Surface Flow Research Articles

Ekman revisited: Surface currents to the left of the winds in the Northern Hemisphere.

Ekman's theory of wind-driven ocean currents on a rotating planet is central to our understanding of why surface currents are deflected to the right of the winds in the Northern Hemisphere and to the left of the winds in the Southern Hemisphere. The theory admits solutions for currents deflected in the opposite direction at periods shorter than the local inertial period, but Ekman did not mention these currents, and they have only rarely been observed. Here, we describe a prominent example of surface flow in the Bay of Bengal directed to the left of clockwise-rotating land breeze wind forcing using multiple years of data from a long-term deepwater surface moored buoy. We further refine Ekman's theory so as to better reconcile it with our own and previous measurements and then conclude by discussing the broad implications of this work for understanding wind-forced ocean circulation.

Optimization Simulation of Mooring System of Floating Offshore Wind Turbine Platform Based on SPH Method

ABSTRACTIn this paper, the Smoothed Particle Hydrodynamics method is used to simulate the dynamic response of the floating offshore wind turbine mooring system in a complex marine environment by using its advantages of dealing with free surface flow and fluid–structure interaction. The single‐cable mooring system and the double‐cable mooring system are introduced into the numerical simulation model of fluid–solid coupling interaction. The first‐order irregular wave and the second‐order regular wave are used to simulate different wave conditions. The operating state of the platform in these two cases is analyzed, and the accurate data such as the velocity change of the geometric center of the platform and the change of six degrees of freedom are obtained. Using visual processing and data analysis, it is found that the optimized double‐cable mooring system structure improves the vibration reduction ability of the platform.

Late Glacial and Holocene history of climate, vegetation landscapes and fires in South Taiga of Western Siberia based on radiocarbon dating and multi-proxy palaeoecological research of sediments from Shchuchye Lake

Abstract To investigate long-term relationships between climate, vegetation, landscape geochemistry and fires in the boreal forest zone of Western Siberia, a sediment core of 345 cm was collected from Shchuchye Lake (located in south taiga zone of southeast part of West Siberian plain) and investigated by spore-pollen, radiocarbon, LOI and charcoal analyses. Quantitative palaeoclimate was reconstructed based on pollen data. Investigation revealed 13.2 cal ka history of vegetation, climate, landscapes and fires. In the dry climate of Late Glacial, the landscape was treeless. Continuous permafrost existed in the soil. In the middle of the YD cooling 12.4–12.2 cal ka BP, our data showed warming that caused degradation of permafrost in soils and settlement of spruce in moist places. Later, thawing and accumulation of moisture in a local lowering in relief increased and a lake was formed. With the beginning of the Holocene, the climate sharply changed to warmer and wetter. Intensified surface flow caused accumulation of mineral and carbonate fraction in the lake. Dense birch forests spread on drylands. As a result, the leaching regime initiated the formation of podzols in the soil. At about 10.0 cal ka BP, Scots pine (Pinus sylvestris) quickly spread in the area of investigation. Fires became more frequent and more intense during the dry Late Glacial time, sharply decreasing with increased precipitation in the Early Holocene, and again moderately increasing with spread of pine forests in the mid Holocene. With the transition to Late Holocene (after 6.0 cal ka BP), the intensity of regional background fires and number of local fires decreased.

Ensemble Kalman Filter Data Assimilation into the Surface Flux Transport Model to Infer Surface Flows: An Observing System Simulation Experiment

Knowledge of the global magnetic field distribution and its evolution on the Sun’s surface is crucial for modeling the coronal magnetic field, understanding the solar wind dynamics, computing the heliospheric open flux distribution, and predicting the solar cycle strength. As the far side of the Sun cannot be observed directly and high-latitude observations always suffer from projection effects, we often rely on surface flux transport (SFT) simulations to model the long-term global magnetic field distribution. Meridional circulation, the large-scale north–south component of the surface flow profile, is one of the key components of the SFT simulation that requires further constraints near high latitudes. Prediction of the photospheric magnetic field distribution requires knowledge of the flow profile in the future, which demands reconstruction of that same flow at the current time so that it can be estimated at a later time. By performing Observing System Simulation Experiments, we demonstrate how the ensemble Kalman filter technique, when used with an SFT model, can be utilized to make “posterior” estimates of flow profiles into the future that can be used to drive the model forward to forecast the photospheric magnetic field distribution.

Coupled volume-of-fluid and level-set lattice Boltzmann method for free surface flows

Coupled volume-of-fluid and level-set lattice Boltzmann method for free surface flows

Analysing Turbulence Patterns in Nature‐Like Fishways: An Experimental Approach

ABSTRACTNature‐like fishways are an important measure for restoring fish passage, mitigating the impacts of barriers, and providing valuable habitat benefits in a more natural and effective way than traditional technical fishways. Their ecological advantages make them a preferred solution in many river restoration projects. The turbulence at the fishway's pool is a key challenge in the design of fishways. This study evaluated the hydraulic performance of the nature‐like fishway section of the Zongyang Fishway Project in China. This utilized a trapezoidal cross‐section with a 1:242 bottom slope, 1:2 side slopes, and an operating water depth of 1–3 m. The bottom and sides were paved with 0.2–0.5 m diameter pebbles to create suitable habitat for bottom‐dwelling fish. The target design velocity was 0.7–0.9 m s−1. A physical model was constructed to assess the hydraulic characteristics of the nature‐like fishway, including flow velocities within the slots and turbulence levels in the pools. The results showed that the slot velocities were within the target range, the head loss was parallel to the bottom elevation, and the flow field near the bottom mimicked technical fishway conditions, whereas the surface flow resembled open channel flow. Turbulence intensity remained below 60% of the design velocity. These findings provide valuable insights into the hydraulic performance and suitability of this nature‐like fishway design for facilitating fish passage of the target freshwater species along with directly aiding to SDGs 6 and 14.

Variation of Surface Tension of Liquid Metal with Fluorides in Tungsten Inert Gas Welding

Real-time measuring and obtaining surface tension of liquid metal during the arc welding process is critical for studying the behavior of the weld pool, such as Marangoni flow and flow velocity. The dynamic variation of surface tension of weld pool during tungsten inert gas welding process with and without fluoride flux was measured by weld pool oscillation sensing system, and the effect of fluoride flux on surface tension and pool behavior was analyzed. The results show that the surface tension gradient of liquid metal can convert from a negative to a positive value in a critical arc time. The flow velocity of liquid metal and critical arc time significantly increased and decreased, respectively, with fluoride flux. The variation of surface tension, flow velocity, and critical arc time with fluoride flux was induced by arc temperature increasing.

PERFORMANCE OF FREE WATER SURFACE FLOW CONSTRUCTED WETLAND FOR LEAD AND CADMIUM IONS REMOVAL USING AZOLLA PINNATA PLANT

Phytoremediation is the ability of some plants to bio accumulate, decompose, or transformation of pollutants in soils, water, or air. In the current study, an effort is made to study the effectiveness of free-floating plants to treat simulated industrial wastewater polluted with Lead and Cadmium ions using Azolla Pinnata plant in a lab condition. Free water surface flow constructed wetland were fed with simulated Cd and Pb ions in different concentrations (5, 10 and 20) mgl-1. Different operating conditions were studied such as; pH, dissolved oxygen, electrical conductivity, temperature, and sodium adsorption ratio to find out the possibility of using treated wastewater for irrigation. Results showed that, Azolla plant had a higher removal efficiency to extract Lead ions (90.1%, 86.67%, and 81.3%) than Cadmium (79.3%, 78.4%, and 69.7%) when the initial concentration is (5, 10, 20) mgl-1 respectively, during 5 days. A slight reducing in pH (8.3 to 7.4) and dissolved oxygen (8.7 to 7.2) mgl-1 observed, all these values mentioned satisfied with the Iraqi standards and World Health Organization. From values of electrical conductivities (250- 750) (µScm-1) and the sodium adsorption ratios (0- 10) it was found that treated wastewater falls into class C2S1 which mean that water has good quality and can be used to irrigate moderately salt-tolerant crops on soils with good permeability.

Fluid Force Reduction and Flow Structure at a Coastal Building with Different Outer Frame Openings Following Primary Defensive Alternatives: An Experiment-Based Review

A well-constructed tsunami evacuation facility can be crucial in a disaster. Understanding a tsunami’s force and the flow structure variation across various building configurations are essential to engineering designs. Hence, this study assessed the steady-state flow structure at building models (BM) incorporating outer frame openings, including piloti-type designs with a different width-to-spacing ratio of piloti-type columns following an embankment model (EM) with a vegetation model (VM). The experiments also demonstrated the outer frame opening percentage’s impact and orientation toward the overtopping tsunami flow at the BM. The results show that the arrangement of an opening on the outer frame and the piloti-type columns are critical in reducing the tsunami force concerning the experimental setup. Moreover, allowing a free surface flow beneath the BM implies that the correct piloti-pillar arrangement is crucial for resilient structure design. In addition, the three-dimensional numerical simulation was utilized to explain the turbulence intensity of the overtopping flow around the critical BM type. The derived resistance coefficient (CR) defined the drag and the hydrostatic characteristics at the BM due to the overtopping tsunami flow. Furthermore, for the impervious BM, the value CR was consistent with the previous studies, while the CR value for the BMs with an outer frame opening was directly coincident with the percentage of porosity.

Unveiling synergistic enhancement mechanism of nitrogen removal in surface flow constructed wetlands: Utilizing iron scraps and elemental sulfur as integrated electron donors

Lacking electron donors generally causes poor denitrification performance in constructed wetlands (CWs). In this study, iron scraps (ISs) and elemental sulfur (S0) were employed as electron donors in different surface flow constructed wetlands (SFCWs): control (C-SF), ISs added (Fe-SF), S0 added (S-SF), and ISs and S0 combined (Fe + S-SF) to investigate the performance and mechanism of nitrogen (N) removal through continuous flow and batch experiments. The impact of hydraulic retention times (HRTs) and temperatures on N removal was explored. The combined use of ISs and S0 significantly improved nitrate (NO3− -N) removal in Fe + S-SF compared to the other SFCWs. During the 3-d HRT at 25 °C, the average NO3− -N removal efficiency in Fe + S-SF reached the highest value of 71.66 ± 12.54%, reducing NO3− -N concentrations from 12.03 mg/L to 3.47 mg/L. The results of the batch experiments revealed an N removal pattern that aligned with the findings of the continuous flow experiment. The microbial community analysis revealed a selective enrichment of key functional genera (e.g., Ferritrophicum and Dechloromonas), contributing to enhanced N removal in Fe + S-SF. These findings suggest that the synergistic use of ISs and S0 can achieve better denitrification efficiency and potentially be utilized for enhanced N removal from low C/N wastewater.

Inertial effects on free surface pumping with an undulating surface

Free surface flows driven by boundary undulations are observed in many biological phenomena, including the feeding and locomotion of water snails. To simulate the feeding strategy of apple snails, we develop a centimetric robotic undulator that drives a thin viscous film of liquid with the wave speed $V_w$ . Our experimental results demonstrate that the behaviour of the net fluid flux $Q$ strongly depends on the Reynolds number $Re$ . Specifically, in the limit of vanishing $Re$ , we observe that $Q$ varies non-monotonically with $V_w$ , which has been successfully rationalised by Pandey et al. (Nat. Commun., vol. 14, no. 1, 2023, p. 7735) with the lubrication model. By contrast, in the regime of finite inertia ( ${Re} \sim O(1)$ ), the fluid flux continues to increase with $V_w$ and completely deviates from the prediction of lubrication theory. To explain the inertia-enhanced pumping rate, we build a thin-film, two-dimensional model via the asymptotic expansion in which we linearise the effects of inertia. Our model results match the experimental data with no fitting parameters and also show the connection to the corresponding free surface shapes $h_2$ . Going beyond the experimental data, we derive analytical expressions of $Q$ and $h_2$ , which allow us to decouple the effects of inertia, gravity, viscosity and surface tension on free surface pumping over a wide range of parameter space.

Quantifying Stream Return Flow of Agricultural Water Using SWAT-MODFLOW-PADDY Model in Korean Paddy Fields

In many countries, the irrigation return flow focuses only on surface and subsurface flows. In contrast, South Korea adopts a broader approach, defining the stream return flow as encompassing both quick and delayed return flows, which include subsurface flow and deep percolation. This study proposes redefining the stream return flow to include only the subsurface return flow, excluding deep percolation. We quantified the subsurface return flow and deep percolation using the SWAT-MODFLOW-PADDY (SMP) model, confirming that the current definition overestimated the stream return flow in Korea. The results show that the subsurface return flow accounted for 20% to 60% of the total infiltration, with the remaining 40% to 80% contributing to deep percolation and groundwater recharge. These findings reveal significant regional variations in the subsurface return flow rates, underscoring the limitations of applying a uniform stream return flow rate. We propose that allocated management water, subsurface, and quick return flows should be the primary components considered in stream return flow calculations, as the current practice of including delayed return flow leads to overestimated results. This study highlights the challenges in monitoring the subsurface return flow and the need for region-specific models that account for local conditions such as topography, soil characteristics, and climate. Our findings provide a more accurate approach to estimating the subsurface return flow, which is crucial for improving the efficiency and sustainability of agricultural water management in Korea.

Effect of different PV modules surface energies and surface types on the particle deposition characteristics and PV efficiency

The particle deposition behavior of solar photovoltaic (PV) modules and its effect on PV efficiency were numerically investigated using computational fluid dynamics (CFD) methods. The surface flow field of PV modules using the shear stress transfer (SST) k-ω model with a user-defined function (UDF) for the development of entrance boundaries is predicted. A UDF coupled discrete phase model (DPM) that takes into account wall bounce and hydrophobic properties is used to predict particulate deposition in the flow field. Mesh independence and average pressure coefficients are verified. The effects of particle diameter, boundary type, surface energy and surface type on particle deposition of PV panel and PV efficiency are investigated. The results show that the smaller the surface energy γ, the smaller the particle deposition rate. At dp = 150 μm, γ = 0.001J/m2, it showed that the most significant reduction of 427.3 % in particle deposition rate compared to the trap boundary type, and γ = 0.001J/m2 showed a 210 % reduction in particle deposition rate compared to γ = 0.1J/m2. However, at dp ≤ 50 μm, the change in surface energy has little effect on the deposition rate. The effect of convex PV modules on particle deposition is more obvious at low surface energy (γ ≤ 0.001J/m2) compared to planar. The reduction in PV efficiency caused by particle deposition at different surface energies is predicted using an empirical model of PV output reductions developed by the researcher.

Rainwater harvesting suitability of ground tanks located on stock watering places across Western NSW

ABSTRACT A stock watering place (SWP) is a type of travelling stock reserve, and Western Local Land Services (WLLS) is the controlling authority of SWPs in the semi-arid Western region of New South Wales, Australia. Over half SWPs have ground tanks that were installed in the 1800s to provide water for travelling stock. The location of many SWP ground tanks is thought to have been influenced by traditional Aboriginal knowledge, however, their position for capturing contemporary surface flows has not previously been assessed. This study aims to use multicriteria analysis within a Geographic Information System (GIS) to investigate whether SWP ground tanks are at the most suitable rainwater harvesting (RWH) location. ArcGIS was used to analyse data to identify RWH suitability based on slope, soil group, and drainage density. These layers were then weighted and combined to produce a final RWH suitability map. Results show that most (50.7%) ground tanks are in high RWH suitability locations, 47.9% are in medium RWH suitability, 1.4% are in low suitability, and none are in unsuitable locations. These results indicate that 1800s RWH suitability selection methods were highly effective. The findings of this study will contribute to the WLLS SWP knowledge base and will assist in prioritising SWPs for works to improve RWH efficiency, thereby ensuring reliable stock water on SWPs.

Vortex Motion on the Surface of Shallow and Deep Water

The attenuation of vortex motion on the surface of shallow and deep water is investigated. The vortex flow was formed by two mutually perpendicular waves excited by plungers at a frequency of 6 Hz (wavelength λ = 5.6 cm) on the surface of water measuring 70 × 70 cm and depth h. After reaching a stationary state in the vortex system, the wave pumping was switched off, and the attenuation of the surface flow was recorded. On the surface of shallow water, λ/2π ≈ h, when the characteristic size of the vortices L exceeds the depth of the liquid, L h, the time dependence of the energy of the vortex flow Е(t) is described by an exponential function at all pumping levels, and the dependence of the enstrophy Ф(t) = Ω2(t) has an exponential dependence only in the range of wave vectors 0–0.3 см–1. On the surface of deep water λ/2π h, L ≈ h dependence Е(t) and Ф(t) are far from exponential in all ranges of wave numbers. At high pumping levels, the dependencies Е(t) and Ф(t) are nonmonotonic, which can be attributed to the influence of volumetric flows.

Experimental Optimization of the SG6043 Airfoil for Horizontal Axis Wind Turbines Using Schmitz Equations

This study presents the experimental optimization of the SG6043 airfoil for horizontal axis wind turbines (HAWTs) using the Schmitz equation, focusing on enhancing power output and elucidating the surface flow structure. Two blade models, M1 (conventional) and M2 (optimized), were designed and tested at rotational speeds of 400 rpm and 600 rpm across a range of tip speed ratios (TSR). The M2 model, optimized using Schmitz equations, demonstrated significantly improved performance compared to the M1 model at both rotational speeds. At 400 rpm, the maximum power coefficient (CP) for M1 was 0.274, while M2 reached 0.419, indicating a 52.91% improvement. At 600 rpm, M1 achieved a maximum CP of 0.293, whereas M2 attained 0.458, representing a 56.31% enhancement. The M2 model also showed superior performance at higher TSRs, with the highest percentage increase in CP recorded at 4.9 TSR, reaching 574.54%. Additionally, dynamic surface oil-flow visualization experiments were conducted to examine flow behavior on the blade surfaces. Results indicated better flow attachment in the M2 blade due to its optimized twist angle and chord length, particularly in the mid-section, leading to delayed flow separation. The reattachment observed on the suction side of the M2 model, following the laminar separation bubble (LSB), which was absent in the M1, contributed to its higher aerodynamic efficiency and overall power performance. These findings confirm that the optimized SG6043 airfoil design, guided by Schmitz equations, offers significant improvements in HAWT performance, particularly under varying operational conditions.

Dynamic event-triggered integrated task and motion planning for process-aware source seeking

The process-aware source seeking (PASS) problem in flow fields aims to find an informative trajectory to reach an unknown source location while taking the energy consumption in the flow fields into consideration. Taking advantage of the dynamic flow field partition technique, this paper formulates this problem as a task and motion planning (TAMP) problem and proposes a bi-level hierarchical planning framework to decouple the planning of inter-region transition and inner-region trajectory by introducing inter-region junctions. An integrated strategy is developed to enable efficient upper-level planning by investigating the optimal solution of the lower-level planner. In order to leverage the information acquisition and computational burden, a dynamic event-triggered mechanism is introduced to enable asynchronized estimation, region partitioning and re-plans. The proposed algorithm provides guaranteed convergence of the trajectory, and achieves automatic trade-offs of both exploration-exploitation and accuracy-efficiency. Simulations in a highly complicated and realistic ocean surface flow field validate the merits of the proposed algorithm, which demonstrates a significant reduction in computational burden without compromising planning optimality.

Insights into the relationship between particulate flow characteristics and local erosion behaviour under waterjet: The role of particle-fluid-surface interaction

In this study, the erosion characteristics of eutectic high entropy alloy under the liquid–solid two-phase flow is investigated by a coupled numerical-experimental method, in order to reveal the intrinsic relationship between microscopic erosion mechanism (experimental test) and the related particle-fluid-surface interaction (CFD modelling). Furthermore, instead of the common relation between average erosion rate and mainstream flow velocity, the relationship between local erosion distribution and local particulate flow characteristics is clarified. The erosion rate and erosion pattern match well between the experiment and simulation. The results demonstrate that NiCoCrFeNb0.45 exhibits superior anti-erosion performance when compared to other widely used equipment metals. The erosion profile agrees well with the shape of surface velocity distribution, indicating a close relationship between surface erosion behaviour and flow characteristics. In particular, the erosion pattern at a normal angle appears as a symmetric ring due to the flow stagnation phenomenon, with slight erosion damage in the centre area and severe erosion in the surrounding, whereas the erosion profile at an oblique angle displays an elliptic shape, with severe erosion damage in centre. Notably, the primary erosion mechanism varies dramatically in different surface regions, induced by the various impact velocities and angles associated with the corresponding changes in the flow field. This study provides a deeper understanding of erosion behaviour in terms of the interrelationship among the material mechanical properties, particulate flow field and particle-surface impingement behaviour.

Study on the Influence of Different Slot Sizes on the Flow Field of Transonic Compressor Rotors

Blade slotting technology is an effective measure to improve the flow structure on the suction surface of a blade and enhance the performance of turbomachinery. To investigate the impact of various slot sizes on the flow field of a single-stage transonic compressor rotor, seven kinds of slot schemes were designed and calculated by numerical simulations. The results show that the above slotting schemes significantly enhance the stability margin of the compressor. In particular, the slotting scheme H9W3 increases the surge margin by 60.9% and slightly reduces peak efficiency by 0.3%, with an almost identical maximum pressure ratio. Slotting promotes high-energy fluid to generate jets from the slot located at the exit of the suction side, effectively controlling blade surface flow separation and reducing channel blockage. Square slots are more effective than elongated slots for controlling separation when using differently shaped slots with equal areas. Increasing slot area gradually decreases outlet total pressure at a constant aspect ratio. A slight increase in the overall blade load causes a backward shift in the front portion load.

The development of undercut and bulge on a solidified surface

Abstract This study numerically investigates the development of undercuts and bulges parallel to the scanning direction on the surface solidified from a thermocapillary molten pool. The analysis considers various parameters, including power-off time, active solute concentration, beam power and radius, surface tension, liquid thermal conductivity, viscosity, and density. The formation and shapes of undercuts and bulges directly impact the yield, fatigue, fracture strength, and stress concentration in the solidified region. Unsteady two-dimensional fluid flow and heat transfer, which drive surface deformation in metals containing surface-active solutes (e.g., iron with sulfur), are solved using COMSOL Multiphase version 5.6. The development of the undercut, bulge, and molten pool is identified in six stages, based on whether the peak temperature is below the melting temperature, between the melting and critical temperatures, or above the critical temperature during heating and power-off periods. The critical temperature, determined as a function of solute content and temperature, leads to inward surface flow in the undercut near the pool edge, while the bulge in the central region can form due to either inward or outward surface flow. The predicted undercut depth and bulge height align well with previous scaling analyses and experimental data from laser polishing. These findings are relevant to various processes, including welding, additive manufacturing, polishing, melting, and solidification.