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Home > News > Thesis defense > 2017 thesis defense

Soutenance de thèse ECL

Nassim Jaouani

Jeudi 12 janvier 2017- 14h30 - ECL - amphi 203

Nassim Jaouani

Modelling of Installation Effects on the Tonal Noise Radiated by Counter-Rotating Open Rotors

The Counter-Rotating Open Rotors (CROR) are identified as a possible alternative to turbofan engines for middle-range aircrafts. Providing significant fuel savings and reducing the green-house gas emissions, they may lead however to an increased noise radiation due to the absence of nacelle shielding. To properly predict the acoustic radiation of such systems is then mandatory both to reduce the source mechanisms of the isolated engine and to offer an optimal noise installation solution. Such an objective is tackled in the present thesis in two steps. In a first part, the research aims at predicting the tonal noise radiated from the first propeller of CROR mounted on the rear fuselage by means of a pylon (pusher configuration), considering both the pylon-wake and the uniform flow effects. From the Ffowcs Williams & Hawkings’ formalism, three noise sources are identified. First the unsteady loading is computed using a similar procedure to the one used for the rotor-rotor wake interaction noise prediction. The velocity deficit in the pylon wake is locally expanded in two-dimensional Fourier gusts in a reference frame attached to the front rotor. The unsteady lift induced by each gust on a blade segment is calculated using a linearized analytical response function that accounts for a realistic geometry. The steady loading is the second source contribution and is evaluated using both a software based on the lifting-line theory and some numerical simulations for different reference source surfaces. Finally the thickness noise due to the blade volume displacement is included in the analysis using Isom’s formulation. From the linear acoustic assumptions, all these sources modelled as equivalent acoustic dipoles rotating in a uniformly moving atmosphere are then summed to calculate the far-field noise. The whole methodology is assessed against wind-tunnel test data and reference software predictions. A parametric study considering several pylon positionings and pylon-wake configurations with blowing is performed in order to emphasize the relative contribution of the three noise sources. Secondly, the rotor-rotor wake interaction noise being recognized as the most significant contribution in isolated configuration, its modelling is completed by introducing the dynamics of the vortex occurring near the rear-rotor leading edge. A semi-analytical methodology is developed to determine a vortex attached over a flat plate embedded in a uniform flow with incidence. Applied to the case of a rear blade going through a front-rotor wake, it provides a first estimate of the noise contribution of the vortex.

JPEG - 40.8 kb
Open rotor in pusher configuration (General Electric)

Jury Composition

Prof. Nicolas GOURDAIN ISAE - Supaero (Reviewer)
Prof. Phillip JOSEPH ISVR (Reviewer)
Prof. Sofiane KHELLADI ENSAM (Reviewer)
Prof. Stéphane MOREAU Université de Sherbrooke (Examiner)
Dr. Hélène POSSON Airbus Operations SAS (Examiner)
Dr. Gilles RAHIER ONERA (Examiner)
Dr. Gilles SERRE DCNS (Examiner)
Prof. Michel ROGER Ecole Centrale de Lyon (PhD Advisor)
Dr. Arnulfo CARAZO MENDEZ Airbus Operations SAS (Guest)
Mr.  Thomas NODE-LANGLOIS Airbus Operations SAS (Guest)

Keywords : open rotor, wake blowing, leading-edge vortex, rotating dipole, thickness noise, analytical method, unsteady aerodynamics, acoustic radiation, complex potential theory


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