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Title: Lift forces on stationary spheres in flow between Reynolds numbers 5000 and 80000
Author: Murray, C. G.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1981
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The lift force exerted on a fixed sphere in air and water flow was investigated experimentally in three circumstances; firstly when the sphere was placed close to a smooth fixed boundary, secondly when it was placed in a shear flow remote from a boundary and thirdly in flow with no time averaged velocity gradient. The instantaneous lift was found to vary significantly with time under fixed flow conditions. The magnitude and sign of the time averaged mean lift were found to vary with changes in the approach velocity of the fluid and with the distance between the sphere and the boundary. Such variations of lift were related to changes in the behaviour of flow separating from the sphere, and the relationship was investigated in each of the three cases examined. In flow with no velocity gradient time related fluctuation of the lift force was important, and appeared to be random. Time averaged lifts were not zero in this case, but often very close to zero. This unexpected finding may be associated with asymmetric flow separation from the sphere. The orientations of the spere wake and separation line were made visible by the injection of smoke or dye into the wake region. This technique revealed curious fluctuating indentations in the separation line which were found to be related closely to the direction in which any lift acted. During the experiments a link from the apparatus to a minicomputer was established, allowing recordings of lift to be analysed statistically. Programs were developed and run on this computer and a larger mainframe computer which calculated mean lifts, standard deviation from these means, and to detect any periodic fluctuations of the lift.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available