Removal of Pedestals and Directional Ambiguity of Optical Anemometer Signals

Durst, F.; Zare, M.

doi:10.1364/ao.13.002562

Cited by 33 publications

(7 citation statements)

References 14 publications

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“…These errors and others due to small fluctuations in seeding density are further reduced by averaging 3-5 such spectral sweeps for each measurement point during data analysis on a PDP 11/45 computer. For the present measurements no problem exists with "spectrum folding" (ef Durst and Zare, 1974) from directional ambiguity, since the external stream (u, = 15.1 m/s) makes the measurement of absolute velocity reversals unnecessary. It should be noted that measurements made in the intermittent jet boundary regions are not only conditional (since only the hydrogen jet is seeded) but are also weighted by the seeding bias, discussed in section 2.4 below.…”

Section: Experimental Conditionsmentioning

confidence: 97%

The Turbulent Jet Diffusion Flame in a Co-flowing Stream—Some Velocity Measurements

Glass

Bilger

1978

Combustion Science and Technology

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Laser-Doppler measurements of mean velocity, axial and radial components of turbulence andReynolds shear stress have been made on a turbulent diffusion flame formed by a jet of hydrogen burning in a co-flowing stream of air at an initial velocity ratio of 10 to I. Results are found to be similar to those for isothermal and heated air jets in co-flowing streams except that there appears to be some suppression of turbulence on the centreline near the hottest part of the flame. The technique used involves some small residual effect of seeding bias and this has been thoroughly analysed and estimates made.

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Section: Experimental Conditionsmentioning

confidence: 97%

The Turbulent Jet Diffusion Flame in a Co-flowing Stream—Some Velocity Measurements

Glass

Bilger

1978

Combustion Science and Technology

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“…A Bragg cell was used to shift the laser light frequency by 40 MHz to remove the directional ambiguity of the measurement. 8 ' 9 ' 16 ' 17 The glass rod shown in Fig. 1 is used to minimize the optical path difference between the two interference arms so as to reduce the phase error induced by the laser thermal wavelength drift effect mentioned earlier.…”

Section: Direction Ambiguitymentioning

confidence: 99%

Differential laser interferometer for nanometer displacement measurements

Lee

1995

AIAA Journal

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A dual beam differential laser interferometer/vibrometer measurement system was developed for studying the steady-state and dynamic behavior of low-weight high-performance mechanical systems. This newly developed optical system employs many optical and mechanical design tactics to achieve design targets such as nanometer displacement accuracy, ease of use, capability of measuring untreated structural surfaces, high-measurement bandwidths, and large-dynamic ranges. Both the optical/mechanical configurations and the design approaches adopted are discussed in detail. A flying slider and thin-film disk system currently used in the disk drive industry were used as the testbed to verify the capabilities of this newly developed nanometer structural displacement/velocity measurement system.

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“…If the apparent frequency f[/ obtained from the frequency analysis is greater than the shift frequency •Xf, it means that the velocity sign is positive. Several frequency shift methods for determining the velocity sign have been summarized by Durst and Zar• [1974, Table 1]. The frequency shift method for groundwater velocity measurements will be described in the following section.…”

Section: Background Of Ld V Measurementsmentioning

confidence: 99%

“…A summary of frequency shift methods by Durst and Zar• [1974] shows that the acousto-optical or electro-optical frequency shift method is not suitable for low-velocity measurements because it cannot derive the low-frequency shift. Furthermore, the multicolor laser method is not sensitive to zero velocity and needs a bigger probe volume compared to our GLDV system.…”

Section: Outline Of the Gldv Systemmentioning

confidence: 99%

Laboratory studies on a new laser Doppler Velocimeter System for horizontal groundwater velocity measurements in a borehole

Momii¹,

Jinno²,

Hirano³

1993

Water Resources Research

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This paper introduces a new instrument for measuring groundwater velocity in a borehole using a laser Doppler velocimeter (LDV) technique. The major improvement of the proposed LDV system is that the probe can be inserted into a borehole that has a minimum diameter of 10 cm and that a disk-type rotating grating is used as a frequency shifter for low velocities in order to determine the velocity sign. The speed of the glass plate passing through the LDV measurement point is calibrated to demonstrate the accuracy of the new LDV system. From a comparison with the true constant speed of the glass plate, we confirm that the new LDV system can measure low speeds in the range from 10 -5 to 10--' cm/s at a measurement error of less than 8%. Laboratory experiments were carded out to investigate the performance of the new LDV system for the horizontal velocity measurement of groundwater in a borehole. The result obtained by the proposed LDV system shows that the horizontal velocity at the center of an unscreened borehole is 3 times larger than the seepage velocity in a confined aquifer. This result agrees with the theoretical solution for groundwater flow in a borehole derived by Sano (1983). The validity of the theoretical solution is experimentally verified in the laboratory using the current LDV system. Although the detectable minimum velocity in a borehole is limited by the velocity fluctuations due to the BrownJan motion of scattering particles, results obtained in the experiments using 0.804-/zm polystyrene particles show that the LDV system described in this paper can measure with a sufficient accuracy both the magnitude and the direction of groundwater velocity down to 10 -4 cm/s in a borehole. INTRODUCTION When groundwater velocity is investigated by injecting a tracer such as a radioactive isotope, dye, or salt into a borehole and the arrival time of the tracer at observation wells arranged a few meters away from the injection well is observed, there are four fundamental problems. First, several observation wells will have to be installed around the injection well if the flow direction is unknown. Second, it is difficult to accurately evaluate the arrival time due to effects of dispersion, diffusion, chemical reaction, and adsorption of the tracer. Third, injection of a large amount of tracer will cause groundwater pollution and a local change in the groundwater movement. Fourth, long-time observations are usually required because the velocity is usually very small. In recent years, the point dilution method [Drost et al., 1968] has been commonly used for groundwater flow measurements. In the point dilution method the velocity measurement is carried out in a single borehole, and the first two obstacles can be eliminated. However, since this method requires a radioisotopic tracer, the third problem still remains. Also, the effects of adsorption and density convection currents need to be carefully considered. Furthermore, as mentioned by Drost et al. [1968], the measuring period by the point dilution method is abou...

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Removal of Pedestals and Directional Ambiguity of Optical Anemometer Signals

Cited by 33 publications

References 14 publications

The Turbulent Jet Diffusion Flame in a Co-flowing Stream—Some Velocity Measurements

The Turbulent Jet Diffusion Flame in a Co-flowing Stream—Some Velocity Measurements

Differential laser interferometer for nanometer displacement measurements

Laboratory studies on a new laser Doppler Velocimeter System for horizontal groundwater velocity measurements in a borehole

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