Borisyuk A. Acoustics of flows in channels with local irregularities in the geometry

A mathematical model of sound generation and propagation in channels with regular and irregular geometry is developed. In the frames of the model, 1) the influence of a local irregularity in the channel's geometry, as well as the mechanical properties of the channel's wall and the flow characteristics on the wall pressure fluctuation field behind the irregularity, as well as the vibration and acoustic fields of channels is studied, and the corresponding relationships and quantitative estimates for the spectral and correlation characteristics of the fields noted are obtained; 2) in the characteristics of sound and wall pressure fluctuation fields signs are found that indicate the presence of irregularity in the channel's geometry, and the relation of those signs to the parameters of flow, channel and its irregularity is established; 3) the spectral characteristics of sound and wall pressure fluctuation fields generated by flow in a channel are found to be much more sensitive compared to their spatial characteristics to local changes in the channel's geometry, mechanical properties of the channel's wall and the flow characteristics. Conditions are found at which the existing pressure fluctuations models for a flat wall can be used to describe the wall pressure fluctuations at cylindrical structures of regular and irregular geometry when interacting with an inner flow. A theory of sound generation by a limited region of disturbed flow in an infinite straight rigid channel is developed that, in contrast to the existing theories of such kind, takes into account both the presence of dipoles at the channel's wall and the most probable inhomogeneous distribution of the quadrupole and dipole sound sources in their domains. A new analytical and numerical method is developed to solve coupled problems of sound radiation by flows in channels with local geometrical irregularities (such as area reductions). Based on the effects found and the relationships established in the dissertation, recommendations of how to use them in developing non-invasive acoustic diagnostic techniques for finding local irregularities in the channel's geometry are developed