Inspired by Nature, Engineered for Speed: Biomimetic Surface Development and Supsersonic Performance Analysis

With advancements in flight as a means of transportation, there is a renewed interest in development of supersonic vehicles to further connect the world in shorter amounts of travel time [1]. Through the history of supersonic flow study, particularly for aircraft design, one of the most prominent roadblocks encountered was supersonic compression leading to shocks that can lower performance efficiency [2][3]. Attempts to combat the adverse performance effects of shocks and expansions caused by compressibility have been varied, but flow control methods have been one of the greatest fields of interest for their potential to allow micro-scale changes to preserve the advantages of macro-scale vehicle design choices and necessities [4][5].

This thesis investigates a novel application of a bio-inspired surface coating comprised of a lattice of axisymmetric divergent micropillars. Additionally, this thesis tests a variety of methods for manufacturing the axisymmetric divergent micropillars being investigated. This research demonstrates a previously unexplored use case for a shark denticle-inspired coating that will yield benefits in supersonic vehicles and enables versatility in future testing of variations to the geometry.

The first part of this work details the testing of bio-inspired micropillar coatings in reduction of separation bubble size in a shockwave boundary layer interaction. Through use of schlieren imaging, separation bubble reductions as high as 60% were measured over the bio-inspired coatings within a shockwave boundary layer interaction. Additionally, pressure fluctuation measurements have demonstrated attenuation of downstream turbulent pressure fluctuations downstream of an impinged shock wave.

The second part of this work covers the comparison of multiple methods of fabricating axisymmetric divergent bio-inspired coating samples. This was accomplished by a qualitative analysis of printed models viewed through scanning electron microscopy. In order to determine what method of manufacturing might be most advantageous for fabricating bio-inspired coatings, models would need to be replicated and printed using three additive manufacturing techniques.

Axisymmetric divergent bio-inspired coatings have shown a number of intriguing and beneficial applications such as delaying flow separation over an airfoil by [6] and reduction in presence of biofouling on submerged bodies [7], and now the use cases have been expanded into supersonic applications. Other potential applications still to be discovered are only limited by the ability to generate and fabricate more complex geometries, and the latter half of this work is one of the first steps in further exploring those applications. This work contributes to the library of bio-inspired coating applications in supersonic flow control, as well as applications of this specific geometry and the ability to further develop/investigate its potential.

The results of this work can be applied to improve upon the design of commercial and private supersonic vehicles. By reducing the impact of shockwave boundary layer interactions, which are common in high-speed vehicle design, the axisymmetric bio-inspired coatings investigated in this thesis offer a solution that will improve the design performance of the commercial and private air industries. Additionally, the parametrization and fabrication work will improve the accessibility to this geometry for future studies into optimization and new applications for shark denticle-inspired coatings.