Date of Award
Engineering and Applied Science
School of Naval Architecture and Marine Engineering
Boundary layer information local to three longitudinal positions has been characterized for a 130 cm long biomimetic self-propulsor known as NEELBOT-1.1 that swims with undulatory anguilliform-like motions, via analysis of stereo particle image velocimetry (PIV) measurements for key moments in the undulation cycle and for numerous combinations of swimming conditions and motion parameters, ideal and non-ideal. No obvious turbulent flow structures or indications of boundary layer separation were observed at nonzero advance speeds, and skin friction coefficients were subsequently estimated for magnitude relative to the dynamic pressure associated with operation at the design swimming speed of Uo = 0.25 m/s. Estimates were correlated with measurements made for an oscillating and non-oscillating cylindrical test article that were benchmarked by initial mono PIV investigations of steady laminar flow over a flat plate at zero incidence which was tested while stationary and oscillating in its own plane. Behavior of boundary layer profiles pertaining to the robot, apparently significantly influenced by the traveling flexion waves characteristic of the anguilliform motions, is clearly distinguished from local oscillatory flow structures related to the other two test articles. Approximately 10–15% increases in local skin friction are observed for the robot over similar conditions for the cylinder, and downstream vortex shedding is readily observed for the oscillating cylinder.
The results of this thesis will be used in validation of numerical analyses performed in parallel with this research for the purpose of calculating the time-mean frictional drag experienced by the robot and to determine whether it can produce enough thrust to overcome its drag without simultaneously increasing it beyond realizable thrust generation capabilities. Theoretical hydrodynamic descriptions of the wake velocity field agreed well with previous PIV measurements, but the theory does not treat viscous effects. Furthermore, the preliminary semi-empirical, quasi-static attempts to estimate frictional drag were shown to under-predict the actual drag by net force measurements taken while towing the robot at its design speed which was undulating for that expected swimming speed, hence the necessity of this thesis as further investigation.
Eastridge, Jonathan R., "Experimental Investigation into the Boundary Layer of a Robotic Anguilliform Propulsor" (2020). University of New Orleans Theses and Dissertations. 2807.