Abstract
Swirling flows are present in many engineering applications, such as emissionsaftertreatment or turbomachinery. However, due to the complex physics of the flow involving high pressure gradients, a range of flow instabilities and highly anisotropic turbulence, experimental and numerical studies of such flows are challenging. This study is focused on improving our understanding of the swirling flows, along with the development of experimental and numerical methods suitable for practical applications.
One important topic overlooked in the existing literature is the effect of asymmetry (often encountered in applications) on the swirling flows. In this study, a swirling flow in a sudden expansion with a downstream resistance has been used to investigate the effect of offset inlet on the flow structure. It is shown that the flow undergoes significant changes, with the swirling "jet" in the diffuser following a complex path rather than proceeding in the axial direction, and both the wall separation zone and the central recirculation zone change their size and shape. This is a unique 3-dimensional effect that cannot be observed in 2-dimensional geometries often used. The impact of asymmetry on the global parameters such as flow uniformity and total pressure loss (often used for device performance assessment) has however been shown to be small.
The study provides a critical assessment of some measurements techniques adopted for the study of swirling flows, such as Hot Wire Anemometry (HWA), wall pressure measurements and Particle Image Velocimetry (PIV). The experimental data collected for a simplified geometry (annular pipe) provides detailed information about the swirling flow downstream a swirl generator, which can be used for the definition and development of inflow boundary conditions for complex flow modelling approaches (LES and DES) and for model validation. It has also been shown that the effect of swirl dominates the flow structure, and that the Reynolds number has no significant effect on the flow for the cases considered.
Finally, a new formulation for the model of high resistance devices has been proposed and developed. The novel porous modelling approach allows to retain the low computational requirements of standard porous medium models and their capability to provide reasonable predictions of first order properties, such as velocity, while improving the prediction of flow structure and turbulence downstream the device where the classical porous medium approach fails. Another advantage of the new approach is its high flexibility for the inclusion of the complex flow passages to account for the geometry of the device.
| Date of Award | Jul 2021 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Svetlana Aleksandrova (Supervisor), Stephen Benjamin (Supervisor) & Humberto Medina (Supervisor) |