Semester

Summer

Date of Graduation

2018

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Patrick Browning

Committee Member

Wade Huebsch

Committee Member

Edward Sabolsky

Abstract

The ever increasing demand for global travel coupled with increasing costs of fuels have prompted many researchers to study new methods to save fuel to make travel more efficient. One of the proverbial low-hanging fruits for fuel efficiency is aerodynamic drag reduction. Simple changes in the shape or placement of structures on the surface of different types of vehicles have been shown to increase fuel efficiency by reducing drag (e.g., add-on lower and aft wake fairings on tractor trailers which have seen a tremendous rise in popularity on US highways in recent years). Areas of interest in drag reduction have typically been in flow control of the boundary layer. Flow control techniques include both passive and active methods. Passive methods include biomimetic structures, riblets, and vortex generators. Active control techniques that are zero mass injection include dielectric barrier discharge (DBD) techniques, dynamic roughness (DR) employed by actively moving specific parts of the skin on the aerodynamic surface, or methods as simple as vibrating the entire surface. Biomimetic micro and macro structures were investigated in these experiments to determine their efficacy as methods of aerodynamic drag reduction. Wind tunnel experiments were conducted to determine the viscous drag on a flat plate covered with several different micro- and macro surface treatments. The biomimetic surface treatment structures use various geometric forms cast in Sylgard-170 and applied to a smooth, flat, glass substrate. The near-wall boundary layer velocity profiles were determined using planar particle image velocimetry (PIV), a method which utilizes a particle-seeded flow and a pulsed laser illumination and a camera system to capture and cross-correlate the flow field within the region of interest to statistically determine its 2D flow field velocity vectors. Four different Reynolds numbers with varying degrees of free stream turbulence were tested, as well as passive and active vibration modes for all of the surface treatment test articles. Post processing analysis of the flow field within the boundary layer of each model was performed, including determination of the shear stress at the wall of each boundary layer, as well as numeric integration of the velocity profiles for a direct momentum analysis. Boundary layer shape factors were calculated to help determine the likelihood of local flow separation related to viscous drag. Results indicated that the tested biomimetic micro- and macro surface structures can provide some drag reduction in both passive and active flow control modes in both laminar and turbulent flow at low Reynolds numbers O(104). With improved scaling of the casting size, biomimetic micro- and macro structures could potentially be an effective form of drag reduction for many different aerodynamic applications.

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