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Abstract:

Inlet design must fulfill geometrical constraints and engine requirements. One of these requirements is the homogeneity of the flow impacting the fan which is quantified by the distortion levels of stagnation pressure. When the airplane is on the ground and ready to take-off, crosswind conditions are critical for the distorsion level. The most critical case is when the wind direction is normal to the engine axis. Subsonic and supersonic separations occur near the inlet lip. The so-created heterogeneity produces an unsteady stress on the fan blades which can lead to surge. Furthermore, short inlets are designed nowadays reducing the distance available for the flow to homogenize before the fan leading to a coupling between the fan and the separated flow region. The aim of this study is to numerically predict the flow in a short inlet under crosswind conditions and to investigate the fan influence on the distortion. First of all, the distortion definition is based on stagnation quantities. Therefore, the stagnation quantities behavior and the numerical parameters influence must be investigated. The behavior of the stagnation quantities near the boundary layer edge is studied with analytical and numerical approaches. The numerical parameters chosen for the inlet simulation come from the so-obtained results obtained. In order to highlight the fan influence on the distortion, two kinds of simulations were proceeded and compared to experimental results : an isolated inlet simulation and a inlet/fan simulation. To correctly predict the distortion, transition has to be be taken into account. Therefore an innovative solution using transport equations is used. As the computation cost for the inlet/fan computation is prohibitive, the decoupling which consists in injecting on a isolated fan the distortion obtained during a isolated inlet computation, is discussed. In fact, crosswind conditions occur when the airplane is on the ground, thus, the ground influence over the inlet distortion is studied for an isolated inlet. Finally, the distortion criterion used in this study has evidenced some strong defects and can be questioned. Another approach of measurement with another criterion definition is investigated.

keywords :

Fan/nacelle interaction, numerical simulation, transition and turbulence, separation and reattachement, compressible and incompressible areas, distortion

Jury:

Pr. Eric Goncalves                 Referee           ISAE-ENSMA institut P’

Pr. Bruno Koobus                  Referee           IMAG Univ. Montpellier

Pr. Nicolas Gourdain             President       ISAE-DAEP

Pr. Bertrand Aupoix              Director          ONERA

M. Jean-François Boussuge  Member         CERFACS

M. Philippe Chanez               Member         SNECMA