ADVANCED APPROACH FOR VIBRO-ACOUSTIC AND AERO-ACOUSTIC ANALYSIS OF PIAGGIO P180 AVANTI

TURBOPROP AIRCRAFT CABIN NOISE IS STRONGLY INFLUENCED BY LOW FREQUENCY TONAL EXCITATION ASSOCIATED WITH THE PROPELLER BLADE-PASSAGE FREQUENCY (BPF) AND ITS HARMONICS. IN THIS FREQUENCY RANGE, THE INTERIOR ACOUSTIC FIELD IS GOVERNED BY THE INTERACTION BETWEEN FUSELAGE STRUCTURAL MODES, CABIN ACOUSTIC MODES AND FLUID-STRUCTURE COUPLING EFFECTS, LEADING TO A HIGHLY RECEIVER-DEPENDENT RESPONSE. THE ACCURATE PREDICTION OF THESE MECHANISMS REQUIRES DETERMINISTIC NUMERICAL MODELS ABLE TO REPRESENT BOTH THE STRUCTURAL DYNAMICS OF THE FUSELAGE AND THE ACOUSTIC BEHAVIOUR OF THE ENCLOSED CABIN CAVITY. THIS THESIS DEVELOPS A HIGH-FIDELITY COUPLED STRUCTURAL--ACOUSTIC FE MODEL OF THE PIAGGIO P180 AVANTI EVO COCKPIT-CABIN FUSELAGE ASSEMBLY FOR CABIN NOISE PREDICTION UP TO THE THIRD BPF HARMONIC OF THE REFERENCE PROPELLER OPERATING CONDITION. IN ADDITION TO THE CONSTRUCTION OF THE NUMERICAL MODEL, THE WORK PROPOSES A MODAL-BASED MESH-SIZING STRATEGY FOR THE STRUCTURAL DOMAIN, WHERE REPRESENTATIVE FUSELAGE SUBCOMPONENTS ARE DYNAMICALLY CHARACTERISED AND THEIR MODAL BEHAVIOUR IS USED, WITH REFERENCE TO THE MAXIMUM FREQUENCY OF INTEREST, TO DEFINE APPROPRIATE ELEMENT SIZES. THE ACOUSTIC MESH IS DEFINED FROM WAVELENGTH-BASED CRITERIA AND MADE COMPATIBLE WITH THE STRUCTURAL DISCRETISATION ALONG THE FLUID-STRUCTURE INTERFACES. THE MODELLING FRAMEWORK IS ASSESSED THROUGH A PROGRESSIVE VERIFICATION AND VALIDATION PROCEDURE. THE STRUCTURAL MODEL SHOWS SATISFACTORY CORRELATION WITH THE AVAILABLE EXPERIMENTAL MODAL DATA, WHILE THE ACOUSTIC CAVITY MODEL IS SUCCESSFULLY VERIFIED AGAINST ANALYTICAL SOLUTIONS FOR AN EQUIVALENT RIGID-WALLED CYLINDRICAL CAVITY. THE COUPLED STRUCTURAL-ACOUSTIC RESPONSE IS THEN VALIDATED AGAINST FULL-SCALE LABORATORY ACOUSTIC TEST DATA OBTAINED ON A PIAGGIO P180 AVANTI EVO FUSELAGE BARREL. THE VALIDATION CONSIDERS BOTH A BODY-IN-WHITE CONFIGURATION AND A TRIMMED CONFIGURATION WITH ACOUSTIC ABSORBING MATERIAL APPLIED TO THE CABIN INNER SURFACES. FOR THE UNTREATED CONFIGURATION, A SENSITIVITY ANALYSIS ON THE EFFECTIVE LOADED AREA IS PERFORMED TO ASSESS THE INFLUENCE OF THE EQUIVALENT REPRESENTATION OF THE EXPERIMENTAL ACOUSTIC SOURCE. A FURTHER SENSITIVITY STUDY INVESTIGATES THE EFFECT OF THE ACOUSTIC IMPEDANCE ASSIGNED TO THE CLOSING PANELS OF THE CAVITY. FOR THE TRIMMED CONFIGURATION, THE ABSORBING MATERIAL IS REPRESENTED THROUGH EQUIVALENT IMPEDANCE BOUNDARY CONDITIONS RECONSTRUCTED FROM MEASURED ABSORPTION DATA. IN THE FREQUENCY RANGE CONSIDERED FOR THE NUMERICAL--EXPERIMENTAL COMPARISON, FROM 80 HZ TO 250 HZ IN ONE-THIRD OCTAVE BANDS, THE MAIN EXPERIMENTAL NR TRENDS ARE REPRODUCED, WITH THE BEST AGREEMENT OBSERVED AT RECEIVER LOCATIONS CLOSE TO THE EXCITATION REGION. AT THESE LOCATIONS, THE PREDICTED NR VALUES GENERALLY FALL WITHIN THE SENSITIVITY ENVELOPE DEFINED BY THE EQUIVALENT LOADED AREA VARIATIONS. LARGER DISCREPANCIES OCCUR AT MORE DISTANT RECEIVERS, WHERE THE RESPONSE IS MORE STRONGLY AFFECTED BY REFLECTED-FIELD CONTRIBUTIONS AND BY UNCERTAINTIES IN THE REPRESENTATION OF THE EXPERIMENTAL TEST ARTICLE, PARTICULARLY THE CABIN FLOOR. THE DEVELOPED FRAMEWORK PROVIDES A PHYSICALLY CONSISTENT NUMERICAL BASIS FOR LOW-FREQUENCY CABIN NOISE PREDICTION IN THE PIAGGIO P180 AVANTI EVO FUSELAGE. IT ALSO SUPPORTS FUTURE STUDIES INVOLVING REALISTIC PROPELLER-INDUCED EXCITATION, CABIN NOISE REDUCTION STRATEGIES AND THE EXTENSION TOWARDS PASSENGER CENTRED PSYCHOACOUSTIC INDICATORS.