Ultrasonic Doppler Velocimetry Research Articles

The global flow state in a precessing cylinder

We examine the fluid flow forced by precession of a rotating cylindrical container using numerical simulations and experimental flow measurements with ultrasonic Doppler velocimetry. The analysis is based on the decomposition of the flow field into contributions with distinct azimuthal symmetry or analytically known inertial modes and the corresponding calculation of their amplitudes. We show that the predominant fraction of the kinetic energy of the precession-driven fluid flow is contained only within a few large-scale modes. The most striking observation shown by simulations and experiments is the transition from a flow dominated by large-scale structures to a more turbulent behaviour with the small-scale fluctuations becoming increasingly important. At a fixed rotation frequency (parametrized by the Reynolds number, $Re$ ) this transition occurs when a critical precession ratio is exceeded and consists of a two-stage collapse of the directly driven flow going along with a massive modification of the azimuthal circulation (the zonal flow) and the appearance of an axisymmetric double-roll mode limited to a narrow range of precession ratios. A similar behaviour is found in experiments which make it possible to follow the transition up to Reynolds numbers of $Re\approx 2\times 10^6$ . We find that the critical precession ratio decreases with rotation, initially showing a particular scaling ${\propto }Re^{-({1}/{5})}$ but developing an asymptotic behaviour for $Re\gtrsim 10^5$ which might be explained by the onset of turbulence in boundary layers.

Effect of hemispherical ash slag simulants on the thickness distribution and fluctuation characteristics of turbulent liquid film

To explore the influence of ash slag adhering to the scrubbing-cooling tube on the turbulent falling film flow, three hemispheres with different radii (R = 2 mm, 4 mm, and 6 mm) were used to simulate the slag. Ultrasonic Doppler Velocimetry was used to investigate the liquid film’s thickness distribution and fluctuation characteristics under Reynolds number of liquid film Ref ≈8.75 × 103 ––2.63 × 104. The liquid film thickness distribution at low Reynolds numbers exhibits an isosceles triangle when subjected to R = 4 mm and 6 mm hemispheres. At high Reynolds numbers, the average thickness of the liquid film is smaller downstream of the three simulants. The simulants can enhance the liquid film’s perturbations. A mathematical model has been established to predict the mean liquid film thickness on hemispherical simulants, and the relative difference is within 10 %. The probability density distribution curves of the instantaneous liquid film thickness on the simulant exhibit multimodality.

Numerical Analysis of Water–Sediment Flow Fields within the Intake Structure of Pumping Station under Different Hydraulic Conditions

The vortices, backflow, and siltation caused by sediment-laden flow are detrimental to the safe and efficient operation of pumping stations. To explore the effects of water–sediment two-phase flow on the velocity field, vorticity field, and sediment distribution within intake structures, field tests and numerical simulations were conducted in this study with consideration for the sediment concentration, flow rate, and start-up combination. We applied a non-contact laser scanner and ultrasonic Doppler velocimetry to obtain the field data and reverse modeling of the three-dimensional model of the intake structure under siltation. A multiphase flow model based on the Euler–Euler approach combined with the k-ε turbulence model was adopted for numerical simulation under 10 working conditions, and the reliability was verified with field data. The results indicate that sediment promotes the evolution of coaxial vortices into larger-scale spiral vortices along the water depth, and the process of sediment deposition is controlled by the range, intensity, and flow velocity of the backflow zone. Furthermore, the maximum volume fraction of the near-bottom sediment increased by 202.01% compared to the initial state. The increase in flow rate exacerbates the turbulence of the flow field. Although the increase in sediment concentration benefits the flow diffusion, it further promotes sediment deposition. This study provides a new idea for modeling complex surfaces and considers different operating conditions. It can serve as a scientific reference for the structural optimization and anti-siltation design of similar water-conservancy projects.

Evolution of turbulent liquid films on the corrugated plate—rivulets and slender water columns necking rupture

The evolution of turbulent liquid film on the corrugated plate is experimentally studied with the help of ultrasonic Doppler velocimetry and a high-speed camera, revealing the formation mechanism of rivulets and water columns necking rupture. The results show that the flow pattern of the liquid film on the corrugated plate is divided into three regions: stable region, fluctuating region, and oscillating region. In the fluctuating region, the connection between adjacent solitary waves leads to the generation of primary rivulets. In contrast, the formation of secondary rivulets mainly comes from the extinction of solitary waves. In the oscillating region, the collision between secondary rivulets promotes the formation of slender water columns. The necking diameter of the water column tended to decrease exponentially with time. The increase in Rel (liquid phase Reynolds number) promotes the necking rupture process of the water column due to the presence of corrugated structures. When Rel increased from 1.72 × 104 to 2.57 × 104, the characteristic time of necking rupture was shortened by about 25.7%.

Laboratory model of electrovortex flow with thermal gradients for liquid metal batteries

We present a novel laboratory setup for studying the fluid dynamics in liquid metal batteries (LMBs). LMBs are a promising technology suited for grid-scale energy storage, but flows remain a confounding factor in determining their viability. Two important drivers of flow are thermal gradients, caused by internal heating during operation, and electrovortex flow (EVF), induced by diverging current densities. Our setup explores thermal gradients and electrovortex flow separately and in combination in a cylindrical layer of liquid gallium, simulating the behavior in a single layer of an LMB. In this work, we discuss the design principles underlying our choices of materials, thermal control, and current control. We also detail our diagnostic tools - thermocouple measurements for temperature and Ultrasonic Doppler Velocimetry (UDV) probes for velocities - and the design principles which go into choosing their placement on the setup. We also include a discussion of our post-processing tools for quantifying and visualizing the flow. Finally, we validate convection and EVF in our setup: we show that scaling relationships between the nondimensional parameters produced by our data agree well with theory and previous studies.

Vortex breakdown in time-dependent electromagnetically driven flow between concentric spheres

The electromagnetically driven flow in the wide gap of a concentric sphere system is studied experimentally and numerically in the laminar regime (Re≤1540). The azimuthal driving Lorentz force is primarily promoted by the interaction of a direct current and a dipolar magnetic field. The current is injected through two ring-shaped copper electrodes located at the equatorial zone of each sphere, and the magnetic field is produced by a permanent magnet located inside the inner sphere. Velocity profiles for the azimuthal component in the equatorial plane were obtained with particle image velocimetry, and the radial velocity component of the flow was recorded using ultrasonic Doppler velocimetry. Laser-fluorescein technique was used for flow visualization. It was found that for a critical electric current (Re = 1140), an instability occurs and the flow becomes time-dependent. We found, theoretically and experimentally, a vortex breakdown structure at each of the polar zones of the spherical gap, and to the best knowledge of the authors, this is the first time it is reported with electromagnetic forcing. A full three-dimensional numerical simulation reproduces the experimental observations qualitatively and quantitatively.

Endometrial thickness and uterine artery Doppler parameters as soft markers for prediction of endometrial cancer in postmenopausal bleeding women: a cross-sectional study at tertiary referral hospitals from Vietnam.

ObjectiveTo determine the value of endometrial thickness (ET) and Doppler indices of uterine artery (UtA) as sonographic markers in predicting endometrial cancer (EC) among postmenopausal bleeding (PMB) women in low-resource settings as Vietnam.MethodsThis cross-sectional study was conducted at the Hue University Hospital and Hue Central Hospital between June 2016 and June 2019. The study enrolled all women who complained of PMB and were followed by transvaginal Doppler ultrasound. Their definitive histopathological examination was the gold standard for comparison.ResultsThe UtA Doppler indices, including resistance index (RI), pulsatility index (PI), and peak systolic velocity (PSV), were significantly lower in the malignant group than in the benign group. The threshold values of the UtA, RI ≤0.73 and PI ≤1.42, were found with an area under receiver operating characteristic curve (AUC) of 0.85–0.88, and the sensitivity and specificity were 91.3% and 83.3%, respectively. Unlike PSV, the diagnostic value was the lowest, with an AUC of 0.72. ET was a good predictor for the diagnosis of EC, with an AUC of 0.89. In women with PMB, when using the cutoff value of EC more than 12.5 mm, the sensitivity and specificity were 93.8% and 77.8%, respectively. In addition, the higher the stage of EC, the lower the RI and PI and the greater the EC.ConclusionET, and RI, PI, and PSV of the UtA could help in differentiating malignant from benign endometrial changes. Pulsed ultrasonic Doppler velocimetry seems to play a role in predicting the higher stages of EC. Further studies are needed to confirm these findings.

Computer modeling of different shaped patches in classical carotid endarterectomy

Objective: to construct geometric models of carotid bifurcation and build a computer modeling for carotid endarterectomy (CEA) operations with patches of various configurations.Materials and methods. The method uses reconstructed models of a healthy blood vessel obtained from a preoperative computed tomography (CT) study of the affected blood vessel of a particular patient. Flow in the vessel is simulated by computational fluid dynamics using data from the patient's ultrasonic Doppler velocimetry and CT angiography. Risk factors are assessed by hemodynamic indices at the vessel wall associated with Wall Shear Stress (WSS).Results. We used the proposed method to study the hemodynamic results of 10 virtual CEA operations with patches of various shapes on a reconstructed healthy artery of a particular patient. The reason for patch implantation was to ensure that the vessel lumen is not narrowed as a result of the surgery, since closing the incision without a patch can reduce the vessel lumen circumference by 4–5 mm, which adversely affects blood flow. On the other hand, too wide a patch creates aneurysmorphic deformation of the internal carotid artery (ICA) mouth, which is not optimal due to formation of a large recirculation zone. In this case, it was found that the implanted patch width of about 3 mm provides an optimal hemodynamic outcome. Deviations from this median value, both upward and downward, impair hemodynamics. The absence of a patch gives the worst of the results considered.Conclusion: The proposed computer modeling technique is able to provide a personalized patch selection for classical CEA with low risk of restenosis in the long-term follow-up.

Dual-modality UDV-PIV system for measurement of solid-liquid flow in sewage facilities

Population growth and global industrialization cause a dramatic increase in the amount of sewage sludge produced annually worldwide from Municipal and Industrial Wastewater treatment. The efficient measurement of sewage, which is a typical solid-liquid two-phase flow, has become an important issue that requires to be urgently addressed. In this study, an improved Ultrasonic Doppler Velocimetry (UDV) is proposed to optimize the probe design and hardware design, which reduces the influence of working frequency and echo reverberation on accuracy and improves the stability of the system. A Doppler peak extraction and superposition method is also put forward to correct the offset of Doppler peak frequency. In this paper, Particle Image Velocimetry (PIV) is used to calibrate the UDV system to modify the measurement model of ultrasonic Doppler liquid-solid two-phase flow, and dynamic experiments are carried out in a vertical steel pipe with inner diameter of 50 mm at different flow conditions. The results show that the accuracy and stability of UDV measurement system are greatly improved, with a maximum relative error of 1.49%.

Thickness distribution and fluctuation characteristics of liquid falling film under turbulent conditions

The thickness distribution and fluctuation characteristics of turbulent falling film on vertical flat and corrugated plates were investigated by ultrasonic Doppler velocimetry and a high-speed camera under Rel (liquid phase Reynolds number) of 8.64 × 103–2.59 × 104, and a liquid film rupture model was established at the corrugated plate corner. The experimental results show that the crests and troughs in the corrugated plate produce “jet” and “reflux” effects compared with the flat plate, increasing the liquid film thickness and enhancing the fluctuation in the liquid film. The intensification of the liquid film fluctuation makes the probability density function of the instantaneous liquid film thickness tend to be a normal distribution. Plateau-Rayleigh instability hinders the growth of the liquid film thickness. The calculated values of the critical rupture velocity of the liquid film agree with the experimental values, and the relative error is within 15%.

Low-cost Solutions for Velocimetry in Rotating and Opaque Fluid Experiments using Ultrasonic Time of Flight

Many common techniques for flow measurement, such as Particle Image Velocimetry (PIV) or Ultrasonic Doppler Velocimetry (UDV), rely on the presence of reflectors in the fluid. These methods fail to operate when e.g centrifugal or gravitational acceleration leads to a rarefaction of scatterers in the fluid, as for instance in rapidly rotating experiments. In this article we present two low-cost implementations for flow measurement based on the transit time (or Time of Flight) of acoustic waves, that do not require the presence of scatterers in the fluid. We compare our two implementations against UDV in a well controlled experiment with a simple oscillating flow and show we can achieve measurements in the sub-centimeter per second velocity range with an accuracy of sim 5-10%. We also perform measurements in a rotating experiment with a complex flow structure from which we extract the mean zonal flow, which is in good agreement with theoretical predictions.

Laboratory Characterization of a Liquid Metal MHD Generator for Ocean Wave Energy Conversion

Harnessing ocean wave energy is an old challenge that has gained momentum in recent years. In this paper, we present the flow and electrical characterization of a prototype of an alternate liquid metal magnetohydrodynamic (MHD) generator at a laboratory scale which has the potential to make use of the energy of marine waves for its conversion into electrical energy. The eutectic alloy Galinstan, used as a working fluid, was driven in oscillatory motion in a duct of a rectangular cross-section exposed to a transverse magnetic field generated by permanent neodymium magnets. The electric current induced by the motion of the liquid metal in the magnetic field was collected through copper electrodes and delivered to the load. The oscillatory axial velocity component along the duct was measured using ultrasonic Doppler velocimetry for different oscillation frequencies. In turn, the output currents and voltages were measured for different operation conditions and the electric power and efficiency were estimated from experimental measurements. The coupling of this generator to a wave energy converter (WEC) is discussed.

Flow Characteristics of the Vertical Turbulent Falling Film at High Reynolds Numbers

The experimental study on flow characteristics of the turbulent falling film flowing along a vertical Perspex plate was carried out using ultrasonic Doppler velocimetry (UDV, a non-intrusive techni...

The influence of the waveguide on the quality of measurements with ultrasonic Doppler velocimetry

The article is devoted to the study of the influence of geometric parameters of sound-conducting walls on the quality of measurement of liquid metal flow velocities by ultrasonic Doppler velocimetry. It was shown that the thickness and radius of a sound-conducting wall (waveguide) have a notable effect on the resulting velocity profiles. The flow in a round pipe, the length of which is much larger than its diameter, is considered as a reference flow. The positive effect of a stepwise waveguides with a diameter smaller than the diameter of the piezoelectric element of an ultrasonic transducer on the quality of velocity measurements was verified experimentally. It was found that the accuracy of the resulting velocity profiles largely depends on the length and the material of the waveguides, as well as the velocity of the incoming flow of liquid metal.

Doppler ultrasound flow measurement of non-parallel velocity fields in a deformed elastic tube

The ultrasonic Doppler velocimetry (UVP) method is well known for the laminar flow stream in a circular tube. In many practical situations, deformed tubes or, non-parallel streamlines are involved. An improved experimental arrangement of the UVP transducer is needed to define the real velocity-vectors of the flow when the streamlines are not parallel to its wall. An experimental approach has been used with two sets of transducers in perpendicular to each other to obtain the magnitude of the real velocity vector (vreal), the direction of velocity-vector, and axial velocity component along the flow direction. The experiments were carried out using a proposed arrangement of UVP transducer for flow visualisation in a squeezed elastic tube. The results show that the 2D velocity profiling found to be more accurate using the present transducer arrangement, which is important for generating further information such as shear rate, flow rate, etc.

Experimental study on the slip velocity of turbulent flow over and within porous media

The phenomenon of coupled flow between free flow and porous media is characteristic of fluid flowing across porous media, but the slip characteristics at the coupling interface need to be further studied. The purpose of this work is to investigate the velocity distribution of turbulence with a high Reynolds number above and in porous media. In this paper, a visual flume test bench is built to simulate porous media as an accumulation of spherical glass beads with a diameter of 10 mm. The free flow velocity of fluid crossing the porous media and the velocity inside the porous media are measured by ultrasonic Doppler velocimetry. The effects of Reynolds number, relative water depth, and porosity parameters on the slip velocity and momentum transfer near the interface are studied. The results show that the slip coefficient of a porous-media bed with 0.331 porosity ranges from 0.000 082 to 0.000 594, while that of a porous-media bed with 0.476 porosity ranges from 0.000 034 to 0.001 068. The slip velocity increases with the increase in Reynolds number but decreases with the increase in relative water depth and porosity. The thickness of the transition layer in the porous-media region is insensitive to the Reynolds number and relative depth, but sensitive to porosity and increases with the increase in porosity. In this study, the influence of effective parameters on turbulent velocity is studied by experiments, which provides an important reference value for the development of a theoretical model in turbulent flow.

Wave characteristics of the falling liquid film in the development region at high Reynolds numbers

The wave characteristics of the turbulent falling liquid film in the development region along the vertical Perspex plate were studied by using an Ultrasonic Doppler Velocimetry (a non-intrusive technique). The instantaneous thickness of the falling film at the center of the plate with axial distance ranges from 50 mm to 1300 mm was measured and the Rel (the liquid film Reynolds number) ranges from 2.28 × 103 to 1.43 × 104. The results show that the mean thickness, wave frequency and amplitude increase while the growth rate decreases with the increase of Rel. The Probability Density Function of the liquid film instantaneous thickness tends to an approximately normal distribution with increasing Rel. Furthermore, the Plateau-Rayleigh instability can cause the breakup of the liquid film surface and resist the increase of the liquid film thickness, which results in the fluctuation range of the liquid film approximate to a fixed value when the Rel > 1.20 × 104.

Numerical approaches for the simulation of the yeast distribution in a fermentation tank

AbstractIn recent years, in addition to the experimental investigation of a flow phenomena, numerical investigation has become increasingly established. Especially in investigations where conventional flow measurement techniques such as PIV or LDA fail, numerical computation can offer new possibilities. Models for the simulation of the natural convection flow in a fermentation tank and in second step a superposition of the natural convection by gas bubbles have already been presented in earlier publications. Based on these results, this paper examines the simulation of yeast using the Euler‐Lagrange model. The aim is to extend the existing simulation, which is based on the Eulerian‐Eulerian time‐averaged model and to validate it with measurements from real experiments with the Ultrasonic Doppler Velocimetry (UDV). Starting point is the Dense Discrete Phase Model (DDPM), which is based on the Kinetic Theory of Granular Flow (KTGF). Especially the physical interaction models, for example the lift force, virtual mass force and collision models, play an important role. These fundamental studies must be conducted because the behaviour of the real yeast is really complex. During real fermentation, the yeast increases over time and also combines with other yeast particles. As a result, the proportion of yeast in the process increases and the equivalent particle size also increases due to the combination of the yeast. The goal of this paper is a numerical simulation of the flow processes in the fermentation tank, based on the Eulerian‐Eulerian model with the additional DDPM as realistic as possible, taking into account the natural convection flow and the actual bubble behaviour as well as the yeast distribution.

Investigation of slug flow characteristics in hilly terrain pipeline using ultrasonic Doppler method

An ultrasonic Doppler method is proposed for investigating the two-phase slug flow in a hilly terrain pipeline. To obtain the distribution of the velocity and gas–liquid interface, the velocity profile and echo profile of the slug flow were measured via ultrasonic Doppler velocimetry (UDV) with and without the addition of tracer particles in the liquid phase, respectively. An individual 8 MHz transducer with a diameter of 3 mm and an individual 2 MHz transducer with a diameter of 5 mm were employed for the liquid film and liquid slug measurement respectively. Using MATLAB programs based on the measured data, the investigation of the flow characteristics of the slug flow was divided into three parts: the liquid film, the front of the liquid slug, and the center of the liquid slug. The statistical analysis of the average length of every part indirectly reflected the formation and development behavior of the slug flow. The characteristic parameters of the gas–liquid interface, such as the thickness of the liquid film and the bubble distribution in the liquid slug, were extracted from the echo signals. The boundary layer of the liquid film was extracted from the velocity profiles. The average value and variation coefficient of the velocity profile were calculated for the liquid film and the center of the liquid slug. The effects of the superficial velocities and measured positions on the aforementioned flow parameters were examined. The UDV measurement and relevant data processing offer an effective method for the non-intrusive investigation of the slug flow in a hilly terrain pipeline.

Stirring flow of liquid metal generating by low-frequency modulated traveling magnetic field in rectangular cell

In the present work the influence of low frequency modulation of a travelling magnetic field (TMF) on a process of generation of electro-vortex flows in electrically conducting media are numerically and experimentally investigated. The measurements are carried out on a low melting temperature GaZnSn alloy by means of Ultrasonic Doppler Velocimetry. For numerical simulation, Comsol Multiphysics software was used. The dependencies of average and pulsating Reynolds numbers on the magnitude of electromagnetic impact and two modes of low frequency modulation are considered. A positive influence of reversed TMF modulations on the stirring process is determined. In particular the formation of a small-scale vortex structure in the main volume of liquid media.