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Title: Low Reynolds number turbulent boundary layers and wakes
Author: Gough, Tim D.
ISNI:       0000 0001 3507 397X
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1996
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A detailed study of the flow over and behind a flat plate using closely matched experiments and numerical simulations is reported. This thesis concentrates on the experimental studies. One symmetric and one asymmetric wake were generated and detailed mean and turbulence measurements made using hot wire anemometry. So that the simulations could maintain suitably high resolution the flows were kept at very low Reynolds numbers - no boundary layer exceeding Re of 800. The small scale of the flows required careful attention to the effects of probe size. The wakes studied complement previous experiments at higher Reynolds number. Boundary layer tripping is shown to exhibit dependence on the layer upstream of the trip not previously demonstrated. Fully developed layers free of trip effects were found to exist for Re of 405. A logarithmic region was still apparent at Re as low as 250, though residual trip effects were present in the outer layer. Near the plate trailing edge the inner layer was significantly affected by the downstream wake development, the acceleration leading to non-equilibrium in the inner layer. Turbulent kinetic energy balances show the existence of a near-wall region of high loss by turbulent transport not previously demonstrated experimentally. As the boundary layers leave the trailing edge the Reynolds stresses exhibit marked increases in magnitude near the centreline. These 'overshoots' are partially caused by vortex shedding from the blunt trailing edge; the flow outside this region behaves as an apparently quasi-steady free stream, implying, interestingly, a Strouhal number of about 0.16. An inner wake develops propagating outwards from the edge of the wake centreline. The streamwise development of the inner wake is Reynolds number dependent in a manner consistent with its growth into the layers of the original boundary layers. Balances of the turbulent kinetic energy and uv transport equations have been produced at several streamwise positions and along the wake centreline. Measurements extend into the far wake and comparisons between the experiment and the simulation are also reported.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Computational fluid dynamics; Wind tunnels