Fluid Velocity Measurements Research Articles

Improvement and validation of a computational model of flow in the swirling well cell culture model.

Effects of fluid dynamics on cells are often studied by growing the cells on the base of cylindrical wells or dishes that are swirled on the horizontal platform of an orbital shaker. The swirling culture medium applies a shear stress to the cells that varies in magnitude and directionality from the center to the edge of the vessel. Computational fluid dynamics methods are used to simulate the flow and hence calculate shear stresses at the base of the well. The shear characteristics at each radial location are then compared with cell behavior at the same position. Previous simulations have generally ignored effects of surface tension and wetting, and results have only occasionally been experimentally validated. We investigated whether such idealized simulations are sufficiently accurate, examining a commonly-used swirling well configuration. The breaking wave predicted by earlier simulations was not seen, and the edge-to-center difference in shear magnitude (but not directionality) almost disappeared, when surface tension and wetting were included. Optical measurements of fluid height and velocity agreed well only with the computational model that incorporated surface tension and wetting. These results demonstrate the importance of including accurate fluid properties in computational models of the swirling well method.

Three-dimensional temperature and velocity measurements in fluids using thermographic phosphor tracer particles

Many flows of technical and scientific interest are intrinsically three-dimensional. Extracting slices using planar measurement techniques allows only a limited view into the flow physics and can introduce ambiguities while investigating the extent of 3D regions. Nowadays, thanks to tremendous progress in the field of volumetric velocimetry, full 3D-3C velocity information can be gathered using tomographic PIV or PTV hence eliminating many of these ambiguities (Discetti and Coletti, 2018; Westerweel et al., 2013). However, for scalar quantities like temperature, 3D measurements remain challenging. Previous approaches for coupled 3D thermometry and velocimetry combined astigmatism PTV with encapsulated europium chelates particles (Massing et al., 2018) or tomographic PIV with thermochromic liquid crystals particles (Schiepel et al., 2021). Here we present a new technique based on solid thermographic phosphor tracer particles, which have been extensively used for planar fluid temperature and velocity measurements (Abram et al., 2018) and are applicable in a wide range of temperatures. The particles are seeded into a gas flow where their 3D positions are retrieved by triangulation from multiple views and their temperatures are derived from two-colour luminescence ratio imaging. In the following, the experimental setup and key processing steps are described before a demonstration of the concept in a turbulent heated jet is shown.

Deployment of Time-Resolved Particle Image Velocimetry between two PWR surrogate bundles

There is a need to expand detailed experimental data on PWR thermal hydraulics to capture larger scale features than at the sub-bundle level. However, measuring fluid velocity between PWR fuel bundles is particularly challenging due to narrow gap geometries; to date, only point-wise data are available in the literature. Here, Time-Resolved Particle Image Velocimetry (TR-PIV) is performed in this intricate configuration. To prevent glare and scattering between laser beam and rods in the test section, a very careful optimization of the optical setup is necessary. The employed design rules are summarized in this manuscript. Sample velocity fields illustrate the successful design; they correlate well with bundle motion recorded independently with motion sensors. Captured flow structures (Re≈104) between bundles will set the foundation to improve the physical understanding of hydrodynamic coupling between bundles.

Pumpless, modular, microphysiological systems enabling tunable perfusion for long-term cultivation of endothelialized lumens.

Given the increased recognition of the importance of physiologically relevant microenvironments when designing in vitro assays, microphysiological systems (MPS) that mimic the critical function and structure of tissues and organs have gained considerable attention as alternatives to traditional experimental models. Accordingly, the field is growing rapidly, and some promising MPS are being tested for use in pharmaceutical development and toxicological testing. However, most MPS are complex and require additional infrastructure, which limits their successful translation. Here, we present a pumpless, modular MPS consisting of 1) a resistance module that controls flow rate and 2) a physiologically relevant, three-dimensional blood vessel module. Flow is provided by an attached reservoir tank that feeds fluid into the resistance channel via hydrostatic pressure. The flow rate is controlled by the height of the media in the tank and the resistance channel's dimensions. The flow from the resistance module is streamed into the blood vessel module using a liquid bridge. We utilize optical coherence tomography (OCT) to measure fluid velocity at regions of interest. The endothelial cells cultured in the MPS remain viable for up to 14days and demonstrate the functional characteristics of the human blood vessels verified by tight junction expression and diffusion assay. Our results show that a modular MPS can simulate a functional endothelium in vitro while simplifying the operation of the MPS. The simplicity of the system allows for modifications to incorporate other microenvironmental components and to build other organ-modeling systems easily.

In vitro evaluation of cerebrospinal fluid velocity measurement in type I Chiari malformation: repeatability, reproducibility, and agreement using 2D phase contrast and 4D flow MRI

BackgroundPhase contrast magnetic resonance imaging, PC MRI, is a valuable tool allowing for non-invasive quantification of CSF dynamics, but has lacked adoption in clinical practice for Chiari malformation diagnostics. To improve these diagnostic practices, a better understanding of PC MRI based measurement agreement, repeatability, and reproducibility of CSF dynamics is needed.MethodsAn anatomically realistic in vitro subject specific model of a Chiari malformation patient was scanned three times at five different scanning centers using 2D PC MRI and 4D Flow techniques to quantify intra-scanner repeatability, inter-scanner reproducibility, and agreement between imaging modalities. Peak systolic CSF velocities were measured at nine axial planes using 2D PC MRI, which were then compared to 4D Flow peak systolic velocity measurements extracted at those exact axial positions along the model.ResultsComparison of measurement results showed good overall agreement of CSF velocity detection between 2D PC MRI and 4D Flow (p = 0.86), fair intra-scanner repeatability (confidence intervals ± 1.5 cm/s), and poor inter-scanner reproducibility. On average, 4D Flow measurements had a larger variability than 2D PC MRI measurements (standard deviations 1.83 and 1.04 cm/s, respectively).ConclusionAgreement, repeatability, and reproducibility of 2D PC MRI and 4D Flow detection of peak CSF velocities was quantified using a patient-specific in vitro model of Chiari malformation. In combination, the greatest factor leading to measurement inconsistency was determined to be a lack of reproducibility between different MRI centers. Overall, these findings may help lead to better understanding for application of 2D PC MRI and 4D Flow techniques as diagnostic tools for CSF dynamics quantification in Chiari malformation and related diseases.

The method of fundamental solutions for Brinkman flows. Part I. Exterior domains

The method of fundamental solutions (MFS) is developed for solving numerically the Brinkman flow in the porous medium outside obstacles of known or unknown shapes. The MFS uses the fundamental solution of the Brinkman equation as in the boundary element method (BEM), but the single-layer representation is desingularized by moving the boundary sources to fictitious points outside the solution domain. In the case of unbounded flow past obstacles, these source points are placed in the domain inside the obstacle on a contracted fictitious pseudo-boundary. When the obstacle is known, then the fluid flow in porous media problem is direct, linear and well-posed. In the case of Brinkman flow in the porous medium outside an infinitely long circular cylinder, the MFS numerical solution is found to be in very good agreement with the available analytical solution. However, when the obstacle is unknown and has to be determined from fluid velocity measurements at some points inside the fluid, the resulting problem becomes inverse, nonlinear and ill-posed. The \(\hbox {MATLAB}^{\copyright }\) optimization toolbox routine lsqnonlin is employed for minimizing the least-squares gap between the computed and measured fluid velocity which is further penalized with extra smoothness regularization terms in order to overcome the instability of the solution. For proper choices of the regularization parameters involved, accurate and stable numerical reconstructions are achieved for various star-shaped obstacles.

Improving sand flow rate measurement using the wavelet transform and ultrasonic sensors

Abstract Accurate sand flow rate measurement is needed to minimize the side effects of sand production in gas fields. There are concerns about the accuracy of sand flow measurement using the sand measuring devices available on the market. In this paper, ultrasonic sensors and discrete wavelet transform signal analysis method is used to measure the sand flow rate. It is found that the strength of the discrete wavelet coefficients in the frequency range of 15–62 kHz has a linear relationship with sand flow rate. This finding provides a new methodology to accurately measure sand flow rate. The proposed method does not need fluid velocity as a prerequisite for sand rate measurement, so it greatly simplifies the system design when flow meters are not used for fluid velocity measurement. Also, this method has a much simpler calibration procedure compared to that of the sand detectors commonly used in the industry.

RainbowPIV with improved depth resolution—design and comparative study with TomoPIV

RainbowPIV is a recent imaging technology, proposed for time-resolved 3D-3C fluid velocity measurement using a single RGB camera. It dramatically simplifies hardware setup and calibration procedures as compared to alternative 3D-3C measurement approaches. RainbowPIV combines optical design and tailored reconstruction algorithms, and earlier preliminary studies have demonstrated its ability to extract physically constrained fluid vector fields. This article addresses the issue of limited axial resolution, the major drawback of the original RainbowPIV system. We validate the new system with a direct, quantitative comparison with four-camera Tomo-PIV on experimental data. The reconstructed flow vectors of the two approaches exhibit a high degree of consistency, with the RainbowPIV results explicitly guaranteeing physical properties, such as divergence free velocity fields for incompressible fluid flows.

A methodology for improving both performance and measurement errors in PIV

Accurate and efficient measurement of fluid velocities in several kind of experiments, has been acquiring high relevance, for several kind of applications. Particle Image Velocimetry is a noninvasive technique which also provides velocity estimates in several points of the measuring region. Regarding the PIV computations, high resolution of the digital input images, may lead to poor performance. There are also many error sources, regarding the PIV setup itself. This paper describes a method aimed both to speeding up the PIV computations, and minimizing the divergences (noise) present in the output velocity fields. The obtained results are promising, obtaining a speedup of up to 55%, with respect to the traditional cross correlation based method, with a comparable precision.

Spatial-temporal characteristics of temperature fluctuations of turbulent fluid flow and velocity measurements based on them

The paper describes the temperature cross-correlation velocimetry method applied to flows of water or liquid metal. The technique allows us to measure temperature waveforms and averaged longitudinal velocity in a flow simultaneously. This approach is a simple and reliable method for measuring the velocity in flows of opaque coolants. At the same flow parameters, liquids of different origins provide non-similar spatial-temporal characteristics having a different impact on the applicability of the temperature correlation method. This work is devoted to the development of practical methods allowing to form a set of specific recommendations on the application of the technique of temperature correlation velocimetry and to determine the metrological characteristics of the technique in various conditions. Calibration was carried out using water and mercury as a model liquid. Used experimental facility and measuring system are described, accompanied by a detailed description of the developed temperature-correlation sensor. Measuring directly from within a flow is made possible by a unique micro thermocouple immersion probes technique. Data obtained are presented as fields of temperature and intensity of temperature fluctuations. Autocorrelation and cross-correlation functions are compared and analysed for two studied fluids under identical conditions.

Application of the PTV with the use of a light-field camera to study three-dimensional wave regimes of liquid film flow

We present the results of studying the influence of surfactants on three-dimensional waves, in particular, on the flow structures in the wave. Volumetric fluid velocity measurements in waves, as well as the determination of their shape, were carried out using a light field camera. An aqueous solution of the nonionic surfactant Triton-X was used as a working fluid. The presence of surfactant leads to a significant change in the structure of the transverse flow regions under the main hump of the wave. Besides, capillary precursor and backflow in it are suppressed.

Optical Fiber-Based Level Sensor for High Temperature Applications

The novel optical fiber-based level sensing probe previously developed by Weathered was optimized to operate at higher temperatures and modified to measure local flow rates. The probe was submerged into a molten salt pool and a heating element run along the length of the probe was used to create a distinct temperature profile at the fluid-gas interface. An optical fiber was run in parallel which utilized optical frequency domain reflectometry to measure the temperature along the length of the probe at fine increments providing a quasi-continuous temperature profile. A numeric model was created in ANSYS to determine the optimal level sensor design. Three unique designs were then created and compared against one another to verify performance. A new level determining algorithm was generated in an attempt to increase the robustness of the sensor. With the optimal design and newly developed algorithm, the new level sensor was successfully tested up to 750 °C with an accuracy of ±1.5 mm and a response time of 3.0 ± 1.2 s and 7.5 ± 3.5 s for increasing and decreasing fluid levels, respectively. Additionally, the optimized level sensor was also tested under dynamic fluid level conditions to analyze the level sensors capability to measure fluid velocity. The velocity measurement capabilities were successfully tested in temperatures up to 750 °C with fluid velocities of 0.2 cm/s and 0.1 cm/s for increasing and decreasing fluid levels, respectively.

Physical simulation of flow field and construction process of horizontal salt cavern for natural gas storage

Underground salt caverns provide appropriate space for storing natural gas. However, salt caverns have to be constructed in bedded salt formations in China. The traditional construction method of salt cavern encounters serious problems in such formations. Instead, horizontal salt caverns are proposed as a possible alternative for gas storage. Horizontal caverns can be created by “multi-step retreating” (MSR) method. Two laboratory tests were conducted to understand the shape development and flow field of such cavern. In one test, we measured fluid velocity distribution in a simulated salt cavern environment by particle image velocimetry technology. In another test, the construction process of a salt cavern was simulated through MSR method. Results show that the flow field in horizontal cavern can be divided into five regions. The flow characteristics and rock salt dissolution properties in these regions are different. A semi-cylindrical cavern with similar cross section shape along the horizontal direction is obtained through the physical experiment. This study provides important guidance for analyzing the flow field and construction process of the horizontal salt cavern.

Clustering behaviour and settling velocity of bidisperse inertial particles in turbulent open channel flow

The clustering behaviour and settling velocity of bidisperse inertial particles with sub-millimetre diameters travelling in a turbulent open channel flow are investigated using the simultaneous particle image velocimetry and particle tracking velocimetry measurement technique. Instantaneous images of flow field and inertial particles are separated based on different wavelengths of light emitted by fluorescent seeding particles and inertial particles. Four flow configurations of turbulence are generated by turbulence grids with different sizes in the open channel. The clustering behaviour of monodisperse and bidisperse inertial particles and the discrepancy between them in the different flow cases are studied. We found that bidisperse inertial particles have weaker clustering phenomenon as compared with corresponding monodisperse inertial particles and this weak clustering phenomenon is almost consistent when the Taylor microscale Reynolds number Reλ changes from 90 to 267. The relationship between settling velocity and local concentration of inertial particles is then investigated. The results support the preferential concentration as the mechanism for the enhancement of settling velocimetry when the normalized particle concentration is in the range of 0.1~10. However, the anisotropy property and large eddy effect in turbulence will greatly change the interaction between inertial particles and turbulent flows and further alter their settling velocity, such as the average settling velocity decreasing with increasing Stokes number which depends on the dissipation time scale. Accordingly, we propose a new dimensionless multiscale parameter SvηReL1/2 to take into account the effect of large eddies and turbulence anisotropy on the settling velocity. With the simultaneous measurement of particle settling velocities and fluid velocities, we also analyse the unsteady force term in the particle dynamic equation. When the turbulence intensity is small and/or the particle inertia related to particle diameter and density ratio between inertial particle and fluid is small, the unsteady term can have a large contribution and it should not be neglected in the particle dynamic equation for the point-particle method in the numerical simulations of particle-laden flows.

An innovative ultrasonic time of flight method based on extended Kalman filter for wind speed measurement

Ultrasonic measuring systems have high speed response, good accuracy and they are used in measuring fluid velocity and distance. Techniques based on time difference and signal processing have been used to time of flight estimation in order to reduce uncertainties. This work presents the development of a new methodology for time of flight estimation with ultrasound signals for wind speed measurement. The proposed method, based on the extended Kalman filter, uses a model for indirect time of flight measurement, through signal amplitude measurements of the receiving transducer. Experimental results performed using a wind tunnel, showed a performance of the proposed technique with time of flight values with an accuracy comparable to the phase difference technique in frequency domain, however without restricting the measurement range to one signal cycle (2π).

Observations of mean and wave orbital flows in the ocean’s upper centimetres

Sophisticated measurements of fluid velocity near to an undulating air–water boundary have traditionally been confined to the laboratory setting. Developments in camera technology and the opening of novel modes of analysis have allowed for sensitive measurements of the current profile in the ocean’s uppermost layer. Taking advantage of the Research Platform R/P FLIP as a ‘laboratory at sea’, here we present first-of-their-kind thermal and polarimetric camera-based observations of wave orbital velocities and mean shear flows in the upper centimetres of the ocean surface layer. Measurements reveal a well-defined logarithmic layer as seen in laboratory measurements and described by classical surface layer theory; however, substantial spread of observations is found at low levels of wind forcing, where the Stokes drift of swell may have a substantial impact on the near-surface current profile. A novel application of short time window Fourier transforms allows for the estimation of near-surface wave orbital velocity magnitudes. These are found to be in general agreement with the prescriptions of linear wave theory, although observations diverge from theory at high levels of wind forcing where the interface is subject to surface wave breaking. Finally, the surface gravity wave phase-coherent short wave growth is presented and discussed in the context of hydrodynamic wave and airflow modulation.

Optimization of injected radiotracer volume for flow rate measurement in closed conduits

In chemical processes it is essential that the flow in the process is accurately defined. Fluid velocity measurements are important for fluid flow quality performance in flow systems. This study focuses on determination of the volumetric flow rate and its standard (relative) deviation for calibration of conventional flow meters by using a radiotracer approach. The measurements for flow meter calibration were performed at a pilot-scale flow rig using Technetium-99 m (99mTc) as a radiotracer in the form of pertechnetate ion (99mTcO4-). The measured data were analyzed, and precision of the experimental setup was investigated under two different approaches ? IAEA?s RTD software and sum approximation of raw data. For the first time, the variation of standard deviation of calculated flow rate with the injection volume and activity of the radiotracer was determined. Plug flow with axial dispersion was used to simulate the measured RTD curves and investigate the flow dynamics of the flowing water. The results of the study have shown the possibility of in situ calibration of flow meters with a relative error lower than 1 %. They also revealed a slight dependency of the precision of output results on the injection volume as well as similar results for manual and specialized RTD software data processing.

Spatial-temporal characteristics of temperature fluctuations of turbulent fluid flow and velocity measurements based on them

Spatial-temporal characteristics of temperature fluctuations of turbulent fluid flow and velocity measurements based on them

A novel flowrate measurement method for small-diameter pipeline based on bidirectional acoustic resonance

Traditional acoustic flowmeters are difficult to use in small-caliber, low-velocity piping systems. In this study, a novel method for fluid velocity measurement in small-diameter pipelines is developed based on the characteristic of acoustic resonance and standing wave tube. This method solves the problem of mutual interference between bidirectional acoustic loops, and realizes the simultaneous measurement of bidirectional resonant frequency. The tiny variation of flow velocity in a small-diameter pipeline can be sensitive by measuring the difference in bidirectional high-order resonance frequency. Experimental results show that the measurement system with a 15 mm diameter pipe has good linearity and high sensitivity to low velocity. Hence, this new method widens the application scope of acoustic flowmeters, especially in small-diameter, low-velocity piping systems.

Turbulent Schmidt Number Measurements Over Three-Dimensional Cubic Arrays

We present turbulent Schmidt number Sc_t estimations above three-dimensional urban canopies, where Sc_t is a property of the flow defined as the ratio of the eddy diffusivity of momentum (K_M) to the eddy diffusivity of mass (D_t). Despite the fact that Sc_t modelling is of great interest, inter alia, for pollutant dispersion simulations conducted via computational fluid dynamics, no universal value is known. Simultaneous measurements of fluid velocity and mass concentration are carried out in a water channel for three staggered arrays of cubical obstacles corresponding to isolated flow, wake-interference, and skimming-flow regimes. A passive tracer is released from a continuous point source located at a height z=1.67H, where H is the obstacle height. The results show an increase of Sc_t with height above the canopy for all three arrays, with values at z=2H (Sc_t = 0.6) about double compared to that at z=H. The observed Sc_t agrees well with that modelled by using a simple formulation for Sc_t based on expressions for K_M and D_t published in previous studies. Comparisons with other Sc_t models found in the literature are also presented and discussed.