Flow Measurements Research Articles

Near-Wall Flow Measurements Using Frequency-Modulating Filtered Rayleigh Scattering (FM-FRS)

The frequency-modulating filtered Rayleigh scattering (FM-FRS) technique has been developed and applied for the boundary layer measurements. The FM-FRS technique effectively extracts Rayleigh scattering information from noisy low SNR signals caused by intense wall glare. The boundary layer velocity profiles measured by FM-FRS show excellent agreement with an independent pressure probe measurement and the law-of-the-wall, including approximately 100 μ m above the wall. This technique is desirable for the practical applications of the Rayleigh scattering technique for flow diagnostics to regions that were limited due to strong background and low signal-to-noise ratio.

Fourier light-field microscope for micro tomo-PTV in a cross-junction microfluidic channel

This paper presents a novel approach for comprehensive flow analysis within microfluidic systems by integrating particle tracking velocimetry (PTV) and shake-the-box (STB) techniques with plenoptic imaging. By combining the strengths of PTV and STB, which offer particle trajectory tracking and high-resolution particle position determination, respectively, our method enables accurate and detailed flow characterization. Leveraging Fourier light-field microscopy, a recent development of plenoptic imaging (or integral microscopy), we eliminate the need for multiple imagers and achieve high-resolution three-dimensional flow measurements using a single high-speed camera. The diffraction-limited resolution is on the order of 2 um in 3D, with the lateral and depth resolution within 25% of each other. This is an unprecedented depth resolution for a 3D velocimeter. Particle positions can in fact be resolved to less than the imaging wavelength. We demonstrate the effectiveness of this approach by capturing and analyzing a complex flow within a microfluidic device with a cross-junction channel. This measurement technique will provide valuable insights for optimizing microfluidic device design and performance as well as wall-bounded flows.

Turbulent Channel Flow Diagnostics By Means Of Shake-The-Box (STB): Flow Structures And Sublayer Profiles

Time-resolved Shake-the-Box (STB) experiments have been conducted in the channel-flow facility at the Institute of Fluid Mechanics (ISTM) at f = 30 kHz repetition rate to study the near-wall velocity field at a viscous Reynolds number of Reτ = 350 (centerline velocity Ucl = 8.4 m/s, channel half-height h = 12.6 mm, viscous unit δv ≈ 36 μm) to testify the STB method for the applicability to provide high-resolution velocity information of the given flow field including the sublayer region of the channel flow. In addition to the extraction of Lagrangian particle tracks and corresponding Eulerian iso-surfaces of vortical structure the major emphasis of the study centers around an evaluation of the resulting near wall velocity profile. Particularly, it is discussed how the choice of data-processing steps and strategies affects the resulting velocity estimates in the immediate vicinity of the wall, where the major impact for the current study has been identified to result from image-arithmetic efforts during data pre-processing. The achieved results are discussed and further compared with direct numerical simulations (DNS) of similar Reτ and earlier experimental efforts at ISTM of the same flow configuration by means of stereoscopic particle image velocimetry (stereo PIV) and a laser-Doppler velocimetry profile sensor (LDV-PS). Finally, future perspectives of the experimental efforts for near-wall shear flow measurements are outlined on the grounds of the achieved insights.

Towards Time-Resolved Multi-Property Measurements By Single-Frequency FRS

The filtered Rayleigh scattering technique (FRS), extended by the method of frequency scanning, has historically been limited to time-averaged multi-property flow measurements. In our recently published work, we present a concept that potentially enables the combined measurement of time-resolved pressure, temperature and three-component (3C) velocity fields. It is based on the observation of the region of interest from six perspectives and a single excitation frequency. This work summarizes and expands on a follow-up publication that experimentally verifies this concept on an aspirated circular duct flow. For this purpose, the results obtained from single-frequency data processing are compared with reference pressures, temperatures and corresponding LDA velocity measurements. Overall, a very good agreement is found for all operating points with accuracies of 3.4% in pressure, 1.3% in temperature and ±2 m/s in axial velocity. Concerning precision, a newly developed multistage evaluation procedure enables values for pressure, temperature and velocity as low as 3 hPa, 2.2 K and 1.7 m/s. In a second flow configuration, an axial swirler is introduced into the duct. The resulting secondary flow structure and deformation of the axial velocity field caused by swirler geometry and support are very well captured with the single-frequency analysis. A closing discussion on the implementation challenges of a single-frequency multi-property FRS instrument with pulsed laser radiation reveals significant obstacles to overcome. Due the considerable optimization potential identified, chances are high that true time-resolved multi-property measurements by FRS will become a reality.

FlowFit3: Efficient Data Assimilation Of LPT Measurements

Lagrangian particle tracking (LPT) techniques such as Shake-The-Box provide accurate flow measurements by following the movement of tracer particles within a flow. The technique gives measured values of position, velocity and acceleration at the locations of the scattered particles as opposed to a Eulerian grid like with window based techniques such as PIV. This is advantageous for e.g spatially highly resolved flow statistics. Often it is also desirable to have access to a grid-structured representation of the data, especially for the calculation of spatial gradients of flow field measures. While a simple interpolation onto a grid is possible, data assimilation techniques using physics based regularization such as FlowFit2 or VIC+ and VIC#are frequently used nowadays. Through knowledge of the Navier-Stokes equations a higher spatial resolution can be obtained than from interpolation alone. We present the new and highly efficient FlowFit3 approach and its evaluation on synthetic data.

Characteristic parameters measurement and flow prediction of slug flow based on ultrasound technology

Slug flow exists over a wide range of gas and liquid flow rates. For the case of smaller liquid volume fraction, this paper proposes a method for accurately identifying the flow structure of horizontal pipe slug flow based on the ultrasonic inner wall echo signal at the top of the pipe. The arrival and departure time of the slug is determined by analyzing the amplitude of the inner wall echo signal from both the test signal and reference signal and the rate of change of the test signal, respectively. Based on the accurate flow structure identification results, characteristic parameters can be calculated including the length ratio between the liquid film zone and the slug unit (lf/lu) and the average liquid film thickness in the liquid film zone (hf). The system of equations describing the relationship between the two parameters and the two-phase flow rates is constructed. By solving it, the flow rates of gas and liquid can be predicted. Experiments are carried out with the superficial velocity of gas and liquid ranging from 0.8 to 2.5 m/s and 0.1 to 0.4 m/s, respectively, where the pipeline’s inner diameter is 50 mm. The experimental results indicate that the mean absolute percentage errors for the predicted gas and liquid flow rates are 12.9605 % and 6.3517 %, respectively.

Invariant flow rate measurement system for three-component oil-gas-water flow

The paper presents an invariant flow rate measurement system for individual components for a flow that consists of oil, water, and gas. The proposed flow measurement system is a continuation of the work of the authors, which is based on the application of the multichannelling principle of invariance theory. The paper proposes and discusses the structure of the invariant system for measuring the flow rate of oil-water-gas, analytical expressions are obtained for the implementation of algorithms for measuring the flow rate of individual substances that make up the flow. The uncertainty of the flow rate measurement results was assessed separately for oil, water, and gas. In this work, it is shown that by selecting flow meters of the main and additional channels with an uncertainty of less than 0.5 %, for almost any ratio of components in the additional pipeline, it is possible to measure the flow rate of water or oil with an uncertainty of less than 3 %, and the flow rate of the gas fraction in free form can be measured with an uncertainty value of less than 1 %. The paper discusses the practical aspects of the implementation of an industrial prototype of the system and the characteristics that affect its accuracy and efficiency.

An integrated approach through controlled experiment and LCIA to evaluate water quality and ecological impacts of irrigated paddy rice.

This study used an integrated approach to mainly assess the water quality of paddy field during cultivation and quantify its equivalent ecological damages. Accordingly, an isolated pilot area with 0.6 ha and subsurface drainage pipes was prepared for flow measurement and multiple pollutant examination (DO, EC, pH, COD, TKN, TN, TP, NO3, butachlor) under controlled condition during 94 days of rice cultivation. Based on life cycle impact assessment (LCIA) database, the indices of ReCiPe (2016) were used to convert the examined nutrient and herbicide pollution. Results showed that TKN and TP were significant pollutants and reached the maximum concentrations of 7.2 and 4.9 mg/L in pilot outflow, respectively. Here, their average discharged loads were 56.2 gN/day and 45.3 gP/day. These loads equal leaching 8.5% and 9.4% of applied urea and phosphate fertilizers, respectively. The nutrient export coefficients were 8.4 kgN/ha and 6.8 kgP/ha. Nevertheless, the majority of this pollution was transferred by inflow. The net export coefficients were 0.3 kgN/ha and 2.6 kgP/ha while net leaching rates were 0.3%TN and 3.3%TP. The trend of combined ecological damages also showed that the 11-17th day of cultivation imposed the highest ecological risks. The state-of-the-art index of ecological footprint per food production estimates the equivalent ratio of lost lives by impaired ecosystem against lives saved from starvation. This index showed that 7% of the potential of produced paddy rice in this area for saving lives would be spoiled by releasing pollution to the terrestrial ecosystem in the long term. Yet, it can be enhanced as a matter of direct discharge to the freshwater. Therefore, using suitable agricultural operations or improving farm management practices for pollution abatement or assimilation potential is highly recommended.

Early Prediction of Native Arteriovenous Fistula for Maturation by Doppler Ultrasound Study

Introduction: There are significant chances of maturation failure in arteriovenous fistulas (AVFs) made for vascular access for hemodialysis. AVFs are usually assessed for maturation 6 weeks after the operation. Significant time is lost for performing a salvage radiological procedure or making an alternative AVF, in case the AVF fails to mature. Materials and Methods: This prospective observational study was conducted to predict the chances of maturation of AVF by Doppler ultrasound (USG) study. One hundred and thirty-seven patients in whom native AVF was made as a vascular access procedure for hemodialysis were included in the study. In five patients, palpable thrill was absent after 48 h of operation and were excluded from the study. The velocity of the blood, diameter of the vessel, and depth of the vessel from the skin were assessed by USG Doppler 3 weeks after the operation and were correlated with AVF maturation. Results: Successful maturation occurred in 114 (86.3%) AVF. The flow rate of the blood and depth of the vein were statistically different in successful and unsuccessful AVF maturation for both the groups of radial artery (RA) and brachial artery (BA) based AVF. For RA AVF, successful maturation was predicted by the flow rate of 539 mL/min (sensitivity 95% and specificity 83%) and 4.2 mm diameter of the vein (sensitivity 93% and specificity 100%). For BA AVF, successful maturation was predicted by the flow rate of 456 mL/min (sensitivity 93% and specificity 100%) and 5.7 mm diameter of the vein (sensitivity 77% and specificity 100%). The measurement of flow and depth at 3 weeks after AVF may predict the maturation of AVF. Conclusion: It will be beneficial to do a USG Doppler study 3 weeks after making AVF, as the measurement of flow may predict the maturation of AVF.

Basal Force Fluctuations and Granular Rheology: Linking Macroscopic Descriptions of Granular Flows to Bed Forces With Implications for Monitoring Signals

AbstractGranular flows are ubiquitous in nature with single flows traversing a wide range of dynamic conditions from initiation to deposition. Many of these flows are responsible for significant hazards and can generate remotely detectable seismic signals. These signals provide a potential for real‐time flow measurements from a safe distance. To fully realize the benefit of seismic measurements, basal‐granular forces must be linked to macroscopic internal flow dynamics across a wide range of flow conditions. We utilize discrete element simulations to observe dry and submerged granular flows under plane‐shear and inclined‐flow configurations, relating bulk kinematics to basal‐force distributions. We find that the power and frequency of force fluctuations scale with non‐dimensional shear rate (I). This scaling tracks three pre‐established regimes that are described by μ(I) rheology: (a) an intermittent particle rearrangement regime, where basal forces are dominated by low frequencies; (b) an intermediate regime where basal forces start to increase in frequency while showing correlations in space and (c) a fully collisional regime where the signal is nearly flat up to a cutoff frequency. We further identify a newly defined fourth regime that marks a “phase change” from the intermediate to collisional regime where increases in basal force fluctuations with increasing shear rates stalls as the granular bed dilates, partially destroying the contact network. This effort suggests that basal forces can be used to interpret complex granular processes in geophysical flows.

Assessing Coriolis meter performance in multicomponent carbon dioxide-rich mixtures

Accurate flow measurement plays a pivotal role in monitoring CO2 flows across the CCS value chain. This not only bolsters the overall business model of the CCS industry, but also ensures adherence to environmental legislations and regulatory requirements. Unlike other industrial process fluids, such as water, oil & natural gas, it is unclear whether current commercially available metering technologies can meet the requisite accuracy levels, specifically the ±2.5 % recommended within the EU/UK European Trading Scheme for CO2 mass transfer. Accordingly, the aim of this work was to gain a comprehensive understanding of CO2 flow measurement within the context of CCS transport conditions. Firstly, GERG-2008 equation of state was implemented on REFPROP v10 to predict the optimal transport conditions for CO2-rich mixtures and to understand the influence of non-condensable gas impurities in CCS flow operations. Then, a dedicated laboratory-scale gravimetric flow facility was designed and used to evaluate the performance of a Coriolis flow meter under gas, liquid, and supercritical flow conditions. The results indicate that the impurities have a relatively minor impact on the measurement performance of the meter, with maximum mean absolute measurement errors of 0.25 %, 0.12 %, and 0.28 % observed in gas, liquid, and supercritical CO2 flow conditions, respectively. The findings support the use of Coriolis metering technology as a reliable option for CCS metering, underscoring its suitability for accurate measurements in single-phase CO2 transport applications.

Genome-wide quantification of RNA flow across subcellular compartments reveals determinants of the mammalian transcript life cycle

Dissecting the regulatory mechanisms controlling mammalian transcripts from production to degradation requires quantitative measurements of mRNA flow across the cell. We developed subcellular TimeLapse-seq to measure the rates at which RNAs are released from chromatin, exported from the nucleus, loaded onto polysomes, and degraded within the nucleus and cytoplasm in human and mouse cells. These rates varied substantially, yet transcripts from genes with related functions or targeted by the same transcription factors and RNA-binding proteins flowed across subcellular compartments with similar kinetics. Verifying these associations uncovered a link between DDX3X and nuclear export. For hundreds of RNA metabolism genes, most transcripts with retained introns were degraded by the nuclear exosome, while the remaining molecules were exported with stable cytoplasmic lifespans. Transcripts residing on chromatin for longer had extended poly(A) tails, whereas the reverse was observed for cytoplasmic mRNAs. Finally, machine learning identified molecular features that predicted the diverse life cycles of mRNAs.

Static and dynamic analysis of cerebral blood flow in fifty-six large arterial vessel networks

Objective. The cerebral vasculature is formed of an intricate network of blood vessels over many different length scales. Changes in their structure and connection are implicated in multiple cerebrovascular and neurological disorders. In this study, we present a novel approach to the quantitative analysis of the cerebral macrovasculature using computational and mathematical tools in a large dataset. Approach. We analysed a publicly available vessel dataset from a cohort of 56 (32/24F/M) healthy subjects. This dataset includes digital reconstructions of human brain macrovasculatures. We then propose a new mathematical model to compute blood flow dynamics and pressure distributions within these 56-representative cerebral macrovasculatures and quantify the results across this cohort. Main results. Statistical analysis showed that the steady state level of cerebrovascular resistance (CVR) gradually increases with age in both men and women. These age-related changes in CVR are in good agreement with previously reported values. All subjects were found to have only small phase angles (<6°) between blood pressure and blood flow at the cardiac frequency. Significance. These results showed that the dynamic component of blood flow adds very little phase shift at the cardiac frequency, which implies that the cerebral macrocirculation can be regarded as close to steady state in its behaviour, at least in healthy populations, irrespective of age or sex. This implies that the phase shift observed in measurements of blood flow in cerebral vessels is caused by behaviour further down the vascular bed. This behaviour is important for future statistical models of the dynamic maintenance of oxygen and nutrient supply to the brain.

Elevated aerosol enhances plant water-use efficiency by increasing carbon uptake while reducing water loss.

Aerosols could significantly influence ecosystem carbon and water fluxes, potentially altering their interconnected dynamics, typically characterized by water-use efficiency (WUE). However, our understanding of the underlying ecophysiological mechanisms remains limited due to insufficient field observations. We conducted 4-yr measurements of leaf photosynthesis and transpiration, as well as 3-yr measurements of stem growth (SG) and sap flow of poplar trees exposed to natural aerosol fluctuation, to elucidate aerosol's impact on plant WUE. We found that aerosol improved sun leaf WUE mainly because a sharp decline in photosynthetically active radiation (PAR) inhibited its transpiration, while photosynthesis was less affected, as the negative effect induced by declined PAR was offset by the positive effect induced by low leaf vapor pressure deficit (VPDleaf). Conversely, diffuse radiation fertilization (DRF) effect stimulated shade leaf photosynthesis with minimal impact on transpiration, leading to an improved WUE. The responses were further verified by a strong DRF on SG and a decrease in sap flow due to the suppresses in total radiation and VPD. Our field observations indicate that, contrary to the commonly assumed coupling response, carbon uptake and water use exhibited dissimilar reactions to aerosol pollution, ultimately enhancing WUE at the leaf and canopy level.

Development of a condition monitoring of heat exchangers for corrosion progress and coolant condition

The transport sector, and thus also rail transport, needs to be completely decarbonised by 2050 at the latest. Considering the long service life of rail vehicles, this goal means enormous innovation and growth potential for the vehicle and supplier industry of railway technology in the coming years. This contribution presents the first results of an R&amp;D project to reduce the total cost of ownership of passenger and freight rail vehicles. The reduced life cycle costs can be achieved over the operating life, among other things, with condition monitoring approaches for critical components of cooling systems to enable diagnosis-based maintenance. Based on guided elastic waves, an integrated system is being developed to analyse the depth and position of corrosion damage to heat exchangers in rail vehicles. This method is to be supplemented by a refractive index sensor integrated in the coolant circuit which can be used to derive influences of the coolant condition on corrosion. First, an acoustic measuring technique was put into operation. Suitable piezoelectric transducers were selected and test measurements, including the introduction of artificial damages, along different paths on a representative heat exchanger were carried out and evaluated. Measurement signals can be received over different distances, and a monitoring of larger areas of the heat exchanger seems possible. For the development of the monitoring of the coolant, plasmonically active sensor substrates with a gold nanostructure were produced and installed in a measuring flow cell. In laboratory tests, concentrations of water-coolant mixtures could be distinguished with the refractive index sensor. In the future, the refractive index sensing will be carried out by means of bypass flow measurement. Since the coolant is pumped in a circuit, the sensor system can be attached to one of the inlet/outlet lines.

Conceptual design of a Doppler spectrometer for 102m/s cross-field flows in tokamak divertors.

The cross-field transport in the scrape-off-layers (SOLs) and divertors in tokamaks is of a similar size to the poloidal component of the parallel flow, thereby significantly impacting the plasma transport there. However, its direct observation has been challenging because the drift velocity (102-103 m/s) is significantly below the detection limit of conventional diagnostics. To realize cross-field ion flow measurement, a variety of systematic uncertainties in the system must be narrowed down. Here, we develop a conceptual design of the Doppler spectrometry that enables us to measure the impurity flows with 102-m/s accuracy based on an in situ wavelength-calibration technique developed in the astrophysics field, the iodine-cell method. We discuss its properties and applicability. In particular, the scaling relation between wavelength accuracy and various spectroscopic parameters is newly presented, which suggests the high importance of the wavelength resolution of the system. Based on transport simulations for the JT-60SA divertor, the feasibility of the system is assessed.

A novel method of reconstructing planar flow field from given distribution of single velocity component: comparison to conventional divergence-free approach

Measurements of a single flow velocity component are still prevalent due to their reasonable costs and some difficulties in multiple-component measurements. If the transverse component can be obtained additionally by a numerical technique, qualitative features of the flow will be understood more effectively. In this context, methods based on the 2-dimensonal divergence-free assumption have been widely used for problems in which a single velocity component is measured over a planar domain. In this study, the authors proposed a method of approximating the second planar velocity component by minimising an objective function expressed with divergence and vorticity so that the mass transport in the out-of-plane direction could be taken into consideration. The present method was tested with numerically produced 3-dimensional flows in a hexahedral chamber and a flow around a bluff body measured by particle image velocimetry. There was a tendency that the present method calculated the second velocity component with smaller errors than existing divergence-free approaches. It was also shown that the present method had a high capability to locate strong suction and generation caused by the mass transport in the out-of-plane direction. The present method is deemed promising for many one-component flow measurements in engineering and medicine.

Effect of trailing-edge blowing on the acoustic and aerodynamic characteristics of a flatback airfoil

This study investigated the impact of trailing-edge uniform air blowing on the acoustic and aerodynamic characteristics of a flatback airfoil. Near- and far-field pressure fluctuations, surface static pressure distribution, as well as boundary layer and wake flow measurements were conducted to comprehensively understand the effects of the method on both the noise generation mechanism and the aerodynamic characteristics of the airfoil. It was revealed that tonal noise originates from surface pressure fluctuations induced by upstream flow disturbances due to vortex shedding. The application of blowing was found to shift large-scale vortices generated during vortex shedding further downstream, resulting in the suppression of surface pressure fluctuations on both the pressure and suction sides of the airfoil, consequently reducing far-field noise. Additionally, blowing enhanced spanwise coherence at the vortex shedding frequency. In terms of aerodynamic behavior, blowing was shown to increase base pressure, leading to drag reduction without affecting lift. Interestingly, the significant drag reduction was found to occur at the same blowing parameter associated with maximum tonal noise reduction.

Quantifying and visualizing abdominal hemodynamics in patients with Fontan circulation by 4D phase-contrast flow magnetic resonance imaging at 1.5 T

BackgroundLiver fibrosis has been recognized as a long-term morbidity associated with Fontan circulation (Fontan-associated liver disease, FALD). The pathophysiology of FALD is not completely understood and abnormal flow dynamics may be associated with this condition. Liver hemodynamics can be quantitatively evaluated with four-dimensional phase-contrast flow magnetic resonance imaging (4D PC flow MRI). The study aimed to evaluate suitability of liver 4D PC flow MRI in Fontan patients and relate flow measurements to normal values and FALD severity. Patients and methodsTwenty-two Fontan patients were examined by 4D PC flow MRI at 1.5 Tesla to assess mesenteric, portal, splenic, and hepatic venous blood flow. Severity of FALD was graded based on routine screening, including abdominal ultrasound and laboratory tests. ResultsMedian age was 18.5 (interquartile range, IQR 15.5–20.2) years. FALD was graded as “none or mild” in 16 and as “moderate to severe” in six cases. Ten patients presented at least one feature of portal hypertension (ascites, splenomegaly, or thrombocytopenia). For the entire cohort, blood flow in the superior mesenteric, splenic, and portal vein was lower than reported in the literature. No significant differences were observed in relation to FALD severity. Features of portal hypertension were associated with a higher splenic vein blood flow (0.34 ± 0.17 vs. 0.20 ± 0.07 l/min, p = 0.046). Splenic vein blood flow was negatively correlated to platelet count (r = −0.590, p = 0.005). Conclusions4D PC flow MRI appears suitable to assess liver hemodynamics in Fontan patients and integration into clinical follow-up might help to improve our understanding of FALD.

An exploratory study on bamboo permeability for evaluation of treatability with chemical solutions

The rapid and uniform impregnation of resins and preservative fluids is critical to improving the quality and durability of wood-based materials. Permeability coefficients obtained in laboratory experiments aid in the development of optimal conditions for uniform resin filling on an industrial scale. However, due to the shape and orientation of pores in the bulk structure of bamboo, simplified permeability equations may not be sufficient to provide realistic resin impregnation predictions. In this study, the permeability coefficients for Dendrocalamus asper bamboo were determined using air flow measurements and Forchheimer's equation in the x, y, and z directions, and they were correlated to the bamboo microstructure, providing a detailed perspective on how to further investigate this property for real-world applications, such as pressure treatments with chemical solutions. Porosity was measured using mercury intrusion porosimetry (MIP) and water immersion methods to aid in the permeability analysis. The results showed that the longitudinal direction had 1000 to 10,000 times higher permeability coefficients than the radial and tangential directions. This finding is consistent with the alignment of transport vessels as well as the limited pore network in the transversal bamboo section. The outer region of bamboo had higher radial permeability than the middle and inner layers, despite having lower porosity. It is hypothesized that the greater number of vessels, albeit smaller, provides a more direct path for air to flow. The Darcian permeability coefficients of bamboo were found to be comparable to those reported in the literature for wood. This exploratory study provided insights into a novel approach for assessing the treatability of bamboo species.