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  • 11
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    Measurement of flow fields in a large transonic wind tunnel using a laser velocimeter (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: An investigation to determine the feasibility of using a laser velocimeter for measuring the mean flow velocities about airplane models in the Langley 16-foot transonic tunnel has recently been completed. The laser velocimeter was a two-component fringe-type used in the back scatter mode. The tunnel airflow was seeded with oil droplets to provide scattering sources for the laser velocimeter. Measurements of the tunnel free-stream velocity were in good agreement with the tunnel calibration, and measurements of the velocity along the stagnating streamline of a hemisphere model, when adjusted for particle lag, were in good agreement with theoretical predictions. The study showed that the laser, optics, and electronics system operated satisfactorily, but that further development is required to reduce scattering particle size and substance accumulation in the tunnel.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA PAPER 75-1425 , General Aviation Technologyfest; Nov. 13, 14, 1975; Wichita, Kan.
    Format: text
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    NASA TECHNICAL REPORTS
  • 12
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    Processing of the laser Doppler velocimeter signals (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The laser Doppler velocimeter (LDV) is a probeless technique that provides a remote measurement of mean and fluctuating velocities. The measurement is actually obtained from small particles embedded in the flow which scatter light from an illuminating laser beam interference pattern. A portion of this scattered light is collected by a photomultiplier which yields an electronic signal whose frequency is directly proportional to the velocity of the small particles. The purpose of this paper is to describe and critically compare three techniques most used to process this electronic signal. These techniques are: (1) spectrum analyzer - a frequency scanning filter (frequency domain instrument), (2) wide-band frequency tracker - a frequency lock loop (frequency domain instrument), and (3) high-speed frequency counter - an interval timer (time domain instrument). The study determines the ability of each technique to process the LDV signal and yield velocity data to be used in determining the flow characteristics.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ICIASF ''73; International Congress on Instrumentation in Aerospace Simulation Facilities; Sep 10, 1973 - Sep 12, 1973; Pasadena, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 13
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    Laser velocimeter measurements in a large transonic wind tunnel (1976)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A two-component fringe type laser velocimeter operated in the backscatter mode was used to measure the free-stream velocity in an undisturbed flow field in a wind-tunnel test section from Mach 0.2 to Mach 1.0 and to measure the velocity along the stagnating streamline of a hemisphere model from Mach 0.2 to Mach 0.8. Burst signals from the laser velocimeter were processed by high-speed burst counters, and histograms of the number of occurrences of a particular counter output were collected by means of a pulse height analyzer. Arithmetic means of the histograms were calculated, and the results were compared with predicted local gas velocities with allowance for the lag of the scattering particles with respect to the gas flow. The free-stream measurements were accurate to within 2% of the calibration measurements. The stagnation streamline measurements show trends similar to theoretical predictions.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Minnesota Symposium on Laser Anemometry; Oct 22, 1975 - Oct 24, 1975; Bloomington, MN
    Format: text
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    NASA TECHNICAL REPORTS
  • 14
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    Computer simulation of a fringe type laser velocimeter (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A computer simulation of a fringe type laser velocimeter has been written to determine the theoretical characteristics of the laser velocimeter when applied to a given flow field. The program includes the effect of particle size and composition on particle lag, light scattering characteristics and signal contrast. The model of the laser velocimeter includes the laser, optical system, photomultiplier, and counter type data processing electronics. The LV particle size analyzer is also modeled and incorporated in the program. An example application of the program to a Mach 5 wind tunnel using a backscatter laser velocimeter is presented.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: International Workshop on Laser Velocimetry; Mar 27, 1974 - Mar 29, 1974; West Lafayette, IN
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  • 15
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    A feasibility test of the laser velocimeter in the Mach 5 nozzle test chamber (1974)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A one-component, fringe type laser velocimeter in the backscatter mode was used to measure flow velocities from 732 to 792 m/sec about a shock from an inclined flat plate in a Mach 5 tunnel. This test was chosen to determine system characteristics in applying the laser velocimeter to measure velocities in hypersonic flow fields. The seeding particles, less than 20 microns in diameter, were injected into the tunnel supply pipe, approximately 1 meter upstream of the nozzle throat, through a rake along the diameter. The LV signals were processed by two methods, a scanning spectrum analyzer and a high-speed counter. The measured velocity distributions obtained were analyzed to determine the errors due to particle lag, transit time broadening and high-speed counter quantizing error.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: International Workshop on Laser Velocimetry; Mar 27, 1974 - Mar 29, 1974; West Lafayette, IN
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    NASA TECHNICAL REPORTS
  • 16
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    Laser velocimetry with diode junctions semiconductor lasers (1978)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Measurements of mean and fluctuating axial velocity have for the first time been made in a seeded pipe flow with a semiconductor laser velocimeter. Several compact velocimeters have been constructed using laser diodes. While the intended applications have restricted the final instrument to operate in a coaxial backscatter mode, operation has been demonstrated in forward and side scattering modes. In all cases the instrument could be classed as dual beam. An instrument has been constructed to be installed in a model airfoil and will be mechanically driven to measure the flow over a 75-mm chord distance. The instrument occupies a volume measuring 100 mm x 100 mm x 40 mm. The compactness has been aided by using an avalanche photodiode instead of a photomultiplier tube.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: In: Electro-Optics/Laser Conference and Exposition; Sep 19, 1978 - Sep 21, 1978; Boston, MA
    Format: text
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    NASA TECHNICAL REPORTS
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