Boundary layer development from transition provoking devices

Data on stream and spanwise variation in four representative transitional boundary layers is presented, the test cases encompassing free transition, transition due to a two-dimensional trip wire, with laminar and with turbulent re-attachment, and transition due to isolated spherical roughness elements.<br/><br/>The concept of statistical similarity in transition regions has been confirmed for the cases of free transition and for transition due to a two-dimensional trip wire, with the streamwise mean intermittency distribution described by the normal distribution function. Significantly, the condition of "transition at the wire" is found to have a very small but well defined intermittency growth region.<br/><br/>Transition due to isolated roughness elements is however seen to have a fundamentally different character. The elements induce large amplitude fluctuations, related to vortex shedding, which degenerate downstream to become random, three-dimensional, turbulent fluctuations in the developing wakes, with only mild recourse to an intermittent type of breakdown.<br/><br/>Spanwise variation in the layer is related to inconsistencies in the turbulent spot source density and occurrence frequency, and can result in substantial non-uniformity of the boundary layer if the transition region is long.<br/><br/>The resulting low Reynolds number turbulent boundary layer exhibits a moderate increase in the additive constant in the law of the wall, and is characterised by a deeper penetration of the transverse intermittency distribution. The choice of transition agent however, has no apparent influence on the rate at which the developing turbulent boundary layer approaches self- preserving conditions.<br/><br/>A general relation, based on local boundary layer parameters, has been developed for the estimation of the transitional skin friction coefficient and has been tested via momentum balance principles.<br/><br/>The skin friction relation has also been employed in a general integral prediction technique, for the incompressible transitional boundary layer in two-dimensional, arbitrary pressure gradient flows.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral Thesis

Year dc:date.issued

1979

Author dc:creator

• Fraser, Charles

Language dc:language

eng

Identifier

oai:rke.abertay.ac.uk:studenttheses/d09c8e79-aeb9-42b8-afd2-2449c7c6bad9

OAI identifier oai:identifier

oai:rke.abertay.ac.uk:studenttheses/d09c8e79-aeb9-42b8-afd2-2449c7c6bad9