Author: William S. Saric
Publisher:
ISBN:
Category :
Languages : en
Pages : 25
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Book Description
An overview of research on the three dimensional nature of boundary layer transition conducted by the contractor and others is reviewed in this report. The report reviews the implications of three-dimensionality arising from several sources, including background and free-stream disturbances, curvature, cross flow and imposed streamwise vorticity. Keywords: Boundary layer transition; Secondary instability; Navier stokes computations.
Author: William S. Saric
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 26
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Author: William S. Saric
Publisher:
ISBN:
Category :
Languages : en
Pages : 34
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Book Description
Detailed experiments were performed for boundary layers undergoing transition to turbulence. The experiments utilized multiple hot wire anemometer techniques in combination with recently developed flow visualization and computational techniques. The use of a phase-correlated and conditionally sampled measurements permitted the study of the origin and evolution of the characteristic of transitional boundary layers. Fundamental transition mechanisms and the receptivity of the boundary layer to external disturbances that led to transition were studied.
Author: Thorwald Herbert
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Book Description
A unified theory of secondary instability in wall-bound shear flows has been developed. This theory rests on Floquet systems of stability equations and permits classification and quantitative analysis of different modes of secondary instability in the three-dimensional stage of laminar-turbulent transition. The catalogue of solutions is consistent with observations and predicts other phenomena that have not been identified in experiments. The theoretical results have been used to reproduce patterns in flow visualizations by computer animation. Analysis of the energy balance has shown a feedback loop between mean flow, two-dimensional, and three-dimensional disturbances that is considered key to the process of self-sustained transition. Various techniques have been developed to investigate details of the nonlinear three-dimensional processes involved in this feedback loop. Keywords: Boundary layer, Stability, Transition.
Author: Roger L. Kimmel
Publisher:
ISBN: 9781423547921
Category :
Languages : en
Pages : 83
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Book Description
The stability and transition of three-dimensional boundary layers was studied. In the first phase of the investigation, arrays of hot film probes were used to measure the three-dimensional structure of instability waves on an axisymmetric cone at Mach 8. In the second phase, linear stability theory was used to design a cone with an elliptic cross section, which was also tested at Mach 8. Results show that disturbances on the axisymmetric cone travel in wave packets with predominantly zero wave angle. On the elliptic cone, only weak evidence for stationary waves was found. The predominant waves were traveling waves at about 12 kHz. Additional waves, probably second mode, occurred near 80 kHz.
Author: O. Sendstad
Publisher:
ISBN:
Category : Simulation methods
Languages : en
Pages : 130
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 28
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Author: J. C. Cooke
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Peter W. Duck
Publisher: Springer Science & Business Media
ISBN: 9400917007
Category : Science
Languages : en
Pages : 458
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Book Description
Most fluid flows of practical importance are fully three-dimensional, so the non-linear instability properties of three-dimensional flows are of particular interest. In some cases the three-dimensionality may have been caused by a finite amplitude disturbance whilst, more usually, the unperturbed state is three-dimensional. Practical applications where transition is thought to be associated with non-linearity in a three- dimensional flow arise, for example, in aerodynamics (swept wings, engine nacelles, etc.), turbines and aortic blood flow. Here inviscid `cross-flow' disturbances as well as Tollmien-Schlichting and Görtler vortices can all occur simultaneously and their mutual non-linear behaviour must be understood if transition is to be predicted. The non-linear interactions are so complex that usually fully numerical or combined asymptotic/numerical methods must be used. Moreover, in view of the complexity of the instability processes, there is also a growing need for detailed and accurate experimental information. Carefully conducted tests allow us to identify those elements of a particular problem which are dominant. This assists in both the formulation of a relevant theoretical problem and the subsequent physical validation of predictions. It should be noted that the demands made upon the skills of the experimentalist are high and that the tests can be extremely sophisticated - often making use of the latest developments in flow diagnostic techniques, automated high speed data gathering, data analysis, fast processing and presentation.
Author: Steven Philip Schneider
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 374
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