UA cloudflare authentication

 

An Experimental Study of Drag Reduction Due to the Roller Bearing Effect Over Grooved Surfaces Inspired by Butterfly Scales

Simple item page
dc.contributorMacPhee, David
dc.contributorHubner, James
dc.contributorSharif, Muhammad
dc.contributorOlcmen, Semih
dc.contributor.advisorLang, Amy
dc.contributor.authorGautam, Sashank
dc.contributor.otherUniversity of Alabama Tuscaloosa
dc.date.accessioned2022-02-04T20:16:38Z
dc.date.available2022-02-04T20:16:38Z
dc.date.issued2021
dc.descriptionElectronic Thesis or Dissertationen_US
dc.description.abstractMonarch butterfly wings are covered in minuscule scales (approximately 100 µm in length) which align together in a pattern that resembles roof shingles. Flight tests performed on live butterflies showed that these scales provide a beneficial aerodynamic function. The scales are angled upwards such that transverse cavities form for a flow passing perpendicular to the rows of scales. Flow visualization of butterfly inspired cavities has shown that the entrapped vortex (or vortices) inside each cavity can act as a fluidic bearing to the outer boundary layer flow resulting in reduced surface or skin friction drag. This study conducted experiments on cavity embedded flat plates, mimicking the butterfly scale geometry, documenting this “roller-bearing effect”. The experiments were performed in a tow-tank facility, and DPIV measurements were used to calculate the surface drag based on the measured boundary layer velocity profiles. Initially, a net skin friction or surface drag reduction for a simple rectangular cavity of aspect ratio (AR) 2 was measured. However, as the cavity geometry was varied to better mimic the butterfly scales, the shape of the vortex and the dividing streamline also changed, which in turn affected the surface drag. This study aimed to determine the cavity geometry that results in the highest drag reduction. Experimental models with cavity geometries of AR 2 and 3 and wall inclination angles of 22°, 45° and 90° were tested, where the slanted models were inspired from observed butterfly scale geometries. Each of these models exhibited net surface drag reduction for lower Red range of 4.5 to 8.5, except for the 22° cavity with AR 2 which showed an increase in drag for all the Red cases. The Red is defined based on the cavity depth which is kept constant for all the models. The model with a 45° cavity wall inclination and AR 2 had the highest surface drag reduction ranging from 18.63% to 26.33% at lower Red range. Additionally, the critical Red region, beyond which the embedded vortex becomes unstable, and fluid begins to enter and eject out of the cavity, mixing with the outer boundary layer flow and thereby eliminating the drag reduction effect, is documented for various cavity geometries and ranged from Red 90 to 120. As was hypothesized, the increase in Red beyond the critical region resulted in an increase in surface drag.en_US
dc.format.mediumelectronic
dc.format.mimetypeapplication/pdf
dc.identifier.otherhttp://purl.lib.ua.edu/181728
dc.identifier.otheru0015_0000001_0004018
dc.identifier.otherGautam_alatus_0004D_14653
dc.identifier.urihttp://ir.ua.edu/handle/123456789/8293
dc.languageEnglish
dc.language.isoen_US
dc.publisherUniversity of Alabama Libraries
dc.relation.hasversionborn digital
dc.relation.ispartofThe University of Alabama Electronic Theses and Dissertations
dc.relation.ispartofThe University of Alabama Libraries Digital Collections
dc.rightsAll rights reserved by the author unless otherwise indicated.en_US
dc.subjectBio-inspired
dc.subjectButterfly scales
dc.subjectCavity vortex
dc.subjectExperimental Low Re flow
dc.subjectRoller-bearing effect
dc.subjectSurface drag reduction
dc.titleAn Experimental Study of Drag Reduction Due to the Roller Bearing Effect Over Grooved Surfaces Inspired by Butterfly Scalesen_US
dc.typethesis
dc.typetext
etdms.degree.departmentUniversity of Alabama. Department of Aerospace Engineering and Mechanics
etdms.degree.disciplineAerospace Engineering
etdms.degree.grantorThe University of Alabama
etdms.degree.leveldoctoral
etdms.degree.namePh.D.

Files

Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
u0015_0000001_0004018.pdf
Size:
4.67 MB
Format:
Adobe Portable Document Format
Download

Collections

Theses and Dissertations
Theses and Dissertations - Department of Aerospace Engineering and Mechanics