Aircraft noise prediction in realistic operative conditions
Adamo, Francesco Paolo (2010) Aircraft noise prediction in realistic operative conditions. [Tesi di dottorato] (Inedito)
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The area of interest is the aeroacoustics, a specific branch of the aerodynamics that has as main the modelling and analysis of problems correlated with production of sound from aircraft (especially rotary wing) and with the jet noise problems. The aims of the research are: o o o o For the noise producted by the jet, we using the approach of the analogy acoustic, that consists into recast the governing equation of fluid motion in a simple wave equation, putting at the left-hand side the propagator term of the sound and at the right-hand side the source term of the sound. There are many types of analogy; the one that we use is the Lighthill equation, who permits to write a quadrupole-like source term. Further we are verifying some semi-empirical model, taken from the literature, that permits to estimate the sound pressure level in a subsonic regime (The Tam and Auriault model) and in a supersonic regime (The Shen model). In this last model, the analysis is more complicated caused by the presence of shock cell structures, that born when the mach number, that measures the velocity of an object in a fluid respect to the sound speed, corresponds at a supersonic regime (Mach number greater than 1.2 and lower than 5). The study is realised trough a Fortran-code and many commercial softwares of fluidodynamics, necessary for evaluating numerically the turbulent variables necessary for the application of the model. For the noise produced by a propeller, has been used the Ffowcs-Williams Hawkings Equation: is a re-arrangement of the Navier-Stokes Equation as non homogenus wave equation with source terms categorized as thickness noise, loading noise and quadrupole noise. A typical solution is provided by Farassat (2007) for discrete frequency noise involving only surface terms. The capabilities are I)to classify the rotor-noise sources and to supply a framework for qualitative analysis of noise generation mechanisms; II) basis of analytical derivation of prediction formulas. The noise from landing gear, that is one of the noise derived from the aircraft, is analyzed trough an empirical model: The fink model. This model is also used by NASA for an experimental investigation of the aircraft landing gear noise,, trough data provided by BOEING 737.
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