The objective of this paper is to calculate the far-field sound generated from low mach number flow around a two-dimensional and three-dimensional circular cylinder in the subcritical regime using the Lighthill acoustic analogy. For the two-dimensional case, the timedependent incompressible flow is predicted using unsteady Reynolds-averaged Navier-Stokes models. For the three-dimensional case, the flow was obtained by solving the filtered Navier-Stokes equations of the Large Eddy Simulation model. As a benchmark, a flow-field with a Reynolds number of 90,000 is employed. The obtained numerical results such as Strouhal number, fluctuating lift and mean drag are compared with experiments. The computed unsteady pressure fluctuations on the cylinder wall are used as a sound source for the acoustic solver. Comparison between the two-dimensional numerical results and the experiment shows that computed acoustic field overpredict the noise amplitude; however, good agreement is obtained if an appropriate correlation length is taken into account. The sound measurements obtained by Revell et al. were carried out with a much longer span cylinder length when compared to the span used for the three-dimensional LES simulations. Therefore, the far-field sound is estimated by two correction methods proposed, respectively, by Kato et al. and Seo & Moon. The aerodynamic and acoustic results obtained by the threedimensional approach agree favorably well with the corresponding experimental data.

The lattice Boltzmann method (LBM) is applied to simulate the complete three-dimensional transient flow and noise generated on the Advanced Noise Control Fan (ANCF) geometry. The ANCF is a model developed by NASA Glenn composed by a rotor-stator system enclosed by a duct. The experimental noise spectra provided by NASA at 30 microphones around the fan are used to validate the results obtained with the LBM. Overall, the predicted sound spectra pattern and the main tonal frequencies agree well with the noise measurements; in terms of tonal noise levels, the agreement varies depending on the frequency and microphone position. The noise at the 30 microphone positions is also computed by employing the porous Ffowcs Williams and Hawkings (FW-H) formulation with noise sources located on two integral surfaces placed at the ANCF openings. The good agreement obtained between the sound levels calculated with the FW-H formulation and those computed by the LBM show that the FW-H analogy may be applied in place of the LBM numerical simulation. In addition, the FW-H formulation is applied to compute the sound generation with sources located on different physical surfaces of the ANCF model such as the rotor, stator, hub, and nacelle, procedure known as noise source breakdown. A comparison of the FW-H results applied on different surfaces of the ANCF model with the noise computed by the LBM shows that most of the tonal noise levels observed at the far-field microphones (predicted by the LBM simulation) correspond to the noise sources generated on the stator vane surfaces. Such a study of the noise sources breakdown also evidences the interaction effect between the rotor and the stator, whose mechanism is the main contributor to the tonal noise generation content.

Many components of machines, equipments and means of transport can be represented as a bluff body whose motion through a fluid can generate noise. In this context, this thesis is focused on the study of numerical prediction of noise generated by the flow around bluff bodies. As an example of bluff body, the sound generated from flow around a circular cylinder is studied. The flow over a circular cylinder is investigated by considering the wake as tridimensional and turbulent in the subcritical regime, which is characterized by a laminar boundary layer separation. The flow over a circular cylinder is obtained by time-dependent numerical simulation considering three-dimensional computational domain. In order to cope with turbulence and three-dimensionality, the flow is solved using the Large Eddy Simulation (LES) methodology. The computational domain is discretized by the finite volume method. The noise is calculated separately using the Ffwocs Williams & Hawkings (FW-H) analogy, whose wave equation has as a source term the flow solution provided by the numerical simulation. With regard to the FW-H analogy, the acoustic pressure fluctuation is obtained in the far-field by assuming a quiescent medium between the sound sources region (near-field) and the location considered for acoustic computation. Due to the high computational cost of three-dimensional (3D) simulation, the numerical simulations were conducted with a cylinder span length limited in size, which allows taking into account part of the wake three-dimensionality. Regarding the final acoustic computation, the acoustic correction methods of Kato et al. (1993) and Seo & Moon (2007) are used in order to match the sound obtained by the short cylinder span to the correspondent sound obtained experimentally for a long cylinder span. This thesis contributed to investigate numerically the computational method of applying the Ffwocs Williams & Hawkings analogy for solving the noise generated from a threedimensional flow over a circular cylinder with high Reynolds number, particularly, at Re = 90,000 and Re = 22,000. The results show that this computational method is able to predict the far-field sound for the simulated cases, since the noise spectra obtained are found to be in agreement with the corresponding experimental data. In addition, the acoustic correction method of Kato et al. (1993) and Seo & Moon (2007) provided good predictions with regard to the adding noise computation, however, its results are dependent on accurate estimation of the spanwise coherence length of the flow. Finally, the sound spectrum obtained in the far-field is tied to the flow behavior provided by the numerical simulation, especially regarding the coherence between the pressure fluctuations over the spanwise length of the cylinder and the lift force fluctuation amplitude exerted on the cylinder wall.

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