The investigation has been conducted in the form of experimental measurements, using high-speed stereoscopic particle image velocimetry, of a turbulent boundary layer in the Cambridge University Engineering Department’s water tunnel facility. All the results produced in this project showed indications that long structures are a ubiquitous feature of turbulent boundary layer flow. The instantaneous velocity fields and a variety of flow-field statistics (averages and correlations) all demonstrated the presence of both high and low speed long structures that had reasonably consistent characteristics. The results also indicated that hairpin-like vortices were frequently present in the turbulent boundary layer. Although the instantaneous fields showed that these vortices were generally asymmetric and distorted from the archetypal hairpin shape, conditionally averaged fields showed that the average shape was very much like an ideal hairpin. As such the hairpin vortex seems an ideal candidate as a representative eddy in any statistical model of a turbulent boundary layer. The view of the turbulent boundary layer as seen in the results of this project is of hairpin-like vortices creating Q2 and Q4 events, that are aligned such that the streamwise component of successive events can merge and lead to the formation of long structures.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598501 |
| Date | January 2009 |
| Creators | Dennis, D. J. C. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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