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Author : M. S. Chandrasekhara
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (11 download)
Download or read book Amplitude Effects on Dynamic Stall of an Oscillating Airfoil written by M. S. Chandrasekhara and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Bruce E. Brydges
Publisher :
ISBN 13 :
Total Pages : 116 pages
Book Rating : 4.:/5 (227 download)
Download or read book Flow Visualization of Dynamic Stall on an Oscillating Airfoil written by Bruce E. Brydges and published by . This book was released on 1989 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stroboscopic schlieren photography was used to investigate the effects of compressibility, reduced frequency, and amplitude on the dynamic stall of a NACA 0012 airfoil subjected to sinusoidal oscillation. The Mach number was varied from M at infinity = 0.25 to M at infinity = 0.45 (corresponding to a Reynolds number variation of Re = 450,000 to Re = 810,000); the reduced frequency was varied from k = 0.025 to k = 0.10. Oscillation amplitudes of alpha sub m = 5 deg and alpha sub m = 10 deg were compared. Schlieren photographs are presented, which document the dynamic stall vortex formation, convection, and shedding sequence for various experimental conditions. Additionally, a preliminary examination of the flow reattachment process was conducted. Data derived from the photographs indicates that increasing the compressibility causes dynamic stall to occur at lower angles of attack; while, increasing the reduced frequency and/or the oscillation amplitude effectively delays dynamic stall effects to a higher angle of attack. Flow reattachment is sensitive to both Mach number and reduced frequency for low values of these parameters; when either the Mach number or reduced frequency is sufficiently high, the reattachment process stabilizes. Keywords: Dynamic stall; Dynamic lift; Unsteady lift; Helicopter retreating blade stall; Oscillating airfoil; Flow visualization; Schlieren method. Theses. (jhd).
Author :
Publisher :
ISBN 13 :
Total Pages : 43 pages
Book Rating : 4.:/5 (227 download)
Download or read book Compressibility Effects on Dynamic Stall of Oscillating Airfoils written by and published by . This book was released on 1990 with total page 43 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study's aim was to obtain a basic understanding of the effect of compressibility on the phenomenon of dynamic stall under typical flight conditions encountered by a helicopter in forward flight, so that eventually a means for its control can be devised and thus, its flight envelope can be expanded. The first phase of the study was devoted to building a drive system to produce the necessary unsteady airfoil motion. A novel design was arrived at and built. It uses a four-bar chain mechanism of which the airfoil is one of the links. The drive can produce a sinusoidal variation of the angle of attack as : alpha = alpha sub 0 + alpha sub m(sin omega+), with the mean angle of attack alpha0, continuously variable from 0 to 15 deg, the amplitude of oscillation alpha sub m, from 2 to 10 degs and the frequency from 0-100 Hz, in an oncoming flow Mach number M, from 0-0.5. The drive was installed in the indraft wind tunnel at NASA Ames Research Center. Stroboscopic schlieren studies and interferograms as well as holographic interferometry studies were conducted for a wide range of flow conditions, amplitudes and frequencies. Results show that compressibility effects appear at M = 0.3, that a dynamic stall vortex forms for all Mach numbers, and that for M> or = 0.3, the dynamic stall angle decreases as M increases. On the other hand, increasing the degree of unsteadiness, delays deep stall monotonically at all Mach numbers. Amplitude has a dominant effect, and dynamic stall occurs at lower angles of attack at lower amplitudes, yet this angle of attack is always higher than the static stall angle. (edc).
Author :
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (227 download)
Download or read book Flow Visualization of Dynamic Stall on an Oscillating Airfoil written by and published by . This book was released on 1989 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stroboscopic schlieren photography was used to investigate the effects of compressibility, reduced frequency, and amplitude on the dynamic stall of a NACA 0012 airfoil subjected to sinusoidal oscillation. The Mach number was varied from M at infinity = 0.25 to M at infinity = 0.45 (corresponding to a Reynolds number variation of Re = 450,000 to Re = 810,000); the reduced frequency was varied from k = 0.025 to k = 0.10. Oscillation amplitudes of alpha sub m = 5 deg and alpha sub m = 10 deg were compared. Schlieren photographs are presented, which document the dynamic stall vortex formation, convection, and shedding sequence for various experimental conditions. Additionally, a preliminary examination of the flow reattachment process was conducted. Data derived from the photographs indicates that increasing the compressibility causes dynamic stall to occur at lower angles of attack; while, increasing the reduced frequency and/or the oscillation amplitude effectively delays dynamic stall effects to a higher angle of attack. Flow reattachment is sensitive to both Mach number and reduced frequency for low values of these parameters; when either the Mach number or reduced frequency is sufficiently high, the reattachment process stabilizes. Keywords: Dynamic stall; Dynamic lift; Unsteady lift; Helicopter retreating blade stall; Oscillating airfoil; Flow visualization; Schlieren method. Theses. (jhd).
Author : Franklin O. Carta
Publisher :
ISBN 13 :
Total Pages : 108 pages
Book Rating : 4.:/5 (317 download)
Download or read book Analysis of Oscillatory Pressure Data Including Dynamic Stall Effects written by Franklin O. Carta and published by . This book was released on 1974 with total page 108 pages. Available in PDF, EPUB and Kindle. Book excerpt: The dynamic stall phenomenon was examined in detail by analyzing an existing set of unsteady pressure data obtained on an airfoil oscillating in pitch. Most of the data were for sinusoidal oscillations which penetrated the stall region in varying degrees, and here the effort was concentrated on the chordwise propagation of pressure waves associated with the dynamic stall. It was found that this phenomenon could be quantified in terms of a pressure wave velocity which is consistently much less than free-stream velocity, and which varies directly with frequency. It was also found that even when the stall region has been deeply penetrated and a substantial dynamic stall occurs during the downstroke, stall recovery near minimum incidence will occur, followed by a potential flow behavior up to stall inception.
Author :
Publisher :
ISBN 13 :
Total Pages : 8 pages
Book Rating : 4.:/5 (318 download)
Download or read book A Study of Compressibility Effects on Dynamic Stall of Rapidly Pitching Airfoils written by and published by . This book was released on 1991 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results of recent experimental studies into the effect of compressibility on dynamic stall of oscillating airfoils are reviewed. Stroboscopic schlieren images of the strongly unsteady flow field are presented, showing the development of the dynamic stall vortex. and its progression down the airfoil. The effect of varying free-stream Mach number, and frequency of oscillation of the airfoil are demonstrated, and examples of local supersonic flow are presented including the presence of a shock near the leading edge of the airfoil.
Author : Lawrence W. Carr
Publisher :
ISBN 13 :
Total Pages : 116 pages
Book Rating : 4.:/5 (31 download)
Download or read book Analysis of the Development of Dynamic Stall Based on Oscillating Airfoil Experiments written by Lawrence W. Carr and published by . This book was released on 1977 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : W. J. McCroskey
Publisher :
ISBN 13 :
Total Pages : 38 pages
Book Rating : 4.:/5 (317 download)
Download or read book The Phenomenon of Dynamic Stall written by W. J. McCroskey and published by . This book was released on 1981 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stall and its consequences are fundamentally important to the design and operation of flight vehicles. A certain degree of unsteadiness always accompanies the flow over an airfoil or other streamlined body at high angle of attack, but the stall of a lifting surface undergoing unsteady motion is even more complex than static stall. Dynamic stall remains a major unsolved problem with a variety of current applications in aeronautics, hydrodynamics, and wind engineering. This report summarizes the main physical features of the phenomenon and the attempts that have been made to predict it. The information presented is drawn mainly from recent review articles and investigations by the author and his colleagues. Since a large fraction of the existing knowledge has come from experimental research, the details of dynamic stall are discussed principally in physical terms.
Author : Torsten H. Fransson
Publisher : Springer Science & Business Media
ISBN 13 : 9401150400
Total Pages : 835 pages
Book Rating : 4.4/5 (11 download)
Download or read book Unsteady Aerodynamics and Aeroelasticity of Turbomachines written by Torsten H. Fransson and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 835 pages. Available in PDF, EPUB and Kindle. Book excerpt: Twenty-one years have passed since the first symposium in this series was held in Paris (1976). Since then there have been meetings in Lausanne (1980), Cambridge (1984), Aachen (1987), Beijing (1989), Notre Dame (1991) and Fukuoka (1994). During this period a tremendous development in the field of unsteady aerodynamics and aeroelasticity in turbomachines has taken place. As steady-state flow conditions become better known, and as blades in the turbomachine are constantly pushed towards lower weight, and higher load and efficiency, the importance of unsteady phenomena appear more clearly. th The 8 Symposium was, as the previous ones, of high quality. Furthermore, it presented the audience with the latest developments in experimental, numerical and theoretical research. More papers than ever before were submitted to the conference. As the organising committee wanted to preserve the uniqueness of the symposium by having single sessions, and thus mingle speakers and audience with different backgrounds in this interdisciplinary field, only a limited number of papers could be accepted. 54 papers were accepted and presented at the meeting, all of which are included in the present proceedings.
Author :
Publisher :
ISBN 13 :
Total Pages : 710 pages
Book Rating : 4.:/5 (319 download)
Download or read book NASA Technical Note written by and published by . This book was released on 1976 with total page 710 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Rush, Olive written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The folder may include clippings, announcements, small exhibition catalogs, and other ephemeral items.
Author : Richard B. Noll
Publisher :
ISBN 13 :
Total Pages : 300 pages
Book Rating : 4.E/5 ( download)
Download or read book Dynamic Stall of Small Wind Systems written by Richard B. Noll and published by . This book was released on 1983 with total page 300 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Myung J. Rhee
Publisher :
ISBN 13 :
Total Pages : 112 pages
Book Rating : 4.:/5 (317 download)
Download or read book A Study of Dynamic Stall Vortex Development Using Two-Dimensional Data from the AFDD Oscillating Wing Experiment written by Myung J. Rhee and published by . This book was released on 2002 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this study is to examine the previously unpublished instantaneous pressure data of the Aeroflightdynamics Directorate Two-Dimensional (2D) and Three-Dimensional (3D) Oscillating Wing Experiment to better understand the process of dynamic stall vortex development on the NACA 0015 airfoil. This report presents representative 2D instantaneous pressure data for the upper and lower surfaces of the airfoil at various chordwise locations obtained at specific angles of attack during upstroke and downstroke cycles. Furthermore, the report contains a complete set of plots of instantaneous pressure distributions for the upper surface for all the 2D data sets obtained in the experiment. First, the lift, drag and pitching moment data of various testing conditions are reviewed and analyzed to classify the data both with and without a boundary layer trip into "no stall," "moderate stall," and "deep stall" data. Next, instantaneous pressure distributions on the upper surface of the airfoil are examined for the study of vortex development. The lift and pitching moment data are analyzed to document the dynamic overshoot which delays the development of the stall on the airfoil. Next, the range of angles of attack are selected where the lift and pitching moment data shows significant changes from unsteady flow behavior daring oscillation cycles. Furthermore, based on the unsteady flow characteristics found in each classification of dynamic stall, analysis is continued to identify the conditions where the reduced frequency clearly affects the unsteady flow behavior of the airfoil during the oscillation. This can result in a change of the dynamic stall classification of the airfoil response under various unsteady flow conditions. These conditions are discussed in detail in the comparative studies.
Author : Kenneth W. McAlister
Publisher :
ISBN 13 :
Total Pages : 172 pages
Book Rating : 4.:/5 (317 download)
Download or read book Dynamic Stall Experiments on the NACA 0012 Airfoil written by Kenneth W. McAlister and published by . This book was released on 1978 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : L. U. Dadone
Publisher :
ISBN 13 :
Total Pages : 172 pages
Book Rating : 4.:/5 (317 download)
Download or read book Two-dimensional Wind Tunnel Test of an Oscillating Rotor Airfoil, Volume 1 written by L. U. Dadone and published by . This book was released on 1977 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Robert L. Halfman
Publisher :
ISBN 13 :
Total Pages : 92 pages
Book Rating : 4.3/5 (91 download)
Download or read book Experimental Aerodynamic Derivatives of a Sinusoidally Oscillating Airfoil in Two-dimensional Flow written by Robert L. Halfman and published by . This book was released on 1951 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental measurements of the aerodynamic reactions on a symmetrical airfoil oscillating harmonically in a two-dimensional flow are presented and analyzed in this paper. Harmonic motions include pure pitch and pure translation, for several amplitudes and superimposed on an initial angle of attack, as well as combined pitch and translation. Considerable consistent data for pure pitch were obtained from a search of available reference material, and several definite Reynolds number effects are evident.
Author : L U. Dadone
Publisher :
ISBN 13 :
Total Pages : 170 pages
Book Rating : 4.:/5 (31 download)
Download or read book Two-dimensional Wind Tunnel Test of an Oscillating Rotor Airfoil, Volume I written by L U. Dadone and published by . This book was released on 1977 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt:
