Cerfacs Enter the world of high performance ...

Abstract :

Regarding the growth of global air transport sustained by the emerging countries and the more and more stringent noise certification, engine manufacturers pay particular attention on the understanding, prediction and control of fan noise. The fan stage of future ultra-high by-pass ratio turbofans may be responsible for a significant part of the noise radiated by an aircraft. Moreover, the fan noise contribution on the current turbofans, whether tonal or broadband, is large at both approach and take-off operating points. Among several physical mechanisms generating the fan noise, the tip clearance noise at the tip of fan blades is considered as a secondary source of noise on the current turbofan architectures and is not accounted for the evaluation of fan noise. The evolution towards ultra-high by-pass ratio architectures may bring the tip clearance noise from a secondary source to a primary one. In this context, large-eddy simulations resolving the large eddies and modelling the small ones, are performed on an isolated airfoil and a rig-scaled fan representative of future ultra-high by-pass ratio turbofan engine. Based on a comparison with measurements, the numerical method shows its capacity to recover the unsteady aerodynamics of the tip flow. A wall-modelled approach allows for the computation of turbomachinery applications such as the rig-scaled fan. Moreover, mesh adaptation based on flow quantities appears to be an appropriate methodology to resolve the complex three-dimensional vortical structure of turbomachinery secondary flows such as the tip flow. Identification functions are also applied to characterise the tip leakage vortex at the tip of fan blades. To bring knowledge for the definition of new models of tip clearance noise, an analysis of tip flows on the two configurations is carried out. Among several aerodynamic source mechanisms of tip clearance noise, the scattering of vortical structures in the gap by the tip edges appears to be the dominant mechanism on ultra-high by-pass ratio turbofan engine.

Keywords :

Tip leakage flow, Tip clearance noise, Isolated airfoil, Rig-scaled fan, Large eddy simulation, Mesh adaptation, Vortex identification.

Jury :

Thomas Carolus – Université de Siegen – Referee

Marlène Sanjosé – Université du Québec – Referee

Jérôme Boudet – LMFA – Member

Xavier Carbonneau – ISEA-Suparéo –  Member

Michel Roger – LMFA –  Advisor

Guillaume Daviller – CERFACS –  Co-Advisor

Hélène De Laborderie – Safran Aircraft Engines – Invited Member