Doppler anemometry, laser

1 Particle Tracking Velocimetry and Laser Speckle Vehcimetry. 

In PTV, the acquired data provide a time sequence of individual tracer particles in the flow. To be able to track individual particles from frame to frame, the seeding density needs to be small. Unlike PIV, the PTV results in sparse velocity information located in random locations. Guezennec et al. (1994) have developed an automated three dimensional particle tracking velocimetry system that provides time-resolved measurements in a volume. 

Laser Doppler anemometry is a nonintrusive technique used to measure the velocity of particles suspended in a flow. If these particles are small, in the order of micrometers, they can be assumed to be good flow tracers following the flow 

During the last four-five decades, the laser-Doppler anemometry (LDA) has become a commonly used experimental technique to measure the instantaneous velocity of seeded single phase flows, and dispersed two-phase flows of very low concentration. A major reason is that LDA is a non-invasive optical technique and does not disturb the flow. Moreover, the LDA system has a high spatial resolution with a fast dynamic response and range. 

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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. 

Velocity vectors of the gas flow measured using laser Doppler anemometry inside a closed chamber during the formation of a tulip flame. Images of the flame are also shown, though the velocity measurements required many repeated runs, hence, the image is only representative. The chamber has square cross sections of 38.1mm on the side. The traces in the velocity fields are the flame locations based on velocity data dropout. The vorticity generated as the flame changes shape appears clearly in the velocity vectors. 

Laser Doppler anemometry data showing the axial velocity along the centerline of a 380 mm long closed chamber during the formation of acetylene/air tulip flames of different equivalence ratios. The velocity is measured 265 mm from the ignition thus, the tulip shape is already formed before the flame reaches the measurement point. This work shows the behavior similar to the results described in Figure 5.3.9. (Adapted from Starke, R. and Roth, R, Combust. Flame, 66,249,1986.)... 

Kried, D. K.,J. M.Creer,J. M. Bates, M. S. Quigley, A. M. Sutey, and D. S. Rowe, 1979, Fluid Flow Measurements in Rod Bundles Using Laser Doppler Anemometry Techniques, Fluid Flow and Heat Transfer over Rod or Tube Bundles, p. 13, ASME Winter Annual Meeting, ASME, New York. (3) Kudryavtsev, A. P., D. M. Ovechkin, D. N. Sorokin, V. I. Subbotin, and A. A. Tsyganok, 1967, Transfer... 

In view of the different requirements as to computer power, it is very worthwhile to compare the outcome of RANS and LES simulations mutually and/ or with quantitative experimental data. Several authors have done this, e.g., Derksen and Van den Akker (1998, 1999), Derksen (2001), Lu et al. (2002), Ranade (2002), Derksen (2002b), and Yeoh et al. (2004a,b). In most cases, the experimental data have been obtained by means of Laser-Doppler Anemometry (LDA, or LDV) see, e.g., Yianneskis et al. (1987), Wu and Patterson (1989), Schafer et al. (1997, 1998), and Derksen et al. (1999). In this review, we will mainly refer to the validation study due to Hartmann et al. (2004a). 

Electrophoretic mobility measurements can be performed by laser Doppler anemometry (LDA). LDA is fast and capable of high resolution of particle velocities [144]. It measures particle velocity, which is measured in the stationary... 

There have been very few studies of the effects of non-Newtonian properties on flow patterns in hydrocyclones, although Dyakowski et al.,AU have carried out numerical simulations for power-law fluids, and these have been validated by experimental measurements in which velocity profiles were obtained by laser-doppler anemometry. 

There have been several studies in which the flow patterns within the body of the cyclone separator have been modelled using a Computational Fluid Dynamics (CFD) technique. A recent example is that of Slack et a/. 54 in which the computed three-dimensional flow fields have been plotted and compared with the results of experimental studies in which a backscatter laser Doppler anemometry system was used to measure flowfields. Agreement between the computed and experimental results was very good. When using very fine grid meshes, the existence of time-dependent vortices was identified. These had the potentiality of adversely affecting the separation efficiency, as well as leading to increased erosion at the walls. 

With the aid of the two-color Laser-Doppler-Anemometry (LDA), Bewersdorff was able to measure the axial and the radial turbulence intensities simultaneously and also the Reynolds shear stresses. The injection of polymer results in a damping of both intensities in the region of their maxima. In his Reynolds shear stress measurements he showed that the polymer injection results in a drastic damping, and the stress maximum is shifted towards the center of the pipe. In a homogeneous polymer solution the maximum of the Reynolds shear stress remains in the same position-as for water. Only in the region of the buffer zone are the shear stresses reduced. 

NMR imaging techniques were applied to the measurements of velocity field in opaque systems such as tomato juice and paper pulp suspensions [58-60]. In both cases, the particle concentrations are sufficiently high that widely applied techniques such as hot film and laser Doppler anemometry could not be used. The velocity profile for a 6 % tomato juice slurry clearly showed a power-law behavior [58, 59]. Row NMR images for a 0.5 % wood pulp suspension provided direct visual of three basic types of shear flow plug flow, mixed flow and turbulent flow as mean flow rate was increased. Detailed analysis of flow NMR image is able to reveal the complex interaction between the microstructure of suspensions and the flow [60]. 

F. Durst, A. Melling, and J. H. Whitelaw, Principles and practice of laser-Doppler anemometry, Academic Press, New York (1976). 

The size and charge analysis was done using a Coulter DELSA 440SX (Coulter Beckman Corp., Miami, FL). This particular instrument measured the size distribution on the basis of photon correlation spectrometry (PCS) and was limited to particle diameters between 0.02 pm and 3 pm. Measurements were taken at four different angles simultaneously with 256-channel resolution each. Comparison of the spectra allowed for the detection of very small particles. The zeta potential was assessed on the basis of electrophoretic mobility (laser Doppler anemometry, LDA). This was defined as the particle velocity per unit of applied electrical field, with units usually given as pm s 1/V cm-1, while zeta potential is defined as the electrical potential between the bulk solution and the... 

PLGA microspheres. Methods to measure the zeta potential of microspheres are laser doppler anemometry [105] and photon correlation spectroscopy [110]. 

Droplet size may be determined with the use of a laser interferometer. This technique is an extension of the laser Doppler anemometry (LDA) technique commonly used to measure velocities of small particles in a flowing stream. Two equal-intensity Gaussian beams are made to intersect at their focal waists to form a standing electromagnetic wave distribution in the intersection (probe) volume. This standing wave can be visualized conceptually as a set of planar fringes perpendicular to the... 

The original Acoustosizer used a single frequency whereas a later development has a range of 13 frequencies between 0.3 and 13 MHz. This allows the measurement of the dynamic mobility spectrum and the determination of the zeta potential and particle size. In order to invert the mobility spectrum into a size distribution a log-normal distribution of particle size is assumed. A comparison with photon correlation spectroscopy for determining particle size and laser Doppler anemometry for particle charge eonfirmed the results using ACS [266]. These and additional sedimentation measurements confirmed that changes in particle size and zeta potential due to dilution effects are likely to occur in aqueous and non-stabilized systems. 

The present work showed the application of different measuring techniques and numerical simulation studies on a selected commercially available tile stove heating insert. For a basic understanding of the combustion process and therefore, for a further improvement of the emission behaviour, gas analysis by means of suction probes, temperature measurements by suction pyrometry as well as velocity measurements by Laser-Doppler Anemometry are carried out within the reaction zones of the stove. 

Ruck, B. (1987) Laser-Doppler-Anemometrie. AT Fachverlag GmbH, Stuttgart, Germany. 

Durst, F., Melling, A., Whitelaw, J. H. (1987) Theorie und Praxis der Laser-Doppler-Anemometrie. G. Braun, Karlsruhe. Germany. 

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