Transition to turbulence by interaction of free-stream and discrete mode perturbations

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2016-01-01
Authors
Durbin, Paul
Bose, Rikhi
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Aerospace Engineering

The Department of Aerospace Engineering seeks to instruct the design, analysis, testing, and operation of vehicles which operate in air, water, or space, including studies of aerodynamics, structure mechanics, propulsion, and the like.

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The Department of Aerospace Engineering was organized as the Department of Aeronautical Engineering in 1942. Its name was changed to the Department of Aerospace Engineering in 1961. In 1990, the department absorbed the Department of Engineering Science and Mechanics and became the Department of Aerospace Engineering and Engineering Mechanics. In 2003 the name was changed back to the Department of Aerospace Engineering.

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1942-present

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  • Department of Aerospace Engineering and Engineering Mechanics (1990-2003)

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Abstract

Mixed mode transition is studied by direct numerical simulation. Low frequency streaks are induced within the boundary layer by free-stream turbulence and an Orr-Sommerfeld discrete mode eigenfunction is introduced at the inlet. Amplitudes are selected such that the interaction of these modes can cause transition. Aside from the highest amplitude of free-stream turbulence, neither disturbance alone is sufficient to cause transition within the flowdomain. Results are classified into three routes to transition, depending upon the 2D Tollmien-Schlichting (TS) mode strength and free-stream turbulence intensity. (1) At low turbulence intensities, secondary instabilities instigate transition. On a strong TS mode, Λ vortices develop, but they are neither H nor K type. The pattern and spanwise size of Λ vortices depend upon the frequency and spanwise width of Klebanoff streaks by which they are generated. (2) When the TS mode amplitude is low, transition is via streak breakdown.The streaks are induced by the free-stream turbulence, but this case differs from conventional bypass transition in the mechanism of inception of turbulent spots. Three dimensional visualizations of the perturbation flow field show growing, helical undulations similar to n = 1 instability modes observed in axisymmetric jets and wakes. (3) At high turbulenceintensities, the flow undergoes bypass transition. The TS wave has a small effect, but its influence is seen at the larger of the two amplitudes studied.

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This article is published as Bose, Rikhi, and Paul A. Durbin. "Transition to turbulence by interaction of free-stream and discrete mode perturbations." Physics of Fluids 28, no. 11 (2016): 114105. 10.1063/1.4966978. Posted with permission.

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Fri Jan 01 00:00:00 UTC 2016
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