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  • Other Sources  (8)
  • 1985-1989  (8)
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  • 1
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    Direct measurement of skin friction with a new instrument (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The design and performance of a small belt-type skin-friction gage to measure wall shear-stress coefficients in wind-tunnel testing are described, summarizing the report of Vakili and Wu (1982). The sensor employs a flexible belt of variable surface characteristics; this belt, wrapped tightly around two cylinders mounted on frictionless flexures, is equipped with strain gages to estimate the deflection of the belt by the flow. An alternative approach uses IR illumination, optical fibers, and a photosensitive transistor, permitting direct measurement of the belt deflection. Drawings, diagrams, and graphs of sample data are provided.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Compressible flow in a diffusing S-duct with flow separation (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Local flow velocity vectors, as well as static and total pressures along ten radial traverses, were obtained at six stations for secondary flows in a diffusing 30-30-deg S-duct with circular cross section. The strong secondary flow measured in the first bend continued into the second with new vorticity produced in the opposite direction. Contour plots representing the transverse velocity field, as well as total and static pressure contours, have been obtained. As a result of the secondary flow and subsequent separation, substantial total pressure distortion is noted to occur at the duct exit.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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    NASA TECHNICAL REPORTS
  • 3
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    Recent tests at Langley with a University of Tennessee Space Institute (UTSI) skin friction balance (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The experience at LaRC with the University of Tennessee Space Institute skin friction balances is summarized. The Karman-Schoenherr flat plate skin friction formulation is included for comparison. It is concluded that the balance is capable of operation in environments as diverse as cryogenic, transonic, high-shear rate of the 0.3 meter Transonic Cryogenic Tunnel, and high-temperature supersonic environment of the Unitary Plan Wind Tunnel. Proposed new research is outlined.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 407-411
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Vortical sources of aerodynamic force and moment (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is shown that the aerodynamic force and moment can be expressed in terms of vorticity distribution (and entropy variation for compressible flow) on near wake plane, or in terms of boundary vorticity flux on the body surface. Thus the vortical sources of lift and drag are clearly identified, which is the real physical basis of optimal aerodynamic design. Moreover, these sources are highly compact, hence allowing one to concentrate on key local regions of the configuration, which have dominating effect to the lift and drag. A detail knowledge of the vortical low requires measuring or calculating the vorticity and dilatation field, which is however still a challenging task. Nevertheless, this type of formulation has some unique advantages; and how to set up a well-posed problem, in particular how to establish vorticity-dilatation boundary conditions, is addressed.
    Keywords: AERODYNAMICS
    Type: SAE PAPER 892346
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Wall shear stress measurements using a new transducer (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A new instrument has been developed for direct measurement of wall shear stress. This instrument is simple and symmetric in design with small moving mass and no internal friction. Features employed in the design of this instrument eliminate most of the difficulties associated with the traditional floating element balances. Vibration problems associated with the floating element skin friction balances have been found to be minimized by the design features and optional damping provided. The unique design of this instrument eliminates or reduces the errors associated with conventional floating-element devices: such as errors due to gaps, pressure gradient, acceleration, heat transfer and temperature change. The instrument is equipped with various sensing systems and the output signal is a linear function of the wall shear stress. Measurement made in three different tunnels show good agreement with theory and data obtained by the floating element devices.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA PAPER 86-1092
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Development of a new instrument for direct skin friction measurements (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A device developed for the direct measurement of wall shear stress generated by flows is described. Simple and symmetric in design with optional small moving mass and no internal friction, the features employed in the design eliminate most of the difficulties associated with the traditional floating element balances. The device is basically small and can be made in various sizes. Vibration problems associated with the floating element skin friction balances were found to be minimized due to the design symmetry and optional damping provided. The design eliminates or reduces the errors associated with conventional floating element devices: such as errors due to gaps, pressure gradient, acceleration, heat transfer, and temperature change. The instrument is equipped with various sensing systems and the output signal is a linear function of the wall shear stress. Dynamic measurements could be made in a limited range and measurements in liquids could be performed readily. Measurement made in the three different tunnels show excellent agreement with data obtained by the floating element devices and other techniques.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-CR-176818 , NAS 1.26:176818 , UTSI-86-02
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    A theoretical formulation of wave-vortex interactions (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A unified theoretical formulation for wave-vortex interaction, designated the '(omega, Pi) framework,' is presented. Based on the orthogonal decomposition of fluid dynamic interactions, the formulation can be used to study a variety of problems, including the interaction of a longitudinal (acoustic) wave and/or transverse (vortical) wave with a main vortex flow. Moreover, the formulation permits a unified treatment of wave-vortex interaction at various approximate levels, where the normal 'piston' process and tangential 'rubbing' process can be approximated dfferently.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 89-0988
    Format: text
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  • 8
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    Flow control in a diffusing S-Duct (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Accurate measurements have been made of secondary flow in a 1.51 area ratio diffusing 30 deg - 30 deg S-Duct with circulair cross section. Turbulent flow was entering the duct at Mach number of 0.6, the boundary layer thickness at the duct entrance was ten percent of the duct inlet diameter. Through measurements made, local flow velocity vector as well as static and total pressures mapping of the flow at several stations were obtained. Strong secondary flow was measured in the first bend which continued into the second bend with new vorticity produced in there in the opposite direction. Surface oil flow visualization and wall pressures indicated a region of separated flow starting at theta approximately equal to 22 deg on the inside of the first bend up to theta approximately equal to 44 deg on the outside of the second bend. The flow separated in 'cyclone' form and never reattached in the duct. As a result of the secondary flow and the flow separation, significant total pressure distortion was observed at the exit of the duct. Using flow control devices the separation was eliminated while the exit distortion was improved.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-0524
    Format: text
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