Laser Doppler Anemometry

The purpose of this experiment is to determine the shape of the trailing trail behind the cylinder. Decide the calibration of the water tunnel. Both of these goals are achieved using LDA (Laser Doppler Velocimeter). LDA is one of the main speed measurement methods used in professional experiments. The beam is directed at the water flowing from the laser. In Target 1 we will immerse the cylinder in the water stream to determine how to disturb the rear speed of the cylinder. The second goal is to use LDA water without interference.

Other techniques for measuring flow are laser Doppler velocimeters and hot wire wind speed measurements. The main difference between PIV and those techniques is that the PIV generates even a two or three dimensional vector field, while other techniques measure the velocity at a single point. During PIV, particle concentration makes it possible to discriminate individual particles in an image, but it is not certain to track it between images. If the particle concentration is too low to trace a single particle, it is called particle tracking speed, and laser speckle speed is used if the particle concentration is too high to see individual particles in the image.

Laser Doppler velocimeters are used in laser and digital analysis systems before PIV and are widely used in research and industrial applications. The ability to obtain velocity measurements of all fluids at a particular point can be viewed as a direct precursor to 2 dimensional PIV. PIV itself was derived from the laser speckle speedometer, the technology that some groups began experimenting in the late 1970s. In the early 1980's it was found to be advantageous to lower the particle concentration to the level at which individual particles can be observed. At these particle densities it is easier to study the flow if they are divided into several very small "survey" regions, and these regions are analyzed separately and the velocity of each region Can be produced. Images are usually recorded using analog cameras and require a large amount of computing power to analyze.

Scientists now have high precision tools to measure the position of the continent and the size of the earth. Satellite laser ranging, Very long baseline interferometry, GPS, Doppler satellite measurements. These measurements have been periodically calculated and revised since the late 1980s and provide clear evidence that the size of the earth remains essentially the same. As the debris of the universe continues to fall on the earth, a slight increase is expected - NASA predicts a meteoroid body of about 100 tons per day. But most of it was burned by the atmosphere and dust fell to the surface of the earth. Fragments add little or no mass, but they are not enough to support the growing Earth theory.