Examination of LDV Using Laser Diode and Measurement Example of In-Cylinder Flow of an Engine

Laser Doppler Velocimeter (LDV) is one of the most useful method to measure the flow velocity of fluid flow such as swirl velocity in an engine. The laser as the light source of LDV has been usually used high power gas laser because of the weak scattering light from particles as in case of back scattered LDV system or loss of light through the optical fibers. In recent years, laser diode of rather high power output and holding coherency was developed. Suggestion of using laser diode as the light source of LDV was shown, but the ability of its utility has not been clearly examined. In this paper, laser diode was examined to use the light source of LDV and was confirmed to be valid when it was correctly controlled. As the proof of validity of laser diode system, measured examples of mean velocity and turbulence intensity were shown in an engine.