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.
Download or read book Asymmetric Vortex Forces and Wakes on Slender Bodies written by B.L. Hunt and published by . This book was released on 1982 with total page 37 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Geometric Perturbations and Asymmetric Vortex Shedding about Slender Pointed Bodies written by Scott M. Murman and published by BiblioGov. This book was released on 2013-08 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: The flow about slender, pointed bodies can be characterized by different states with angle of attack. At moderate-to-high angles of attack (alpha approx. = 40 deg.), a steady, asymmetric vortex pattern develops along the body, leading to a net lateral force. At higher angles of attack (alpha approx. = 60 deg.), the aft-end of the body develops an unsteady von Karman shedding. As the angle of attack approaches 90 deg., the entire body length exhibits a time-dependent vortex shedding pattern. The current work uses three-dimensional, thin-layer Navier-Stokes simulations to investigate the physical mechanisms of asymmetric vortex shedding at alpha = 40 deg. and alpha = 60 deg. The development of an asymmetric vortex pattern via a convective instability mechanism is investigated using tip bumps, surface roughness, and tip curvature. It's found that surface roughness simulations can incite an asymmetric vortex state at alpha = 60 deg. which is consistent with the application of a tip bump, and the experimentally observed flowfield. The unsteady von Karman vortex shedding on the aft. portion of the body is also well resolved. The use of surface roughness did not incite a flow asymmetry at alpha = 40 deg., and it was necessary to simulate tip curvature at this angle of attack in order to generate an asymmetric vortex state.
Download or read book On the Asymmetric Shedding of Vortices from Slender Cylindrical Bodies at Large Angles of Yaw written by K. D. Thomson and published by . This book was released on 1965 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 464 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book NASA Technical Memorandum written by and published by . This book was released on 1984 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Naval Research Reviews written by and published by . This book was released on 1995 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Asymmetric Vortices and Alleviation on the Slender Bodies with and Without Wings written by Nan-Qian Chen and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Numerical Simulation of Vortex Unsteadiness on Slender Bodies of Revolution at Large Incidence written by Lewis B. Schiff and published by . This book was released on 1989 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Aeronautical Engineering written by and published by . This book was released on 1991 with total page 538 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Computational Study of Vortex Shedding about Slender Bodies written by Scott M. Murman and published by . This book was released on 1999 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1974 with total page 628 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Stability of Symmetric Vortices Over Slender Conical Bodies at High Angles of Attack written by Jinsheng Cai and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book AGARD Index of Publications written by North Atlantic Treaty Organization. Advisory Group for Aerospace Research and Development and published by . This book was released on 1989 with total page 526 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Vortex Separation on Slender Bodies of Elliptic Cross Section written by Leon H. Schindel and published by . This book was released on 1967 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: The lift on slender bodies at high angle of attack is strongly influenced by the separation of a pair of vortices from the lee side. An analytical model of the vortex separation was developed which predicts the vortex development and the consequent nonlinear lift distribution on bodies of elliptic cross section and very general longitudinal contour. The report describes comparisons of the theory with subsonic wind tunnel tests on families of body shapes. Nose contours included pointed ogives, blunt ogives, and hemispheres. Body fineness ratios from 4 to 15 were tested and cross sections from circular to 3.5:1 ellipses. In addition the elliptic bodies were tested with major axes in and normal to the pitch plane. All cases were run with and without boundary layer trips at angle of attack up to 28 degrees. Vortex trajectories, obtained from the behavior of tuft grids, were in general agreement with theory. Normal force and pitching moment predictions also agreed with experiment until the theory failed at high angles of attack. Limitations on the validity of the analysis were thus experimentally established. The predicted locations of separation were generally quite far around to leeward from the positions measured by a China clay technique. (Author).
Download or read book Asymmetric Vortices on a Slender Body of Revolution written by G. G. Zilliac and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book 32nd Aerospace Sciences Meeting Exhibit 94 0145 94 0179 written by and published by . This book was released on 1994 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt:
