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dc.contributor.advisorWhite, Edward
dc.creatorMonschke, Jason Andrew
dc.date.accessioned2016-05-04T13:19:50Z
dc.date.available2017-12-01T06:36:21Z
dc.date.created2015-12
dc.date.issued2015-09-11
dc.date.submittedDecember 2015
dc.identifier.urihttp://hdl.handle.net/1969.1/156395
dc.description.abstractTransient growth is a linear disturbance growth mechanism that plays a key role in roughness-induced boundary-layer transition. It occurs when superposed stable, non-orthogonal continuous spectrum modes experience algebraic disturbance growth followed by exponential decay. Algebraic disturbance growth can modify the basic state making it susceptible to secondary instabilities rapidly leading to transition. Optimal disturbance theory was developed to model the most-dangerous disturbances. However, evidence suggests roughness-induced transient growth is sub-optimal yet leads to transition earlier than optimal theory suggests. This research computes initial disturbances most unstable to secondary instabilities to further develop the applicability of transient growth theory to surface roughness. The main approach is using nonlinear adjoint optimization with solutions of the parabolized Navier–Stokes and BiGlobal stability equations. Three objective functions were considered: disturbance kinetic energy growth, sinuous instability growth rate, and Tollmien–Schlichting (TS) wave growth rate. The first objective function was used as validation of the optimization method. Counter-rotating streamwise vortices located low in the boundary layer maximize the sinuous instability growth rate. Sinuous instabilities were observed at disturbance amplitudes as low as 2:5% spanwise root-mean-square. The near wake of the initial disturbance is potentially much less stable than the far field. TS wave stabilization was achieved for all parameters considered and becomes more effective at higher frequencies.en
dc.format.mimetypeapplication/pdf
dc.language.isoen
dc.subjectTransient growthen
dc.subjectreceptivityen
dc.subjecttransitionen
dc.subjectlaminaren
dc.subjectturbulenten
dc.subjectBiGlobalen
dc.subjectinstabilityen
dc.subjectadjoint optimizationen
dc.subjectparabolized Navier-Stokesen
dc.subjectsecondary instabilityen
dc.subjectroughnessen
dc.titleMost-Critical Transient Disturbances in an Incompressible Flat-Plate Boundary Layeren
dc.typeThesisen
thesis.degree.departmentAerospace Engineeringen
thesis.degree.disciplineAerospace Engineeringen
thesis.degree.grantorTexas A & M Universityen
thesis.degree.nameDoctor of Philosophyen
thesis.degree.levelDoctoralen
dc.contributor.committeeMemberSaric, William
dc.contributor.committeeMemberReed, Helen
dc.contributor.committeeMemberDaripa, Prabir
dc.type.materialtexten
dc.date.updated2016-05-04T13:19:50Z
local.embargo.terms2017-12-01
local.etdauthor.orcid0000-0002-0939-008X


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