The sound produced by gust – airfoil interaction is a major source of broadband noise in many practical applications. In this thesis, both analytical and numerical methods are employed to fill the gaps in predicting the sound with complex flow condition.

Analytical correction to the usual flat plate solution is proposed to account for the effect of non-uniform mean flow. The sound governing equation with varying coefficients is approximated by a classical wave equation by using a new space – time transformation, and is then solved by the Schwarzschild technique. The analytical correction yields more accurate results than the widely used flat plate solution. The influence of the streamwise disturbance in the oncoming turbulence on sound generation is also studied by modelling th...[ Read more ]

The sound produced by gust – airfoil interaction is a major source of broadband noise in many practical applications. In this thesis, both analytical and numerical methods are employed to fill the gaps in predicting the sound with complex flow condition.

Analytical correction to the usual flat plate solution is proposed to account for the effect of non-uniform mean flow. The sound governing equation with varying coefficients is approximated by a classical wave equation by using a new space – time transformation, and is then solved by the Schwarzschild technique. The analytical correction yields more accurate results than the widely used flat plate solution. The influence of the streamwise disturbance in the oncoming turbulence on sound generation is also studied by modelling the coupling between the fluctuations and background mean flow as sources, following the idea of acoustic analogy. The equation is solved by Born approximation, and the analysis reveals that the streamwise disturbance can produce sound in the upstream direction. Taking this effect into consideration can yield a better prediction of far-field directivities than the flat plate solution. State-of-the-art computational aeroacoustics techniques, including low dissipation shock capturing schemes and synthetic turbulence methods, are implemented to study the gust – airfoil interaction in transonic flows. New physics such as extra sound sources, sound scattering by shocks and shock oscillation due to the oncoming unsteady flow are investigated. Also, the influences of airfoil geometries on sound are also investigated. The simulation results suggest that the acoustic properties are different from those at subsonic speeds since the flow patterns are sensitive to the airfoil geometry due to the shocks.

A class of sound extrapolation methods are developed to compute the far-field directivities in turbulent flows. The proposed methods filter out the non-acoustic components in the flow field before being used as the input for the far-field computation. The often exist spurious wave contamination is avoid when off-body integration surfaces are used. Particularly, the thesis work proposed a generalised method based on a third order equation that is applicable to challenging aeroacoustics problems including jet.