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  • INSTRUMENTATION AND PHOTOGRAPHY  (10)
  • 1
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    Correcting for particle counting bias error in turbulent flow (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: An ideal seeding device is proposed generating particles that exactly follow the flow out are still a major source of error, i.e., with a particle counting bias wherein the probability of measuring velocity is a function of velocity. The error in the measured mean can be as much as 25%. Many schemes have been put forward to correct for this error, but there is not universal agreement as to the acceptability of any one method. In particular it is sometimes difficult to know if the assumptions required in the analysis are fulfilled by any particular flow measurement system. To check various correction mechanisms in an ideal way and to gain some insight into how to correct with the fewest initial assumptions, a computer simulation is constructed to simulate laser anemometer measurements in a turbulent flow. That simulator and the results of its use are discussed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA. Langley Research Center Wind Tunnel Seeding Systems for Laser Velocimeters; p 13-28
    Format: application/pdf
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  • 2
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    Time-of-flight anemometer for hot section applications (1983)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The design, construction and testing of laser anemometer configurations for Hot Section velocity measurements is considered. Optimizing the laser anemometer system necessarily included the data processing algorithms used. It is felt that the requirements here are too demanding for standard laser anemometer systems.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA. Lewis Research Center Turbine Eng. Hot Sect. Technol. (HOST); p 69-71
    Format: application/pdf
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  • 3
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    Particle-sampling statistics in laser anemometers Sample-and-hold systems and saturable systems (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The effect of the data-processing system on the particle statistics obtained with laser anemometry of flows containing suspended particles is examined. Attention is given to the sample and hold processor, a pseudo-analog device which retains the last measurement until a new measurement is made, followed by time-averaging of the data. The second system considered features a dead time, i.e., a saturable system with a significant reset time with storage in a data buffer. It is noted that the saturable system operates independent of the particle arrival rate. The probabilities of a particle arrival in a given time period are calculated for both processing systems. It is shown that the system outputs are dependent on the mean particle flow rate, the flow correlation time, and the flow statistics, indicating that the particle density affects both systems. The results are significant for instances of good correlation between the particle density and velocity, such as occurs near the edge of a jet.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 133; Aug. 198
    Format: text
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  • 4
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    Signal broadening in the laser Doppler velocimeter. (1971)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Critical review of a recent paper in which Denison, Stevenson, and Fox (1971) discussed the sources of spectral broadening in the laser Doppler velocimeter. It is pointed out that, in their discussion, the above-mentioned authors indicated that the spread in wave vectors of the incident and detected fields and the finite length of time a scattering center stayed in the sample volume each contributed separately and independently to the observed spectral width of the scattered radiation. This statement is termed incorrect, and it is shown that the two effects are one and the same.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIChE Journal; 17; Nov. 197
    Format: text
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  • 5
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    Optimizing and comparing laser anemometers (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Comparisons can be made only if some single valued measure of the quality of each system can be defined. This concept is illustrated here by specifying the quality variable to be the measurement uncertainty in the mean velocity of a turbulent flow in the presence of a large background noise. The Fisher number is used as a figure of merit for some parts of the system. It is noted that in many cases of practical interest, the reciprocal Fisher number gives the actual variance of an estimator. Its principal advantage here is that it can be computed without detailed assumptions about the statistics of the estimated quantities. The concept of a Fisher number is related to the concept of information gain in a measurement. The variance of the measured mean velocity is expressed in terms of the uncertainty for the individual measurements, the measurement rate, and the velocity correlation time. Conditions are given under which the fringe and the two-spot anemometer are optimized.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Format: text
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  • 6
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    Infrared image construction with computer-generated reflection holograms (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Computer-generated reflection holograms hold substantial promise as a means of carrying out complex machining, marking, scribing, welding, soldering, heat treating, and similar processing operations simultaneously and without moving the work piece or laser beam. In the study described, a photographically reduced transparency of a 64 x 64 element Lohmann hologram was used to make a mask which, in turn, was used (with conventional photoresist techniques) to produce a holographic reflector. Images from a commercial CO2 laser (150W TEM(00)) and the holographic reflector are illustrated and discussed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics; 16; Nov. 197
    Format: text
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  • 7
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    Spectral analysis of the signal from the Laser Doppler Velocimeter - Turbulent flows. (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A method for prediction and analysis of the spectrum of the signal from the Laser Doppler Velocimeter is presented. The results relate the heterodyne spectrum of the signal to the space-time correlation function for the turbulent transport of tracer particles in the fluid and to the characteristics of the optical system.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Applied Physics; 44; Apr. 197
    Format: text
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  • 8
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    Binary phase digital reflection holograms - Fabrication and potential applications (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A novel technique for the fabrication of binary-phase computer-generated reflection holograms is described. By use of integrated circuit technology, the holographic pattern is etched into a silicon wafer and then aluminum coated to make a reflection hologram. Because these holograms reflect virtually all the incident radiation, they may find application in machining with high-power lasers. A number of possible modifications of the hologram fabrication procedure are discussed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics; 16; Feb. 197
    Format: text
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  • 9
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    Implementation of a new type of time-of-flight laser anemometer (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A new time-of-flight (TOF) laser anemometer system utilizing a spatial lead-lag filter for bipolar pulse generation has been constructed and tested. This new TOF has been modified to enable measurements in turbulent flows near walls. Good results have been obtained as close as 100 microns from a surface, with a 140-mm focal length final lens. Lading's theory for the behavior of the measurement variance has been confirmed for this configuration.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 25; 644-648
    Format: text
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  • 10
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    Turbulent transport measurements with a laser Doppler velocimeter. (1972)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The power spectrum of phototube current from a laser Doppler velocimeter operating in the heterodyne mode has been computed. The spectral width and shape predicted by the theory are in agreement with experiment. For normal operating parameters the time-average spectrum contains information only for times shorter than the Lagrangian-integral time scale of the turbulence. To examine the long-time behavior, one must use either extremely small scattering angles, much-longer-wavelength radiation, or a different mode of signal analysis, e.g., FM detection.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Pacific Chemical Engineering Meeting; Oct 10, 1972 - Oct 14, 1972; Kyoto; Japan
    Format: text
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