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Coherent Structures In The Wake Of A Stalled Rectangular Wing
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Book Synopsis Coherent Structures in the Wake of a Stalled Rectangular Wing by : Steven A. Yon
Download or read book Coherent Structures in the Wake of a Stalled Rectangular Wing written by Steven A. Yon and published by . This book was released on 1995 with total page 458 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Coherent Structures in the Wake of a Stalled Rectangular Wing by : Steven A. Yon
Download or read book Coherent Structures in the Wake of a Stalled Rectangular Wing written by Steven A. Yon and published by . This book was released on 1995 with total page 514 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental and computational techniques are employed in an investigation of the evolution and behavior of distinct large scale structures in the separated flow field around a finite rectangular wing in high angle of attack orientations. The experimental program includes model surface flow visualization, mean loads, and acquisition of both mean and unsteady static pressure data from the model surface and wake. The computational simulation employs a two-dimensional full Navier-Stokes flow solver (INS2D, developed in the NAS Branch of NASA Ames) in combination with the Baldwin-Barth turbulence modeL Time accurate solution of the governing equations allows investigation of the unsteady structures within the separated flow field. The mean and time dependent characteristics of the separated flow field suggest the existence of two distinct angle of attack regimes. The shallow stall regime occurs over a narrow range of incidence angles (2-3 deg.) immediately following the inception of leading edge separation. In this regime, the principal mean flow structures, termed stall cells, are manifested as a distinct spanwise periodicity in the chordwise extent of the separated region on the model surface. The cells are found to have a preferred lateral extent, consistent with previous investigations, and a distinct lateral mobility not previously reported. The effects of cellular separation on the lift and drag characteristics of the wing are minimal. The mean characteristics of the flow field associated with cellular separation are shown to be inconsistent with current models, and a new model is proposed Within the stall cells, large amplitude pressure fluctuations occur with a frequency much lower than anticipated for bluff body shedding. These fluctuations are not associated with discrete spanwise vortices but appear to be related to a convective instability in the upper surface shear layer. The low frequency pressure fluctuations observed in the vicinity of the model surface do not extend into the far wake. Both the stall cell and low frequency phenomena in the shallow stall regime may result from instabilities in the turbulent separated shear layer. In the deep stall regime, stall cells are not observed and the separated region near the model is relatively free of large amplitude pressure disturbances. The numerical simulation suggests that the two regimes are distinguished by the presence (in the shallow stall regime) or absence (in the deep stall regime) of strong convecting vortex structures resulting from periodic accumulation of lower surface vorticity in the vicinity of the trailing edge.
Book Synopsis Direct Numerical Simulations, Resolvent Analysis, and Flow Control of Laminar Post-stall Wakes Around Finite Tapered Swept Wings by : Jean Helder Marques Ribeiro
Download or read book Direct Numerical Simulations, Resolvent Analysis, and Flow Control of Laminar Post-stall Wakes Around Finite Tapered Swept Wings written by Jean Helder Marques Ribeiro and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: External flows over wings is a traditional flow of interest in aerodynamics. Over the last century, research efforts were dedicated to studying the wake patterns that form in the flows around finite wings. Among others, we can pinpoint the wing tip vortex, the separation region that develops under adverse pressure gradient, and the coherent vortical structures. Thanks to these past efforts, we were able to significantly extend our knowledge in aerodynamics, which paved the way for an impressive evolution of aircraft designs in the last century. Over the years, commercial flight became an ordinary asset in our society. More recently, small and micro air vehicles have also reached the market, being operated by individuals who hold no necessary knowledge of the complexity of the Navier-Stokes equations. The advanced knowledge currently held on flight physics has played a fundamental role in the development of aircraft designs, however, there is still room for improvement. In post-stall flow conditions, the aerodynamic performance of the wing decays considerably, making it challenging to sustain flight at high incidence angles. To enable flight in such flow conditions, it is important to develop physics-based flow control strategies capable of improving the overall aerodynamic performance of the wing and its flight stability. The main implications are reduced fuel (and energy) consumption during flight, increased aircraft range, improvements in safety and productivity of air travel, attenuation of the acoustic signature, as well as enabled capability of aircraft to fly in challenging external environments. Towards this goal, many studies have been performed to analyze and control flows over airfoils in spanwise periodic configurations. These may also be called infinite-span wings. These studies were fundamental to revealing important aspects of flow physics. However, in reality, the flows around wings are three-dimensional (3-D). In addition, modern aircraft wings are usually tapered and swept. The 3-D vortex dynamics of flows over wings has a significant influence on aircraft design, by reducing the overall lift, generating induced drag, and increasing flow unsteadiness. Thus, it is important to develop strategies to control the vortex dynamics that encompass the knowledge of the 3-D characteristics of the flow over finite, swept, and tapered wings. Especially for post-stall flow conditions, the wake dynamics around tapered swept wings is largely unexplored. It is still a challenge to understand how the wing geometry relates to the vortex formation for different aspect and taper ratios, as well as angles of attack and sweep. To design control strategies to improve aerodynamic performance for finite, swept, and tapered wings, we must go beyond the sole characterization of flow structures. In fact, the identification of perturbation dynamics is called for to modify the flow field. Three-dimensional flow control is challenging due to the high-dimensional and nonlinear nature of the flow dynamics of the wakes. Thus, it is necessary to find an appropriate actuation setup for the problem that can alter the base flow behavior. This effort can be guided by modal analysis methods. In our work, we have used resolvent analysis, a method based on the singular value decomposition (SVD) of the resolvent, which is a linear operator constructed using the Navier-Stokes equations linearized with respect to the base flow. For unsteady flows, the statistically converged time-averaged flow field is used as a base flow to construct the resolvent operator. The strength of the resolvent operator through this approach is the capability to find optimal forcing modes which amplify outputs in the flow field and give insights into the perturbed flow through the spatial response modes. The challenge within resolvent analysis is the SVD computation for large-scale resolvent operators that are generated for high-dimensional flow fields, such as three-dimensional and turbulent flows. By taking advantage of low-rank approximation of the resolvent operator, recent developments using randomized numerical linear algebra have accelerated the computation of the dominant resolvent modes. With reduced computational costs, these efforts have enabled the use of resolvent analysis in turbulent flows over spanwise periodic airfoils and expanded its applicability to triglobal problems and higher Reynolds number flows. With the randomized algorithm, we can use resolvent analysis to uncover the dynamics of 3-D flows over finite, swept, and tapered wings, supporting flow control efforts to improve their overall aerodynamic performance. The present study has shown how to develop a 3-D resolvent-based flow control over finite wings. We initiate by studying flows over finite wings and the effects of wing sweep and taper on the post-stall wake dynamics through direct numerical simulations (DNS). We consider laminar flows at chord-based Reynolds numbers of 400 and 600 with weak compressible effects at a freestream Mach number 0.1. The flows are studied around wings at angles of attack between 14 and 30 degrees with semi aspect ratios ranging from 1 to 4, sweep angles up to 50 degrees, and taper ratios from 0.27 to 1. Following a comprehensive characterization of the wake dynamics through DNS results, we extend our knowledge of the dynamics of flow perturbations by analyzing the triglobal resolvent modes. Through the identification of the optimal harmonic perturbations that can be amplified in the flow field, we develop 3-D active flow control that is shown to significantly modify the wake structures around the wings. This comprehensive investigation provides novel and unique insights that reveal the flow structures that can be amplified in the wake and modify their dynamics in post-stall flow conditions.
Book Synopsis AIAA Journal by : American Institute of Aeronautics and Astronautics
Download or read book AIAA Journal written by American Institute of Aeronautics and Astronautics and published by . This book was released on 2007 with total page 960 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis 28th AIAA Fluid Dynamics Conference, 4th AIAA Shear Flow Control Conference by :
Download or read book 28th AIAA Fluid Dynamics Conference, 4th AIAA Shear Flow Control Conference written by and published by . This book was released on 1997 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Vorticity and Vortex Dynamics by : Jie-Zhi Wu
Download or read book Vorticity and Vortex Dynamics written by Jie-Zhi Wu and published by Springer Science & Business Media. This book was released on 2007-04-20 with total page 776 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a comprehensive and intensive monograph for scientists, engineers and applied mathematicians, as well as graduate students in fluid dynamics. It starts with a brief review of fundamentals of fluid dynamics, with an innovative emphasis on the intrinsic orthogonal decomposition of fluid dynamic process, by which one naturally identifies the content and scope of vorticity and vortex dynamics. This is followed by a detailed presentation of vorticity dynamics as the basis of later development. In vortex dynamics part the book deals with the formation, motion, interaction, stability, and breakdown of various vortices. Typical vortex structures are analyzed in laminar, transitional, and turbulent flows, including stratified and rotational fluids. Physical understanding of vertical flow phenomena and mechanisms is the first priority throughout the book. To make the book self-contained, some mathematical background is briefly presented in the main text, but major prerequisites are systematically given in appendices. Material usually not seen in books on vortex dynamics is included, such as geophysical vortex dynamics, aerodynamic vortical flow diagnostics and management.
Book Synopsis Dissertation Abstracts International by :
Download or read book Dissertation Abstracts International written by and published by . This book was released on 1996 with total page 800 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Scientific and Technical Aerospace Reports by :
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 652 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book NASA SP. written by and published by . This book was released on 1992 with total page 548 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis American Doctoral Dissertations by :
Download or read book American Doctoral Dissertations written by and published by . This book was released on 1998 with total page 784 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 1992 with total page 974 pages. Available in PDF, EPUB and Kindle. Book excerpt: A selection of annotated references to unclassified reports and journal articles that were introduced into the NASA scientific and technical information system and announced in Scientific and technical aerospace reports (STAR) and International aerospace abstracts (IAA).
Book Synopsis Thermophysics and Aeromechanics by :
Download or read book Thermophysics and Aeromechanics written by and published by . This book was released on 2001 with total page 660 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Aeronautical Engineering: A Cumulative Index to a Continuing Bibliography (supplement 261) by :
Download or read book Aeronautical Engineering: A Cumulative Index to a Continuing Bibliography (supplement 261) written by and published by . This book was released on 1991 with total page 566 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Mechanics of Animal Locomotion by : R. McNeill Alexander
Download or read book Mechanics of Animal Locomotion written by R. McNeill Alexander and published by Springer. This book was released on 1992 with total page 336 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis International Aerospace Abstracts by :
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1998 with total page 920 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis A Cumulative Index to a Continuing Bibliography on Aeronautical Engineering by :
Download or read book A Cumulative Index to a Continuing Bibliography on Aeronautical Engineering written by and published by . This book was released on 1986 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Aeronautical Engineering: A Cumulative Index to a Continuing Bibliography (supplement 274) by :
Download or read book Aeronautical Engineering: A Cumulative Index to a Continuing Bibliography (supplement 274) written by and published by . This book was released on 1992 with total page 648 pages. Available in PDF, EPUB and Kindle. Book excerpt: