Velocimeter

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. 

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. 

Sullivan, J. R, Windnall, S. E., and Ezekiel, S., Study of vortex rings using a laser Doppler velocimeter, AIAA Journal, 11, 1384-1389, 1973. 

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High Pressure Sound Velocimeters. As discussed earlier, sound velocity measurements can yield precise compressibilities of solutions. Wilson (109) was the first to develop a high pressure sound velocimeter that could be used over a wide range of pressures and temperatures. He used the "sing around" system to measure the high pressure sound speeds of water (109), D2O (120), and seawater (121) to a precision of 0.2 m sec l which is equivalent to 0.012 x 10 bar- in 6s Barlow and Yazgan... 

The system was calibrated with water and the sound path (A) was found to increase slightly as the pressure is increased (assuming t is independent of pressure) (112). Since we are interested in measuring the relative speed of sound (Au) in aqueous solutions, we use the velocimeter in a differential mode. The value of t is not a function of pressure (or temperature), as the electronics are kept under ambient pressures. The values of Au were determined from... 

Figure 12, Sketch of the high pressure sound velocimeter (A) constant temperature bath (B )bomb stand (C) pressure bomb (D) plug (E) transmitting transducer (F) reflector (G) O-ring (112)...

Wj) Velocimeter (Radar) Test. The purpose of this test, developed at PicArsn, is to track by radar high-velocity artillery projectiles as well as mortar rounds during their flights. This is done in order to obtain continuous informa tion on the in-flight velocities and on any changes in the projectile (such as projectile breakup) that occur in flight. The radar that has been used at PicArsn is the modified HAWK (p HIB-21 of Ref 39)... 

Benton s Electro-Ballistic Pendulum. An instrument used in Springfield Armory and Frank-ford Arsenal in the 1870 s for detn of velocities of projectiles. A modified model was known as Thread Velocimeter... 

Thread Velocimeter. See under Benton s Electro-Ballistic Pendulum in Vol 2, B34-R... 

Figure 6.1 Optical configuration for a laser Doppler velocimeter.

Schematic diagram showing the integration of a polarization modulated birefringence apparatus within a laser Doppler velocimeter. This shows the side view. L light source (a diode laser was used) PSG rotating half-wave plate design LS lens FC flow cell (flow is into the plane of the figure) CP circular polarizer D detector 2D-T two dimensional translation stage 3D-T three dimensional translation stage LDVP laser Doppler velocimeter probe.

The current status of prediction and modelling in the area of fuel spray combustion requires, among other parameters, the measurement of droplet or solid particle size distribution and the relative velocity between the fuel and the surrounding gas. Many optical techniques, based on laser light scattering, have been investigated to this purpose (Refs.1,2,2,]+,, 6 and j), but the only system able to simultaneously determine the size and the velocity is the dual-beam laser Doppler velocimeter shown in Figure 1. 

Flack, R. D., and C. L. Witt Velocity Measurements in Two Natural Convection Air Flows Using a Laser Velocimeter, J. Heat Transfer, vol. 101, p. 256, 1979. 

In measurement and visualization of gas-solid flow in fast fluidization, various techniques have been developed and used, such as pressure gradient, pressure fluctuation, capacitance probe, optical fiber probe, momentum probe, laser Doppler velocimeter, night-television, and video camera. The resulting data on local gas and solid velocity, solids concentration and its... 

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