Design, build and testing of a laminar flow drag-plate

Murphy, Alan John (2005) Design, build and testing of a laminar flow drag-plate. University of Southampton, Faculty of Engineering, Science and Mathematics, School of Engineering Sciences, Doctoral Thesis, 309pp.

Record type: Thesis (Doctoral)

Abstract

Theory indicates that compliant materials are able to reduce the frictional drag of a marine body by delaying the transition from laminar to turbulent flow.
Recent experimentation on relatively small samples of compliant material suggest that correctly designed compliant materials are able to damp instabilities in the boundary layer and delay transition.
In this research the challenge was to design a device that could be used to test relatively large panels of complaint material and subsequently use the device to make an experimental comparison between the drag of complaint material and a standard non-compliant surface.
In particular, the principal requirement of the test device was that laminar flow persisted over the leading edge and was incident on the compliant material surface over the desired test speed range. A drag-plate with a laminar flow nose section was designed for this purpose.
In the first part of this thesis basic drag assessments are made using engineering formulae followed by a rigorous computational assessment of fluid flow, boundary layer properties and transition prediction for alternative laminar flow drag-plates.
An optimum geometry is established for the laminar flow nose and other practical design requirements are assessed, resulting in the final design of the laminar flow drag-plate. In addition a suitable dynamometer with associated fixtures is designed.
In the second part of this thesis, the experimental facility is characterised and experimental procedures established.
The drag of a compliant material is compared to a standard non-compliant material. No drag reduction was evident, although the compliant material (supplied from an external source) had inconsistencies in manufacture.
A number of different demonstrations of the laminar flow performance of the drag-plate are presented. These include a novel practical transition detection method and flow visualisation. It is demonstrated that the design challenge of producing a laminar flow device has been achieved despite the fact that the drag-plate exhibits a degree of roughening over the experimental period.

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