Date of Award

4-2020

Document Type

Thesis - Open Access

Degree Name

Master of Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Ebenezer Gnanamanickam

First Committee Member

Dr. Reda Mankbadi

Second Committee Member

Dr. Mark Ricklick

Abstract

An experimental study of the interaction between hairy structures modeled as high-aspect ratio micro-pillars (HAMuP) and wall turbulence is presented. Micro-pillars are elastic, hair-like microstructures which have been inspired by naturally occurring examples like lateral line sensors in fish and air flow sensors in bats. The objective of this thesis was two fold: to develop a manufacturing process for consistent production of HAMuP arrays, and to conduct a study focusing on the interaction of HAMuP arrays with wall turbulence. Hotwire anemometry measurements were carried out in two different experimental facilities at three different streamwise locations to describe the interaction between the HAMuP array and the wallturbulence. There is a shift of the laminar sublayer away from the wall indicated by a shift in the turbulent-intensity peak in the inner region of the flow over HAMuP array. The energy spectra also reveals a shift of the energetic structures away from the wall. Measurements taken downstream of the HAMuP array point to a damping of the energetic structures in the flow over the HAMuP array. The amplitude modulation coefficient is increased in the nearwall region which points to a possible mechanism by which the naturally occurring micro-pillars detect oncoming predators. A parametric approach was adopted to further study the effect of HAMuP arrays on turbulent boundary layer. The parameter study also reveals that a decrease in elastic modulus may lead to a decrease in the amount of energy the HAMuP arrays can extract from the flow. Also, increasing the height of the pillars might increase the potential elastic energy they can store but there is also a potential increase in the form drag due to the micro-pillars.

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