Laser velocimetry

This procedure offers the possibiUty of remote noncontact velocity measurement, where no probes disturb the flow. It is thus compatible for use with hot or corrosive gases. Commercial laser velocimeters have become weU-developed measurement tools. Examples of laser velocimetry include remote measurement of wind velocity, measurement of vortex air flow near the wing tips of large aircraft, and in vivo measurement of the velocity of blood flow. 

Many laser-based droplet diagnostic techniques have evolved from the fields such as spray combustion and spray drying. Phase-Doppler particle analyzer is now recognized as the most successful and advanced diagnostic instrument for spray characterization. Other proven diagnostic techniques include laser velocimetry and... 

By contrast, laser scattering methods now permit temperature composition and flow measurements that are both nonintrusive and give very high spatial resolution. These light scattering methods include laser Raman spectroscopy, laser-induced fluorescence, coherent Raman spectroscopy as well as laser velocimetry... 

Here, Instantaneous Value X = Mean Value X + Fluctuation Value X LV denotes laser velocimetry RS, Raman scattering, RayS, Rayleigh scattering and pdf, probability density function. 

Time- and space-resolved fluctuation data for flame gas temperature and major species densities have been obtained from Raman scattering and from stronger inelastic scattering processes. When combined with information about velocity from laser velocimetry, these data and their correlations provide key new information for flow field and combustion field modeling. 

We present here preliminary results for the (temperature x vj ljjcity) probability density function shown in this paper as , where the quantities within the average brackets are instantaneous values. These data have been obtained from a coordinated experimental program utilizing pulsed laser vibrational Raman scattering and cw real fringe laser velocimetry (LV). 

Figure 5. Current overall optical layout for laser velocimetry and Raman scattering diagnostics, shown here on new fan-induced square-cross-section movable combustion tunnel. Note the co-linear Raman and LV probe laser source axes and the colinear detection optics.

A significant advantage of the technique is that the equipment requirements are relatively modest and share a strong commonality with equipment and data analysife required for correlation or spectral density measurements, and laser velocimetry. 

Local measurements by using laser velocimetry, marking the flowing polymer or by optical techniques [12]. 

It thus appears necessary to perform experimental studies to zmalyze and elucidate the physics of this type of flow. The experimental conditions must therefore be carefully controlled to avoid introducing further difficulties that would make interpretation of the results even more complicated. Hence it must be possible to cheu-acterize the fluids by their specific properties (rheometry, molecular characteristics, etc.). The experimental techniques (visualization, laser velocimetry, etc.) must also be varied or adapted so as to break free of technological limitations and widen the field of investigation as much as p>ossible. Lastly, a minimum of care must be taken when interpreting the experimental results, in order to provide consistent interpretations of the phenomena observed and the mechanisms involved in their appearance and evolution. 

Radiation which is scattered from a moving particle is shifted in frequency by the Doppler effect the magnitude of the Doppler shift allows an exact determination of the velocity of the object. Laser velocimetry in biology and medicine is reviewed by Ware 24). 

Lading, L. Spectrum Analysis of LDA Signals. Proc. of The Use of Computers in Laser Velocimetry, ISL, France, paper 20 (1987)... 

The above remarks point out the interest of direct measurements of the boundary condition (BC) for the fluid velocity at a fluid solid interface. To obtain reliable information on the flow velocity BC of a fluid, with a spatial resolution from the wall down to molecular sizes, is a particularly difficult challenge. Conventional velocimetry techniques (even laser velocimetry) are far from such a resolution. We have developed a near field laser velocimetry technique which allows to increase significantly the spatial resolution compared to more conventional velocimetry techniques. This technique has been used to characterize the friction between a polymer melt and a solid wall and to understand how surface modifications weakening the interactions between a solid and a given simple fluid affected the fluid -- wall friction. 

Principle of the Near Field Laser Velocimetry technique... 

J.D. Pendleton, Mie and Refraction Theory Comparison for Particle Sizing with the Laser Velocimetry, Applied Optics, 21 (1982) 684-688. 

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