Publication Date:
2022-05-26
Description:
Submitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy at the Massachusetts Institute of Technology
and the Woods Hole Oceanographic Institution February 2005
Description:
In biology, the importance of fluid drag, diffusion, and heat transfer both internally and
externally, suggest the boundary layer as an important subject of investigation, however,
the complexities of biological systems present significant and unique challenges to
analysis by experimental fluid dynamics. In this investigation, a system for automatically
profiling the boundary layer over free-swimming, deforming bodies was developed and
the boundary layer over rigid and live mackerel, bluefish, scup and eel was profiled. The
profiling system combined robotics, particle imaging velocimetry, a custom particle
tracking code, and an automatic boundary layer analysis code. Over 100,000 image pairs
of flow in the boundary layer were acquired in swimming fish alone, making spatial and
temporal ensemble averaging possible.
A flat plate boundary layer was profiled and compared to known laminar and turbulent
boundary layer theory. In general, profiles resembled those of Blasius for sub-critical
length Reynolds numbers, Reχ. Transition to a turbulent boundary layer was observed
near the expected critical Reχ and subsequent profiles agreed well with the law of the
wall. The flat plate analysis demonstrated that the particle tracking and boundary layer
analysis algorithms were highly accurate.
In rigid fish, separation of flow was clearly evident and the boundary layer transitioned to
turbulent at lower Reχ than in swimming fish and the flat plate. Wall shear stress, τo
forward of separation was slightly higher than flat plate values. Friction drag in rigid and
swimming fish was determined by integrating τo over the surface of the fish. The
analysis was facilitated by the definition of the relative local coefficient of friction. In
general, there was no significant difference in friction drag between the rigid-body and
swimming cases. In swimming, separation was, on average, delayed. Therefore,
pressure drag was estimated on the basis of thickness ratio and used to calculate an
upper-bound total drag on a swimming fish. Total drag was used to determine the
required muscle power output during swimming and compare that with existing muscle
power data. τo and boundary layer thickness oscillated with undulatory phase. The
magnitude of oscillation appears to be linked to body wave amplitude.
Description:
The author is grateful for the funding received from the Office of Naval Research, Grants
N00014-99-1-1082 and N00014-96-1141, the MRI program of the National Science
Foundation, Grant OCE-9724383, the National Science Foundation Graduate Research
Traineeship in Coastal Oceanography, the WHOI Ocean Ventures Fund, the WHOI
Academic Programs Office, and the MIT Department of Ocean Engineering.
Keywords:
Boundary layer
;
Fishes
;
Locomotion
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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