Yasushi Takeda

Development of an ultrasound velocity profile monitor

Abstract An ultrasound velocity profile (UVP) monitor has been developed. It utilises a pulsed echographic ultrasound technique and can instantaneously measure a velocity profile along one line in a vector form. The principle and characteristics of the method and the developed systems are described. The results of confirmation experiments have proved that the method measures the velocity profile to high accuracy (5% for velocity and 1% for position). Applications in various configurations demonstrate its efficiency for obtaining spatial information about flow structures as well as its effectiveness in measuring flow in liquid metals.

Velocity profile measurement by ultrasound Doppler shift method

Abstract The application of an external blood flowmeter, an ultrasonic Doppler shift detection device, to the one-dimensional velocity profile measurement of the general flow of water was studied. Experiments were carried out for Poiseuille flow in a 12 mm diameter pipe and for Taylor vortex flow in a roating double cylinder with a 5 mm gap. Measured velocity profiles showed good agreement with theoretical predictions, implying that the device works quite successfully for this purpose.

VELOCITY PROFILE MEASUREMENT BY ULTRASONIC DOPPLER METHOD

Abstract The ultrasonic velocity profile measuring method has been developed at PSI for application in fluid mechanics and fluid flow measurement. It uses pulsed ultrasonic echography together with the detection of the instantaneous Doppler shift frequency. This method has the following advantages over the conventional techniques: (1) an efficient flow mapping process, (2) applicability to opaque liquids, and (3) a record of the spatiotemporal velocity field. After a brief introduction of its principle, the characteristics and specifications of the present system are given. Then examples in fluid engineering for oscillating pipe flow, T-branching flow of mercury, and recirculating flow in a square cavity are described that confirm the methods advantages. Several other works under way by other investigators are introduced. A potential for in-depth study of fluid dynamics is demonstrated by several examples from an investigation of modulated wavy flows in a rotating Couette system. The position-averaged power spectrum and the time-averaged energy spectral density were used to study the dynamic characteristics of the flow, and subsequently the velocity field was decomposed into its intrinsic wave structure based on two-dimensional Fourier analysis.

Measurement of velocity profile of mercury flow by ultrasound doppler shift method

The ultrasound velocity profile monitor has been developed. It utilizes the pulsed echo techniques of ultrasound, and it can measure the velocity profile quasi-instantaneously. Its applicability to flow in mercury was investigated, and measurements for bifurcating flow in a T tube were made. Profiles were obtained for different configurations of measuring lines and flow directions, and lengths of flow fields were evaluated and compared with the pipe lengths. Results showed good agreement, implying that the method can measure the velocity profile in liquid-metal flows successfully.

Collective behavior of wakes downstream a row of cylinders

This experimental study is devoted to visualisation and ultrasonic velocity measurement of the wakes formed behind a row of parallel cylinders placed side by side, perpendicular to an incoming flow at low Reynolds numbers. When the distance separating the cylinders is small compared to their diameter, two instability mechanisms, associated with different patterns and dynamics compete. A first spatial symmetry breaking appears when the stationary wakes behind each cylinder are deviated towards one side or the other and form large clusters containing from two to sometimes more than ten wakes. These clusters are separated by intense recirculating zones. When the Reynolds number is increased, the wakes belonging to the widest clusters experience a secondary temporal oscillatory bifurcation. Classical Benard‐Von Karman vortex streets are thus shed in phase by these cylinders (acoustic mode), by contrast with the wakes outside these cells which stay stationary. Finally, the flow around far apart cylinders is al...

Decomposition of the Modulated Waves in a Rotating Couette System

The time-dependent velocity field in a rotating Couette system has been decomposed. Successive instantaneous velocity profiles were obtained by an ultrasonic Doppler velocity profile method, and the spatiotemporal velocity field had been analyzed by two-dimensional Fourier transform. The Fourier spectrum is depicted by intrinsic peaks, and the velocity field cpan be reconstructed with these peak components only, indicating a successful decomposition of the velocity field. This method shows that the so-called broadband component, which is purely spatiotemporal and attributed to chaos, corresponds to a global motion of the wave propagating from roll to roll.

High time resolution ultrasonic velocity profiler

Abstract The objective of the present study is to develop a high time resolution ultrasonic velocity profiler (UVP) system by improving a signal processing and apply it to turbulent flow. The UVP system is able to obtain one-dimensional velocity distribution on an ultrasonic beam line from echo signals reflected at tracer particles. The position is determined from a time delay between emission of ultrasound pulse and reception of corresponding echo signals. The time resolution of conventional UVP systems is limited to the order of 10 ms at the best due to its signal processing technique, that needs more than a few ten echo signals to obtain the velocity distribution. In order to improve the time resolution of the UVP, we use a cross-correlation technique to estimate a time difference between two echo signals of a pair of emissions of ultrasound pulses. The pipe flow was examined by the present UVP system with the new signal processing. The result showed in a good agreement with that of laser doppler velocimetry measurement. In this experiment, we could improve the time resolution of UVP up to 500 μs to obtain a line profile of velocities and demonstrated a possibility to realize measurements of a smaller time scale velocity fluctuation in flows.

Velocity profile measurements of magnetic fluid flow using ultrasonic Doppler method

Abstract In the present study, successful applications of the ultrasound velocity profile measuring technique to velocity fields of a magnetic fluid are presented. After a brief introduction of its principle, various examples applied for the magnetic fluid flow are demonstrated.

observation of the transient behaviour of Taylor vortex flow between rotating concentric cylinders after sudden start

Transient behaviour of Taylor vortex flow between rotating concentric cylinders after sudden start has been observed by measuring axial velocity distributions Vz(z) for Reynolds number between 70–1,300. We found that a somewhat noisy roll structure is established at an early time after the start. Azimuthal partial rolls can exist and fusions of rolls occur. These phenomena dissipate, and while definite sizes and locations of the rolls are adjusted, the system approaches the ordered structure steady state. The time needed for this transient process is in the order of (or shorter than) the diffusion time.

Spatial characteristics of dynamic properties of modulated wavy vortex flow in a rotating Couette system

Time-dependent velocity profiles Vz(z, t) have been measured in a cylindrical Couette system for a range of Reynolds numbers corresponding to wavy vortex flow (WVF) and modulated wavy vortex flow (MWV). The spatial distribution of the power spectrum was obtained and the behaviour of the dynamic properties of WVF and MWV was investigated with respect to Reynolds number (Re) at four corners of cells (inside-outside and Inflow-Outflow). All modes of f1, f2 and B were found to be equally strong and broad at different corners for lower Re number. At large Re, however, f2 remains broad only at the outside-Inflow corner, while B is strong at Outflow. It was also found that B disappears at the outside-Inflow corner for R* > 18. These results suggest that the dynamic properties of WVF and MWV would have a spatial dependence within a cell structure scale.