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Title: Multi-scale CFD modelling towards resolving machined roughness
Author: Kapsis, Marios
ISNI:       0000 0004 7971 6676
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2019
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Recent advances in manufacturing technologies, such as additive manufacturing, have introduced the potential of selecting the roughness characteristics as a design parameter. Hence, the understanding and prediction of aerothermal effects of manufacturable (machined) micro-structures would be of paramount importance. So far, roughness has been largely considered as a stochastic attribute and, therefore, had been empirically modelled. Thus, the question arises of whether the shape and pattern of regular roughness and the fine flow structures around them require detailed resolution. Initially, a systematic computational study is carried out on the aerothermal behaviour and impact of some discrete micro-structures. Micro-structure configurations are considered for a Reynolds number range typical for those roughness elements (Re < 5000). Several RANS and LES analyses are performed to compare the behaviour in a well-established turbulent flow regime to a transitional one. The results highlight the significance of resolving such fine scales and their interactive wakes, as they are dependent on both the shape and the pattern of the micro-structures. Considering the need for resolving both the geometric and flow fine scales efficiently, a new multi-scale approach, the novel Block Spectral Method, is adopted. This method aims to provide efficient resolution of the local spatial and temporal flow variations due to the large scale micro-structures. This resolution is provided without resorting to the modelling of every single micro-structure in detail, as a conventional large scale CFD simulation would demand, but still demonstrating similar time-accurate and time-averaged flow properties. The emphasis is then put into developing a parallelised solver of the method to enable tackling large problems. The present work also includes a first of the kind verification of the Block Spectral Method application to surfaces fitted with 3D micro-structures that promote unsteadiness in the flow.
Supervisor: He, Li Sponsor: Engineering and Physical Sciences Research Council ; SIEMENS Turbomachinery Ltd
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Computational fluid dynamics ; Multiscale ; Regular roughness ; Additive manufacturing ; Block Spectral Method