Cross-sectional Velocity Research Articles

Statistical roughness properties of the gravel bed surfaces in a meandering channel

To investigate the statistical roughness properties of gravel bed surfaces in meandering channels, a meandering channel model is constructed, the flowrate is selected as the control variable, and the cross-sectional water levels, cross-sectional velocities and bed surface elevations are measured. The experimental results show that the elevation probability distributions of the detrended water-worked bed surfaces in the meandering channel are positively skewed and leptokurtic. With the increasing flowrate, the elevation standard deviation and the elevation skewness increases, but the elevation kurtosis decreases. The armoring layer in the meandering channel can resist a certain extent of increasing flow strength, but its protective ability is very limited. Once the armoring layer is destructed, the bed surface roughness will increase significantly. The bed surface roughness and the averaged influence scale of the constituent grains are large in the main stream path, while those in the main stream separating areas are small and decrease along the longitudinal direction. For any local zone, the roughness and the averaged influence scale in the longitudinal direction are obviously larger compared with the corresponding values in the lateral direction.

Velocity String Drainage Technology for Horizontal Gas Wells in Changbei

The Changbei gas field is dominated by wells with large horizontal displacement, which have exhibited high gas production performance at an early stage of development. With the decrease in reservoir pressure, the liquid loading in the gas well is relatively high and gas production rapidly decreases. Therefore, suitable drainage measures are required to maintain stable gas production. Based on the characteristics of the unconnected oil jacket of gas wells in Changbei, a velocity string was used for drainage. A critical liquid-carrying model was established to determine the location of liquid loading in horizontal gas wells in Changbei. First, the coefficients of the liquid-carrying model were determined through theoretical analysis of the characteristics of the gas well formation. Then, the depth setting of the velocity string was analyzed. The critical liquid-carrying model was employed to calculate the liquid-carrying flow rate of each section; the calculated flow rates were compared with the actual flow rates to determine whether fluid accumulation occurred in each section of the gas well. Thereafter, with the help of the oil and casing position, the suitable setting position of the velocity string was determined. The formation fluid was driven from the tubing into the casing owing to the increase in the overflow area, based on the principle of reducer fluid mechanics. The fluid velocity in the larger overflow cross-section decreased, thereby reducing the drainage capacity of the gas well and resulting in liquid loading. Finally, a timing analysis was performed. After the formation pressure decreased, the well production and flow rate changes were analyzed by placing two velocity strings of different sizes at different wellhead pressures in the gas well with fluid accumulation. The results indicated that although the velocity string was set at a position suitable for fluid drainage, fluid accumulation still occurred after a production period, thus necessitating replacement deliquification.

Experimental Study of Bubble Dispersion Characteristics in a Nonuniform Electric Field

The application of electric fields can intensify the dispersion characteristics of discrete phase in continuous phase. In charged liquid–gas dispersion systems, there are important processes, such as bubble formation, motion, and interaction, which are quite different from hydrodynamic processes without external fields. In the present study, the bubble dispersion characteristics were experimentally studied in ethanol under a direct current (DC) nonuniform electric field. By considering the voltage and flow rate, the dispersion pattern, trajectory, size distribution, velocity, and deformation of the bubbles were examined using high-speed photography. A considerable control over the bubble dispersion patterns, including isolated, chain, and diffusion patterns, can be achieved by careful consideration of the experimental parameters. The bubbles dispersion in liquid under the electric field can detach with a considerably smaller diameter than that without electric field. Both the increase in electrical Bond number (BoE) and gas Reynolds number (Reg) intensifies the interaction between bubbles. The BoE works to accelerate the separation of smaller bubbles, while the Reg works to reinforce the wake induction. In addition, the cross-sectional bubble size distributions, velocities, and bubble shapes corresponded to the bubble dispersion patterns.

Numerical Investigation of Flow Characteristics for Gas–Liquid Two–Phase Flow in Coiled Tubing

Coiled tubing (CT) is widely used for horizontal well fracturing, squeeze cementing, and sand and solid washing in the oil and gas industry. During CT operation, a gas–liquid two-phase flow state appears in the tubing. Due to the secondary flow, this state produces a more extensive flow-friction pressure loss, which limits its application. It is crucial to understand the gas–liquid flow behavior in a spiral tube for frictional pressure drop predictions in the CT technique. In this study, we numerically investigated the velocity distribution and phase distribution of a gas–liquid flow in CT. A comparison of experimental data and simulated results show that the maximum average error is 2.14%, verifying the accuracy of the numerical model. The gas and liquid velocities decrease first and then rise along the axial direction due to the effect of gravity. Due to the difference in the gas and liquid viscosity, i.e., the flow resistance of the gas and liquid is different, the gas–liquid slip velocity ratio is always greater than 1. The liquid velocity exhibits a D-shaped step distribution at different cross-sections of spiral tubing. The secondary-flow intensity, caused by radial velocity, increases along the tubing. Due to the secondary-flow effect, the zone of the maximum cross-section velocity is off-center and closer to the outside of the tube. However, under the combined action of centrifugal force and the density difference between gas and liquid, the variation in the gas void fraction along the tubing is relatively stable. These research results are helpful in understanding the complex flow behavior of gas–liquid two-phase flow in CT.

Spatiotemporally resolved 5-MHz visualization and particle image velocimetry in early time multiphase blasts

Explosive blasts, used in a variety of engineering applications, have coupled multiphase dynamics, and require high-fidelity spatiotemporally resolved measurements to understand and accurately predict key design parameters. This study evaluates burst-mode laser-based particle-field visualization and particle image velocimetry (PIV) for planar measurements up to 5 MHz. This enhancement of time-resolved PIV represents an order-of-magnitude increase over the prior state of the art enabling measured velocities in the km/s regime. The technique is applied to a multiphase blast’s early (<10 µs) development to quantify the cross-sectional flow structure, velocity, acceleration, and pressure within the rapidly expanding particle field. The morphological evolution of the solid explosive products is characterized by a scale-independent shape parameter and the fractal dimension. This analysis highlights two flow development regimes (separated by 2 µs) in the expansion process. The high measurement resolution enables the characterization of significant differences in velocity and acceleration between the primary and secondary expansion directions. These orthogonal directions are located where the shock is attached and detached respectively from the solid products: each is driven by different forces in the flow. These measurements yield information about complex transport processes and may be useful for subsequent validation of high-fidelity multiphase blast simulations.

Abstract 13551: Non-Invasive Assessment of Systemic Microvascular Function in Patients With Severe Aortic Stenosis Pre- and Post- Transcatheter Aortic Valve Intervention

Background: Aortic stenosis (AS) is associated with pathophysiological changes in both left ventricular and coronary microvascular structure and function. The treatment of AS with transcatheter aortic valve replacement (TAVR) has been associated with improvements in invasive indices of coronary microvascular function. This study sought to address whether systemic microvascular dysfunction was present in patients with AS and if microvascular function was altered by treatment of aortic stenosis with TAVR. The conjunctival microcirculation was used as the site for the non-invasive assessment of systemic microvascular function. Methods: Patients undergoing TAVR for the treatment of severe AS were compared to a cohort of age- and sex-matched controls without valvular heart disease. Conjunctival vascular imaging was performed in all subjects using a previously validated combination of a smartphone and slit-lamp biomicroscope. This technique allowed measurement of vessel diameter and other indices of microvascular function by tracking erythrocyte motion. Conjunctival hemodynamics were compared pre- and post-TAVR, in addition to between the severe AS and control cohorts. Results: A total of 165 patients were included (90 severe AS and 75 controls). Baseline characteristics were well matched between groups. In comparison to the control cohort, arteriole axial (Va) and cross-sectional velocity (Vcs) were significantly lower in females with AS (Va severe AS 0.53 ± 0.11mm/s vs control 0.59 ± 0.12mm/s, p=0.047; Vcs severe AS 0.38 ± 0.07mm/s vs control 0.41 ± 0.08mm/s, p=0.043), but not in males (Va severe AS 0.61 ± 0.11mm/s vs control 0.58 ± 0.10mm/s, p=0.19; Vcs severe AS 0.43 ± 0.08mm/s vs control 0.41 ± 0.07mm/s, p=0.20). Arteriole Va and Vcs significantly increased following TAVR in females (Va Pre-TAVR 0.52 ± 0.16mm/s vs post-TAVR 0.59 ± 0.15mm/s, p&lt;0.001; Vcs Pre-TAVR 0.37 ± 0.11mm/s vs post-TAVR 0.42 ± 0.11mm/s, p&lt;0.001). Conclusion: This study highlights sex-specific differences in conjunctival microvascular function in patients with severe AS. In this study TAVR resulted in significant improvements in conjunctival arteriolar V a and V cs . These findings are consistent with severe AS being a reversible cause of systemic microvascular dysfunction.

Estimating forces from cross-sectional data in the wake of flows past a plate using theoretical and data-driven models

We report a comparative study of theoretical and data-driven models for estimating forces from velocity data in the wake of three-dimensional flows past a plate. The datasets with a range of angles of attack are calculated using the immersed boundary method. First, we develop a theoretical model to estimate forces on a flat plate from cross-sectional velocity data in the far wake. This algebraic model incorporates the local momentum deficit and pressure variation. Second, we develop several data-driven models based on the convolutional neural network (CNN) for force estimation by regarding the velocity field on a series of cross sections as images. In particular, we design three CNN architectures for integrating physical information or attention mechanism, and use different training datasets for interpolation and extrapolation tasks. The model performances indicate that the optimized CNN can identify important flow regions and learn empirical physical laws. The theoretical and CNN models are assessed by multiple criteria. In general, both models are accurate (with errors less than 10%), robust, and applicable to complex wake flows. The theoretical model is superior to the CNN model in terms of the completeness, cost, and interpretability, and the CNN model with the appropriate training data and optimized CNN architecture has better description and accuracy.

Design of signal processing circuit for acoustic Doppler Current Profiler

according to the measurement principle and performance requirements of acoustic Doppler velocity profile, a circuit for weak frequency signal processing is designed. The measurement principle, circuit structure, data comparison before and after signal processing and frequency measurement accuracy data analysis are introduced. The performance comparison and application of the instrument are carried out according to the relevant standards. The experimental results show that the signal processing circuit realizes the constant amplitude amplification of the wide dynamic range frequency signal, and the processed signal is converted by A / D and then measured by digital frequency to obtain a high frequency accuracy. In the application of channel flow measurement, the velocity profile can reflect the change trend of cross-section velocity and complete the accurate measurement of flow rate. It shows that the flow profile instrument based on the signal processing circuit can meet the requirements of on-line monitoring of flow velocity and flow of river and channel.

Development and validation of non-invasive endothelial shear stress (ESS) estimations of coronary artery haemodynamics using computational modelling

Abstract Background Vascular remodelling is influenced by various biomechanical forces such as endothelial shear stress (ESS) and is associated with development and progression of coronary artery disease (CAD). ESS is the parallel frictional force exerted by blood flow on the endothelial luminal surface of the arterial wall. While ESS may not be the only cause of atherosclerosis, it is postulated that low ESS creates a pro-atherogenic environment and high ESS is athero-protective. Computational fluid dynamics (CFD) is an engineering method used to analyse fluid flow and has been increasingly applied to simulate ESS in cardiovascular research. However, current CFD-derived ESS estimates have never been validated and can display significant variability between research groups. Purpose This study aims to provide a comparative analysis of coronary flow using in-silico modelling of coronary flow and particle image velocimetry (PIV). Methods A proximal left anterior descending (pLAD) coronary phantom model was constructed from a patient who had received same day cardiac computed tomography angiography (CTCA) and invasive coronary haemodynamic (Combowire XT) assessment. Patient-specific coronary flow data was applied to CFD boundary conditions and a mock circulatory loop. CFD was validated using PIV under steady flow in a 4-times-scaled model. Same plane velocity field and flow patterns (at mid-luminal of pLAD) from both in-silico and in-vivo data were compared and analysed. Results Mean velocity contours and magnitude were analysed from CFD and PIV. Patient specific average peak velocity obtained from invasive assessment was 0.21m/s. Patient-specific velocity average from CFD was 0.22m/s. The approximated magnitude difference is 4.7%. Both same-axial average cross-sectional velocity estimated by CFD-pLAD and PIV-pLAD are 0.087m/s. Velocity contours and flow patterns simulated in the CFD were also comparable with the PIV results. Conclusion Simulation data from CFD correlate well with experimental PIV results. This early data allows for a non-invasive approach to determine patient-specific coronary haemodynamics (such as velocity profiling and ESS) and form the basis of personalising cardiovascular risk. Insights from this work may aid future development of a novel tool that incorporates CFD-derived ESS estimates with patient-specific risk factors to better predict rapid CAD progression. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): Cardiac Society of Australia and New Zealand Monash Institute of Medical Engineering

Hydrodynamic characteristics of grass swale runoff in Guanzhong area of Loess Plateau, Northwest China.

Grass swale has been widely used in sponge city construction, which can effectively improve the urban ecological environment. To explore the regulation mechanism of runoff in grass swale, runoff scouring experiment was carried out to study the hydrodynamic characteristics of runoff and the distribution of cross-section velocity under the combined conditions of five slopes (1%, 2%, 3%, 4%, 5%) and five scour flows (20, 30, 40, 50, 60 L·min-1). With the increases of flow rate and slope, flow velocity, Reynolds number and Froude number all increased gradually, while the Manning roughness coefficient and Darcy-Weisbach friction coefficient decreased gradually. The velocity (V) could be expressed as a power function V=0.3387Q0.555S0.6601 of flow rate (Q) and slope (S). The variation ranges of Reynolds number and Froude number were 1160.95-6596.82 and 0.17-1.21, respectively. The runoff flow patterns were all turbulent. The flow pattern was greatly affected by the slope. When flow rate and slope were small, they had great influence on friction coefficient. Under the experimental conditions, the Darcy-Weisbach friction coefficient was negatively correlated with Reynolds number. The velocity distribution of cross-section showed symmetrical distribution on both sides of the center. The maximum velocity point was located at the center of water surface. With the increases of flow rate and slope, the velocity contours of cross section gradually became dense and the gradient of the velocity change increased. Our results provide a theoretical basis for the design, application and hydraulic calculation of grass swale in the construction of sponge cities in loess areas, and reveal the runoff regulation mechanism by analyzing the hydraulic characteristics of grass swale runoff.

Fiber-Concentration Distributions of Pulp Suspension Flow behind a Partition Plate Inserted in a Channel as Applied to a Papermaking Machine

This study involved an experimental investigation of the distribution of pulp fiber concentration in the region behind a partition plate with a tapered trailing-edge inserted in a convergent channel. The channel was modeled at the laboratory scale for the dispersion and rectification components of the headbox passage in a papermaking machine. For the experiments, the inlet cross-sectional average flow velocity, USUBa/SUB, of an actual pulp suspension was in the range of 0.03-3.3 m/s. The flow was visualized, and the fiber-concentration distribution was measured. Subsequently, the effects of the flow velocity on the time-averaged and fluctuating fiber-concentration distributions (CSUBa/SUB and C’, respectively) in the flow direction were examined through comparisons with those in the cases where the plate was installed in the parallel channel or had a simple rectangular edge. In the convergent channel with the tapered trailing-edge, the fiber-concentration defect behind the plate was reduced abruptly. Moreover, the uniformity of the fiber-concentration distribution at the convergence exit did not vary with the flow velocity, thereby having a low value. Overall, the fundamental observations obtained in this study can contribute to the optimization and improvement of the headbox channels of papermaking machines.

The Influence of Floodplain Vegetation Patches on Hydrodynamic Characteristics: A Case Study in the Old Course of Fuhe River

As an important part of the river ecosystem, vegetation has a significant influence on hydrodynamic characteristics, water quality, river morphology, and ecological habitat. Combining vegetation survey with the verified numerical model, this study aims to analyze the impact of floodplain vegetation patches on hydrodynamic characteristics in the old course of Fuhe River under various combinations of incoming flow discharges, and flood diversion discharges, and changes in the land use type. The equivalent Manning coefficient was adopted to quantify the additional resistance induced by plants in the vegetation module of the numerical model. According to simulating results, vegetation patches would cause the water level to rise and velocity to decrease, which mainly affects the upstream of the old course of Fuhe River. And with the increase in incoming discharge, water level difference and velocity difference have an upward trend. It is also found that the resistance of Zizania latifolia to river flow is strongest followed by sugarcane, crops, and weeds because of the differences in vegetation characteristics. Furthermore, compared with existing vegetation conditions, converting farmland to Zizania latifolia and expanding farmland induce a moderate rise in water level upstream while the decreasing velocity happens in the area where land use type is changed. And there are areas where velocity increases located opposite to the velocity decreasing area because of the adjustment of cross-section velocity distribution caused by plants.

Experimental Study on Grouting and Flow Characteristics of Rough Vertical Fractures

It is of great engineering significance to study the seepage characteristics and flow field distribution of rough fractured rock masses for grouting to stop leakage. Through the visual fracture seepage test device we developed, the visual seepage characteristics of tension fractures under vertical angles and different stress paths of grout and water were studied. Through silica gel secondary mould turning technology, the fracture morphology is accurately reprinted; based on GIS simulation technology, the visualization of the fracture surface spatial data is realized; the actual seepage area and flow path of the fluid are measured accurately by using digital image self-recognition technology, and the variation law of the grout and water seepage area under the coupling of normal stress and water pressure is obtained. Through visualization, it is pointed out that, with the increase of normal stress, the fracture water can be divided into three stages, archipelago flow, transition flow, and groove flow, while the grout has no capillary permeability and no archipelago flow effect because of its high viscosity. The critical point of grout antiseepage is defined and calibrated by data. Based on the analysis of the cross-sectional velocity of the groove flow, it is pointed out that the relationship between the velocity on the flow path and JRC is an exponential function. The main flow path is mainly distributed in the area where the JRC is relatively small. As the normal stress increases, the first deflection point of the grout flow path appears in the maximum region of JRC (6.42); the secondary deflection point appears in the second largest region of the flow path JRC (4.53), and the fluid of deflection point has the maximum kinetic energy on the main flow path. The current study can accurately obtain the relevant parameters of vertical fracture grouting seepage characteristics and provide theoretical guidance for solving the key scientific problems in grouting engineering, such as invisible flow paths and unmeasurable velocity vectors.

Effect of inlet volute wrap angle on the flow field and performance of double inlet gas cyclones

In response to the divergent understanding of double inlet cyclone performance in the literature, the effect of inlet volute wrap angle on the performance and flow field of double inlet cyclone separator was studied by Computational Fluid Dynamic (CFD) method. The results showed that the inlet volute wrap angle can affect the comparison results of the single and double inlet gas cyclones with the same total inlet cross-sectional area and velocity. 0° and 90° volute double inlet improved the efficiency mainly by separating particles below 10 μm, while 180° volute double inlet had no separation advantage for any particles, so the symmetrical double inlet does not always improve the efficiency, and the appropriate inlet volute wrap angle should be selected according to the actual situation, otherwise, the expected performance requirements of the symmetrical double inlet cyclone cannot be achieved. Compared with the flow field, it is found that the inlet volute wrap angle changed the tangential velocity of the symmetrical double inlet cyclone separator, thus changing the performance.

Study on the Hydraulic Characteristics of the Trapezoidal Energy Dissipation Baffle Block-Step Combination Energy Dissipator

The step-type energy dissipator is widely used to construct small- and medium-sized reservoirs with its high energy dissipation rate. In order to further improve its air entrainment characteristics and energy dissipation, and reduce the influence of cavitation, in this paper, we added a trapezoidal energy dissipation baffle block at the convex corner of the traditional step to form a trapezoidal energy dissipation baffle block-step combination energy dissipator. We used a combination of hydraulic model experiments and numerical simulation to study the hydraulic characteristics. The results showed that the trapezoidal energy dissipation baffle block-step combination energy dissipator initial entrainment point, with the increase in flow rate, gradually moved backward. A step horizontal surface pressure change in the cavity recirculation area showed a prominent “V” shape; in front of the trapezoidal energy dissipation baffle block, there was a rising trend, and in the energy dissipation baffle block gap, there was a declining trend. The step vertical surface pressure showed a decreasing trend, and negative pressure appeared near the convex angle. The cross-section velocity distribution presented a trend of being small at the bottom and large at the surface, with a large velocity gradient in the longitudinal section of the energy dissipation baffle block and a small velocity gradient in the longitudinal section of the nonenergy dissipation baffle block. The energy dissipation rate reached more than 70% within the test range, and the energy dissipation rate gradually decreased with the increase in the flow rate. The combined energy dissipator is conducive to reducing the cavitation hazard and improving the energy dissipation effect, providing a reference for engineering design and existing step energy dissipators to remove risks and reinforcement.

Experimental study of self-sustained spanwise streaks and turbulent mixing in separated shear flow

The self-sustained streaks in turbulent backward-facing step flow are experimentally studied at a step height Reynolds number of 1.0 × 103. As one of the featured dynamic behaviors, evolution of the spanwise streaks plays an important role in the large-scale, aperiodic and vertical flapping motions of the separated/reattaching shear layer. By time-resolved particle image velocimetry, we measure the velocity vector fields in the streamwise-spanwise and streamwise-vertical planes downstream of a two-dimensional backward-facing step. The two cross-sectional velocity fields show that the shear layer remains two-dimensional along the span in the initial half of the shear layer, and then three-dimensional structures start to evolve in the latter half, leading to an unsteady reattaching shear layer and a shifting reattachment point on the downstream wall. By analyzing the finite-time Lyapunov exponent in the spanwise field of view, we find that low-speed fluid elements are vertically entrained upwards into the shear layer. As a result, the entrained fluid elements produce transient and localized low-speed fluid patches in the streamwise-spanwise plane, which move and decay downstream with strong straining and stretching motions along their boundaries. Furthermore, the large-scale streak-type and flap-type flows are clearly extracted and reconstructed by the energy-containing proper orthogonal decomposition modes.

A new calculation model of critical liquid-carrying velocity in inclined wells based on the principle of liquid film delamination slippage

Liquid loading has always been a production problem in the middle and late production of gas wells. Severe loading will even lead to the shutdown of gas wells. In actual production, critical liquid-carrying velocity is often used to judge the loading of gas wells. Most conventional calculation models are modified vertical pipe models for the critical liquid-carrying gas velocity of an inclined pipe. They are established based on liquid film inversion without considering the characteristics of liquid film delamination slippage. In this study, the elliptical distribution model of the liquid film of the inclined pipe is first established. Then the cross-sectional velocity distribution model is coupled to solve the cross-sectional flow rate integrally. When the cross-sectional liquid flow rate is 0, the gas velocity is the critical liquid carrying velocity. Model calculations reveal that the critical liquid-carrying velocity is the largest when the inclination angle is 50°, consistent with experimental data. Using the data of production wells in the Changning block, Sichuan, China, to analyze well loading, the accuracy between the prediction results of loading in this study and field production judgment reached 93.75%, which is 25% higher than that of the Belfroid model. The model in this study accounts for the delamination slippage of the liquid film for the first time, and the calculated critical liquid carrying velocity can better reflect the flow state of gas-liquid two-phase flow in inclined pipe, which is beneficial for researchers to accurately evaluate and understand the production status of gas wells.

OPERATION FEATURES OF AN ULTRASONIC FLOW TRANSDUCER WITH A COMPLEX TRAJECTORY OF THE MEASURING PATH

To measure the flowrate of fuel and energy resources, different methods are used, which determine the range of measuring instruments. Instruments based on ultrasonic measurement methods are widely used in measurement practice due to the provision of high accuracy, a wide range of measured flowrates, the absence of additional pressure losses and the design simplicity. Such instruments are easily integrated into automated readout systems for collecting and transmitting information. The asymmetry of the measured medium flow is a significant problem in the use of single-channel ultrasonic meters. This issue is successfully solved by using multi-channel flow transducers.&#x0D; The disadvantages of multi-channel ultrasonic flow transducers include a significant complication of the hydraulic channel design, the need to use more complex mathematical algorithms for processing the obtained output signal. This requires the use of high performance electronic elements, first of all microprocessors.&#x0D; The use of a transducer with multiple reflection of one measuring beam from the wall of the measuring path acts as an alternative to multi-channel measurement.&#x0D; The aim of the work is to create a mathematical model of an ultrasonic flow transducer with a complex measuring path trajectory. For research, a scheme with sounding along three chords was chosen, which implements the time-pulse measurement method, it provides for determining the flow rate by the difference in the time of passage of the measuring path along the flow and against it. In this case, the projections of the chords on the cross section of the measuring section create an equilateral triangle. An analytical expression for the conversion response is obtained for the case of several beam reflections in different planes.&#x0D; The authors reproduced the hydraulic part of the investigated flow transducer using simulation modeling implemented on the basis of the finite element method. Transducer’s operation simulation in the range of measured flow rates in the conditions of an ideally formed profile of the gas flow velocity in the transducer inlet cross-section has been carried out. The results obtained confirmed the absence of influence of the measuring circuit elements (beam reflectors) on the flow profile and the measuring beam trajectory.&#x0D;

Discrete Bubble Flow in Granular Porous Media via Multiphase Computational Fluid Dynamic Simulation

The coal seam gas industry has raised public concerns about the potential risk of groundwater contamination, where gases leaked from coal seams are thought to pollute groundwater. However, the basic principles and controlling parameters for gas seepage from deep ground formations to the ground surface have not been fully understood. As a possible mechanism for gas transport in the subsurface environment, discrete bubble flow was previously investigated using laboratory experiments by Ma et al. (Water Resour. Res, 2015, 51 (6), 4359–4373). This study developed a multiphase computational fluid dynamic (CFD) model to simulate discrete bubbly flow in a two-dimensional granular porous media at the pore scale. Following the experimental setup from Ma et al. (Water Resour. Res, 2015, 51 (6), 4359–4373), a “point source” with preset bubble fluxes was specified in a simulating domain representing the flume size in the earlier experiments. There were around 7,000 granular particles within this domain to model the porous media. This numerical model was validated by conserving the gas mass in the simulating domain. The simulation results provide more physical insights into complex bubble transport behaviour in porous media through specific plume parameters. The breakthrough time of the bubble plume and the cross-sectional averaged velocity of ambient pore water flow were manifested to be proportional to the gas release rates in the logarithmic scales. Also, the bubble plume width was also observed to be proportional to the gas release rates. Moreover, the gas distribution on the top boundary could be observed. The outcomes were further tested against the scaling solutions proposed by Ma et al. (Water Resour. Res, 2015, 51 (6), 4359–4373) with disagreements. The limitations of this multiphase computational fluid dynamic model were finally discussed.

Laser Doppler velocimetry for three-dimensional distribution measurement of the velocity component by combining two-dimensional spatial encoding and non-mechanical scanning.

We present a differential laser Doppler velocimeter (LDV) for measuring the velocity distribution in a three-dimensional (3D) space. Our conventional research so far has proposed some methods for measuring two-dimensional (2D) distribution measurement. One of the proposed methods was spatial encoding of measurement points arranged on a 2D plane. Besides, we also have proposed laser Doppler cross-sectional velocity distribution measurement based on a non-mechanical scanning method. We propose a 3D method by combining 2D spatial encoding and non-mechanical scanning, in which the measurement points distributed on a 2D plane are spatially encoded with different bias frequencies, and these points are scanned non-mechanically in another direction by changing the wavelength. As a feasibility study of the proposed method, experiments were conducted using a 4×4 channel optical setup and were performed at five wavelengths over 1537-1553 nm. The experimental results indicate that the proposed method could successfully measure the 3D distribution of the velocity component. The spectral peaks of the beat signals for 68 measurement points for the rotational speed of the target of 2.0s-1 and those for 67 measurement points for the rotational speed of -2.0s-1 out of 80 measurement points were successfully observed within the measurement error of 2.8%-4.8%.