Titre:	Analysis of the dynamic modes of transonic flow past a cylinder
Autre(s) titre(s):	Análise dos modos dinâmicos de escoamento transônico em torno de um cilindro
Auteur(s):	Santana, Guilherme Mendes
Orientador(es)::	Fabro, Adriano Todorovic
Coorientador(es)::	Miserda, Roberto Francisco Bobenrieth
Assunto::	Aeroacústica Escoamento (Engenharia)
Date de publication:	8-jui-2024
Data de defesa::	27-jui-2023
Référence bibliographique:	SANTANA, Guilherme Mendes. Analysis of the dynamic modes of transonic flow past a cylinder. 2023. 102 f., il. Dissertação (Mestrado em Ciências Mecânicas) — Universidade de Brasília, Brasília, 2022.
Abstract:	The most common approaches for computational aeroacoustics are the direct noise computation through the solution of the governing equations and the use of linear equations to describe sound propagation. An interesting alternative to these methods is a data-driven approach. The Dynamic Modes Decomposition (DMD) and the Proper Orthogonal Decomposition (POD) are analysis tools that have been used recently that also provide data-based models. With that in mind, this dissertation aims to use the POD and DMD methods to study the transonic flow past a 2D circular cylinder with Mach numbers 0.5 and 0.75 and modelled with the Euler equations. The flow past the cylinder was chosen as the subject of this work because it is a classical problem in fluid mechanics but presents rich dynamics. The acceleration of the flow as it passes around the cylinder causes the formation of shock waves, and the resulting adverse pressure gradient causes the separation of the flow. As vortices are emitted and form a von Karman street at the wake, the shock waves also detach and propagate through the domain as sound waves. The Strouhal numbers for both cases were around 0.2, the well-known value for the flow around a cylinder. The POD and DMD are methods that decompose a data set, in this case composed of pressure field snapshots, into coherent structures, or modes. The POD modes are spatially orthogonal structures, while the DMD modes have specific frequencies and rates of growth. The analysis of the modes’ structures revealed that the cylinder emits noise in a manner similar to an acoustic dipole, with contributions from other multipoles. Furthermore, the modes for 𝑀∞ = 0.75 revealed that the vortex wake is also a noise source in this case. The DMD decomposition also provided frequencies associated with the modes that matched the peaks in the pressure spectra. The POD and DMD modes were also used to reconstruct the flow fields. The reconstruction with the POD agreed almost exactly with the original data, while those obtained with the DMD presented more discrepancies. For 𝑀∞ = 0.5 the error for the pressure fluctuations root mean square value was around 15% to 25% for most of the domain and had a maximum value of over 200%, but the frequency and amplitude of the sound waves represented the original data reasonably well. The results showed that the POD and the DMD are interesting analysis tools, capable of revealing important information about the system but the POD is a better method to reconstruct the data set.
metadata.dc.description.unidade:	Faculdade de Tecnologia (FT) Departamento de Engenharia Mecânica (FT ENM)
Description:	Dissertação (mestrado) — Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2022.
metadata.dc.description.ppg:	Programa de Pós-Graduação em Ciências Mecânicas
Licença::	A concessão da licença deste item refere-se ao termo de autorização impresso assinado pelo autor com as seguintes condições: Na qualidade de titular dos direitos de autor da publicação, autorizo a Universidade de Brasília e o IBICT a disponibilizar por meio dos sites www.bce.unb.br, www.ibict.br, http://hercules.vtls.com/cgi-bin/ndltd/chameleon?lng=pt&skin=ndltd sem ressarcimento dos direitos autorais, de acordo com a Lei nº 9610/98, o texto integral da obra disponibilizada, conforme permissões assinaladas, para fins de leitura, impressão e/ou download, a título de divulgação da produção científica brasileira, a partir desta data.
Agência financiadora:	Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).
Collection(s) :	Teses, dissertações e produtos pós-doutorado

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