A Laser-Two-Focus (L2F) Velocimeter for Automatic Flow Vector Measurements in the Rotating Components of Turbomachines

Numerous results—most of them are published—have proved the applicability of the L2F-velocimeter to experimental studies of the complex compressor flow: e.g. the blade wakes and the shock-wave system within the blade passages. Furthermore, measurements close to the compressor surfaces provide information about boundary layers and flow separation. However, the measuring procedure is rather time-consuming. It takes about one hour to accumulate 10 to 15 vector measurements within a rotor blade channel. This paper presents a technique whereby the measuring time is reduced by a factor of ten. Mathematical considerations of the L2F-signal statistics lead to a modified calculation model and a new measuring procedure. Now, about 100 to 150 flow points can be acquired in one hour which includes the magnitude and direction of the mean flow vector as well as its turbulent components. This paper describes the innovations in optics, operational procedures, and electronics that have resulted in an enhanced state-of-the-art in flow measurement. Experimental results are also submitted and discussed.