Experimental study of swirling flows in symmetric and asymmetric sudden expansions with downstream resistance

Abstract

The effect of residual swirl from turbochargers undergoing near-sudden expansion on the flow distribution in catalyst monoliths is largely undocumented. Obtaining a uniform flow distribution in automotive catalysts is not straightforward, yet it is a key criterion for maximising conversion efficiency and improving service life. This thesis investigates swirling flows in axisymmetric and non-axisymmetric sudden expansions with a downstream resistance. Experiments were performed on isothermal flow rigs using hot-wire anemometry, particle image velocimetry and pressure transducers. A novel hot-wire technique was developed to critically evaluate the level of swirl introduced into the sudden expansion. Highly complex flow was exhibited in the sudden expansion at the different swirl levels. With a purely axial flow, a free-jet traverses the axial length of the sudden expansion creating a large separation zone at the wall. Adding swirl reduces the size of the separation zone and, at high swirl, creates a recirculation region on the sudden expansion axis. Displacing the inlet pipe from the sudden expansion axis results in the swirling jet being drawn towards the near wall. At high swirl levels, the jet impinges the near wall and is deflected in the opposite direction. A large amount of experimental data has been collected from this study suitable for computational fluid dynamics validation. The effect of inlet swirl and flow uniformity has been determined showing that an optimum level of swirl exists for providing a uniform flow distribution in the catalyst monolith.

Date of Award	Aug 2019
Original language	English
Awarding Institution	Coventry University
Supervisor	Svetlana Aleksandrova (Supervisor)