Three-dimensional Velocity Research Articles

Detailed unsteady dynamics of flame-flow interactions during combustion instability and its transition scenario for lean-premixed low-swirl hydrogen turbulent flames

This experimental study elucidates the unsteady dynamics of flame-flow interactions during unique thermoacoustic instability (TI) and the transition mechanism from stable combustion to TI for lean-premixed hydrogen turbulent jet flames in a low-swirl combustor (LSC), where a swirler assembly consists of an unswirled central region (CR) and an annular swirler region (SR). Simultaneous 200-kHz pressure fluctuation p’ measurements and 10-kHz OH* chemiluminescence imaging, as well as 40-kHz stereoscopic particle image velocimetry (SPIV) and two-dimensional PIV measurements for steady-state and transient data acquisitions, respectively, were conducted. The SPIV was performed in multiple planes to explore three-dimensional velocity fields. During TI, periodic flashback was possibly caused by significant axial velocity oscillations, resulting in the local mixture velocity falling below the turbulent flame speed. The large-scale vortex ring generated by the velocity oscillations caused axisymmetric radial velocity Vr oscillations with switching signs during the TI period. Similar to a typical low-swirl flow, the positive Vr away from the combustor axis created diverging flow, whereas unlike the typical flowfield, the negative Vr toward the combustor axis generated converging flow while flattening the axial velocity distributions, which was the signature phenomenon for this TI. Using the transient data and dynamic mode decomposition, variations in delay times between the mixture injection and its convection to a region with positive local Rayleigh indices were investigated. During stable combustion, the mixture jet from the SR predominantly induced thermoacoustic coupling (TC). As the combustion transitioned into the TI, the mixture jet from the CR began to induce TC and, eventually, achieved predominance in inducing TC during fully evolved TI. The transition from the SR jet- into CR jet-dominant TI arising from the dynamic flame-flow interactions resulted from the inherent physical characteristics of hydrogen flames, thereby yielding the larger p’ amplitude compared to typical TIs.

A Framework for Distributed LEO SAR Air Moving Target 3D Imaging via Spectral Estimation

This paper aims to perform imaging and detect moving targets in a 3D scene for space-borne air moving target indication (AMTI). Specifically, we propose a feasible framework for distributed LEO space-borne SAR air moving target 3D imaging via spectral estimation. This framework contains four subsystems: the distributed LEO satellite and radar modeling, moving target information processing, baseline design framework, and spectrum estimation 3D imaging. Firstly in our method, we develop a relative motion model between the satellite platform and the 3D moving target for satellite and radar modeling. In a very short time, the relative motion between the platform and the target is approximated as a uniform motion. We then establish the space-borne distributed SAR moving target 3D imaging model based on the motion model. After that, we analyze the influencing factors, including the Doppler parameters, the three-dimensional velocity, acceleration, and baseline intervals, and further investigate the performance of the 3D imaging of the moving target. The moving target spectrum estimation 3D imaging finally obtains the 3D imaging results of the target, which preliminarily solves the imaging and resolution problems of slow air moving targets. Simulations are conducted to verify the effectiveness of the proposed distributed LEO space-borne SAR moving target 3D imaging framework.

4D flow MRI in abdominal vessels: prospective comparison of k-t accelerated free breathing acquisition to standard respiratory navigator gated acquisition

Volumetric phase-contrast magnetic resonance imaging with three-dimensional velocity encoding (4D flow MRI) has shown utility as a non-invasive tool to examine altered blood flow in chronic liver disease. Novel 4D flow MRI pulse sequences with spatio-temporal acceleration can mitigate the long acquisition times of standard 4D flow MRI, which are an impediment to clinical adoption. The purpose of our study was to demonstrate feasibility of a free-breathing, spatio-temporal (k−t) accelerated 4D flow MRI acquisition for flow quantification in abdominal vessels and to compare its image quality, flow quantification and inter-observer reproducibility with a standard respiratory navigator-gated 4D flow MRI acquisition. Ten prospectively enrolled patients (M/F: 7/3, mean age = 58y) with suspected portal hypertension underwent both 4D flow MRI acquisitions. The k−t accelerated acquisition was approximately three times faster (3:11 min ± 0:12 min/9:17 min ± 1:41 min, p < 0.001) than the standard respiratory-triggered acquisition. Vessel identification agreement was substantial between acquisitions and observers. Average flow had substantial inter-sequence agreement in the portal vein and aorta (CV < 15%) and poorer agreement in hepatic and splenic arteries (CV = 11–38%). The k−t accelerated acquisition recorded reduced velocities in small arteries and reduced splenic vein flow. Respiratory gating combined with increased acceleration and spatial resolution are needed to improve flow measurements in these vessels.

FSVPy: A python-based package for fluorescent streak velocimetry (FSV)

Predictive constitutive equations that connect easy-to-measure transport properties (e.g., viscosity and conductivity) with system performance variables (e.g., power consumption and efficiency) are needed to design advanced thermal and electrical systems. In this work, we explore the use of fluorescent particle-streak analysis to directly measure the local velocity field of a pressure-driven flow, introducing a new Python package (FSVPy) to perform the analysis. Fluorescent streak velocimetry combines high-speed imaging with highly fluorescent particles to produce images that contain fluorescent streaks, whose length and intensity can be related to the local flow velocity. By capturing images throughout the sample volume, the three-dimensional velocity field can be quantified and reconstructed. We demonstrate this technique by characterizing the channel flow profiles of several non-Newtonian fluids: micellar Cetylpyridinium Chloride solution, Carbopol 940, and Polyethylene Glycol. We then explore more complex flows, where significant acceleration is created due to microscale features encountered within the flow. We demonstrate the ability of FSVPy to process streaks of various shapes and use the variable intensity along the streak to extract position-specific velocity measurements from individual images. Thus, we demonstrate that FSVPy is a flexible tool that can be used to extract local velocimetry measurements from a wide variety of fluids and flow conditions.

Probabilistic approach for seismic microzonation integrating 3D geological and geotechnical uncertainty

A novel probabilistic methodology for regional seismic site characterization is proposed and applied to a region with highly heterogeneous surficial geology and varying soil sediment thickness and stiffness. The method combines various sources of geological and geotechnical uncertainties to develop a three-dimensional (3D) shear-wave velocity ( Vs) model and evaluate the associated uncertainties. A 3D geological model of the unconsolidated deposits was developed using geostatistical interpolation and simulation methods. Sequential indicator simulations produced a quantitative geologic model that explicitly quantified geological uncertainties based on the likelihood of specific soil types occurring. In situ measurements and multivariate statistical analysis allowed the development of empirical correlations between Vs, geotechnical parameters, depth, and soil types. The resulting 3D Vs values were estimated on the basis of Vs-depth correlations and the probability of occurrence of each soil type. In this approach, the propagated uncertainty was also quantified by considering the combined variance. Seismic microzonation mapping was then conducted by transforming the 3D Vs model into two-dimensional (2D) maps that represent the spatial distributions of the time-averaged shear-wave velocity of the top 30 m ( Vs,30) and the fundamental site period ( T0), along with their respective uncertainties using Monte Carlo simulations. The results indicate that microzonation maps and their uncertainties are influenced by the thickness, occurrence probability, and geotechnical properties of soils. The proposed method can be used to assess the probabilistic seismic risk at local and regional scales in areas with geologically and geotechnically complex soil properties.

CMT inversion for small-to-moderate earthquakes applying to dense short-period OBS array at off Ibaraki region

We conducted centroid moment tensor (CMT) inversion for small-to-moderate aftershocks in the off Ibaraki region of the 2011 off the Pacific coast of Tohoku earthquake. In this study, we used high-frequency (0.4–1.0 Hz) seismograms from a dense array of short-period ocean bottom seismometers (OBSs) and a reliable three-dimensional (3-D) seismic velocity model. Higher frequency analysis and dense OBS arrays offer CMT solutions with high spatial resolutions. Since our OBS array observed aftershocks occurring immediately following the 2011 off the Pacific coast of Tohoku earthquake, we determined 536 CMT solutions for small-to-moderate aftershocks in the off Ibaraki region (JMA-scale magnitudes of 2.5–4.0). According to our CMT solutions, characteristics of the aftershock activities in the off Ibaraki region are classified into 5 groups: (1) thrust earthquakes, which are considered as interplate earthquakes, separated by the large slip area of the 2011 Ibaraki-oki earthquake (the largest {mathrm{M}}_{mathrm{w}} 7.6 aftershock of the 2011 off the Pacific coast of Tohoku earthquake) and the tectonic tremors; (2) intraslab strike-slip earthquakes located at the north of the fault area of the 2011 Ibaraki-oki earthquake; (3) intraslab normal-fault earthquakes, which suggest a tensional stress field within the subducting Pacific Plate due to the plate bending by the overriding Philippine Sea Plate; (4) various earthquake focal mechanisms above a subducting seamount, which suggest the 3-D complex fractures; and (5) normal-fault earthquakes shallower than the interplate earthquakes, which were possibly caused by the heterogeneity of the subducting seamount.Graphical

Numerical Study of the Coalescence and Mixing of Drops of Different Polymeric Materials.

In this study, we employ direct numerical simulation (DNS) to investigate the solutal hydrodynamics dictating the three-dimensional coalescence of microscopic, identical-sized sessile drops of different but miscible shear-thinning polymeric liquids (namely, PVAc or polyvinyl acetate and PMMA or polymethylmethacrylate), with the drops being in partially wetted configuration. Despite the ubiquitousness of the interaction of different dissimilar droplets in a variety of engineering problems ranging from additive manufacturing to understanding the behavior of photonic crystals, coalescence of drops composed of different polymeric and non-Newtonian materials has not been significantly explored. Interaction of such dissimilar droplets often involves simultaneous drop spreading, coalescence, and mixing. The mixing dynamics of the dissimilar drops are governed by interphase diffusion, the residual kinetic energy of the drops stemming from the fact that coalescence starts before the spreading of the drops have been completed, and the solutal Marangoni convection. We provide the three-dimensional velocity fields and velocity vectors inside the completely miscible, dissimilar coalescing droplets. Our simulations explicate the relative influence of these different effects in determining the flow field at different locations and at different time instances and the consequent mixing behavior inside the interacting drops. We also show the non-monotonic (in terms of the direction of migration) propagation of the mixing front of the miscible coalescing drops over time. We also establish that the overall mixing (on either side of the mixing front) speeds up as the Marangoni effects dictate the mixing. We anticipate that our study will provide an important foundation for studying miscible multi-material liquid systems, which will be crucial for applications such as inkjet or aerosol jet printing, lab-on-a-chip, polymer processing, etc.

Direct surface-wave tomography under Northeast China: New insights into 3-D crustal S-wave velocity structure and dynamics of intraplate volcanism

A new three-dimensional shear-wave velocity structure of the crust beneath Northeast China is constructed by inversion of phase velocity dispersion curves between 5 and 40 s using the direct surface-wave ambient noise tomography method. In addition to 127 NECESSArray (NorthEast China Extended SeiSmic Array) seismic stations, 19 SCVDSZ (Study of Changbai Volcanoes and Deep Subduction Zone) plus 3 CDSN (China Digital Seismograph Network) stations are added in the data collection. The addition of these data greatly improves the ray path coverage and imaging results around the Zhangguangcai range and the Changbaishan mountain. Our results show an obvious low-velocity anomaly extending from the surface down to uppermost mantle under the Changbaishan, suggesting that the volcano formation could be related to mantle upwelling. One more striking feature is a widely distributed mid-lower crustal low-velocity layer under the entire Northeast China, which is connected to those in the upper crust under the volcanoes, indicating that these volcanoes could have exchanges of material and energy in the mid-lower crust. In addition, under the Shuangliao and Erke volcanoes, low-velocity anomalies are visible in the upper and middle crust but high-velocity anomalies in the lower crust, whereas under the Abaga and Halaha volcanic groups, the low-velocity anomalies extend from the crust down to uppermost mantle, suggesting their continuous mantle magma provision. Integrating with previous global and regional body-wave tomographic models, our results suggest that the volcanoes in Northeast China could be related to hot and wet mantle upwelling in the big mantle wedge caused by the deep subduction of the subducted Pacific slab in the mantle transition zone.

Three-dimensional Crustal Radial Anisotropy Velocity Model in Northeastern Tibet

Three-dimensional Crustal Radial Anisotropy Velocity Model in Northeastern Tibet

High speed stereoscopic PIV investigation of the statistical characteristics of the axially restricted turbulent swirl flow behind the axial fan in pipe

Investigation of the turbulent swirl flow in the piping system is one of the most complex investigations in the field of energetics and turbulence. Axial fans in a pipe, without guide vanes, are widely used in practice and the problem of their duty point and energy efficiency is still extensively discussed. Analysis of the interaction between axial fans energy and construction parameters is one of the main topics in defining the fans energy efficiency potential. On one side, there is a three-dimensional velocity field in the wall-bounded flow with regions of great turbulence intensity. On the other side, there is a complex blade geometry, which generates the turbulent swirl flow. This paper presents research on the turbulent swirl flow, Rankine type, in an axially restricted system, using high-speed stereo particle image velocimetry (HSS PIV). Axial fan impeller, with outer diameter 0.399 m and nine twisted blades is the flow generator. The Reynolds number Re = 176,529 is achieved in the pipe. Reynolds stresses, statistical moments of higher order, and invariant maps are calculated based on the three component velocity fields. Here, intensive changes of all statistical parameters occur in radial and axial direction. In the flow region, four flow regions can be identified. Interaction of all these four flow regions produces extremely complex turbulent swirl flow, which is generated behind the axial fans. Determined invariant maps reveal turbulence structure. It is shown that the state of turbulence on the pipe axis is three-component isotropic, which is contrary to the case of axially unrestricted turbulent swirl flows. In the rest of the space, in the region up to r/ R = 0.52, the states of turbulence occur in the area in between the boundaries which designate axis-symmetric turbulence (contraction) and axis-symmetric turbulence (expansion), in the vicinity of the state of three-component isotropic turbulence.

Scaling law for the viscoelasticity-induced particle migration in stirred vessels

In this study, we investigate the viscoelasticity-induced migration of solid particles immerged in the three-dimensional flow field created by the rotation of a Rushton turbine. At the same time, we propose a scaling law for predicting the characteristic particle migration time as a function of the Weissenberg number. Particle image velocimetry is adopted to reconstruct the three-dimensional velocity and deformation rate fields generated by the rotation of the Rushton turbine in both Newtonian and viscoelastic fluids; concurrently, particle tracking is used to measure the evolution of the particle distribution in the tank. The experimental campaign shows that the deformation rate field is essentially bi-dimensional and confined to the r-θ plane. Accordingly, the particles migrate only in the radial direction driven by the presence of gradients of shear rate on the r-θ plane. Finally, the scaling law is validated against experimental data obtained at different Weissenberg numbers, impeller diameters and fluid compositions. The results show good agreement between the scaling law and the experimental data.

RESEARCH ON THE CHARACTERISTICS OF PRESENT CRUSTAL DEFORMATION IN BEIJING AREA BASED ON GNSS

Abstract. We use the GAMIT/GLOBK software to process more than 100 GNSS sites observation covering the Beijing area from 1999–2021 to obtain the three-dimensional velocity field of present-day crustal movement, and the deformation and strain characteristics of Beijing were calculated and comprehensively analyzed by combining with historical earthquakes. The results show that: 1) The present-day horizontal crustal motion of Beijing is dominated by the SEE direction with a rate of 5-10 mm/a with relative to the stable Eurasian reference frame, and the northern and southern areas show uplift as a whole with a rate of 1–3 mm/a, while the central plain area shows overall subsidence, with a maximum subsidence rate of about 130 mm/a. 2) The horizontal deformation is mainly N-E/N-W extension, accompanied by weak shear activity. 3) The N-W trending faults show sinistral strike slip movement as a whole, with about 1.1–2.0 mm/a, and N-E trending faults show dextral strike slip with a rate of less than 1 mm/a. 4) The historical large earthquakes are distributed within the positive and negative gradient zones of the first shear strain rate, transition zones of the rotation rate, and are mostly distributed at the edges of the high and low value zones of the second shear strain rate, and the edges of the high value zones of the east-west strain rate also have a background of large earthquakes.

Assessment of the Flow Field and Heat Transfer in a Vane Cooling System Using Magnetic Resonance Velocimetry, Thermochromic Liquid Crystals, and Computational Fluid Dynamics

AbstractComputational fluid dynamics (CFD) is the standard tool in the turbomachinery industry to analyze and optimize internal cooling systems of turbine components, but the code applied has to be validated. This paper presents a combined experimental and numerical study on the flow field and heat transfer in a cooling system consisting of a three-pass serpentine with rib turbulators and trailing edge ejection. The cooling geometry is taken from a stator vane currently used in an industrial gas turbine and operates at a coolant inlet Reynolds number of 45,000. As an experimental technique, magnetic resonance velocimetry (MRV) was used to obtain the three-dimensional time-averaged velocity field of the isothermal flow. The measurements were conducted in a large-scale model and resulted in 3.2 million velocity vectors and measurement uncertainty of 6.1% of the bulk inlet velocity. The local wall heat transfer was measured in a separate experiment using thermochromic liquid crystals (TLC). These measurements yielded the distribution of the heat transfer coefficient on both the pressure and the suction side internal walls with a measurement uncertainty of 12%. The experimental data are used as a reference for the numerical study. In total, eight turbulence models are evaluated here, including one-equation, two-equation, algebraic and differential Reynolds stress models, and a scale adaptive simulation. The results show the differences between the velocity fields and the heat transfer coefficient distribution, allowing for the identification of the optimum turbulence model for this particular type of flow.

Comparison and Agreement between Simplified and Three-dimensional Methods for Estimating the Front Crawl Stroke Arm Stroke Efficiency

Aims: To compare and verify the agreement of the arm stroke efficiency (ȠF) results obtained by simplified (ȠFS) and three-dimensional (ȠF 3D) methods. Background: Arm stroke efficiency (ȠF) estimates how much of the force applied by the swimmers’ upper limbs contribute to their propulsion. To estimate ȠF, in front crawl stroke, three-dimensional (ȠF3D) and simplified (ȠFS) methods are highlighted. Objective: To verify if different methods estimate similar arm stroke efficiency values. Methods: Ten male swimmers (age: 21.5 ± 2.6 years; height: 1.78 ± 0.05 m; competitive swimming experience: 12.2 ± 5.0 years) were tested in three 25 m front crawl stroke bouts at low, moderate, and high intensities. The ȠF data were obtained after collecting swimming images with six synchronized cameras and later analyzed in motion reconstruction software. Results: The mean results of ȠF, respectively for ȠF3D and ȠFS, were: 34.7±2.1% and 47.4±6.4% at a low; 34.8±2.7% and 42.3±3.3% in moderate; and 33.1±2.6% and 32.4±2.9% at high intensity. Along the intensities, ȠF remained similar with ȠF3D and reduced with ȠFS. ȠF was lower with ȠF3D than with ȠFS at low and moderate intensities (p &lt; 0.05) and similar at maximum intensity (p &gt; 0.05). Conclusion: At maximum intensity, the ȠF values agree between the methods. The results obtained by both methods were not fully similar. ȠF3D and ȠFS results agree just at high intensity. The differences between the methods may be due to the different variables used to measure ȠF, stroke rate in the ȠFS and three-dimensional hand velocity in the ȠF3D.

Major sources of North Atlantic Deep Water in the subpolar North Atlantic from Lagrangian analyses in an eddy-rich ocean model

Abstract. The North Atlantic Deep Water (NADW) is a crucial component of the Atlantic meridional overturning circulation and is therefore an important factor of the climate system. In order to estimate the mean relative contributions, sources, and pathways of the NADW at the southern exit of the Labrador Sea, a Lagrangian particle experiment is performed. The particles were seeded according to the strength of the velocity field along the 53∘ N section and traced 40 years backward in time in the three-dimensional velocity and hydrography field. The resulting transport pathways, their sources and corresponding transit timescales were inferred. Our experiment shows that, of the 30.1 Sv of NADW passing 53∘ N on average, the majority of this water is associated with a diapycnal mass flux without contact to the atmosphere, accounting for 14.3 Sv (48 %), where 6.2 Sv originate from the Labrador Sea, compared to 4.7 Sv from the Irminger Sea. The second-largest contribution originates from the mixed layer with 7.2 Sv (24 %), where the Labrador Sea contribution (5.9 Sv) dominates over the Irminger Sea contribution (1.0 Sv). Another 5.7 Sv (19 %) of NADW crosses the Greenland–Scotland Ridge within the NADW density class, where about two-thirds pass the Denmark Strait, while one-third crosses the Iceland–Scotland Ridge. The NADW exported at 53∘ N is hence dominated by entrainment through the diapycnal mass flux and mixed-layer origin in the Labrador Sea.

Developing a Consistent Travel-Time Framework for Comparing Three-Dimensional Velocity Models for Seismic Location Accuracy

Location algorithms have historically relied on simple, one-dimensional (1D) velocity models for fast seismic event locations. 1D models are generally used as travel-time lookup tables, one for each seismic phase, with travel-times pre-calculated for event distance and depth. These travel-time lookup tables are extremely fast to use and this fast computational speed makes them the preferred type of velocity model for operational needs. Higher-dimensional (i.e., three-dimensional—3D) seismic velocity models are becoming readily available and provide more accurate event locations over 1D models. The computational requirements of these 3D models tend to make their operational use prohibitive. Additionally, comparing location accuracy for 3D seismic velocity models tends to be problematic, as each model is determined using different ray-tracing algorithms. Attempting to use a different algorithm than the one used to develop a model usually results in poor travel-time prediction. We demonstrate and test a framework to create first-P and first-S 3D travel-time correction surfaces using an open-source framework (PCalc + GeoTess, https://www.sandia.gov/salsa3d/software/geotess) that easily stores 3D travel-time and uncertainty data. This framework produces fast travel-time and uncertainty predictions and overcomes the ray-tracing algorithm hurdle because the lookup tables can be generated using the exact ray-tracing algorithm that is preferred for a model.

Numerical simulation and dynamic mode decomposition analysis of the flow past wings with spanwise waviness

This paper presents an investigation on the compressible flow past spanwise wavy wings with an incoming flow of and . The scale adaptive simulation is employed here to solve the Favre-averaged equations. Three wings, with the ratio of wavelengths (λ) to chord length (c) respectively equaling to 1/2 (W4), 1/3 (W6), 1/4 (W8), are aerodynamically investigated. The aerodynamic force and separation were compared. The results obtained show that the lift-to-drag ratio of W-8 is 12.7% and 14.4% higher than W-4 and W-6 because of the larger low-pressure regions, while the lift and drag coefficient curves of W-8 oscillate more strongly. Leading edge separated bubbles and dilation-type recirculation regions are observed in the flow field structures. Spanwise momentum transportation and local airflow downwash effect are generated by the flow around the separation regions. Spanwise momentum transportation and downwash effect play important roles in the flow control mechanism of spanwise wavy wings. Three components of three-dimensional velocity vectors are modally decomposed by dynamic mode decomposition method to reveal the flow control mechanisms and vortex structures. The main modes characterizing the motions of arched vortices and shear layer vortices have been obtained. Strouhal number (St) is adopted to define the periodic oscillations of vortex shedding. The St of the modes are related to the scale of the vortex structures in the flow field. Small-scale eddy motions have been decomposed in high-frequency modes, and thus the modes of the flow field are more meticulous for higher St.

Power density capacity of tidal stream turbine arrays with horizontal and vertical axis turbines

Tidal and wind energy projects almost exclusively adopt horizontal axis turbines (HATs) due to their maturity. In contrast, vertical axis turbines (VATs) have received limited consideration for large-scale deployment, partly because of their earlier technology readiness level. This paper analyses the power density of turbine arrays comprising aligned and staggered configurations with decreasing turbine spacing of HATs and VATs with height-to-diameter aspect ratios from one to four at three real tidal sites. The VAT rotor has vertical blades extending over a portion of the water depth on a circular frame. Equivalent diameter is defined as D_0 = sqrt{A} based on the projected rotor area for both VATs and HATs. The three-dimensional velocity field is computed using analytical wake models that capture cumulative wake effects. At highly energetic sites, e.g. Ramsey Sound (UK), HATs are the most suitable technology attaining power densities beyond 100 W m^{-2}, whilst VATs provide higher power densities than HATs at those sites with low-to-medium velocities, e.g. Ría de Vigo (Spain) and Kobe Strait (Japan). At the latter site, VATs provided up to 35% larger energy yield than HATs over a 14-day tidal cycle. Our results show that VATs with height-to-diameter aspect ratios larger than three notably reduce wake effects even when deployed with a normalised turbine spacing of two D_0, reaching an average power density capacity of 40.7 W m^{-2} compared to HATs that attain 49.3 W m^{-2}. This study outlines the higher efficiency of tidal stream energy compared to other renewable energy resources, e.g. offshore wind farms, reaching power densities at least one order of magnitude larger, and that VATs counterbalance their smaller individual performance with improved array synergy as wake effects are limited.

Experimental investigations of open-channel flow and velocity to develop a predictive tool from a laboratory small scale to real-world large scale

Open channel flow and velocity behaviour presents a dilemma for drainage systems designers where hydrologic parameters are fluctuating in space and time. The experience of having extreme flash floods almost every year is flustering the need for understanding the flow behaviour at different altitudes. In this study, open channel experimental efforts were made to model flow and velocity profiles. The three-dimensional (3D) open channel flow and velocity profiles are generated at two types of roughness namely steel (smooth) and concrete (rough beds). The experiments included different slope gradients and flow measurements at different distances. The channels slope ranges between 0 and 4.7% with an interval of 0.2%. Multiple linear regression (MLR) was applied to quantify the flow for longer distance while Kriging extrapolation proxy was used to generate 3D surfaces of flow and velocity. The results showed that the flow in concrete channel is decreasing by moving to the end of channel due to higher frictional resistance while it is rising up for the steel channel. In average, the velocity has been increased by 7.4% for steel and 6.1% for concrete channels at a changing slope.

Reynolds number and submergence ratio effects on turbulence structures in the shallow wake of a horizontal pipe located on a rough bed

The effects of Reynolds number and submergence ratio on mean velocity, separation length, Reynolds shear stresses (RSS), correlation coefficient, anisotropy, and turbulent kinetic energy (TKE) are evaluated by modifying the free-stream velocity and pipe diameter to understand the fluid–structure interaction in the presence of a rough channel bed. Acoustic Doppler velocimetry is used to acquire three-dimensional velocity data in the experiments. The experimental data demonstrate that the non-dimensional separation length is linearly varying with the Reynolds number up to a critical Reynolds number, and after that, it becomes independent of the Reynolds number. The vertical profiles of the mean velocity, RSS, correlation coefficient, anisotropy, and TKE are not affected by the Reynolds number; however, their profiles are affected by the submergence ratio. The RSS and TKE are found to be larger for the higher submergence ratio below the top level of the pipe throughout the wake region. The reattachment point is found to be the most turbulent as the most pronounced peaks of RSS and TKE are occurring at this point. The quadrant analysis reveals that the RSS contribution of ejection events is higher for a lower submergence ratio, whereas the RSS contribution of the sweep events is higher for a higher submergence ratio. In conclusion, this study provides an in-depth understanding of the turbulent flow characteristics in the wake region of a bed-mounted horizontal circular pipe located on a fixed sand bed, especially the modification of the turbulence properties due to changes in the Reynolds number and submergence ratio.