Engelsk titel / English titleFlow Transitions and Sound Generation in a Collapsible Tube

Sammanfattning

This thesis investigates sound generation and flow topology in vessels present in the human respiratory system. One of these vessels is the pharynx, modelled as a collapsible tube, which can collapse when subjected to forces. When air flows through the collapsed pharynx, for example on inspiration, the flow separates from the vessel walls, becomes unsteady and induce pressure fluctuations which can generate noise. Understanding which degree of collapse generates the highest pressure fluctuations and understanding the flow topology is not fully understood. To bring further understanding to the questions at hand, Computational Fluid Dynamics (CFD) and Computational Aero Acoustics (CAA) is used to analyse several collapsed states. The CFD model is set up in STAR-CCM+ (version 2502) using a 3D Large Eddy Simulation (LES). Pressure fluctuation Root-Mean-Square (RMS) values, Power Spectral Densities (PSD) and mean axial flow velocity in the axial, radial and azimuthal directions were analysed in the computational domain. The analyses reveals that a clear transition is visible with increased collapse with minimum RMS at the least collapsed state and maximum RMS is achieved in the second to last most collapsed state. At the most collapsed state, the RMS decreases sharply with a small change in collapse. The flow topology also sees a transition where the flow becomes increasingly complex the more the tube collapses.