Aero-engine applications of laser anemometry

The measurement of flow inside an aero-engine or component rig is made difficult by the hot, high-pressure environment, problem of access, and the requirement not to disturb the flow. Laser anemometry offers an almost ideal solution to several of these problems and has been used under laboratory conditions for several years. However, because it is extremely difficult to add particles evenly to the very high mass flow involved, methods based on the naturally occurring particles in the flow have been developed and are described here. The information available from the light signal scattered from particles in a flow is examined and a real fringe system with fringe counting or photon correlation is chosen as the most useful processing method for laser anemometry in this situation. Measurements obtained from engine component rigs using a counting system are presented together with measurements from several aero-engines obtained using photon correlation. All results were obtained using a 15-mW HeNe laser.