Vortex-induced vibrations of an elasticallymounted cylinderwith lowmass-ratio at RE=3900

The present paper deals with the numerical study of vortex-induced vibrations (VIV) of an elastically mounted cylinder in a cross flow with uniform inflow. It is well known that, in the case of low mass-damping, three distinct types of transverse amplitude response can be observed depending on the range of the reduced velocity. However, the accurate numerical simulation of the VIV amplitudes at the lock-in upper branch remains a great challenge. Moreover, few studies deal with the investigation of the hysteretic loop due to the jump between the initial excitation branch and the upper branch. Here, we propose to compute the transverse motion of the structure at a Reynolds number equal to 3900 Large Eddy Simulation. The Navier-Stokes equations are solved on a moving and deforming grid by means of an Arbitrary Lagrangian Eulerian (ALE) co-located finite volume method for unstructured meshes. An iterative algorithm is used at each time step based on Newton’s or fixed point method. This algorithm uses convergent explicit predictions of the coupled fluid structure system and sub-cycling is involved to get convergence towards the implicit solution of the fully coupled system. A criterion based on the structure velocity is used to stop the numerical sub-cycling process. First, we compare the transverse amplitude response of the cylinder for various reduced velocities with the DNS results obtained by Lucor et al. (2005) for zero structural damping and a mass ration equal to 2. Next, the experimental data of Hover et al. (1998) are considered to demonstrate the ability of the present solver to predict the VIV response for lowmass-damping

3D global optimal forcing and response of the supersonic boundary layer

3D optimal forcing and response of a 2D supersonic boundary layer are obtained by computing the largest singular value and the associated singular vectors of the global resolvent matrix. This approach allows to take into account both convective-type and component-type non-normalities responsible for the non-modal growth of perturbations in noise selective amplifier flows. It is moreover a fully non-parallel approach that does not require any particular assumptions on the baseflow. The numerical method is based on the explicit calculation of the Jacobian matrix proposed by Mettot et al. [1] for 2D perturbations. This strategy uses the numerical residual of the compressible Navier-Stokes equations imported from a finite-volume solver that is then linearised employing a finite difference method. Extension to 3D perturbations, which are expanded into modes of wave number, is here proposed by decomposing the Jacobian matrix according to the direction of the derivatives contained in its coefficients. Validation is performed on a Blasius boundary layer and a supersonic boundary layer, in comparison respectively to global and local results. Application of the method to a boundary layer at M = 4.5 recovers three regions of receptivity in the frequency-transverse wave number space. Finally, the energy growth of each optimal response is studied and discussed

Vibrations d'un cylindre induites par détachement tourbillonnaire en régime sous-critique

Les vibrations induites par le sillage d'un cylindre seul oscillant librement sous l'effet d'un écoulement transverse en régime sous-critique sont modélisées par simulation des grandes échelles. Le système couplé fluide structure est résolu par une méthode itérative. La branche supérieure de réponse ainsi que l'intermittence vers la branche inférieure et l'hysteresis vers la branche initiale sont examinées pour différents nombres de Scruton, vitesses réduites et rapports de masse. Des comparaisons sont effectuées avec des données numériques et expérimentales de la littérature

Model-form and predictive uncertainty quantification in linear aeroelasticity

In this work, Bayesian techniques are employed to quantify model-form and predictive uncertainty in the linear behavior of an elastically mounted airfoil undergoing pitching and plunging motions. The Bayesian model averaging approach is used to construct an adjusted stochastic model from different model classes for time-harmonic incompressible flows. From a set of deterministic function approximations, we construct different stochastic models, whose uncertain coefficients are calibrated using Bayesian inference with regard to the critical flutter velocity. Results show substantial reductions in the predictive uncertainties of the critical flutter speed compared to non-calibrated stochastic simulations. In particular, it is shown that an efficient adjusted model can be derived by considering a possible bias in the random error term on the posterior predictive distributions of the flutter index

A high-order density-based finite volume method for the computation of all-speed flows

In this paper we present a high-order density-based finite-volume framework for all-speed flows. The formulation is based on high-order variable reconstructions performed using Moving Least Squares approximations. In particular, we show that combining high-order discretization schemes with low-Mach fixes, it is possible to remove the grid dependency problem at low Mach numbers on both structured and unstructured grids. In order to maintain the accuracy and the robustness of the numerical method at transonic conditions, different procedures are proposed, based on the use of a selective limiting

New high-resolution-preserving sliding mesh techniques for higher-order finite volume schemes

This paper presents a new sliding mesh technique for the computation of unsteady viscous flows in the presence of rotating bodies. The compressible Euler and incompressible Navier–Stokes equations are solved using a higher-order (>2) finite volume method on unstructured grids. A sliding mesh approach is employed at the interface between computational grids in relative motion. In order to prevent loss of accuracy, two distinct families of higher-order sliding mesh interfaces are developed. These approaches fit naturally in a high-order finite volume framework. To this end, Moving Least Squares (MLS) approximants are used for the transmission of the information from one grid to another. A particular attention is paid for the study of the accuracy and conservation properties of the numerical scheme for static and rotating grids. The capabilities of the present solver to compute complex unsteady vortical flow motions created by rotating geometries are illustrated on a cross-flow configuration

An a posteriori-implicit turbulent model with automatic dissipation adjustment for Large Eddy Simulation of compressible flows

In this work we present an a posteriori high-order finite volume scheme for the computation of compressible turbulent flows. An automatic dissipation adjustment (ADA) method is combined with the a posteriori paradigm, in order to obtain an implicit subgrid scale model and preserve the stability of the numerical method. Thus, the numerical scheme is designed to increase the dissipation in the control volumes where the flow is under-resolved, and to decrease the dissipation in those cells where there is excessive dissipation. This is achieved by adding a multiplicative factor to the dissipative part of the numerical flux. In order to keep the stability of the numerical scheme, the a posteriori approach is used. It allows to increase the dissipation quickly in cells near shocks if required, ensuring the stability of the scheme. Some numerical tests are performed to highlight the accuracy and robustness of the proposed numerical scheme

Aérodynamique 3-D et aéroélasticité non-linéaire et linéarisée en temps

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocPARIS-BIUSJ-Lab.Mécanique the (751055218) / SudocSudocFranceF

Optimal sensor placement for variational data assimilation of unsteady flows past a rotationally oscillating cylinder

International audienc

Low-frequency resolvent analysis of the laminar oblique shock wave/boundary layer interaction

Resolvent analysis is used to study the low-frequency behaviour of the laminar oblique shock wave/boundary layer interaction (SWBLI). It is shown that the computed optimal gain, which can be seen as a transfer function of the system, follows a first-order low-pass filter equation, recovering the results of Touber & Sandham (J. Fluid Mech., vol. 671, 2011, pp. 417–465). This behaviour is understood as proceeding from the excitation of a single stable, steady global mode whose damping rate sets the time scale of the filter. Different Mach and Reynolds numbers are studied, covering different recirculation lengths L. This damping rate is found to scale as 1/L, leading to a constant Strouhal number StL as observed in the literature. It is associated with a breathing motion of the recirculation bubble. This analysis furthermore supports the idea that the low-frequency dynamics of the SWBLI is a forced dynamics, in which background perturbations continuously excite the flow. The investigation is then carried out for three-dimensional perturbations for which two regimes are identified. At low wavenumbers of the order of L, a modal mechanism similar to that of two-dimensional perturbations is found and exhibits larger values of the optimal gain. At larger wavenumbers, of the order of the boundary layer thickness, the growth of streaks, which results from a non-modal mechanism, is detected. No interaction with the recirculation region is observed. Based on these results, the potential prevalence of three-dimensional effects in the low-frequency dynamics of the SWBLI is discussed