Laser-Doppler velocity meter

Kostiuk et al. [40] measured experimentally the flow field of the vertical co-axial turbulent impinging streams with a two-component Laser Doppler velocity meter. The opposing gas streams were ejected from two burner nozzles, which were designed to produce a uniform axial velocity profile at their exits. The turbulence in the flow was generated by a perforated plate located at the end of the contraction section in each nozzle. The air velocity at the exit of the nozzle was varied from 4.1 to 11.4 m s and... 

There is a need to distinguish at this point how the shear rate in the impeller zone differs from the shear rate in the tank zone. To do this, however, one must carefully define shear rate and the corresponding concepts of macroscale shear rate and microscale shear rate. When one studies the localized fluid velocity through utilization of a small dimension probe, or as is currently used, a laser Doppler velocity meter device, one sees that at any point in the... 

Utkin, E. N. Study of gas-saturated turbulent streams using a laser-Doppler velocity meter. Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki (1975) 147-153. 

Laser Doppler Velocimeters. Laser Doppler flow meters have been developed to measure Hquid or gas velocities in both open and closed conduits. Velocity is measured by detecting the frequency shift in the light scattered by natural or added contaminant particles in the flow. Operation is conceptually analogous to the Doppler ultrasonic meters. Laser Doppler meters can be appHed to very low flows and have the advantage of sensing at a distance, without mechanical contact or interaction. The technique has greatest appHcation in open-flow studies such as the deterrnination of engine exhaust velocities and ship wake characteristics. 

Figure 16. Typical laser output from the measurement of velocities by means of a Doppler velocity meter.

Although various interchanges of laser wavelengths, power meters, etc. will be made to control systematics, the basic technique for the measurement is indicated in fig. 5. The lasers are set on laser lines approximately equidistant from, but on either side of the resonance centroid, and balanced in power. The lasers are chopped in anti-phase and the difference signal, S(u> 1) — S(u>2) is recorded. The beam velocity is varied till the zero-crossing (where the signals are equal) is found. The resonance centroid (in the ion s rest frame) is then obtained from the relativistic Doppler formula and the mean of the two laser frequencies. 

Figure 8.6. Laser Doppler systems have been used to determine the velocity and size distributions of fineparticles within a system concurrently, a) Data reported by Baukage and Schone for spray droplets from a simple nozzle, b) Size and velocity distributions of Albuterol from a metered dose inhaler as reported by Rudoff et al. (Used by permission of Particle and Particle Systems Characterization.)...

The temperature distribution in the loop is measured with chromel-alumel thermocouples and two Pt-100 temperature sensors for reference measurements. Absolute pressure is measured at the top of the riser and at the inlet of the core. The liquid level in the steam dome is measured with a differential pressure sensor. The differential pressure over the friction settings of the individual channels is a measure for the flow distribution over the coolant channels and bypass channels. The total flow in the loop is measured at 2 different positions with electromagnetic flow meters. The void fraction at a given height can be measured with gamma transmission techniques. At a fixed height at the top of the riser the radial void distribution is measured with a wire-mesh sensor, which measures the conduction of the two-phase mixture on a two-dimensional grid. Furthermore, laser doppler anemometry is used to study the local liquid velocity in the core or in the riser. 

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