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Title: Secondary flows in curved channels
Author: Sanmuganathan, Kathiravelu
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1966
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Though the existence of secondary flows in curved channels was deduced early in the history of Hydraulics, a complete understanding of the phenomena does not seem to have evolved. One of the causes of this lack of understanding is the difficulty experienced in measuring the small secondary components of velocity in the presence of the larger tangential component. This difficulty was overcome by a technique developed by the author, which maps the secondary flow pattern in a cross-section. It was found that the pattern in a shallow curved channel is of a two cell form 'similar to those observed by Einstein and Horder (1954) and Wadekar (1957). However, the pattern was not steady but varied gradually with time. Thompson (1876) attributed the origin of secondary flows in curved channels to the bed and predicted the motion near the bed to be towards the inner bank. However, he ignored viscous effects. It is shown that, when viscous stresses are considered, the motion at the bed need not always be inwards to satisfy the equations of motion. Indeed flow conditions were reproduced where the motion was outwards in some parts of the bed. Nor can Thompson's explanation account for the second cell near the outer bank or the variation of the pattern with time. In this work, these observations are interpreted as being caused partly by the bed effect and partly by the instability of the motion similar to the instability of flow between rotating cylinders studied by Taylor (1923). In doing so, the criterion for instability and the form of the disturbance that grows in a wide curved channel was obtained by a theory similar to that developed by Taylor. The flow characteristics when the instability occurs and at higher velocities were studied experimentally with the aid of a small deep channel. The effect of free surface, bed and depth was also studied in this channel. This work indicates that the phenomena observed in curved channels cannot be explained fully by the effect of the bed alone, but by a combination of the bed effect and the instability of the flow.
Supervisor: White, C. M. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available