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

Abstract

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.

Experimental investigation of axial fan erosion and performance degradation

“…The diameter of the focused beam (spot) is about 10 mm with a separation distance of approximately 0.2 mm [9], which makes a light gate in which a particle passing through produces two successive pulses stored in memory. As a result, a spectrum representing a number of measured flight time intervals is obtained [10,11]. This information provides the flight time but not the flow direction, which is obtained by taking measurements at different spot orientations and noting which orientation provides the greater number of successful transits.…”

Inlet Flow Angle Determination of Transonic Compressor Cascades

“…A comparison ofs the measured surface Mach number distribution (Schreiber 1981) to a viscous calculation for a transonic cascade is shown in Fig.4. In this case, the inlet flow angle was measured by a Laser Two Focus system (Schodl 1980). The Mach number distributions agree quite well on the pressure side and also on the first 30% of chord on the suction side of the blade.…”

An Investigation of a Strong Shock-Wave Turbulent Boundary Layer Interaction in a Supersonic Compressor Cascade

“…A non-automated Laser-2-Focus anemometer (L2F) (Schodl, 1980) was used for velocity and flow angle measurements in the region of shock-wave/boundary layer interaction, which included the blade suction surface boundary layer at different midspan positions downstream of 58 percent of chord. The L2F anemometer operated in a back scatter mode and had the following characteristics:…”