Application of a RANS-informed analytical model for fast noise prediction of contra rotating open rotors

The present work focuses on the fast prediction of the interaction noise (IN) components of a Contra Rotating Open Rotor (CROR) engine at take-off. The flow field past the CROR is computed using a steady RANS approach coupled with the concept of mixing plane between the rotors to remove the flow unsteadiness due to the propeller interaction. The effects of such interaction are then recovered applying the analytical model of Jaron et al. (2014), balanced with data extracted from the RANS solution, to extrapolate the information about the wake of the front rotor and the potential flow fields through the mixing plane. This RANS-informed approximation allows recovering the unsteadiness of the flow-blades interaction in terms of unsteady blade response. The tonal noise at the blade passing frequency and the interaction noise are then estimated using the analytical frequency domain model proposed by Hanson (1985). The present method for the fast prediction of CROR noise has been validated by comparison with the results of URANS simulations and noise measurements. CROR geometry UDF F7/A7 with both 8 x 8 and 11 x 9 blade counts has been considered. The flow velocity profiles extrapolated through the mixing plane agree well with the URANS results, except in the vicinity of the blade tip, where the analytical extrapolation method is not able to deal properly with the strongly 3D tip vortex flow. The comparison of the predicted interaction noise with acoustic measurements shows that the present fast RANS-informed approach is capable of estimating the directivity of the CROR noise with reasonable accuracy.