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  • INSTRUMENTATION AND PHOTOGRAPHY  (8)
  • 2000-2004
  • 1980-1984  (4)
  • 1970-1974  (4)
  • 1955-1959
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  • 1
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    A comparison of turbulence intensity measurements using a laser velocimeter and a hot wire in a low speed jet flow (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The study involves a simultaneous measurement with both instruments along radial scans at two axial locations in the jet exiting from the turbulent pipe and an axial scan at the 75-percent radial location in the jet from the convergent nozzle. The results suggest that, within the limits of flow stationarity, both instruments yield measurements in good agreement, + or - 0.8-percent in turbulence intensity, below a turbulence intensity (the ensemble standard deviation divided by the local mean velocity) of 20 percent. From turbulence intensities of 20 percent to a maximum of 75 percent, the measurements exhibit the same trends; for reasons discussed here, however, the comparisons are not of the quality as those below 20 percent. It is found that correcting the turbulence intensity data for velocity bias errors increases the results by an average of 2 percent in turbulence intensity above the hot wire results and the uncorrected laser velocimeter data. The results are seen as calling into question the validity of using the velocity bias correction and time average techniques for turbulence intensity measurements.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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  • 2
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    Simultaneous Raman and laser velocimeter measurements (1974)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: The feasibility of performing Raman and laser velocimeter measurements simultaneously is demonstrated, and it is shown that the background radiation associated with the Mie scattering and large particulate concentrations does not saturate or distort the relatively weak rotational Raman signals. Under stringent conditions of low static gas densities and large particulate concentrations, Raman density and temperature measurements agree to within plus or minus 5% of the calculated values.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA Journal; 12; Oct. 197
    Format: text
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  • 3
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    Velocity vector analysis of a juncture flow using a three component laser velocimeter (1984)
    In:  Other Sources
    Details
    Publication Date: 2018-12-01
    Description: A specialized single-axis, five-beam three-component laser velocimeter was constructed and used to study the flow field in a juncture. The juncture was defined by a blunt leading edged vertical splitter plate and a sharp leading edged horizontal plate. The investigations were conducted in the Low Turbulence Pressure Tunnel at a Mach number of 0.1 and a Reynolds number of 2.2 x 10 to the 6th per meter over the model. The three-component velocity flow field in the juncture was measured, Reynolds stresses calculated, and the velocity vector analysis performed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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  • 4
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    Comparison of hot wire/laser velocimeter turbulence intensity measurements (1982)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The question of whether a random measure of particle velocities yields a good statistical estimate of the stationary condition of the turbulence flow field was investigated by comparing hot-wire and laser velocimeter turbulence intensity measurements. Great care was taken to insure that the instrument precision of both the laser velocimeter and hot wire was maximized. In this attempt to reduce the measurement uncertainties in the hot wire, direct digitization of the analog output signal was performed with point-by-point conversion to velocity through a spline fit calibration curve and the turbulence intensity function was calculated statistically. Frequent calibrations of the hot wire were performed using the laser velocimeter as the velocity standard to account for the presence of the small seed particles in the air flow and signal drift in the hot wire.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Flow Visualization and Laser Velocimetry for Wind Tunnels; p 303-322
    Format: application/pdf
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  • 5
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    Laser velocimetry technique applied to the Langley 0.3 meter transonic cryogenic tunnel (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A low power laser velocimeter operating in the forward scatter mode was used to measure free stream mean velocities in the Langley 0.3 Meter Transonic Cryogenic Tunnel. Velocity ranging from 51 to 235 m/s was measured. Measurements were obtained for a variety of nominal tunnel conditions: Mach numbers from 0.20 to 0.77, total temperatures from 100 to 250 K, and pressures from 101 to 152 kPa. Particles were not injected to augment the existing Mie scattering materials. Liquid nitrogen droplets were the existing liqht scattering material. Tunnel vibrations and thermal effects had no detrimental effects on the optical system.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-81913 , L-14244
    Format: application/pdf
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  • 6
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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
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  • 7
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    Computer simulation of a fringe type laser velocimeter (1974)
    In:  Other Sources
    Details
    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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  • 8
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    A feasibility test of the laser velocimeter in the Mach 5 nozzle test chamber (1974)
    In:  Other Sources
    Details
    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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