A new Lattice Boltzmann collision model for large eddy simulation (LES) of weakly compressible flows is proposed. This model, referred to as the Hybrid Recursive Regularised Bhatnagar–Gross–Krook (HRR-BGK) model, is based on a modification of previously existing regularised collision models defined with the BGK Lattice Boltzmann method (LBM) framework. By hybridising the computation of the velocity gradient with an adequate Finite Difference scheme when reconstructing the non-equilibrium parts of the distribution function, a hyperviscosity term is introduced in the momentum equation, whose amplitude can be explicitly tuned via a weighting parameter. A dynamic version of the HRR-BGK is also proposed, in which the control parameter is tuned at each grid point and each time step in order to recover an arbitrarily fixed total dissipation. This new collision model is assessed for both explicit and implicit LES considering the flow around a circular cylinder at . The dynamic HRR-BGK is observed to yield...

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A new hybrid recursive regularised Bhatnagar-Gross-Krook collision model for Lattice Boltzmann method-based large eddy simulation

An overset grid method for large eddy simulation of turbomachinery stages

Direct computation of the noise induced by a turbulent flow through a diaphragm in a duct at low Mach number

The noise generated by a rod–airfoil configuration is investigated using unstructured Large-Eddy simulation coupled with a Ffowcs-Williams and Hawkings technique. The detailed experimental database and several numerical simulations available enable an extensive validation of the proposed methodology. Similar or improved results are obtained both in the near field (surface coefficient distributions and velocity profiles) and in the acoustic far field (power spectral densities obtained with both porous and solid surfaces, and directivities) compared with the best and most recent simulations. Dipolar noise radiation at the rod vortex-shedding frequency and its harmonics are found to be dominant. Some additional quadrupolar source contributions are seen at low and high frequencies. The rod is shown to have a significant contribution to the far-field noise at grazing angles. Constructive interferences occur normal to the rod–airfoil axis, whereas destructive interferences appear at grazing angles.

Noise Source Analysis of a Rod–Airfoil Configuration Using Unstructured Large-Eddy Simulation

Numerical investigations of body-wake interactions were carried out by simulating the flow over a rod–airfoil configuration using high-order implicit large eddy simulation (HILES) for the incoming velocity and a Reynolds number based on the airfoil chord . The flow over five different rod–airfoil configurations with different distances of , 4, 6, 8 and 10, respectively, were calculated for the analysis of body-wake interaction phenomena. Various fundamental mechanisms dictating the intricate flow phenomena including force varying regulation, flow structures and flow patterns in the interaction region, turbulent fluctuations and their suppression, noise radiation and fluid resonant oscillation, have been studied systematically. Due to the airfoil downstream, a relatively higher base pressure is exerted on the surface of the cylinder upstream, and the pressure fluctuation on the surface of the rod–airfoil configuration with is significantly suppressed, resulting in a reduction of the fluctuating lift. Following the distance between the cylinder and airfoil strongly decreases, Karman-street shedding is suppressed due to the blocking effect. The flow in this interaction region has two opposite tendencies: the influence of the airfoil on the steady flow is to accelerate it and the counter-rotating vortices connecting with the leading edge of the airfoil tend to slow the flow down. There may be two flow patterns associated with the interference region, i.e. the Karman-street suppressing mode and the Karman-street shedding mode. The primary vortex shedding behind the cylinder upstream, and the shedding wake impingement onto the airfoil downstream, play a dominant role in the production of turbulent fluctuations. When primary vortex shedding is suppressed, the intensity of impingement is weakened, resulting in a significant suppression of the turbulent fluctuations. Due to these factors, a special broadband noise without a manifestly distinguishable peak is radiated by the rod–airfoil configuration with . The fluid resonant oscillation within the flow interaction between the turbulent wake and the bodies was further investigated by adopting a feedback model, which confirmed that the effect of fluid resonant oscillation becomes stronger when and 10. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the body-wake interaction.

Numerical investigation on body-wake flow interaction over rod-airfoil configuration

https://acoustique.ec-lyon.fr/publi/daude_cf12.pdf

A high-order finite-difference algorithm for direct computation of aerodynamic sound

https://hal.archives-ouvertes.fr/hal-01242983/document

Validation of a two-fluid model on unsteady liquid–vapor water flows

A high-order finite-difference algorithm is proposed in the aim of LES and CAA applications. The subgrid scale dissipation is performed by the explicit high-order numerical filter used for numerical stability purpose. A shock-capturing non-linear filter is also implemented to deal with compressible discontinuous flows. In order to tackle complex geometries, an overset-grid approach is used. High-order interpolations make it possible to ensure the communication between overlapping domains. The whole algorithm is first validated on canonical flow problems to illustrate both its properties for shock-capturing as well as for accurate wave propagation. Then, the influence of the multi-domain approach on the high-order spatial accuracy is assessed. Afterwards, the algorithm is extended to dynamic mesh applications with overlapping grids. Finally, two industrial cases are presented to highlight the potential of the proposed algorithm.

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A high-order algorithm for compressible LES in CAA applications

We examine in this paper the accuracy of some approximations of the Baer-Nunziato two-phase flow model. The governing equations and their main properties are recalled, and two distinct numerical schemes are investigated, including a classical second-order extension relying on symmetrizing variables. Shock tube cases are considered, and two simple Riemann problems based on well-balanced initial data are detailed. These enable to recover the expected convergence rates. However, it is shown that these simple cases are indeed very difficult and that the accuracy of basic schemes is rather poor.

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Fabien Crouzet

Papers

A high-order finite-difference algorithm for direct computation of aerodynamic sound

Validation of a two-fluid model on unsteady liquid–vapor water flows

A high-order algorithm for compressible LES in CAA applications

Approximate solutions of the baer-nunziato model

Mechanical consequences of LOCA in PWR: Full scale coupled 1D/3D simulations with fluid–structure interaction