Anemometers laser-Doppler

Nonintrusive Instrumentation. Essential to quantitatively enlarging fundamental descriptions of flow patterns and flow regimes are localized nonintmsive measurements. Early investigators used time-averaged pressure traverses for holdups, and pilot tubes for velocity measurements. In the 1990s investigators use laser-Doppler and hot film anemometers, conductivity probes, and optical fibers to capture time-averaged turbulent fluctuations (39). 

The laser-Doppler anemometer measures local fluid velocity from the change in frequency of radiation, between a stationary source and a receiver, due to scattering by particles along the wave path. A laser is commonly used as the source of incident illumination. The measurements are essentially independent of local temperature and pressure. This technique can be used in many different flow systems with transparent fluids containing particles whose velocity is actually measured. For a brief review or the laser-Doppler technique see Goldstein, Appl. Mech. Rev., 27, 753-760 (1974). For additional details see Durst, MeUing, and Whitelaw, Principles and Practice of Laser-Doppler Anemometry, Academic, New York, 1976. 

The corresponding laser-based experimental methods are covered below, with special regard to the laser Doppler anemometer technique, which offers the greatest application use in industrial ventilation at the lowest cost. 

Laser Doppler anemometer An instrument for determining fluid velocity by measuring the difference in frequency between the incident beam and that... 

The flow patterns for single phase, Newtonian and non-Newtonian liquids in tanks agitated by various types of impeller have been repotted in the literature.1 3 27 38 39) The experimental techniques which have been employed include the introduction of tracer liquids, neutrally buoyant particles or hydrogen bubbles, and measurement of local velocities by means of Pitot tubes, laser-doppler anemometers, and so on. The salient features of the flow patterns encountered with propellers and disc turbines are shown in Figures 7.9 and 7.10. 

In addition to the anemometers using the laser Doppler principle, there are also laser anemometers utilizing two-focus and transmit-time principles. The laser two-focus anemometer (L2F) measures the time needed for particles to pass the known distance between two focused beams. The signal... 

Bankel, J., and Olsson, E. Measurements of Particle Velocity in a Cyclone Separator Using Laser Doppler Anemometer, in Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 630-635. Somerset, Pennsylvania (1993). 

Figure 5.4 Laser-doppler anemometer profiles of mean velocity in and above a wind tunnel model study of flow over an isolated sinusoidal two-dimensional ridge covered with a tall canopy. Profiles are located upwind (x = -2L, dot dash line) on the hilltop (solid line) and downwind (x = +2L, dotted line). The hill parameters were H/L = 0.1 hc/H = 1.0. Full details of the experiment can be obtained from the author (Finnigan and Hughes, pers. comm.)...

Fig. 1.5. A typical velocity signal recorded by a laser Doppler anemometer (LDA) in a liquid flow at NTNU. (v) dentotes the time average of the velocity over the time period displayed. The work was performed as a part of the strategic university program (SUP) entitled CFD Applied to Reactor ProcEss Technology (CARPET) .

The chapter begins with the fundamental measurements of resistance, capacitance, charge, and particle force. We proceed with flow measurements with various probes followed by a listing of some commercial electrostatic instruments. Nonelectrosatic measurements in multiphase flow such as the laser-Doppler anemometer, radioactive tracers, and stroboscopic techniques (Polaskowski, et. al, 1995 Soo, 1982) have not been discussed unless in relation to an electrostatic effect. 

Stieglmeier, M. and Tropea, C., Mobile fiber-optic laser doppler anemometer. Appl. Optics, 31, 4096-4105, (1992)... 

Intrusive measurement techniques such as a Pitot static tube and hot-wire anemometer [24-26], and nonintrusive techniques such as laser Doppler velocimeter and particle image velocimetry (PIV) have been used to study the flow field. Goh, Kusadomi, and Gollahalli [13-15] mapped the velocity field in the flame using a Pitot static tube with a pressure transducer (Barocel). Details of the techniques and selection guidelines are presented in books on experimental aspects of fluid mechanics. Interested readers are referred to Holman [27], Goldstein [28], and Miller [29], to name a few. 

Historically, most turbulence measurements have been made with hot-wire anemometers. In recent years laser-Doppler anemometers have been widely used as well. 

Phillips, W.M., Brighton, J.A., and Pierce, W.S. 1979. Laser Doppler anemometer studies in unsteady ventricular flows. Trans. ASAIO 25 56-60. 

Anemometry is a general term to represent the measurement of wind speed— anemos is the Greek word for wind. The earliest anemometer for meteorology is credited to Alberti in 1450. Hooke reinvented the device, which relied on cups or disks mounted on a pole that would rotate by the force of wind. Modern instruments to measure wind speed rely on laser Doppler shift, ultrasonic waves, propellers, and hot wire anemometers. The hot wire anemometer is commonly used for fluid flow measurements and in particular for research applications that require a detailed analysis of velocity in localized areas or for conditions... 

Nezu I Rodi W. 1986. Open-channel Flow Measurements with a Laser Doppler Anemometer. Journal... 

Einav, S., and Berman, H. J., Fringe mode transmittance laser Doppler microscope anemometer. Its adaptation for measurement in the microcirculation, J. Biomech. Eng., 10 393-399,1988. 

Ku, D. N., and Giddens, D. P., Laser Doppler anemometer measurements of pulsatile flow in a model carotid bifurcation, J. Biomech., 20 407-421, 1987. 

A semi-emperical turbulent one-equation model is developed for rectangular open channel flows of water and viscoelastic fluids. The model is used to predict friction factor vs. Reynolds number relations, velocity profiles, eddy viscosity distributions and turbulent energy budgets. Comparisons are made between the model and the measured results using a Laser Doppler Anemometer. 

Reishman, M. M. and W. G. Tiederman,"Laser-Doppler Anemometer Measurements in Drag-Reducing Channel Flows", J. Fluid Mech., 70,(1975) 369-392... 

A Thermo-Systems (TSI) Laser-Doppler Anemometer was used to measure the resulting vortex shedding frequencies. This was accomplished by measuring the velocity fluctuations in the direction of flow at some distance downstream from the cylinders. This type of measurements, being inherently optical in nature, did not disturb the flow field and was not influenced by the presence of the polymer. 

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