Inertial Bodies in Unsteady Flows
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Turbulence plays a leading role in the shaping and evolution of the world around us but in most cases the precise implication of turbulence is unknown. It assists in the formation of dunes and ripples in deserts and seas; it forces bugs, birds, and bats to evolve and learn fly in the chaotic winds. The interaction between turbulent fluid and solid bodies appears random and unpredictable; however, in many cases, patterns begin to appear. In the first part of this dissertation, we look at the formation of a sand heap in oscillatory flow. We oscillate a square plate above a bed of glass beads. Under certain conditions, the vertical pressure gradients imposed on the bed cause the grains to become mobile and produce a heap. We develop a model to quantify the conditions that generate heaps and relate the shape and size of the heap to characteristics of the flow. This model compares favorably to our experimental results. In the second part of this dissertation, we relate the trajectory of a golden eagle with the flows experienced by the eagle. We record the accelerations of the eagle over a period of 16 days and isolate those associated with soaring flight. We then bin the soaring data according to mean winds which we find using a weather database. We analyze both the probability density functions and energy spectra of the soaring accelerations and find that the accelerations of the golden eagle are closely related to the turbulence experienced by the eagle. Finally, in the last part of this dissertation, we quantify the flight performance of unmanned aerial vehicles (UAVs) in cylinder wakes. We autonomously fly a quadcopter in a wake and vary the wind speed and cylinder size to determine the relationship between the wake characteristics and the standard deviation of the quadcopter's displacement. We find that we can explain the stream-wise displacements using a simple balance of forces.
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