Control Of Unsteady Separated Flow Associated With The Dynamic Stall Of Airfoils PDF Download
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| Author | : National Aeronautics and Space Administration (NASA) |
| Publisher | : Createspace Independent Publishing Platform |
| Total Pages | : 42 |
| Release | : 2018-06-30 |
| Genre | : |
| ISBN | : 9781722129781 |
Download Control of Unsteady Separated Flow Associated with the Dynamic Stall of Airfoils Book in PDF, ePub and Kindle
An effort to understand and control the unsteady separated flow associated with the dynamic stall of airfoils was funded for three years through the NASA cooperative agreement program. As part of this effort a substantial data base was compiled detailing the effects various parameters have on the development of the dynamic stall flow field. Parameters studied include Mach number, pitch rate, and pitch history, as well as Reynolds number (through two different model chord lengths) and the condition of the boundary layer at the leading edge of the airfoil (through application of surface roughness). It was found for free stream Mach numbers as low as 0.4 that a region of supersonic flow forms on the leading edge of the suction surface of the airfoil at moderate angles of attack. The shocks which form in this supersonic region induce boundary-layer separation and advance the dynamic stall process. Under such conditions a supercritical airfoil profile is called for to produce a flow field having a weaker leading-edge pressure gradient and no leading-edge shocks. An airfoil having an adaptive-geometry, or dynamically deformable leading edge (DDLE), is under development as a unique active flow-control device. The DDLE, formed of carbon-fiber composite and fiberglass, can be flexed between a NACA 0012 profile and a supercritical profile in a controllable fashion while the airfoil is executing an angle-of-attack pitch-up maneuver. The dynamic stall data were recorded using point diffraction interferometry (PDI), a noninvasive measurement technique. A new high-speed cinematography system was developed for recording interferometric images. The system is capable of phase-locking with the pitching airfoil motion for real-time documentation of the development of the dynamic stall flow field. Computer-aided image analysis algorithms were developed for fast and accurate reduction of the images, improving interpretation of the results. Wilder, M. C. Unspecified Center NCC2-637...
| Author | : National Aeronautics and Space Administration (NASA) |
| Publisher | : Createspace Independent Publishing Platform |
| Total Pages | : 88 |
| Release | : 2018-07-08 |
| Genre | : |
| ISBN | : 9781722323097 |
Download Control of Unsteady Separated Flow Associated with the Dynamic Pitching of Airfoils Book in PDF, ePub and Kindle
Although studies have been done to understand the dependence of parameters for the occurrence of deep stall, studies to control the flow for sustaining lift for a longer time has been little. To sustain the lift for a longer time, an understanding of the development of the flow over the airfoil is essential. Studies at high speed are required to study how the flow behavior is dictated by the effects of compressibility. When the airfoil is pitched up in ramp motion or during the upstroke of an oscillatory cycle, the flow development on the upper surface of the airfoil and the formation of the vortex dictates the increase in lift behavior. Vortex shedding past the training edge decreases the lift. It is not clear what is the mechanism associated with the unsteady separation and vortex formation in present unsteady environment. To develop any flow control device, to suppress the vortex formation or delay separation, it is important that this mechanism be properly understood. The research activities directed toward understanding these questions are presented and the results are summarized. Ahmed, Sajeer Unspecified Center...
| Author | : Marvin Luttges |
| Publisher | : |
| Total Pages | : 30 |
| Release | : 1993 |
| Genre | : Aerofoils |
| ISBN | : |
Download Unsteady Separated Flows Book in PDF, ePub and Kindle
| Author | : M. W. Luttges |
| Publisher | : |
| Total Pages | : 67 |
| Release | : 1982 |
| Genre | : |
| ISBN | : |
Download Unsteady Separated Flows: Vorticity and Turbulence Book in PDF, ePub and Kindle
Recent research progress on this multi-investigator program in unsteady seperated flows is summarized. Specific projects reviewed include: (a) oscillating airfoil dynamic stall; (b) vortex entrapment and stability analysis; and (c) natural flight lift mechanisms. Research is continued under AFOSR contract F49620-83-K-0009. (Author).
| Author | : |
| Publisher | : |
| Total Pages | : 702 |
| Release | : 1995 |
| Genre | : Aeronautics |
| ISBN | : |
Download Scientific and Technical Aerospace Reports Book in PDF, ePub and Kindle
| Author | : National Aeronautics and Space Administration (NASA) |
| Publisher | : Createspace Independent Publishing Platform |
| Total Pages | : 28 |
| Release | : 2018-06-30 |
| Genre | : |
| ISBN | : 9781722115975 |
Download Compressibility Effects on Dynamic Stall of Airfoils Undergoing Rapid Transient Pitching Motion Book in PDF, ePub and Kindle
The research was carried out in the Compressible Dynamic Stall Facility, CDSF, at the Fluid Mechanics Laboratory (FML) of NASA Ames Research Center. The facility can produce realistic nondimensional pitch rates experienced by fighter aircraft, which on model scale could be as high as 3600/sec. Nonintrusive optical techniques were used for the measurements. The highlight of the effort was the development of a new real time interferometry method known as Point Diffraction Interferometry - PDI, for use in unsteady separated flows. This can yield instantaneous flow density information (and hence pressure distributions in isentropic flows) over the airfoil. A key finding is that the dynamic stall vortex forms just as the airfoil leading edge separation bubble opens-up. A major result is the observation and quantification of multiple shocks over the airfoil near the leading edge. A quantitative analysis of the PDI images shows that pitching airfoils produce larger suction peaks than steady airfoils at the same Mach number prior to stall. The peak suction level reached just before stall develops is the same at all unsteady rates and decreases with increase in Mach number. The suction is lost once the dynamic stall vortex or vortical structure begins to convect. Based on the knowledge gained from this preliminary analysis of the data, efforts to control dynamic stall were initiated. The focus of this work was to arrive at a dynamically changing leading edge shape that produces only 'acceptable' airfoil pressure distributions over a large angle of attack range. Chandrasekhara, M. S. and Platzer, M. F. Ames Research Center AF-AFOSR-0012-90; AF-AFOSR-0007-91; AF-AFOSR-0004-92; AF PROJ. 2307...
| Author | : Charles Paul Gendrich |
| Publisher | : |
| Total Pages | : 344 |
| Release | : 1999 |
| Genre | : Aerofoils |
| ISBN | : |
Download Dynamic Stall of Rapidly Pitching Airfoils Book in PDF, ePub and Kindle
| Author | : |
| Publisher | : |
| Total Pages | : 29 |
| Release | : 1993 |
| Genre | : |
| ISBN | : |
Download Control and Management of Unsteady and Turbulent Flows Book in PDF, ePub and Kindle
Active input of tuned and detuned two-dimensional and oblique modes in a layer was found to lead to the growth of near-subharmonic modes as well as numerous sum and difference modes, thereby emulating 'natural' transition. Acoustic receptivity of laminar boundary layers with nonlocalized low-amplitude periodic waviness was experimentally investigated and compared favorably to theoretical predictions. Closed loop excitation of axisymmetric and azimuthal modes in a free round jet were used to reveal the character of high Reynolds number transition (i.e., supercritical Hopf bifurcation) and to study mode selection and switching. Suction and blowing were shown to be capable of controlling the asymmetric flow about the forebodies of aircraft and missiles and the experiments indicate that the suction bleed coefficient must increase like the 3.9 power of the velocity to balance the effects of geometric instability at the tip. The effects of yaw on such asymmetries were also documented. A strategy to suppress the dynamic-stall vortex over a range of operating parameters, using controlled leading-edge suction to prevent accumulation of reverse-flowing fluid, was successfully developed from a study of the mechanisms responsible for the evolution of the vortex. The National Diagnostic Facility was completed and several collaborative experiments are scheduled during 1994. Turbulence, Separated flows, Unsteady flows, Transition, Forebody flows, Pitching airfoils, Jet flows, Control.
| Author | : |
| Publisher | : |
| Total Pages | : 470 |
| Release | : 1995 |
| Genre | : |
| ISBN | : |
Download Aeronautical Engineering: A Cumulative Index to a Continuing Bibliography (supplement 325) Book in PDF, ePub and Kindle
| Author | : Rudibert King |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 417 |
| Release | : 2010-04-06 |
| Genre | : Technology & Engineering |
| ISBN | : 364211735X |
Download Active Flow Control II Book in PDF, ePub and Kindle
The interest in the field of active flow control (AFC) is steadily increasing. In - cent years the number of conferences and special sessions devoted to AFC org- ized by various institutions around the world continuously rises. New advanced courses for AFC are offered by the American Institute of Aeronautics and Ast- nautics (AIAA), the European Research Community on Flow, Turbulence and Combustion (ERCOFTAC), the International Centre for Mechanical Sciences (CISM), the von Karman Institute for Fluid Dynamics (VKI), to name just a few. New books on AFC are published by prominent colleagues of our field and even a new periodical, the ‘International Journal of Flow Control’, appeared. Despite these many activities in AFC it was felt that a follow-up of the highly successful ‘ACTIVE FLOW CONTROL’ Conference held in Berlin in 2006 was appropriate. As in 2006, ‘ACTIVE FLOW CONTROL II’ consisted only of invited lectures. To sti- late multidisciplinary discussions between experimental, theoretical and numerical fluid dynamics, aerodynamics, turbomachinary, mathematics, control engineering, metrology and computer science parallel sessions were excluded. Unfortunately, not all of the presented papers made it into this volume. As the preparation and printing of a book takes time and as this volume should be available at the conf- ence, the Local Organizing Committee had to set up a very ambitious time sch- ule which could not be met by all contributors.
