In this article, we present a novel interpolation based procedure to construct a solution state using reduced basis. The POD basis functions are optimal in capturing the averaged

The unsteady loads in a tube bundle are studied at moderate and high Reynolds number by means of URANS and hybrid (DDES) modelling. The onset of fluid-elastic instability is analysed for different structural parameters, Scruton number and reduced velocity. The simulations have been carried out with the code NSMB (Navier-Stokes Multi Block) by using turbulence modelling methods URANS and DDES (Delayed Detached Eddy Simulation). The CEA-DIVA configuration is considered for the cylinders array for an inter-tube Reynolds number 60, 000. The study is carried out for a configuration of (4 × 5) cylinders in static conditions as well as for the vertical free motion of one of the central cylinders in one DOF (Degree Of Freedom).The inter-tube Reynolds number is 60, 000. It is found that this cylinder spontaneously displays an oscillatory motion which first corresponds to Vortex Induced Vibration (VIV), associated to a lock-in mechanism for low values of the reduced velocity and secondly develops Movement Induced Vibration, MIV for higher values of the reduced velocity. The variation of the cylinder's oscillations frequency, of the unsteady loads and the structure's displacement are studied as a function of the reduced velocity for low and high values of the Scruton number. The increase of the phase-lag between the forces and the * Corresponding author. displacement is predicted and discussed for different Scruton number values and reduced velocities.

A Galerkin-free model reduction approach for fluid-structure interaction (FSI) is presented in this article. The reduced order model (ROM) is based on proper orthogonal decomposition (POD), where a reduced basis is formed using energy dominant POD modes. The reduced basis also consists of characteristics POD time modes that are derived from the POD time modes (coefficients) by using their periodicity. In addition to flow variables, the solution state vector comprises the mesh deformation, taking into account the structural deformation in FSI. A ROM solution is obtained by performing a linear interpolation of the reduced basis for changing operating/control parameters. The proposed Galerkin-free POD-ROM approach is demonstrated in terms of two test cases: a canonical case study of vortex-induced vibration (VIV) of a cylinder at Reynolds number Re = 100, where simulations are performed for various structural-to-fluid mass ratios; and a shock wave boundary layer induced panel flutter. For the second case, we use previously computed high-fidelity simulations, considering only the effect of panel thickness on the aeroelastic coupling between the flexible panel and shock wave boundary layer interaction (SWBLI); the inflow is at Mach 2 and Reynolds number based on panel length Re a = 50000. The presented Galerking-free ROM procedure is clean and robust for large mesh deformations, in addition to a significantly lower cost of computation compared to the FSI high-fidelity simulations.