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	Laser Doppler Anemometry
Last modified: 01/05/2003
Introduction Laser Doppler Anemometry (LDA) is a technology used to measure velocities of flows or more specifically of small particles in flows. The technique is based on the measurement of laser light scattered by particles that pass through a series of interference fringes (a pattern of light and dark surfaces). The scattered laser light oscillates with a specific frequency that is related to the velocity of the particles. If the flow is perpendicular to the fringes the relation between this frequency fd, and the velocity vx is determined by the angle 2q  between the two intersecting laser beams and the wavelength l0 of the laser light:
The technology has numerous advantages over other techniques. There is for instance no need for physical contact with the flow, so no disturbances occur and the technique can be applied to flows of highly reactive or extremely hot fluids and the like. Furthermore a relatively high spatial resolution can be obtained by focusing the two laser beams. These characteristics make LDA a valuable measuring technique with many applications. For example airflow measurements within combustion engines and airplane engines to improve fuel efficiency, reduce pollution and airplane noise (see also "nasa.gov"-link in Literature).
Learning Objectives Gain knowledge of a modern technology to perform flow velocity measurements Build a simple Laser Doppler Anemometer set up Interpret measured data correctly to establish flow profiles
	Relevant Topics Theory Experimental Design and Measurement Procedure Signal Processing and Data Analysis Example Complications Suggestions for other Experiments Teachers Section Literature
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