Inflow Direction Research Articles

Applicability of Convolutional Neural Network for Estimation of Turbulent Diffusion Distance from Source Point

For locating the source of leaking gas in various engineering fields, several issues remain in the immediate estimation of the location of diffusion sources from limited observation data, because of the nonlinearity of turbulence. This study investigated the practical applicability of diffusion source-location prediction using a convolutional neural network (CNN) from leaking gas instantaneous distribution images captured by infrared cameras. We performed direct numerical simulation of a turbulent flow past a cylinder to provide training and test images, which are scalar concentration distribution fields integrated along the view direction, mimicking actual camera images. We discussed the effects of the direction in which the leaking gas flows into the camera’s view and the distance between the camera and the leaking gas on the accuracy of inference. A single learner created by all images provided an inference accuracy exceeding 85%, regardless of the inflow direction or the distance between the camera and the leaking gas within the trained range. This indicated that, with sufficient training images, a high-inference accuracy can be achieved, regardless of the direction of gas leakage or the distance between the camera and the leaking gas.

Aerodynamic investigation of extremely efficient vehicles under side wind conditions

A vehicle is more stable when the geometric center, center of gravity, and stagnation point are in line. However, the inflow direction and velocity magnitude of the operational environment of road vehicles are varying. This study aims to investigate the aerodynamic behavior of a water-drop-shaped vehicle under side wind conditions. Some essential aerodynamic performances of the vehicle are numerically and graphically analyzed at 0 deg, 10 deg, and 20 deg of side wind directions. The value of the coefficient of drag, drag force, coefficient of lift, and lift force exponentially increases as the yaw angle elevates. The lower part on the area of the front-wheel compartment becomes the critical location indicated by the results on pressure coefficient, friction coefficient, and total wall shear stress distribution along the vehicle surface. Increasing the side wind angle triggers more significant vortex regions generated around the wheel compartment and on the leeward side of the vehicle.

Field Measurements and Numerical Simulation of Snowdrift on Railway Subgrade

Abstract Snowdrift is a major natural hazard, endangering basic installation and human life in cold regions. Drifting snow can cause snow grains to accumulate on the road, blocking transportation, reducing visibility, and even leading to fatal traffic accidents. Field measurements and numerical simulations of roadbed snow characteristics were carried out along the railway in snowy weather to study the effect of snowdrift on railway subgrade. The influence of a typical roadbed structure is considered, and the basic model of a typical subgrade structure under the action of snowdrift is proposed. Snow particles that accumulate on the embankment present a U-shaped distribution along the inflow direction. Within the increase of embankment height, wind velocity on the roadbed surface is accelerated, and snow cover is reduced, thus mitigating the snow drift disaster of the embankment. Snow covers at embankment heights of 1 and 2 m are considerably greater than those at 3 and 5 m, and identical with those at roadbed heights of 3 and 5 m. Along the inflow direction, the snow cover on the cutting presents an M-shaped distribution. As cutting depth is reduced, wind velocity inside the cutting is decelerated, and snow cover is increased, which aggravates the snow drift disaster of the cutting. The snow depths of roadbed parts at 1-, 2-, and 3-m depths of the cutting are nearly the same, and that at a 5-m depth of the cutting is relatively small but still larger than that on the embankment. Numerically simulating the snow-driving wind via computational fluid dynamics, which can consider the motion characteristics of snow particles and their influence on flow field, is feasible. Simulation results agree with the measured results. Thus, this research provides a path for the further prediction of snow cover pattern.

Model Predictive Control for Wind Farm Power Tracking With Deep Learning-Based Reduced Order Modeling

Dynamic power control of wind farms (WFs) is necessary to provide automatic generation control (AGC) services for the power system. However, cooperative WF control for AGC remains a great challenge because of the nonlinear and high-dimensional nature of the wake flow dynamics. To address this challenge, this article proposes a model predictive control (MPC) framework with deep learning-based reduced-order modeling (ROM). Two novel neural network architectures are designed, which successfully formulate a WF ROM capturing the dominant wake steering dynamics in a computationally efficient manner. Compared to physical models, the data-driven ROM reduces the number of model states by orders of magnitude. Then, a novel WF AGC framework embedding the derived WF ROM is proposed. Thrust coefficient and yaw steering are both employed to optimize WF power tracking performance. Compared to prior WF AGC controllers, the dynamic yaw actuation is first optimized for AGC considering the wake steering dynamics. Case studies validate the effectiveness of the deep learning-based WF ROM at capturing the wake traveling dynamics. The WF controllers were stress-tested under time-varying inflow directions. The proposed MPC can react to different wind directions and generates higher-quality control performance than existing alternatives with extended trackable AGC range and better dynamic power tracking performance.

Numerical research on the effect of brackets installation angle on the propeller wake field and propulsion performance in a four-screw ship

A series of full-scale self-propulsion simulations of a four-screw ship with different bracket installation angles using the Reynolds-averaged Navier–Stokes (RANS) method were conducted. The effects of the bracket installation angle on the propeller wake field and propulsion performance were investigated and studied. The result shows that the nominal wake low-speed region generated by the shedding vortex moved inward with the bracket angle increased. When the bracket angle turns inward 3°, the effect of shedding vortex almost disappeared in the outer propeller disc. The outer propeller shows a significant increase in thrust and torque, and the time-average load difference between inner and outer propeller drops to below 5%. The research conducted in this paper fills a gap in the study of full-scale four-screw ship appendages. The design method for determining the bracket installation angle by inflow direction is of practical significance to the design of four-screw ships.

Bulge formation inside quiescent lopsided stellar disks: Connecting accretion, star formation, and morphological transformation in a z ∼ 3 galaxy group

We present well-resolved near-IR and submillimeter analysis of the three highly star-forming massive (> 1011 M⊙) galaxies within the core of the RO-1001 galaxy group at z = 2.91. Each of them displays kpc scale compact starbursting cores with properties consistent with forming galaxy bulges, embedded at the center of extended, massive stellar disks. Surprisingly, the stellar disks are unambiguously both quiescent and severely lopsided. Therefore, “outside-in” quenching is ongoing in the three group galaxies. We propose an overall scenario in which the strong mass lopsidedness in the disks (ranging from factors of 1.6 to > 3) likely generated under the effects of accreted gas and clumps, is responsible for their star-formation suppression, while funnelling gas into the nuclei and thus creating the central starbursts. The lopsided side of the disks marks the location of impact of accretion streams, with additional matter components (dust and stars) detected in their close proximity directly tracing the inflow direction. The interaction with the accreted clumps, which can be regarded as minor mergers, leads the major axes of the three galaxies to be closely aligned with the outer Lyman-α-emitting feeding filaments. These results provide the first piece of observational evidence of the impact of cold accretion streams on the formation and evolution of the galaxies they feed. In the current phase, this is taking the form of the rapid buildup of bulges under the effects of accretion, while still preserving massive quiescent and lopsided stellar disks at least until encountering a violent major merger.

Cross-sectional blockage effect on the drag force of a scaled round-ended pier model under directional flow

Flume testing of a scaled model under steady flow is an essential reference for accessing the flooding-induced drag force on a prototype pier, but is highly susceptible to the cross-sectional blockage effect. Round-ended bridge piers have a non-axisymmetric cross-section, of which the drag force varies significantly with inflow direction. A flume testing program was carried out to illustrate the cross-sectional blockage effect under different inflow directions. CFD numerical simulations were then conducted to understand the blockage effect on the drag force, flow field and hydrodynamic pressure of the round-ended pier with different blockage ratios and inflow directions. The major findings include: 1) the blockage effect affects the drag force of the scaled model and changes with inflow direction; and 2) the limit of occurrence of the cross-sectional blockage effect is defined by the critical blockage ratio and given as a function of inflow direction. An empirical approach was finally developed to correct the cross-sectional blockage effect on the drag force of the round-ended pier model under directional flow. The influences of the blockage ratio and inflow direction were included in the empirical calculation of the drag force on the prototype from the scaled model test.

Quantification of motion-induced measurement error on floating lidar systems

Abstract. Floating lidar systems (FLSs) are widely used for offshore wind site assessment, and their measurements show good agreement when compared to trusted reference sources. However, some influence of motion on mean wind speed data from FLS has to be assumed but could not have been quantified with experimental methods yet because the involved uncertainties are larger than the expected impact of motion. This study describes the motion-induced bias on horizontal mean wind speed estimates from FLS with the help of simulations of the lidar sampling pattern of a continuous-wave (CW) velocity–azimuth display (VAD) scanning wind lidar. Analytic modeling is used to validate the simulations. It is found that the mean bias depends on amplitude and frequency of motion, the angle between motion and wind direction, and wind speed and strength of wind shear. The simulations are used to quantify the measurement deviation that is caused by motion for the example of the Fugro SEAWATCH Wind LiDAR Buoy (SWLB) carrying a ZX 300M profiling wind lidar. The strongest bias of −0.67 % of the measurement values was estimated for a test case with “strong” waves aligned with the inflow wind direction. Under “normal” wave conditions the bias is smaller. The reason for these low errors lies in a fortunate combination of the frequencies of lidar prism rotation and tilt motion.

A Comparative Study of the Simulation Accuracy and Efficiency for the Urban Wind Environment Based on CFD Plug-Ins Integrated into Architectural Design Platforms

The deterioration of the urban environment is a problem which has captured the attention of governmental departments and researchers, who are committed to improving the urban environment from the perspective of optimizing urban morphology. Although many researchers have applied computational fluid dynamics (CFD) plug-ins to study the problems of urban ventilation and pollutant accumulation, studies on the reliability and simulation accuracy verification of CFD plug-ins are currently scarce. Therefore, we used three CFD plug-ins based on different architectural design platforms to evaluate and compare their operation difficulty, simulation accuracy, and efficiency through the analysis of the simulation results of urban ventilation. This study complements the reliability validation of CFD plug-in simulations and guides urban planners and architects in the selection and application of CFD plug-ins. The results show that the CFD plug-in generally underestimates the wind speed at the pedestrian level and the prediction accuracy is poor in the wake area of obstacles, especially with the GH_Wind plug-in. Under the 0° inflow direction, the simulation results of the Butterfly plug-in were the most consistent with the experimental values. When the inflow direction increased to 22.5° and 45°, the Autodesk CFD showed the best simulation accuracy. Overall, Autodesk CFD achieves a balance between simulation accuracy and speed in urban airflow simulation.

Effects of wedge-angle change on the evolution of oblique detonation wave structure

Compared to pulse detonation engine and rotating detonation engine, oblique detonation engine has the advantage of higher flight Mach number. However, it is still challenging to achieve stabilized oblique detonation wave for a broad range of flight conditions. To control oblique detonation wave, this study focuses on the oblique detonation wave structure evolution induced by changing the wedge angle. Transient two-dimensional simulations are conducted for wedge-stabilized oblique detonation wave in a stoichiometric hydrogen/air mixture. The detailed chemistry of hydrogen combustion is considered, and the thermal states of the reactants are determined by the specified flight altitude and the Mach number. The angle change between inflow and wedge can be achieved in two ways: inflow-angle change with fixed wedge angle and wedge-angle change with fixed inflow direction. Results indicate that no new autoignition zone exists in the transient wave evolution caused by wedge-angle change, which is different from that of inflow-angle change observed in previous studies. For the wedge-angle change process, the effects of wedge-angle change rate on transient oblique detonation wave structure evolution are further assessed. It is found that the transient oblique detonation wave structure is more sensitive to the wedge-rotation angular velocity for increasing wedge angle (controlled by the thermodynamic properties of the mixture) than that for decreasing wedge angle (controlled by the shock wave dynamic). For the quasi-steady triple-wave structure during wedge-angle decreasing process, a normal detonation wave occurs and becomes dominant in the wave structure evolution, whose formation mechanism is analyzed by the polar curve theory.

Removal of Pb(II) by lignin-sodium alginate composite in a fixed-bed column

ABSTRACT A kind of adsorbent (Hydrogel-I) derived from sodium alginate and modified alkaline lignin (MAL) has been proved to possess a good adsorption performance for Pb(II)-loaded wastewater based on batch experiments. However, practical removal of Pb(II)-loaded-wastewater is a continuous and dynamic process. Herein, Hydrogel-I was further evaluated by packing it into a fixed-bed column. The breakthrough curves were established under different inflow rates (0.159–0.318 L/min), inflow directions (down-inflow mode and top-inflow mode), initial concentrations (5–20 mg/L) of Pb(II), and bed depths (20–60 cm). The results indicated that the slower inflow rate (0.159 L/min), down-inflow mode, lower initial concentration (5 mg/L), and higher bed depth (60 cm) prolonged breakthrough times (t b) and saturation times (t s). Compared to the top-inflow mode, the down-inflow mode guaranteed enough contact between Hydrogel-I and Pb(II). The values of adsorption capacity at t b, t s, and the removal efficiency under the down-inflow mode were higher than that under top-inflow mode by 2.33, 0.78, and 0.07 times, respectively. Hydrogel-I beads exhibited better adsorption performance than other adsorbents by comparing the rate constant (k AB) and the adsorption capacity (N 0). The k AB and N 0 of Hydrogel-I beads were calculated to be 0.0034 L/(mg·min−1) and 678 mg/L. Hydrogel-I beads showed good regeneration ability in a three-adsorption-desorption cycle. Meanwhile, FT-IR analysis showed that the groups of –NH/–NH2, C=S, and C–S were proved to be the adsorption sites. This study could prove valuable insight into the practical application of Hydrogel-I for dynamic removal of Pb(II) in an inflow-through column.

Improvement of Airflow Simulation by Refining the Inflow Wind Direction and Applying Atmospheric Stability for Onshore and Offshore Wind Farms Affected by Topography

For this study, the annual frequency of atmospheric stability and the effects of topography were investigated, using ERA5 data and data from wind observation masts installed at four locations on an island for a site under development, where bidding will soon begin. As a result, we found that a variety of atmospheric stabilities appeared at the site, and that the annual average events were not neutral but, instead, unstable. Moreover, the deviation from neutral varied depending on wind direction and the wind speed varied greatly, depending on the mast position and wind direction. Additionally, it was necessary to reproduce the wind flow separation due to topography, in order to predict the wind conditions of wind turbines located close to the island. The accuracy of the airflow simulation by large eddy simulation was validated using the mast-to-mast wind speed ratio. For simulations, we used the commercial software RIAM-COMPACT, which has been widely used in Japan, as it allows the atmospheric stability to be freely set. As a result, we found that the accuracy could be improved by refining the inflow wind direction and taking the average of the results calculated under several atmospheric stability conditions.

Study on the effect of inflow conditions on wind flow acceleration in mountainous micro-topography

The acceleration of wind flow in mountainous areas can cause the destruction or collapse of transmission towers. The wind speed and direction of inflow have a significant impact on the flow acceleration in mountainous areas. The mountain terrain in the coastal area of Fujian was selected to study the influence of the inflow wind speed and direction on the acceleration effect. By analyzing the radar chart of the wind speed acceleration ratio of the monitoring points under 24 wind direction angles, the variation law of the wind speed acceleration ratio is consistent with the trend of the influence law obtained by the analysis of the surrounding terrain. The obtained simulation results are correct and credible, which can be used to correct the design wind speed of transmission lines in mountainous areas.

Wind Field Characteristics of Complex Terrain Based on Experimental and Numerical Investigation

With the intensification of energy consumption, how to make rational and efficient use of wind energy has been studied all over the world. The construction of facilities to obtain wind energy requires an accurate assessment of the wind characteristics of the local terrain. In order to study the wind characteristics on an island in Southeast China, a 1:1300 terrain model is established, and the characteristics of mean wind and fluctuating wind are studied by numerical simulation and wind tunnel test. The results show that wind speed is affected by the incoming wind direction and local terrain. Wind speed on windward slopes and flat areas with no obstructions is higher, and wind speed on leeward slopes and valleys is lower. Then, the wind attack angle of each measuring point is mainly in the range of −10°~10°, which is much higher than that in flat areas. The positive and negative wind attack angles are controlled by the incoming wind direction, and the size is closely related to the local terrain. As for pulsation characteristics, the disturbance of the inflow determines the turbulence intensity. The incoming wind direction mainly affects the turbulence intensity on the hillside, while the turbulence intensity in the valley and flat area is controlled by the local terrain. In addition, the fluctuating wind speed power spectra on the island is more consistent with the von Karman spectrum, which is quite different from the Kaimal spectrum. The bandwidth on hillsides and valleys will not change with the change in inflow, but for flat areas, the bandwidth is greatly affected by the inflow direction.

Development of a dynamic wake model accounting for wake advection delays and mesoscale wind transients

With tip height often above 200 meters, currently installed wind turbines are increasingly interacting with the atmospheric boundary layer. Therefore, the research intends to develop a new dynamic wake model that considers weather transient inputs. The Flow Redirection and Induction in Steady State (FLORIS) framework has been proven to be a powerful wake modelling tool even though lacking dynamical effects. An extension of the FLORIS framework is presented in order to include wake advection delays between wind turbines, time-varying and spatially heterogeneous wind conditions. The so-called Observation Points (OPs) are generated at the rotor centre location. Following a Lagrangian approach, the OPs are convected downstream, along the wake of the wind turbine, defining the wake centreline. It is during this process that the dynamics of wind turbine wake and background flow field unsteadiness are included. Finally, using the same approach currently implemented for yaw-misalignment wake deflection, the wake is shifted to match the unsteady wake centreline. The developed model is validated against Large Eddy Simulation for unsteady inflow with variable wind turbine control and wake interactions. The new model is applied to a simulation of the Horns Rev wind farm with a sinusoidally time-varying wind inflow direction to show an hysteresis in the wind farm power extraction curve.

Whence the Interstellar Magnetic Field Shaping the Heliosphere?

Abstract Measurements of starlight polarized by aligned interstellar dust grains are used to probe the relation between the orientation of the ambient interstellar magnetic field (ISMF) and the ISMF traced by the ribbons of energetic neutral atoms discovered by the Interstellar Boundary Explorer spacecraft. We utilize polarization data, many acquired specifically for this study, to trace the configuration of the ISMF within 40 pc. A statistical analysis yields a best-fit ISMF orientation, B magpol, aligned with Galactic coordinates ℓ = 42°, b = 49°. Further analysis shows the ISMF is more orderly for “downfield” stars located over 90° from B magpol. The data subset of downfield stars yields an orientation for the nearby ISMF at ecliptic coordinates λ, β ≈ 219° ± 15°, 43° ± 9° (Galactic coordinates l, b ≈ 40°, 56°, ±17°). This best-fit ISMF orientation from polarization data is close to the field direction obtained from ribbon models. This agreement suggests that the ISMF shaping the heliosphere belongs to an extended ordered magnetic field. Extended filamentary structures are found throughout the sky. A previously discovered filament traversing the heliosphere nose region, “Filament A,” extends over 300° of the sky, and crosses the upwind direction of interstellar dust flowing into the heliosphere. Filament A overlaps the locations of the Voyager kilohertz emissions, three quasar intraday variables, cosmic microwave background (CMB) components, and the inflow direction of interstellar grains sampled by Ulysses and Galileo. These features are likely located in the upstream outer heliosheath where ISMF drapes over the heliosphere, suggesting Filament A coincides with a dusty magnetized plasma. A filament 55° long is aligned with a possible shock interface between local interstellar clouds. A dark spot in the CMB is seen within 5° of the filament and within 10° of the downfield ISMF direction. Two large magnetic arcs are centered on the directions of the heliotail. The overlap between CMB components and the aligned dust grains forming Filament A indicates the configuration of dust entrained in the ISMF interacting with the heliosphere provides a measurable foreground to the CMB.

Influence of pitching motion on the hydrodynamic performance of a horizontal axis tidal turbine considering the surface wave

A CFD numerical method is established under the wave-current condition, used to analyze the hydrodynamic performance of a horizontal-axis tidal turbine based on floating platform with rotation and pitching motion. The inflow direction load, pitch moment and power coefficients with different depths of the blade tip-immersion, the periods and amplitudes of the pitch, wave heights are obtained. The three coefficients have obvious periodically fluctuated with the pitching and wave frequencies, while the time mean of those have changed little with increasing of the depth of blade tip-immersion, wave height, pitch (wave) period and pitching amplitude. So considering damping and additional mass forces, a load fitting model is established, and the damping and additional mass coefficients are calculated by the least square method. The influence of damping coefficient on the hydrodynamic loads is obvious, while the influence of additional mass coefficient on that can be neglected, and the damping coefficient of inflow direction load coefficient is basically stable. The damping coefficients of the pitching moment and power coefficients fluctuate periodically, but the mean value of damping coefficients keep stable. The research results in this paper are important for studying the coupling motion of the turbine and the floating platform.

Wind tunnel studies of wind turbine yaw and speed control effects on the wake trajectory and thrust stabilization

Yaw-based wake steering is pursued as a means to avoid upstream turbine wake influence on downstream turbines. However, the method's effectiveness is likely restricted by rapid wind direction changes that cause wake trajectory oscillations. To address this issue, a thrust-based wake trajectory stabilization method is proposed here. The changes to the cross-stream thrust, resulting from unintentional yaw misalignments, caused due changes in inflow wind direction could be counteracted by changing rotor speed and blade pitch, thus stabilizing wake trajectory oscillations. This paper presents a wind tunnel case study to explore the effect of combining yaw-based wake steering and fast-changing rotor speed control on the cross-stream thrust component and hence on the wake trajectory. Although a feedback controller was not implemented, it is demonstrated that wake trajectory oscillation could be contained using faster actuating mechanisms, such as rotor speed or pitch. Here the wake oscillations due to wind direction changes emulated by sinusoidally yawing the turbine, were restricted by varying turbine rotation speed. Direct thrust measurements as well as detailed Particle Image Velocimetry (PIV) and hotwire wake data show how this combination can successfully suppress the dynamic cross-stream thrust component perturbations and subsequently the wake trajectory oscillation around a desired position.

Comparison of the Gaussian Wind Farm Model with Historical Data of Three Offshore Wind Farms

A recent expert elicitation showed that model validation remains one of the largest barriers for commercial wind farm control deployment. The Gaussian-shaped wake deficit model has grown in popularity in wind farm field experiments, yet its validation for larger farms and throughout annual operation remains limited. This article addresses this scientific gap, providing a model comparison of the Gaussian wind farm model with historical data of three offshore wind farms. The energy ratio is used to quantify the model’s accuracy. We assume a fixed turbulence intensity of I∞=6% and a standard deviation on the inflow wind direction of σwd=3° in our Gaussian model. First, we demonstrate the non-uniqueness issue of I∞ and σwd, which display a waterbed effect when considering the energy ratios. Second, we show excellent agreement between the Gaussian model and historical data for most wind directions in the Offshore Windpark Egmond aan Zee (OWEZ) and Westermost Rough wind farms (36 and 35 wind turbines, respectively) and wind turbines on the outer edges of the Anholt wind farm (110 turbines). Turbines centrally positioned in the Anholt wind farm show larger model discrepancies, likely due to deep-array effects that are not captured in the model. A second source of discrepancy is hypothesized to be inflow heterogeneity. In future work, the Gaussian wind farm model will be adapted to address those weaknesses.

Field tests on model efficiency of twin vertical axis helical hydrokinetic turbines

Twin vertical axis helical hydrokinetic turbines (VAHHTs) are a type of renewable energy conversion device that can generate electricity from the kinetic energy of free flowing water. To optimize its hydrodynamic performance, a typical twin VAHHTs model with a NACA0020 blade profile, diameter (D) of 0.2 m, height (H) of 0.45 m, solidity ratio (σ) of 0.38, and enwinding ratio (ϖ) of 1.25 was tested. Based on the controllable open channel velocity, a test platform was built to study the effect of different rotational direction, spacing, inflow direction, and phase difference on the efficiency of twin VAHHTs. The results show that the torque measurement platform can accurately measure the torque (T), water velocity (V), and rotational speed (ω) simultaneously. When the rotational direction of the twin VAHHTs is not outward opposite (-+), the efficiency is more than 9.52% higher than that of a single VAHHT. The efficiency increases first, and then decreases with an increase of the spacing between the two turbines. The change of inflow direction angle has a large influence on the efficiency of the twin VAHHTs. The initial phase difference has little effect on the performance of the twin VAHHTs. The highest average efficiency of the twin VAHHTs is 0.2315, which is 10.24% higher than that of a single VAHHT. The results supplement the deficiencies of the measured data at high velocity and provide validation for the numerical calculation of the efficiency of twin VAHHTs.