Ultrasound Velocity Profile Research Articles

Ultrasonic Doppler method for velocity profile measurement in fluid dynamics and fluid engineering

An Ultrasound Doppler Velocity Profile method (UVP method) has been developed for fluid mechanical measurements in physics and engineering. The principle of the method is straightforward; echography and Doppler effect. This method was originally developed in medical engineering to measure blood flow. However, due to various constraints arising from its direct application to the human body, the measurement method never realized its full potentiaL We subsequently extended this method to non-medical flow measurements and developed specific application systems. Although the initial motivation was to find a new flow measurement method for liquid metal flows, the method itself was found to be quite useful to flow measurements in general and additionally through years of use has gradually become accepted as a tool to study the physics and engineering of fluid flow. In the sections to follow we \vill describe the measurement method and review the applications to date.

Kinematic characteristics of magnetic fluid sloshing in a rectangular container subject to non-uniform magnetic fields

The dynamic behavior of a magnetic fluid in a laterally vibrated rectangular container subject to a non-uniform vertical magnetic field has been investigated. Flow behavior was observed using the ultrasound velocity profile measuring technique. The effect of the magnetic field on the resonant frequency of the fluid-container system is discussed. Experimental results are compared with the results obtained from nonlinear theory using the perturbation method.

Modeling of Concentration Profiles and Ultrasound Velocity Profiles in a Creaming Emulsion: Importance of Scattering Effects

A computer model which simulates the creaming behavior of a concentrated, nonflocculated polydisperse emulsion is presented. The model includes the effects of hydrodynamic hindrance and thermal diffusion. Concentration profiles for the total volume fraction and for an individual particle size, along with the size distribution, are presented. Numerical results are also presented for ultrasound velocity as a function of sample height, since ultrasound is being increasingly used experimentally to observe the creaming process in concentrated colloidal systems. The velocity is calculated from the Urick equation and also from single- and multiple-scattering theory. Results are presented for two idealized emulsion systems, 20% hexadecane in water, and 10% sunflower oil in water using a log-normal size distribution centered on a diameter of 0.72 μm. It is concluded that the effects of scattering are considerable in these emulsions, especially in the concentrated cream layer. The Urick equation is insufficient to interpret ultrasound velocity data in these systems. Strategies for minimizing and accounting for the errors due to scattering effects are given. The model predicts that a considerable variation in average particle size occurs within the cream layer, and that this significantly affects the ultrasound velocity profile.

Automation of ultrasound velocity scanning for concentrated dispersions

There have been a number of reports of the scanning of concentrated emulsion and suspension systems to obtain ultrasound velocity profiles which are subsequently converted to concentration profiles. These have contributed significantly to the understanding of sedimentation and creaming behaviour. The systems described have generally required manual intervention to measure the ultrasound velocity at each vertical level. For scans which can possess upwards of 100 individual measurements, each taking a significant time (minimum 30 s), the approach is tedious and limiting for dynamic systems. This paper describes an approach to an automated system which utilises an inherently highly accurate ultrasound velocity measuring technique, the sing-around technique. The method is modified to deal with problems of variable ultrasound attenuation and interference, which potentially present some limitations to the application of even the sing-around technique. The result is a “black box” which provides the basis of an automated ultrasound velocity scanner system without the need for relatively expensive signal generation equipment. The results obtained in terms of concentration profiles compare well in terms of volume fraction values with the established manual technique, with each scan point being obtained at least an order of magnitude faster than by the manual technique. Measurement of times of flight to within 1 ns in 30 μs is possible using the modified sing-around approach, compared with 5 ns in 30 μs for the manual pulse comparison technique.

Measurement of flow phenomena using the ultrasonic velocity profile method in a simulated Czochralski crystal puller

An experimental investigation of flow phenomena in a simulated Czochralski (CZ) crystal puller was conducted using an ultrasound velocity profile (UVP) probe to measure fluid velocities. To isolate the various forces that influence the fluid motion, only the crystal was rotated and a water-glycerol mixture was used as the test fluid in this experiment. Measurements of the velocity components, V z and V r , under the initial transient from zero rotation to a set rotation rate as well as under steady-state conditions were made. The corresponding Reynolds number based on the crystal radius and rotation varied from Re Ω , x ≈ 660–5000 (Ω x ≈ 110–2000 rpm). The measured velocity profiles, V z and V r , were processed using a simple color image scheme based on the magnitude and direction of flow with respect to the probe. These profiles were studied to postulate flow patterns in the simulated CZ device. The measurements revealed three major regions of flow: (1) one beneath the crystal, (2) one near the free surface and crucible wall and (3) one beneath the crystal and occupying the extent of the crucible. In the initial transient, spatially symmetric outward flow beneath the crystal developed until the recirculating flow from below disturbed this pattern. At this point the apparent shear between the flow beneath the crystal and that circulating upwards from the bottom of the crucible induced flow instabilities and a non-axisymmetric flow pattern. The non-axisymmety was verified by the color-coded velocity profiles and a power spectrum analysis. The analysis revealed the critical Reynolds number for the onset of the primary instability to be Re Ω crit ≈ 669. The linear variation in the power of the primary peak with the Reynolds number indicates that the onset of the axisymmetry-breaking instability is due to Hopf bifurcation.

Development of an ultrasound velocity profile monitor

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.

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...

A new pulsatile flow visualization method using a photochromic dye with application to Doppler ultrasound.

A nonintrusive method for the visualization of pulsatile flow velocity profiles is described. The method is based on the use of a photochromic dye that is added to the fluid being studied and a nitrogen laser which excites the dye producing a marker "line" whose movement can be photographed. A microcomputer is used as a system controller, to coordinate the system timing and to manage the data transfer. The method used for analysis of the photographs to determine the velocity profiles is described. Examples are presented of instantaneous velocity profiles obtained from velocity waveforms that are similar to those of the femoral artery. In addition, application of the system for studying the relationship between Doppler ultrasound spectral recordings and flow velocity profiles is discussed.

Model studies of the pressure and flow pulses in a viscoelastic arterial conduit

In certain arteries the flow rate of blood can now be quantified by a non-invasive technique based on a newly developed ultrasound velocity profile meter. Clinical applications of this technique indicate that a reliable mathematical model of the circulatory system would facilitate the identification of pathologic patterns of flow rate and the corresponding possible causes. A relatively simple law for the viscoelastic behavior of arterial conduits is hypothesized and its influence on the phasis variations of pressure and flow examined with the aid of the method of characteristics. To test the feasibility of this model, its predictions of the attenuation and dispersion of small sinusoidal pressure waves are compared with data obtained in animal experiments. The results show good agreement and verify the significance of taper in reducing the attenuation of waves propagating towards the periphery and conversely increasing the damping of waves moving towards the heart. Beside this the natural pressure and flow pulses generated by the heart appear to be attenuated in a realistic manner: they no longer exhibit the somewhat exaggerated peaking predicted by the theoretical model when the viscoelasticity of the vessel wall is neglected.