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Type: Theses
Title: The aeroacoustics of finite wall-mounted cylinders
Author: Porteous, Ric
Issue Date: 2016
School/Discipline: School of Mechanical Engineering
Abstract: Community noise is one of the most poorly controlled environmental pollutants. Controlling the noise generated by bluff-body flow can alleviate community noise generated by transportation systems such as aircraft, automobiles and highspeed rail. A foundational example of bluff-body flow is the flow around a square Finite Wall-Mounted Cylinder (FWMC). An FWMC models the major noise producing components of transportation systems, such as landing gear and pantographs, but is also relevant to many facets of engineering including flow around chimney stacks, wind turbine masts, heat exchangers and mountains. This thesis studies the flow-induced noise generated by square FWMCs with aspect ratios ranging from 0 < L/W < 23 immersed in boundary layers of thickness δ/W = 1.3 and δ/W = 3.7 at a Reynolds number based on the side width, W, of Re𝚠 = 1.45 × 10⁴. The flow-induced noise is measured using single microphone, directivity and phased microphone array measurements. The measured noise is related to the flow around the FWMC with fluctuating wake velocity measurements using a single hot-wire. Surface pressure measurements and oil-film flow visualisation are also conducted to further investigate the flow physics. The flow-induced noise of FWMCs is characterised in terms of the frequency, magnitude and directivity of the low frequency acoustic tones generated through periodic vortex shedding and the magnitude of the high frequency broadband component. It is found that as the aspect ratio increases, the FWMC transitions through four vortex shedding regimes based on the number of tones in their acoustic spectra. The aspect ratio where the FWMC transitions from one regime to another is dependent on the boundary layer thickness. Within each shedding regime, the noise producing vortex filaments are observed to have different topological structures, corresponding to either a single or multi-cellular wake. Measurements of the mean and fluctuating aerodynamics using wake velocity and surface pressure measurements provide explanations for the observed acoustic phenomena. In particular, it is discovered that maximum three-dimensional interaction of the free-end downwash with spanwise vortices can disrupt the wake and reduce the flow-induced noise to near background levels, even for aspect ratios as large as L/W = 7. Several numerical models are also developed to aid the analysis. These include a modified version of Curle’s Aeolian tone theory suitable for FWMCs and a wake model of higher aspect ratio FWMCs used to study cellular wake vortex topologies. Finally, phased array source localisation shows that the magnitude of the high frequency broadband noise is closely related to dynamics of the large-scale vortex structures that generate tonal noise. Because of this, broadband noise can be reduced by approximately 30% when the boundary layer is thickened, even when the free-end of the FWMC lies well outside the edge of the boundary layer.
Advisor: Cazzolato, Benjamin Seth
Zander, Anthony Charles
Doolan, Cornelius Joseph
Moreau, Danielle J.
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2016.
Keywords: aeroacoustics
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
DOI: 10.4225/55/5823c711b5717
Appears in Collections:Research Theses

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