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  • 1
    Electronic Resource
    Electronic Resource
    A phase-locked high-speed real-time interferometry system for large amplitude unsteady flows (1995)
    Springer
    Experiments in fluids 20 (1995), S. 61-67 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A high-speed phase-locked interferometry system has been designed and developed for real-time measurements of dynamic stall flow over a pitching airfoil. Point diffraction interferograms of incipient flow separation over a sinusoidally oscillating airfoil have been obtained at framing rates of up to 20 kHz and for free stream Mach numbers of 0.3 and 0.45. The images were recorded on 35 mm ASA 125 and ASA 400 films using a drum camera. Special electronic timing and synchronizing circuits were developed to trigger the laser light source from the camera and to initiate acquisition of the interferogram sequence from any desired phase angle of oscillation. The airfoil instantaneous angle of attack data provided by an optical encoder was recorded via a FIFO data buffer into a microcomputer. The interferograms have been analyzed using software developed in-house to get quantitative flow density and pressure distributions. Mr. N.J. Brock and Mr. B.J. Weber of Aerometrics. Inc. in preparing the laser specifications are gratefully acknowledged.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189295
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    A phase-locked high-speed real-time interferometry system for large amplitude unsteady flows (1995)
    Springer
    Experiments in fluids 20 (1995), S. 61-67 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A high-speed phase-locked interferometry system has been designed and developed for real-time measurements of dynamic stall flow over a pitching airfoil. Point diffraction interferograms of incipient flow separation over a sinusoidally oscillating airfoil have been obtained at framing rates of up to 20 kHz and for free stream Mach numbers of 0.3 and 0.45. The images were recorded on 35 mm ASA 125 and ASA 400 films using a drum camera. Special electronic timing and synchronizing circuits were developed to trigger the laser light source from the camera and to initiate acquisition of the interferogram sequence from any desired phase angle of oscillation. The airfoil instantaneous angle of attack data provided by an optical encoder was recorded via a FIFO data buffer into a microcomputer. The interferograms have been analyzed using software developed in-house to get quantitative flow density and pressure distributions. Mr. N.J. Brock and Mr. B.J. Weber of Aerometrics. Inc. in preparing the laser specifications are gratefully acknowledged.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01061583
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    Paper (German National Licenses)
    Fulltext
  • 3
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    A phase-locked high-speed real-time interferometry system for large amplitude unsteady flows (1995)
    Springer
    Details
    Publication Date: 1995-12-01
    Print ISSN: 0723-4864
    Electronic ISSN: 1432-1114
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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    PAPER CURRENT
  • 4
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    A phase-locked high-speed real-time interferometry system for large amplitude unsteady flows (1995)
    Springer
    Details
    Publication Date: 1995-12-01
    Print ISSN: 0723-4864
    Electronic ISSN: 1432-1114
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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    PAPER CURRENT
  • 5
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    Interferometric investigations of compressible dynamic stall over a transiently pitching airfoil (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The compressible dynamic stall flowfield over a NACA 0012 airfoil transiently pitching from 0 to 60 deg at a constant rate under compressible flow conditions has been studied using real-time interferometry. A quantitative description of the overall flowfield, including the finer details of dynamic stall vortex formation, growth, and the concomitant changes in the airfoil pressure distribution, has been provided by analyzing the interferograms. For Mach numbers above 0.4, small multiple shocks appear near the leading edge and are present through the initial stages of dynamic stall. Dynamic stall was found to occur coincidentally with the bursting of the separation bubble over the airfoil. Compressibility was found to confine the dynamic stall vortical structure closer to the airfoil surface. The measurements show that the peak suction pressure coefficient drops with increasing freestream Mach number, and also it lags the steady flow values at any given angle of attack. As the dynamic stall vortex is shed, an anti-clockwise vortex is induced near the trailing edge, which actively interacts with the post-stall flow.
    Keywords: AERODYNAMICS
    Type: AIAA Journal (ISSN 0001-1452); 32; 3; p. 586-593
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Control of unsteady separated flow associated with the dynamic stall of airfoils (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: 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.
    Keywords: AERODYNAMICS
    Type: NASA-CR-198972 , NAS 1.26:198972 , MCAT-95-09
    Format: application/pdf
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  • 7
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    Control of unsteady separated flow associated with the dynamic stall of airfoils (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A unique active flow-control device is proposed for the control of unsteady separated flow associated with the dynamic stall of airfoils. The device is an adaptive-geometry leading-edge which will allow controlled, dynamic modification of the leading-edge profile of an airfoil while the airfoil is executing an angle-of-attack pitch-up maneuver. A carbon-fiber composite skin has been bench tested, and a wind tunnel model is under construction. A baseline parameter study of compressible dynamic stall was performed for flow over an NACA 0012 airfoil. Parameters included Mach number, pitch rate, pitch history, and boundary layer tripping. Dynamic stall data were recorded via point-diffraction interferometry and the interferograms were analyzed with in-house developed image processing software. A new high-speed phase-locked photographic image recording system was developed for real-time documentation of dynamic stall.
    Keywords: AERODYNAMICS
    Type: NASA-CR-197024 , NAS 1.26:197024 , MCAT-94-20
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Aerothermodynamic Testing of Aerocapture and Planetary Probe Geometries in Hypersonic Ballistic-Range Environments (2005)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: A viewgraph presentation on aerothermodynamic testing of aerocapture and planetary probe design methods in hypersonic ballistic range environments is shown. The topics include: 1) Ballistic Range Testing; 2) NASA-Ames Hypervelocity Free Flight Facility; and 3) Representative Results.
    Keywords: Space Sciences (General)
    Type: 2nd International Planetary Probe Workshop; NASA/CP-2004-213456
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    The Control of Compressible Dynamic Stall Using Adaptive Airfoils (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Ongoing research has shown that compressible dynamic stall can be caused by vastly different mechanisms even for small changes in flow conditions. For example, at low Mach numbers (M less than 0.3) and Reynolds numbers (less than 1 x 10(exp 6)), the bursting of the laminar separation bubble induces dynamic stall. At a slightly higher Mach number (M = 0.45) and around the same Reynolds number, shock induced separation can cause dynamic stall. Also, the mechanism changes from that of laminar separation bubble bursting to that due to excessive adverse pressure gradient, with increase of Reynolds number. Complex interactions occurring between the local supersonic flow and the bubble lead to another possible mechanism of dynamic stall. Since all these mechanisms may be encountered by a rotor-blade during a single cycle, there is a strong need to devise a reliable flow control method for use under such dramatically varying conditions. Whereas it is a Ali 'Beneficent challenge, identification of the fact that these mechanisms are all in some way related to the airfoil leading edge adverse pressure gradient, has resulted in an effective method of flow control to be described.
    Keywords: Aerodynamics
    Type: IUTAM Symposium on Mechanics of Passive and Active Flow Control; Sep 07, 1998 - Sep 11, 1998; Goettingen; Germany
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Interferometric investigations of compressible dynamic stall over a transiently pitching airfoil (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The dynamic stall flow field over NACA 0012 airfoil pitching transiently from 0 - 60 at a constant rate under compressible flow conditions has been studied using the real-time technique of point diffraction interferometry. This investigation using nonintrusive diagnostics provides a quantitative description of the overall flow field, including the finer details of dynamic stall vortex formation, growth and the concomitant changes in the pressure distribution. Analysis of several hundred interferograms obtained for a range of flow conditions shows that the peak leading edge suction pressure coefficient that stall is nearly constant for a given free stream Mach number at all nondimensional pitch rates. Also, this value is below that seen in steady flow at static stall for the same Mach number, indicating that dynamic effects significantly effect the separation behavior. Further, for a given Mach number, the dynamic stall vortex seems to form rapidly at nearly the same angle of attack for all pitch rates studied. As the vortex is shed, it induces an anti-clockwise trailing edge vortex, which grows in a manner similar to that of a starting vortex. The measured peak suction pressure coefficient drops as the free stream Mach number increases. For free stream Mach numbers above 0.4, small multiple shocks appear near the leading edge.
    Keywords: AERODYNAMICS
    Type: NASA-TM-109380 , AIAA PAPER 93-0211 , AD-268794 , NAS 1.15:109380 , Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States
    Format: application/pdf
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