Two-dimensional ultrasound Doppler velocimeter for flow mapping of unsteady liquid metal flows.

We present a novel pulsed-wave ultrasound Doppler system for fluid flow investigations being able to determine two-dimensional vector fields of flow velocities. Electromagnetically-driven liquid metal flows appear as an attractive application field for such a measurement system. Two linear ultrasound transducer arrays each equipped with 25 transducer elements are used to measure the flow field in a square plane of 67×67 mm(2). The application of advanced processing methods as a multi-beam operation, an interlaced echo signal acquisition and a segmental array technique enable high data acquisition rates and concurrently a high spatial resolution, which have not been obtained so far for flow measurements in liquid metals. The extended pulsing strategy and essential operation principles such as the multiplexing electronic concept will be presented within this paper. The capabilities of the measuring system make it suitable for investigations of non-transparent, turbulent flows. Here, we present measurements of liquid metal flows driven by a rotating magnetic field for demonstration purposes. The measuring setup realized here reveals details of the swirling fluid motion in a horizontal section of a cube. Frame acquisition rates up to 30 fps were achieved for a complete two-dimensional flow mapping.

Laser Doppler distance sensor using phase evaluation.

This paper presents a novel optical sensor which allows simultaneous measurements of axial position and tangential velocity of moving solid state objects. An extended laser Doppler velocimeter setup is used with two slightly tilted interference fringe systems. The distance to a solid state surface can be determined via a phase evaluation. The phase laser Doppler distance sensor offers a distance resolution of 150 nm and a total position uncertainty below 1 microm. Compared to conventional measurement techniques, such as triangulation, the distance resolution is independent of the lateral surface velocity. This advantage enables precise distance and shape measurements of fast rotating surfaces.

Method for analysis of the fundamental measuring uncertainty of laser Doppler velocimeters.

A method is presented for analysis of the relationship of the velocity measuring uncertainty and the system parameters of laser Doppler velocimeters. The method permits optimization of the laser Doppler system to minimize the uncertainty of fluid velocity measurements.

Heterodyne detection technique using stimulated Brillouin scattering and a multimode laser.

We present, for the first time to our knowledge, the use of multiple axial laser modes in distributed temperature sensing based on stimulated Brillouin scattering. One axial mode stimulates a Stokes wave with a temperaturedependent Brillouin frequency shift in the 13-GHz range. Optical heterodyning of the stimulated Stokes wave with a second axial laser mode allows one to generate and evaluate a beat signal in a lower frequency range. Using diode-pumped solid-state lasers, we have reduced the Brillouin beat frequency to the 500-MHz range. Hence, low-cost detectors and conventional signal-processing techniques can be applied for the beat signal processing.