On the Receptivity and Non-Parallel Stability of Travelling Disturbances in Rotating Disk Flow

On the Receptivity and Non-Parallel Stability of Travelling Disturbances in Rotating Disk Flow
Author: National Aeronautics and Space Adm Nasa
Publisher:
Total Pages: 34
Release: 2018-10-17
Genre:
ISBN: 9781728851532

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The generation and evolution of small amplitude wavelength traveling disturbances in rotating disk flow is discussed. The steady rotational speed of the disk is perturbed so as to introduce high frequency oscillations in the flow field. Secondly, surface imperfections are introduced on the disk such as roughness elements. The interaction of these two disturbances will generate the instability waves whose evolution is governed by parabolic partial differential equations that are solved numerically. For the class of disturbances considered (wavelength on the order of Reynolds number), it is found that eigensolutions exist which decay or grow algebraically in the radial direction. However, these solutions grow only for frequencies larger than 4.58 times the steady rotational speed of the disk. The computed receptivity coefficient shows that there is an optimum size of roughness for which these modes are excited the most. The width of these roughness elements in the radial direction is about .1 r(sub 0) where r(sub 0) is the radial location of the roughness. It is also found that the receptivity coefficient is larger for a negative spanwise wavenumber than for a positive one. Typical wave angles found for these disturbances are about -26 degrees. Balakumar, P. and Hall, P. and Malik, M. R. Unspecified Center NAS1-18605...

Physics of Transitional Shear Flows

Physics of Transitional Shear Flows
Author: Andrey V. Boiko
Publisher: Springer Science & Business Media
Total Pages: 286
Release: 2011-09-15
Genre: Science
ISBN: 9400724985

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Starting from fundamentals of classical stability theory, an overview is given of the transition phenomena in subsonic, wall-bounded shear flows. At first, the consideration focuses on elementary small-amplitude velocity perturbations of laminar shear layers, i.e. instability waves, in the simplest canonical configurations of a plane channel flow and a flat-plate boundary layer. Then the linear stability problem is expanded to include the effects of pressure gradients, flow curvature, boundary-layer separation, wall compliance, etc. related to applications. Beyond the amplification of instability waves is the non-modal growth of local stationary and non-stationary shear flow perturbations which are discussed as well. The volume continues with the key aspect of the transition process, that is, receptivity of convectively unstable shear layers to external perturbations, summarizing main paths of the excitation of laminar flow disturbances. The remainder of the book addresses the instability phenomena found at late stages of transition. These include secondary instabilities and nonlinear features of boundary-layer perturbations that lead to the final breakdown to turbulence. Thus, the reader is provided with a step-by-step approach that covers the milestones and recent advances in the laminar-turbulent transition. Special aspects of instability and transition are discussed through the book and are intended for research scientists, while the main target of the book is the student in the fundamentals of fluid mechanics. Computational guides, recommended exercises, and PowerPoint multimedia notes based on results of real scientific experiments supplement the monograph. These are especially helpful for the neophyte to obtain a solid foundation in hydrodynamic stability. To access the supplementary material go to extras.springer.com and type in the ISBN for this volume.

Proceedings

Proceedings
Author: Royal Society (Great Britain)
Publisher:
Total Pages: 850
Release: 1995
Genre: Chemistry
ISBN:

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Publishes research papers in the mathematical and physical sciences. Continues: Proceedings of the Royal Society of London. Series A, Mathematical and physical sciences. Continued by: Proceedings. Mathematical, physical, and engineering sciences.

IUTAM Symposium on Nonlinear Instability and Transition in Three-Dimensional Boundary Layers

IUTAM Symposium on Nonlinear Instability and Transition in Three-Dimensional Boundary Layers
Author: Peter W. Duck
Publisher: Springer Science & Business Media
Total Pages: 458
Release: 2012-12-06
Genre: Science
ISBN: 9400917007

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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.

Applied Mechanics Reviews

Applied Mechanics Reviews
Author:
Publisher:
Total Pages: 348
Release: 1992
Genre: Mechanics, Applied
ISBN:

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