CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

ADVANCED METHODS AND MULTIPHYSICS
(a) Near-field vorticity magnitude and far-field sound(b) Influence of the perturbation intensity imposed at the jet
(shown using dilatation contours).
inlet.
FIG. 4.6: Noise computation of a subsonic jet.
was adapted to simulate shocks.
4.2.5 Airfoil noise (H. Deniau, G. Dufour, J.-F. Boussuge)
Broadband noise generation and radiation from rotating blades due to the ingestion of turbulence is a
topic of major interest for fan manufacturers. It becomes the main broadband noise source when the
ingested turbulence is at least stronger than two or three % of the relative mean flow on the blades. In
that context, turbulence-interaction noise due to isotropic turbulence impacting a thick cambered airfoil has
been simulated for the first time at high Reynolds number (Rec = 6.5 10 5 ) by a compressible Large Eddy
Simulation (LES) accounting for the installation effects. The full wind-tunnel has been simulated by a two
dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation that provides the realistic
boundary conditions for the LES on a restricted domain embedded in the potential core of the wind-tunnel
jet (Fig. 4.7a). Radiative boundary conditions are applied around the LES domain to prevent reflection or
drift of flow parameters. Synthetic turbulence is injected at the inlet of the LES domain. Comparison with
experimental data shows excellent agreement for the noise level and directivity if the sources are restricted
to the leading edge area (Fig. 4.7b). Yet LES also shows some extra noise sources at the trailing edge caused
by a large recirculation bubble close to the leading edge yielding some large vorticity up to the trailing edge,
and a late transition on the suction side [CFD27, CFD53].
4.2.6 Landing-gear noise (J-C. Giret, J-C. Jouhaud, J.-F. Boussuge)
Understanding and predicting aerodynamic noise generation is nowadays of a great importance. Particularly,
since huge progresses have been made on the noise reduction of turbofan engines through high bypass ratios,
the design of new aircraft requires the prediction and if needed the reduction of airframe noise (landing gear
and high-lift devices), which is a major source in approach conditions.
A requirement for such simulations is the ability to handle complex geometries. Most numerical
aeroacoustics studies have been performed on structured meshes as it enables the use of high-order schemes.
However, meshing a complex geometry with a block-structured mesh can be at least difficult and at worst
impossible. In order to overcome such limitations, overset grids or unstructured meshes can be used. This
study focuses on the use of unstructured meshes with a special care on accuracy issues.
162 Jan. 2010 – Dec. 2011