Ultrasound Doppler Velocimetry Research Articles

Immiscible non-Newtonian displacement flows in stationary and axially rotating pipes

We examine immiscible displacement flows in stationary and rotating pipes, at a fixed inclination angle in a density-unstable configuration, using a viscoplastic fluid to displace a less viscous Newtonian fluid. We employ non-intrusive experimental methods, such as camera imaging, planar laser-induced fluorescence (PLIF), and ultrasound Doppler velocimetry (UDV). We analyze the impact of key dimensionless numbers, including the imposed Reynolds numbers (Re, Re*), rotational Reynolds number (Rer), capillary number (Ca), and viscosity ratio (M), on flow patterns, regime classifications, regime transition boundaries, interfacial instabilities, and displacement efficiency. Our experiments demonstrate distinct immiscible displacement flow patterns in stationary and rotating pipes. In stationary pipes, heavier fluids slump underneath lighter ones, resulting in lift-head and wavy interface stratified flows, driven by gravity. Decreasing M slows the interface evolution and reduces its front velocity, while increasing Re* shortens the thin layer of the interface tail. In rotating pipes, the interplay between viscous, rotational, and capillary forces generates swirling slug flows with stable, elongated, and chaotic sub-regimes. Progressively, decreasing M leads to swirling dispersed droplet flow, swirling fragmented flow, and, eventually, swirling bulk flow. The interface dynamics, such as wave formations and velocity profiles, is influenced by rotational forces and inertial effects, with Fourier analysis showing the dependence of the interfacial front velocity's dominant frequency on Re and Rer. Finally, UDV measurements reveal the existence/absence of countercurrent flows in stationary/rotating pipes, while PLIF results provide further insight into droplet formation and concentration field behavior at the pipe center plane.

The Relationship between Placental Shear Wave Elastography and Fetal Weight-A Prospective Study.

Background/Objectives: The utility of shear wave elastography (SWE) as an adjunct to ultrasound biometry and Doppler velocimetry for the examination of placental dysfunction and suboptimal fetal growth is unclear. To date, limited data exist correlating the mechanical properties of placentae with fetal growth. This study aimed to investigate the relationship between placental shear wave velocity (SWV) and ultrasound estimated fetal weight (EFW), and to ascertain if placental SWV is a suitable proxy measure of placental function in the surveillance of small-for-gestational-age (SGA) pregnancies. Methods: This prospective, observational cohort study compared the difference in placental SWV between SGA and appropriate-for-gestational-age (AGA) pregnancies. There were 221 women with singleton pregnancies in the study cohort-136 (61.5%) AGA and 85 (38.5%) SGA. Fetal biometry, Doppler velocimetry, the deepest vertical pocket of amniotic fluid, and mean SWV were measured at 2-4-weekly intervals from recruitment to birth. Results: There was no difference in mean placental SWV in SGA pregnancies compared to AGA pregnancies, nor was there any relationship to EFW. Conclusions: Although other studies have shown some correlation between increased placental stiffness and SGA pregnancies, our investigation did not support this. The mechanical properties of placental tissue in SGA pregnancies do not result in placental SWVs that are apparently different from those of AGA controls. As this study did not differentiate between constitutionally or pathologically small fetuses, further studies in growth-restricted cohorts would be of benefit.

Buoyant miscible viscoplastic displacements in vertical pipes: Flow regimes and their characterizations

We experimentally study miscible displacement flows of a light Newtonian fluid by a heavy viscoplastic fluid, in a vertical pipe with a large aspect ratio (δ−1≫1). We use camera imaging, laser-induced fluorescence, and ultrasound Doppler velocimetry techniques, to capture and process data. Four dimensionless parameters, namely, the Reynolds (Re), Bingham (B), viscosity ratio (M), and densimetric Froude (Fr) numbers (or their combinations), mainly govern the flow dynamics. We identify and characterize three distinct flow regimes, including plug, separation, and mixing regimes, while we describe each regime's dynamics in detail, particularly in terms of the velocity and concentration fields as well as the displacement front velocity. In addition, we analyze the plug regime concerning the residual wall layers, the separation regime in terms of the separation dynamics, spatiotemporal separation zone, and viscoplastic layer thinning, and the mixing regime regarding the mixing index and macroscopic diffusion. Finally, we develop a simplified model to help delineate the flow regime classification, in the plane of Re/Fr2 and M.

Analysis of core velocity in the presence of solids using UDV and improved model for cloud height in stirred tanks

Formation of cloud height is undesired due to limited mixing between clear liquid and solids rich volume; therefore, an accurate prediction of the cloud height is crucial. In this work, ultrasound Doppler velocimetry was employed to analyze core velocity in the wall jet in the presence of particles. It was seen that core velocity varies linearly with tip speed. The location of the core velocity is influenced by geometry. The effect of solids loading on the core velocity was found insignificant; however, a decrease was observed in the core velocity when the density and size of the particles were increased. An improved version of the model developed by Bittorf and Kresta (2003) to predict cloud height is proposed based on the analysis of core velocity data for a PBT in six different geometries for solids loadings of 5 to 19 vol%. The model provides accurate predictions for these conditions.

Immiscible displacement flows in axially rotating pipes

We experimentally study buoyant immiscible displacement flows in an axially rotating pipe, with varying flow parameters, such as the mean imposed flow velocity, density difference, pipe rotation speed, and pipe inclination angle. Via employing image processing and ultrasound Doppler velocimetry techniques, we analyze key flow features, including displacement regimes, interfacial instabilities, interfacial front velocities, and velocity and concentration fields. We find that immiscible displacement flows are distinguished by the emergence of one or two heavy fluid fronts, particularly depending on the rotation speed. Furthermore, our dimensional analysis reveals that the displacement flow is governed by four dimensionless parameters, including the Reynolds, densimetric Froude (or Archimedes), and Rossby numbers, as well as the pipe inclination angle. Using these dimensionless groups, we succeed in categorizing the main flow regimes as efficient and inefficient displacements. Moreover, we classify the interfacial regimes as stable, intermittently unstable, kinks, and separating interfacial patterns. Our analysis shows that the interfacial instabilities observed are indeed characterized by the Kelvin–Helmholtz instability. Our analysis of the velocity fields suggests remarkable differences between displacements in stationary and rotating pipes, especially in terms of the absence and presence of a countercurrent flow, respectively. Finally, our assessment of concentration fields using a Fourier transform approach provides a preliminary fundamental understanding of the characteristics of concentration waves and their corresponding amplitudes.

Bent pipe flow reconstruction based on improved ultrasound Doppler velocimetry and radial basis function neural network

In piping systems, the flow through a bend is typically undeveloped, unsteady, and complicated. In this study, we proposed a novel method to accurately predict downstream flow in bent pipes based on radial basis function neural network (RBFNN) and ultrasound Doppler velocimetry (UDV). An improved UDV method was developed for the measurement of complex flow in bent pipes. The downstream flow characteristics of three different bend configurations were investigated using computational fluid dynamics (CFD). The proposed RBFNN models established the relationships between the velocity profile along the symmetric axis and the velocity distribution over the pipe cross-section. Numerical data were used for model training and validation, whereas the combined datasets with UDV data as inputs and the corresponding CFD data as outputs were used for model modification. The model prediction performance was then evaluated with new UDV inputs by comparing the predicted velocities with the associated CFD results. The results indicated that the velocity profiles obtained using modified UDV agreed well with the present numerical simulation. Finally, the trained model exhibited satisfactory flow reconstruction performance and high flowrate prediction accuracy, with a maximum error of approximately 3%. This work contributes to the application of the UDV method in complex flow measurements and further demonstrates that artificial neural networks (ANNs) are promising for modeling fluid mechanics.

Permanent Magnet Pump for Aluminum Transport in a Linear Channel

Electromagnetic systems designed for liquid metal transportation offer a wide range of promising applications within the metallurgical industry. Among these systems, permanent magnet pumps stand out due to their remarkable advantages in processing liquid aluminum. These pumps enable the generation of a vigorous flow of liquid metal, all while maintaining a non-contact approach by bypassing the insulating walls. In this study, we investigate the flow of liquid metal in a rectangular cross-section channel created by a permanent magnet pump. To comprehensively analyze the flow characteristics and assess the technology's scalability, we employ order of magnitude evaluations alongside an experimental model. Ultrasound Doppler velocimetry is utilized to measure the velocity distribution, which reveals an intriguingly asymmetric flow pattern. Furthermore, additional measurements are conducted to determine the integral flow rate and pressure difference. Remarkably, the numerical simulations align closely with the experimental results, demonstrating good agreement in the p-Q curves. These findings provide substantial evidence supporting the remarkable potential of this technology in various applications, such as aluminum degassing, particle agglomerate dispersion, and efficient transportation.

Adnexal and clinical effects of myoinositol and lipoic acid in PCOs patients

Background: Polycistic ovary syndrome (PCOs) is one of the most common endocrine and metabolic disorders in premenopausal women. Our team aimed to know an eventual significant effect of the therapy based on an Alfa Lipoic Acid (ALA)/Myoinositol (Myo) combined drug on adnexal parameters as assessed by ultrasound and follow up clinical analysis. Methods: The following represents the results of a prospective trial considering data from thirty italian nulliparous women considered for the study, chosen from an initial group of fifty-eight women, compared to data taken from a healthy women group paired by age and nulliparous status. The mean age was 30.1 years old. Patients underwent a Myoinositol (400 mg) plus ALA (800 mg) regimen twice a day in a continued fashion in a twenty four months period. Ultrasound examinations were coincident with the fifth day of menstrual period and were set as follows: Time 0 (first evaluation), Time 12 (after twelve months) and finally Time 24 (after 24 months). Results: Comparisons were performed between Time 0 and Time 12 paired data, No significant ultrasound parameters differences were found between paired patients regarding: endometrial width, number of follicles and ovarian volume at the time of the trial. Regarding clinical symptoms, menstrual pelvic pain significantly decreased after a mean time of about four months and menstrual cycle tended to be regular in 12 from 30 patients after eight months under therapy. Parameters dealing with ultrasound color Doppler velocimetry status were studied considering other twelve months and will be described in a further report considering only ultrasound parameters. Conclusions: Considering the preliminary results of this study, we may hypothesize that Inositol may block the vascular effects of hyperadrogenism, and that the ALA in addition may play a role regarding anti oxidant and anti inflammatory pathways

Uterine Artery Doppler Ultrasound Measurement of Preterm Labor in Pregnant Women with Threatened Preterm Labor

Introduction: One of the most common causes of hospitalisation during pregnancy is preterm labour. Nearly one-fifth of women hospitalised for preterm labour. The frequency of preterm births is about 12%–13% in the USA and 5%–9% in many other developed countries. One of the main causes of preterm delivery is preterm premature rupture of membranes, while pre-eclampsia and foetal growth restriction (FGR) can be identified as other common causes that could lead to such complications. Objective: to assess the value of uterine artery doppler ultrasound measured of preterm labor in pregnant women with threatened preterm labor. Methods: We performed a single-center cohort study was carried out at Obstetrics and Gynecology, Sylhet MAG Osmani Medical College Hospital & Jalalabad Clinic, Modhushohid, Sylhet, Bangladesh from January to December 2020. Total 141 women were selected for the present study after applying inclusion and exclusion criteria. All participating women signed informed written consent. The study included singleton pregnant women who present to the casualty at gestations between 28 and 34 weeks of gestation with symptoms and signs of threatened preterm labor (defined as presence of at least one uterine contraction per 10 minutes, lasting at least 30 seconds, with a cervical dilatation ≤ 3 cm, and a cervical effacement < 80%). On admission, during obstetric ultrasound scanning, bilateral uterine artery Doppler ultrasound velocimetry was performed using the transabdominal technique. Uterine artery Doppler scans were both conducted at the peak of uterine contraction and in between contractions when the uterus is fully relaxed. Results: Total 141 women presenting with threatened preterm labor were included in the study. The mean gestational age at presentation was 30.86 ± 1.71 weeks (range: 28 – 33.86 weeks). Among 45 (31.9%) delivered within 7 days, while 96 (68.1%) delivered after 7 days of presentation. The mean uterine artery pulsatility index (UA-PI) measured both basally and at the peak contraction were significantly higher among women who delivered within 7 days. ROC curves showed that both basal and contraction UA-PI were significant predictors of delivery within 7 days. There was a significant negative correlation between contraction UA-PI and birth weight. Conclusion: Uterine artery Doppler ultrasound velocimetry measured in women with threatened preterm labor, seems to be a significant predictor of actual preterm labor within 7 days of admission.

Buoyant fluid injections at high viscosity contrasts in an inclined closed-end pipe

This paper studies the buoyant miscible injection of a high-viscosity fluid in a pipe filled with a low-viscosity fluid. The injection is carried out via an eccentric inner pipe inside an inclined closed-end outer pipe. A heavy fluid is injected into a light fluid at a constant density difference. Although the density difference is small, the buoyancy force, quantified via the Archimedes number (Ar), remains large. Our research relies on non-intrusive experimental methods, via a mix of high-speed camera imaging, ultrasound Doppler velocimetry, planar laser induced fluorescence, and particle image velocimetry techniques, accompanied by complementary numerical simulations. The effects of the viscosity ratio (M), the Reynolds number (Re) and the inclination angle (β) are analyzed on the injection/placement flow dynamics. Accordingly, a detailed description of the flow is presented, in terms of the concentration and velocity fields, the average front velocity of the heavy fluid (V¯f), the mixing index, and the flow regimes. The findings reveal that V¯f is mainly governed by an inertial-buoyant balance, allowing us to develop a correlation for V¯f vs Ar, M, Re and β. The results also show that a heavy fluid front separation occurs when M is small, β is large (i.e., near-vertical inclinations), and Re is large. This observation permits us to classify the flows into separation and non-separation regimes, in a dimensionless group plane based on a combination of the aforementioned dimensionless numbers.

MIDDLE CEREBRAL ARTERY AND UMBILICAL ARTERY DOPPLER STUDIES TO PREDICT OUTCOME OF PREGNANCIES.

In about 30% of post term pregnancies, the foetuses develop a post maturity syndrome. post term pregnancy is associated with increased risk of both intrauterine and postnatal death. Nowadays, Doppler ultrasound velocimetry of uteroplacental umbilical and fetal vessels has become established method of antenatal monitoring, allowing noninvasive assessment of fetal circulation. Circulatory changes, reected in certain fetal Doppler waveforms, predict adverse perinatal outcome. Umbilical arteries are the common vessels assessed by Doppler ultrasound, but recent studies conrm the efcacy of middle cerebral artery (MCA) Doppler assessment for detecting fetal compromise. Objective- To predict outcome of pregnancies by using umbilical artery and Middle cerebral artery doppler ndings. Methodology- Study group consists of 65 pregnant women with gestational age of 40-42 weeks and control groups include the same number of pregnant women with gestational age of 36-40 weeks. All the antenatal women in the subject & control groups were examined by routine ultrasound scan and Doppler subsequently.The peak systolic, end diastolic, and mean velocity were recorded from these vessels, and Umbilical artery S/D ratio, PI and Middle Cerebral Artery PI and CPR were calculated.Comparison of all variables were done using by·a software package Sensitivity, Specicity, Positive predictive value, Negative predictive value of different arterial Doppler indices and cerebroplacental ratio (CPR) were evaluated. ResultNo statistical signicant difference was noted in UA S/D, UAPI, UARI, MCA S/D, MCAPI MCARI in pregnancy with normal and adverse perinatal outcome. Only CPR showed signicant difference for predicting adverse perinatal outcome (p=0.001). Conclusion- None of the Doppler indices except CPR is sensitive enough. Although CPR cut-off value of 1.335 assures the obstetrician of fetal wellbeing, it's low specicity and high false positive results lead to unnecessary tests, undue concern and unnecessary interference.

Immersed buoyant viscoplastic injections

In this study, the injection of a viscoplastic (yield stress) fluid into a quiescent Newtonian medium is experimentally investigated, using a range of experimental methods, including high-speed camera imaging, laser-induced fluorescence (LIF), and ultrasound Doppler velocimetry (UDV) techniques. The case of our consideration is the continuous downward injection of a Carbopol solution, as a core fluid, through an eccentric inner pipe, placed inside a vertical closed-end pipe filled with a glycerin–water solution. The injected fluid is always heavier than the in-situ fluid and the fluids are miscible. As the injection continues, a filament of the core fluid immersed in the in-situ fluid is formed, for which it has been shown that there exist three distinct flow patterns, namely, the breakup, coiling, and bulging (buckling) regimes. Our focus in this study is to analyse the detailed flow features and sub-regimes at longer times, from an experimental perspective. To generalize our results, they are presented versus the governing dimensionless numbers of the flow, i.e. the buoyancy number, the Bingham number, the viscosity ratio, and the falling height. The breakup regime is analysed in terms of the yielding, necking and pinch-off process, the length of filaments, and their subsequent falling behaviours, the coiling regime in terms of the regular, free and irregular coiling behaviours, and the bulging (buckling) regime in terms of the appearance of a detached falling part and the maximum penetration depth. The results of this work can find applications, in particular, in the plug and abandonment (e.g. cementing processes) of oil and gas wells and 3D printing technologies. • Experimental analysis of immersed buoyant viscoplastic injection in Newtonian fluid. • Observed flow regimes classified into breakup, coiling, and bulging. • Analysis of yielding, necking/pinch-off, and length of filaments for breakup regime. • Coiling subregimes categorized as regular, free, and irregular coiling. • Analysis of maximum penetration depth and subregimes in bulging regime.

Role of cerebro-placental ratio in prediction of perinatal outcome in high-risk Pregnancies with intrauterine growth restriction

Background: Antenatal surveillance using Doppler ultrasound velocimetry of the uteroplacental umbilical and fetus arteries has been commonplace. The cerebroplacental ratio has been investigated as a way to predict newborn outcomes. Aim and objectives: In this research, we wanted to see whether the cerebro-placental ratio may help predict perinatal outcomes in high-risk gestation with intrauterine growth restriction. Subjects and methods: This was case-control research done at Al-Hussein University Hospital's Department of Obstetrics and Gynecology; The obstetric color Doppler investigation might be examined in two groups of 100 high-risk pregnant wome: Group Ⅰ - study group: 50 high risk pregnant women with IUGR and Group Ⅱ - control group: 50 high risk pregnant women without IUGR. Results: CPR achieved significance at cutoff point of 1.03 for predicting IUGR with sensitivity of 87.2% and specificity of 71.6% with PPV 83% and NPV 79%. Conclusion: Intrauterine growth restriction in high-risk gestations, the cerebral-placental ratio has a significant prognostic value for perinatal outcome.

Cerebro placental ratio at 30–34 weeks’ gestation in the prediction of perinatal outcome in low-risk and high-risk pregnancy

Doppler ultrasound velocimetry of umbilical and fetal vessels has become an established method of antenatal monitoring, allowing the non-invasive assessment of neonatal circulation. Cerebro placental ratio (CPR) is emerging as a significant predictor of adverse pregnancy outcome. To predict perinatal outcome in low and high-risk pregnancy in early and late-onset FGR using CPR. The study group comprised 410 pregnant women at 30-34 weeks, evaluated with ultrasound Doppler study, and other routine investigations and CPR were calculated. Women were categorized into high-risk and low-risk pregnancies and followed up until delivery, and fetal outcome was noted. Period of prolongation of pregnancy was significantly lower with high-risk patients than low-risk patients (31.09 ± 13.9 vs 37.79 ± 15.1, p=0.0003). NICU admissions significantly increased with high-risk patients than low-risk patients (22.22% vs 9.4%, p=0.002). Low-risk patients underwent significantly more vaginal deliveries as compared to high-risk patients (74.22% vs 44.87%, p < 0.0001). Birth weight, period of prolongation of pregnancy, and gestation period were significantly lower in patients with abnormal CPR than normal CPR group (2.82 Kg vs 1.94 Kg, 37.56 weeks vs 14.64 weeks, 266.47 days vs 245.41 days, respectively). Doppler velocimetry becomes an important tool for high-risk cases and late-onset mild FGR(after 32 weeks). CPR is helpful in high-risk pregnancies and also to predict peripartum fetal distress.

Collapse of Coherent Large Scale Flow in Strongly Turbulent Liquid Metal Convection.

The large-scale flow structure and the turbulent transfer of heat and momentum are directly measured in highly turbulent liquid metal convection experiments for Rayleigh numbers varied between 4×10^{5} and ≤5×10^{9} and Prandtl numbers of 0.025≤Pr≤0.033. Our measurements are performed in two cylindrical samples of aspect ratios Γ=diameter/height=0.5 and 1 filled with the eutectic alloy GaInSn. The reconstruction of the three-dimensional flow pattern by 17 ultrasound Doppler velocimetry sensors detecting the velocity profiles along their beam lines in different planes reveals a clear breakdown of coherence of the large-scale circulation for Γ=0.5. As a consequence, the scaling laws for heat and momentum transfer inherit a dependence on the aspect ratio. We show that this breakdown of coherence is accompanied with a reduction of the Reynolds number Re. The scaling exponent β of the power law Nu∝Ra^{β} crosses eventually over from β=0.221 to 0.124 when the liquid metal flow at Γ=0.5 reaches Ra≳2×10^{8} and the coherent large-scale flow is completely collapsed.

Effects of electrically conductive walls on turbulent magnetohydrodynamic flow in a continuous casting mold

In the present study, we have performed a series of numerical simulations of the turbulent liquid metal flow in a laboratory-scale setup of the continuous casting. The liquid metal flow was subjected to an external non-uniform magnetic field reproducing a realistic electromagnetic brake (EMBr) effect. The focus of this research was on the effects of the finite electrical conductivity of Hartmann walls on the flow and turbulence in the mold. To be able to simulate distributions of the electric potential and current in both the fluid and solid wall domains, we applied our recently developed and validated in-house conjugate MHD solver based on the open-source code OpenFOAM. The dynamic Large Eddy Simulation (LES) method was used to simulate the turbulent flow. The results obtained for the neutral (non-MHD) and MHD cases over a range of the imposed EMBr strengths – all for the perfectly electrically insulated walls – were compared with the available Ultrasound Doppler Velocimetry (UDV) measurements. A good agreement between simulations and experiments was obtained for all simulated cases. Next, we completed a series of simulations including a wide range of the finite electric conductivities (ranging from a weakly to perfectly conducting wall conditions) of the Hartmann walls for a fixed value of the imposed EMBr. The obtained results demonstrated a significant influence of the electric wall conductivities on the flow and turbulence reorganization. It is expected that here provided insights can be applicable for the new generation of the laboratory- and real-scale continuous casting setups.

Interpreting the role of nuchal fold for fetal growth restriction prediction using machine learning

The objective of the study is to investigate the effect of Nuchal Fold (NF) in predicting Fetal Growth Restriction (FGR) using machine learning (ML), to explain the model's results using model-agnostic interpretable techniques, and to compare the results with clinical guidelines. This study used second-trimester ultrasound biometry and Doppler velocimetry were used to construct six FGR (birthweight < 3rd centile) ML models. Interpretability analysis was conducted using Accumulated Local Effects (ALE) and Shapley Additive Explanations (SHAP). The results were compared with clinical guidelines based on the most optimal model. Support Vector Machine (SVM) exhibited the most consistent performance in FGR prediction. SHAP showed that the top contributors to identify FGR were Abdominal Circumference (AC), NF, Uterine RI (Ut RI), and Uterine PI (Ut PI). ALE showed that the cutoff values of Ut RI, Ut PI, and AC in differentiating FGR from normal were comparable with clinical guidelines (Errors between model and clinical; Ut RI: 15%, Ut PI: 8%, and AC: 11%). The cutoff value for NF to differentiate between healthy and FGR is 5.4 mm, where low NF may indicate FGR. The SVM model is the most stable in FGR prediction. ALE can be a potential tool to identify a cutoff value for novel parameters to differentiate between healthy and FGR.

Analysis of the symmetry of 3D silicon melts flow generated by a bitter traveling magnetic field in a cylindrical crucible

Full 3D numerical simulation and experimental characterization of the topology and sensitivity of a magnetohydrodynamic flow pattern driven by a travelling magnetic field generated by a specifically designed cylindrical Bitter coil have been carried out. This Bitter coil has six windings composed of multiple circular copper plates and insulator separators disposed in a specific way for an optimum round circulation of electric currents, which are three-phase currents at a network frequency. For experimental characterization, experimental measurement data of radial components of the induced magnetic field (Br) at different z-positions were used without any liquid metal for different applied electric currents, and ultrasound Doppler velocimetry was employed to acquire the vertical velocity component along the beam axis in the centre and at different azimuthal positions for a fixed radial coordinate in the liquid GaInSn alloy. On the other hand, for numerical characterization, a numerical model has been developed using the Comsol MultiphysicsTM software to resolve the set of magnetohydrodynamic equations, fundamentally based on low frequency and low magnetic induction, and on an averaged expression of the Lorentz force. The results clearly show that the choice of 3D modelling and the Bitter coil design, which generates instabilities, can change significantly the usually expected axisymmetric torus-type magnetohydrodynamic flow topology and result in a distinct 3D flow configuration. Figs 8, Refs 16.

Black-box real-time identification of sub-regime of gas-liquid flow using Ultrasound Doppler Velocimetry with deep learning

Gas-liquid flow has a strong relationship with energy transfer, production, and transportation. A black-box method based on velocity information and deep learning was proposed to identify the sub-regimes of gas-liquid flow in real time, including two parts—data acquisition and establishment of the identification model. The Ultrasound Doppler Velocimetry (UDV) method was employed to acquire the velocity information of gas-liquid flow in a horizontal pipe non-intrusively. Seven different sub-regimes are defined to perform the identification task. Poor identification accuracy was obtained with raw data; therefore, denoising was added to improve the identification accuracy. The results show that the proposed method is feasible and effective, and the Current model can achieve high accuracy similar to existing models while having the fastest identification speed. In addition, the data from untrained flow conditions were tested, and all convolutional neural network (CNN) models achieved identification accuracy higher than 91.5%. The proposed method helps in identifying two-phase flow, and its accurate and straightforward characteristics indicate broad application potential.

Microscale mechanisms of ultrasound velocity measurement in metal melts

Ultrasound Doppler velocimetry (UDV) is a powerful, widely used technique for measuring flow in metal melts. However, UDV in metal melts suffers from substandard reliability because its operation depends on phenomena that are poorly understood. In this study, we investigate the poorly characterized source of bulk echoes in metal melts and the corresponding mechanisms of ultrasound signal deterioration. We present evidence from electron microscopy and ultrasound measurements that oxide inclusions are the main source of bulk echoes in gallium. By measuring their terminal velocity, we estimate the mean size of echoing objects in gallium to be 58–64 μm, implying that Mie scattering is the dominant scattering mechanism. By comparing UDV measurements in which signals were transmitted directly into the fluid, to others in which signals were transmitted through a vessel wall, we show evidence that there are two distinct mechanisms for signal degradation: the loss of echoing objects from the bulk and the deterioration of acoustic coupling and wetting at the transducer surface. We suggest stirring vigorously and using indirect-contact UDV measurement strategy to mitigate the signal degradation in metal melts.