Acoustical technique for Lagrangian velocity measurement

2012

A novel approach for measuring the speed of sound in fluids with scattering particles is presented. Potential fields of application for sound velocity measurements in fluids are process control, environmental measurement technology and medicine, where sound velocity can be used as an indicator of temperature, concentration or mass density. Similar to the pulsed Doppler application, the method also works non-invasively and uses the echo signals from scattering particles suspended in the fluid. The basic idea is that the ultrasonic time of flight to the focus position z depends on the speed of sound c in a well-defined way. The time of flight to the focus can be extracted from the echo signals, because the stray echo is strongest for the scattering particles being located in the sound focus and can thus be used to determine the speed of sound. Results are shown for different homogeneous fluids with sound velocities between 1116 m/s (ethanol, 50 °C) and 2740 m/s (eutectic GaInSn). Meas...

1997

An approximate solutlon for the strearning velocity generated by flat and weakly focused transducers was derived by directly solving the Dirichlet boundary conditions for the Poisson equation. The theoretical calculations were verified using a purpose-designed 32 N1Hz pulsed Doppler unit. The applied average acoustic power was changed from l IlW to 6 mW. The experiments were done on 4 mm diarneter flat and focused transducers. The streaming velocity was measured along the ultrasonic beam from O to 20 mm. Streaming was induced in a solution of water and com starch. The experimental results showed that for a given acoustic power the streaming velocity was independent of the starch density in water changed from 0.3 grams to 40 grams of starch in l litre of distilled water. For applied acoustic powers, the streaming velocity changed Iinearly from 0.2 to 40 mm/s. Both, the theoretical solutions for pIane and focused waves, and the experimentaJ resuJts were in good agreement.

A Laser Doppler Velocimeter is an optical measurement device used for estimating particle velocities, by means of specific signal processing of the light scattered by seeding particles. The velocimeter set-up we used has been adapted in order to measure acoustic particle velocities in gases. In previous works, specific signal processing methods have been developed for harmonic acoustic fields in ducts without flow. Then, the aim of this study is to measure the velocities of harmonic acoustic fields in free space with flow ; signal processing methods, estimating both flow and acoustic velocities, are presented, and their limits are discussed.

Ultrasonics Symposium (IUS), 2009

The challenge of remotely measuring fluid flow through a plane of interest for a wide range of velocities is addressed using an array of ultrasonic transducers. Unlike traditional transit-time ultrasonic flow measurements, the proposed method uses the angle-of-arrival of a reflected ultrasonic wave to measure flow perpendicular to the path of propagation. The use of angle-of-arrival information avoids the inherent requirement of transit-time techniques to have a non-negligible directional component of the propagation path in the flow direction. A successful proof-of-concept was developed to experimentally validate the proposed technique.

2005

The performance (or quality) of a product is often checked by measuring the radiated sound (noise) from the vibrating structure. Often this test has to be done in an environment with background noise, which makes the measurement difficult. When using a (pressure) microphone the background noise can be such that it dominates the radiated sound from the vibrating structure. However, when using a particle velocity sensor, the Microflown [1,2], near the vibrating structure, the background noise has almost no influence (it is almost cancelled) and the sound from the structure is measured with a good S/N ratio. The experimental results are explained in terms of the different boundary conditions at the surface of the vibrating structure for the pressure and the particle velocity.

2003

Comparative flow field measurements in the inlet channel of a hydroelectric power plant were per- formed using an acoustic Doppler probe and an acoustic Doppler profiler. Measurements with a single probe, traversing the entire cross section, are very time consuming. On the other hand measurements with a velocity profiler demand little installation effort and can be performed within short time periods. This advantage, however, comes along with a higher measuring uncertainty. Qualitative comparison showed good agreement of the measured velocity distributions. The results matched also quantita- tively well in case of good signal correlation and if erroneous data due to reflected acoustic signals are rejected.

EPJ Web of Conferences

This paper introduces research and development of a modern non-invasive device for determining flows and velocity fields. This device is based on the ultrasonic method. The measured fluid flow is surrounded by appropriate ultrasonic transmitters and receivers, which communicate with each other. A physical principle of this method consists in an interaction of sound waves with a flow, which generates a certain delay in sound waves transmission. The found quantity is thus time delay. The device is being designed as a flowmeter and with advanced and extended postprocessing as a tomograph, which reconstructs a 3D vector field for big volumes. This whole process requires the following: development of an appropriate design of the ultrasonic flowmeter and tomograph, testing the signal transfer and also various postprocessing methods on a measurement accuracy, building of a special verification experimental equipment and building of an electronic device as a control unit and data acquisitio...

Measurement Science & Technology, 2003

Journal of the Acoustical Society of Japan (E), 1994

A new method is described for non-contact measurement of particle velocity distribution along an elastic bar excited by a PZT transducer. By analyzing two signals measured by a laser Doppler velocimetry (LDV) from two incident angles, the particle velocity distribution for each of the two components, normal and parallel to the bar axis, is separately obtained. The principle of the proposed measurement method is confirmed by the experiments using a Langevin type PZT transducer having a resonant frequency of 17 kHz. The sensitivity of this method is enough high to measure the particle velocity less than 12 ƒÊm/s at the resonant frequency of 17 kHz.