Download or read book Analytical Study of the Origin and Behavior of Asymmetric Vortices written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-08-16 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: An hypothesis advanced originally to explain computational observations is supported by theoretical considerations: The asymmetric mean flow observed on bodies of revolution at moderate to high angles of attack is the result of a convective instability of an originally symmetric flow to a time-invariant space-fixed disturbance. Additionally, the time-dependent fluctuations characteristic of the flow at higher angles of attack (up to 90 deg) are the result of an absolute instability of an originally steady flow to a small temporal disturbance of finite duration. Within a common domain, the instability mechanisms may coexist. The experimentally confirmed existence of bistable states, wherein the side-force variation with nose roll angle approaches a square-wave distribution, is attributed to the dominant influence of a pair of trailing vortices from the ogival forebody. Their existence is made possible by the appearance of foci of separation in the skin-friction line pattern beyond a critical angle of attack. The extreme sensitivity of the asymmetric flow orientation to nose geometry, demonstrated experimentally, is attributed to the presence of an indeterminate phase in the family of possible solutions for the three-dimensional wave system. Tobak, Murray and Degani, David and Zilliac, Gregory G. Ames Research Center NASA-TM-102796, A-90089, NAS 1.15:102796 RTOP 505-61-71...

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Download or read book Nonlinear Partial Differential Equations written by Mi-Ho Giga and published by Springer Science & Business Media. This book was released on 2010-05-30 with total page 307 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work will serve as an excellent first course in modern analysis. The main focus is on showing how self-similar solutions are useful in studying the behavior of solutions of nonlinear partial differential equations, especially those of parabolic type. This textbook will be an excellent resource for self-study or classroom use.

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Download or read book Analysis and Control of Asymmetric Vortex Flows and Supersonic Vortex Breakdown written by Osama A. Kandil and published by . This book was released on 1991 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

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Download or read book A Comprehensive Study of Vortex Asymmetry on Slender Bodies at High Angles of Incidence written by Roopesh Sampath Kumar and published by . This book was released on 2021 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vortex asymmetry develops on slender bodies at high angles of incidence, leading to large side-forcesand yaw moments even in symmetrical flight conditions. This unexpected side force can be large for the control surfaces to produce a restoring moment, thereby affecting the vehicle's trajectory, maneuverability, and performance. Previous studies suggest that the presence of random micro-surface imperfections near the forebody tip, incurred due to the conventional machining process and its coupling with incoming freestream turbulence are the cause for vortex asymmetry. Vortex asymmetry and its control studies have been the subject of numerous experimental and numerical investigations beginning with simplified canonical configurations such as cones and cone-cylinders followed by slender bodies with fins resembling a typical projectile configuration. While previous studies on vortex asymmetry have provided a substantial knowledge base, several fundamental questions about the flow topology and characteristics of the vortices remain unanswered. The key knowledge gaps in the form of a few questions are: what is the effect of aftbody on the initiation and development of vortex asymmetry? What is the role of imperfections on the aftbody, and how do they enhance or suppress vortex asymmetry? What is the role of forebody to aftbody transition junction on vortex initiation and development? How does the forebody vortex-fin interaction alter the control surface effectiveness? To answer some of these questions as research objectives and improve the understanding of flow physics associated with slender bodies at high angles of incidence, a comprehensive experimental and numerical investigation was carried out and the results are presented here. The test configuration involves a long slender body with two interchangeable forebodies (a cone and a tangent ogive). To study the vortex-fin interactions, Army Navy Basic Finner (conecylinder with fins) and ogive-cylinder with fins were designed and tested. Experiments include force measurements using a six-component strain gauge balance, oil flow visualization, velocity and vorticity field measurements using particle image velocimetry. Results show that a pair of counterrotating, nearly-symmetric vortices develop over a polished cone but those become asymmetric over the cylinder. Several secondary shear-layer vortices form at the cone-cylinder junction and over the aftbody due to sharp turn angle (a change on pressure boundary), surface imperfections, and various surface joints. These secondary shear-layer vortices then merge with the primary forebody vortex pair, leading to the flow asymmetry. The flow characteristics and side-forces vary significantly when the conical forebody is rotated about its axis of symmetry and set to different azimuthal positions. The results strongly suggest that a change in the geometry at the cone-cylinder junction and surface imperfections present on the cylindrical aftbody plays a critical role in determining the overall flowasymmetry and the side force magnitude. The effect of forebody change has a significant impact on the flow field development. The peak vorticity, circulation, and trajectory of primary vortices for ogive-cylinder configuration indicate a notable change in both magnitude and location when compared to cone-cylinder configuration. The results show that the formation of secondary shearlayer vortices can be minimized by eliminating the sudden change in geometry and smoothing the surface imperfections. The absence of secondary shear-layer vortices resulted in relatively low levels of side forces for the ogive-cylinder configuration as compared to the cone-cylinder. In the case of vortex-fin interaction investigations, results show that the basic aerodynamic characteristics remain invariant with roll orientation at low angles of incidence. At high angles of incidence, fin orientation plays a significant role in dictating the body's aerodynamic forces. At low angles of incidence, the forebody vortices are symmetric and remain close to the body, and interact with the control surfaces. The forebody vortex interaction seems to be influenced by the body roll orientation. The pressure distributions over the fin surfaces, and in turn, the fins' control effectiveness is significantly affected by the interaction of forebody vortices. At high angles of incidence, the vortices become highly asymmetric, where one vortex is closer to the fins and the other vortex lifted away from the fins. Under such an instance, the resulting pressure distribution is uneven and lead to the generation of side forces and adverse yaw moments. To summarize, the present study has significantly improved the fundamental understanding of vortex flows on slender bodies at high angles of incidence. In particular, it has answered the role of secondary vortices on the development of overall vortex asymmetry and its interaction with control surfaces. The outcome of this study will help guide the design of next-generation projectiles expected to perform maneuvers at high angles of incidence. The high-fidelity experimental database generated over a range of test conditions will be very useful to validate physics based simulation tools being developed at Army Research Laboratory. The present study was focused at low-speeds and incompressible flows and therefore it is suggested that future studies must investigate the effect of compressibility on vortex asymmetry. Also, time-resolved measurements are recommended to understand the role of vortex dynamics on the slender body.