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Continuous mode interaction and the ...

Stanford University.

Continuous mode interaction and the bypass route to transition.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Continuous mode interaction and the bypass route to transition.
作者:	Zaki, Tamer A.
面頁冊數:	120 p.
附註:	Adviser: Paul A. Durbin.
附註:	Source: Dissertation Abstracts International, Volume: 66-08, Section: B, page: 4459.
Contained By:	Dissertation Abstracts International66-08B.
標題:	Engineering, Mechanical.
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3186433
ISBN:	9780542287350

Continuous mode interaction and the bypass route to transition.
Zaki, Tamer A.

Continuous mode interaction and the bypass route to transition. - 120 p.

Adviser: Paul A. Durbin.

Thesis (Ph.D.)--Stanford University, 2005.

Boundary layer transition to turbulence, without the intervention of Tollmien-Schlichting instability waves, is designated 'bypass transition'. That terminology is all-encompassing; many bypass mechanisms are possible, for example transition due to surface roughness, acoustic perturbations, or free-stream vortical disturbances. It is the last that has become synonymous with the term bypass, and is the focus of this work.

ISBN: 9780542287350Subjects--Topical Terms:

212470
Engineering, Mechanical.

Continuous mode interaction and the bypass route to transition.
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245 1 0 $a Continuous mode interaction and the bypass route to transition.
300 $a 120 p.
500 $a Adviser: Paul A. Durbin.
500 $a Source: Dissertation Abstracts International, Volume: 66-08, Section: B, page: 4459.
502 $a Thesis (Ph.D.)--Stanford University, 2005.
520 # $a Boundary layer transition to turbulence, without the intervention of Tollmien-Schlichting instability waves, is designated 'bypass transition'. That terminology is all-encompassing; many bypass mechanisms are possible, for example transition due to surface roughness, acoustic perturbations, or free-stream vortical disturbances. It is the last that has become synonymous with the term bypass, and is the focus of this work.
520 # $a Continuous mode transition is illustrated by numerical simulations of pairwise mode interaction. Only two modes, one low-frequency penetrating and one high-frequency sheltered eigenfunction, can induce transition in a manner that emulates the influence of a spectrum of vortical disturbances. This new framework provides a link between the continuous eigenmodes from linear theory, and the non-linear interaction that causes transition to turbulence.
520 # $a The perspective that bypass is the complement to orderly transition suggests that it be studied by starting from the complement to Tollmien-Schlichting waves. The latter are the discrete modes of the Orr-Sommerfeld operator; their complement is the continuous spectrum. An examination of mode shapes sheds light on boundary layer receptivity to vortical disturbances: Low-frequency modes penetrate the boundary layer, while high frequencies are expelled---a result referred to as shear sheltering. Low frequency penetration can be characterized by a coupling coefficient. Large coupling, Orr-Sommerfeld modes resonantly force the Squire operator. The response is a superposition of Squire modes, and their incomplete cancellation gives rise to Klebanoff modes, which resemble jets in the perturbation field. While this is a route into the boundary layer, transition subsequently involves an inter-action between low and high frequency modes. The lifted, low-frequency perturbation jets are susceptible to a Kelvin-Helmholtz type instability that marks the onset of breakdown and turbulent spots.
520 # $a The role of pressure gradient is also investigated. Both linear theory and direct numerical simulations demonstrate that flow deceleration enhances the intensity of Klebanoff modes. The correlation between the amplitude of these elongated disturbances and transition location is examined in the framework of continuous mode transition. The results confirm that stronger Klebanoff modes are more unstable, and hence transition occurs farther upstream in adverse pressure gradient.
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791 $a Ph.D.
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