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Wind energy in the atmospheric boundary layer serves as the primary source for energy absorption and structural load on wind turbines. However, the impact of turbulent coherent structures on the aerodynamic performance and wake characteristics of wind turbines has not been comprehensively evaluated. In this study, the proper orthogonal decomposition (POD) method is employed to assess the influence of turbulent coherent structures of varying scales on the aerodynamic performance and wake characteristics of wind turbines in the neutral atmospheric boundary layer. The results show that turbulent coherent structures are the main factor that determines the wind velocity fluctuation, aerodynamic performance and wake characteristics of wind turbine in the atmospheric boundary layer. When considering the 13th or lower order POD mode, the wind velocity fluctuation increases with the increase of energy content (more POD modes) of the turbulent coherent structures. When considering the first 19 POD modes, the dynamic loads and power of wind turbine fluctuate with high frequencies, the thrust fluctuates in an amplitude range between 2.4 % and 13.9 % around the mean value, and the power fluctuates from 4.5 % to 28.6 % of the mean value. When considering the first 40 POD modes, the average power generation of the wind turbine increases by 26 % compared to the case with no turbulent structures considered. The study of turbine wake shows that turbulent coherent structures can expand the wind turbine wake approximately to a width of 2.5 D and a height of 3 D (D is the diameter of the wind turbine), offset the wake approximately to 2 D , and move forward the position of the wake vortex beginning to dissipation approximately to 7 D behind the wind turbine. In addition, turbulent coherent structures can accelerate the wake velocity recovery by increasing the momentum exchange between the atmospheric boundary layer and wind turbine wake. • A POD-based inflow generation method is established for wind turbine simulation. • Study into the coherent structures with various energy contributions on wind turbine performance. • Obtained the most influence energy contribution of coherent structures in the ABL. • Unveil the influence of coherent structures on the expansion and deflection of wind turbine wakes. [ABSTRACT FROM AUTHOR]

Commercial scale tidal stream turbines (TST) are expected to be deployed in shallow water where the depth varies from 1.5 to 3 turbine diameters. In this study, numerical simulation is conducted at realistic hydrodynamic conditions of potential tidal sites using the stationary actuator disc method at ambient turbulence varying from 5% to 20%, a range of rotor realistic rotor thrust coefficient from 0.64 to 0.98 and a rotor-diameter-to-depth ratio of 20% to 60%. The result shows that the TST wake is affected by the rotor-diameter-to-depth ratio, ambient turbulence, and thrust coefficient. The new empirical model is in accordance with the numerical simulation of a full-scale turbine and is validated with the TST experiment at different rotor-diameter-to-depth ratios with reasonable results in the far wake. This low computational model can benefit the investigation of tidal turbine parks at different configurations where the far wake is pertinent. [ABSTRACT FROM AUTHOR]

The energy harnessing from flow-induced vibrations (FIV) by an oscillating foil placed tandemly behind a circular cylinder (which serves as a vortex generator) is investigated. The foil is submerged in the wake produced by the fixed cylinder and could oscillate in the direction perpendicular to the incoming flow with single-degree freedom. The spacing ratio ranges from 1.0 to 5.0. The oncoming fluid velocity is U = 1–10 m/s, corresponding to the reduced velocity Ur = 3.81–38.08 and the Reynolds number Re = 9.58 × 103–9.58 × 104. Four harnessing damping ratios (ζharness = 0.0054–0.0216) are used to simulate the energy conversion conditions. The main conclusions are: (1) The optimal oscillation pattern related to the highest harnessed energy emerges as the spacing ratio close to 1.0. (2) The airflow energy converted by the foil is positively correlated with the harnessing damping ratio because the amplitude responses are similar at various harnessing damping ratios. A high velocity yields the highest harnessed power. (3) The harnessing efficiency of the foil could reach 48.89%, which is much more than that of an isolated flapping foil. [ABSTRACT FROM AUTHOR]

Objectives: Premature newborns are exposed to a great deal of over-stimulation, which can affect their cerebral development. For better sleep, certain practices should be recommended. The aim of this study was to evaluate the effect of a professional training program on the improvement of practices promoting respect for the newborn's sleep-wake cycle. Materials and Methods: This was an interventional study with a longitudinal, single-group, and before-and-after design. The experimental design followed a three-stage time series: Eight months before, three months after, then eight months after intervention. It targeted a comprehensive sample of 66 professionals. It took place between October 2020 and March 2022 at the Neonatal Intensive Care Unit of the Hassan II University Hospital in Fez, Morocco. It was based on an observation grid and a self-administered questionnaire, validated and tested with a Cronbach's alpha reliability of 0.91. Results: The light environment showed significant differences between the 1st and 3rd step (3.3% vs. 45.0%; P = 0.02; confidence interval [CI] = 13.644-10.456) for knowledge and (13.3% vs. 78.3%; P = 0.01; CI = 14.412-10.888) for practices; the noise environment showed a positive improvement between the 2nd and 3rd intervention (31.7% vs. 41.7%; P < 0.001; CI = 5.954-2.913) for knowledge and (65.0% vs. 73.3%; P < 0.001; CI = 3.597-1.236) for practices, with an average of (8.98 ± 0.30-28.15 ± 0.48; CI = 3.806-1.094) between the 1st and 3rd step. Practices surrounding sleep and wakefulness reported significant improvement between the three periods (14.35 ± 0.22 vs. 18.10 ± 0.35 vs. 19.90 ± 0.35; P P < 0.001; CI = 4.647-2.853) for sleep and (13.25 ± 0.48 vs. 22.27 ± 0.59; P < 0.001; CI = 10.563-7.471) for wakefulness with statistically significant correlations between knowledge and practices (0.426**) for sleep and (0.606**) for wakefulness. Conclusion: The study demonstrated the positive impact of this sleep management and assessment program on the development of professional skills. Its implementation requires rigorous application of developmental support strategies for individualized care in neonatology. [ABSTRACT FROM AUTHOR]

The present experimental work is focused on designing and standardizing a direct method of measuring the drag force on a tapered cylinder in a water tunnel. The model considered in the present study is a tapered cylinder of 70:1 taper ratio (with a mean diameter( D m ) of 8 mm) placed in a water tunnel test section. The drag force is measured directly, which is acquired by using a force transducer setup (strain-gauge-based), augmented with a lever arm to amplify or attenuate the force. Multiple calibrations of the load cells were done to ensure the repeatability of experiments. The taper cylinder model is suspended inside the water tunnel and the drag force is obtained for various Reynolds numbers (based on mean diameter). It was found that the drag coefficient was ≈ 10-20 % less than a circular cylinder. [ABSTRACT FROM AUTHOR]

The hippocampus (HPC) plays a pivotal role in fear learning and memory. Our two recent studies suggest that rapid eye movement (REM) sleep via the HPC downregulates fear memory consolidation and promotes fear extinction. However, it is not clear whether and how the dorsal and the ventral HPC regulates fear memory differently; and how the HPC in wake regulates fear memory. By chemogenetic stimulating in the HPC directly and its afferent entorhinal cortex that selectively activated the HPC in REM sleep for 3-6 h post-fear-acquisition, we found that HPC activation in REM sleep consolidated fear extinction memory. In particular, dorsal HPC (dHPC) stimulation in REM sleep virtually eliminated fear memory by enhancing fear extinction and reducing fear memory consolidation. By contrast, chemogenetic stimulating HPC afferent the supramammillary nucleus (SUM) induced 3-hr wake with HPC activation impaired fear extinction. Finally, desipramine (DMI) injection that selectively eliminated REM sleep for >6 h impaired fear extinction. Our results demonstrate that the HPC is critical for fear memory regulation; and wake HPC and REM sleep HPC have an opposite role in fear extinction of respective impairment and consolidation. • HPC activation in REM sleep consolidated fear extinction memory. • The dorsal HPC stimulation in REM sleep eliminated fear memory by enhancing fear extinction and reducing fear memory consolidation. • Wake HPC and REM HPC have an opposite role in fear extinction of respective impairment and consolidation. [ABSTRACT FROM AUTHOR]

The mechanisms leading to the alternation between active (UP) and silent (DOWN) states during sleep slow waves (SWs) remain poorly understood. Previous models have explained the transition to the DOWN state by a progressive failure of excitation because of the build‐up of adaptation currents or synaptic depression. However, these models are at odds with recent studies suggesting a role for presynaptic inhibition by Martinotti cells (MaCs) in generating SWs. Here, we update a classical large‐scale model of sleep SWs to include MaCs and propose a different mechanism for the generation of SWs. In the wake mode, the network exhibits irregular and selective activity with low firing rates (FRs). Following an increase in the strength of background inputs and a modulation of synaptic strength and potassium leak potential mimicking the reduced effect of acetylcholine during sleep, the network enters a sleep‐like regime in which local increases of network activity trigger bursts of MaC activity, resulting in strong disfacilitation of the local network via presynaptic GABAB1a‐type inhibition. This model replicates findings on slow wave activity (SWA) during sleep that challenge previous models, including low and skewed FRs that are comparable between the wake and sleep modes, higher synchrony of transitions to DOWN states than to UP states, the possibility of triggering SWs by optogenetic stimulation of MaCs, and the local dependence of SWA on synaptic strength. Overall, this work points to a role for presynaptic inhibition by MaCs in the generation of DOWN states during sleep. [ABSTRACT FROM AUTHOR]

Sleep during the midday, commonly referred to as siesta, is a common trait of animals that mainly sleep during the night. Work using Drosophila led to the identification of the daywake (dyw) gene, found to have anti‐siesta activity. Herein, we show that the DYW protein undergoes signal peptide‐dependent secretion, is present in the circulatory system, and accumulates in multiple organs, but, surprisingly, it is not detected in the brain where wake–sleep centers are located. The abundance of DYW in adult flies is regulated by age, sex, temperature, and the splicing efficiency of a nearby thermosensitive intron. We suggest that DYW regulates daytime wake–sleep balance in an indirect, extracerebral manner, via a multi‐organ network that interfaces with the circulatory system. [ABSTRACT FROM AUTHOR]

The use of wind energy, the area of wind farms, and the length of wind turbine blades continuously increase with the increase in energy demand. This study aims to simulate large wind farms in the atmospheric boundary layer with different double-rotor (DR) wind turbine arrangements using large eddy simulation. The effect of four DR wind turbine arrangements on the efficiency of a large wind farm was investigated in this study. All simulations were performed using the OpenFOAM solver. The performance of different turbine arrangements was investigated based on the mean velocity, the extent of the wake region, mean kinetic energy, and turbine power. Results showed that the arrangement of DR turbines with transverse spacing produces higher power than other layouts. Moreover, DR layouts produce the same power as single-rotor layouts with a short blade length. This scenario is important from an economic point of view. [ABSTRACT FROM AUTHOR]

Summary The circuitry underlying the initiation, maintenance, and coordination of wakefulness, rapid eye movement sleep, and non‐rapid eye movement sleep is not thoroughly understood. Sleep is thought to arise due to decreased activity in the ascending reticular arousal system, which originates in the brainstem and awakens the thalamus and cortex during wakefulness. Despite the conventional association of sleep–wake states with hippocampal rhythms, the mutual influence of the hippocampal formation in regulating vigilance states has been largely neglected. Here, we focus on the subiculum, the main output region of the hippocampal formation. The subiculum, particulary the ventral part, sends extensive monosynaptic projections to crucial regions implicated in sleep–wake regulation, including the thalamus, lateral hypothalamus, tuberomammillary nucleus, basal forebrain, ventrolateral preoptic nucleus, ventrolateral tegmental area, and suprachiasmatic nucleus. Additionally, second‐order projections from the subiculum are received by the laterodorsal tegmental nucleus, locus coeruleus, and median raphe nucleus, suggesting the potential involvement of the subiculum in the regulation of the sleep–wake cycle. We also discuss alterations in the subiculum observed in individuals with sleep disorders and in sleep‐deprived mice, underscoring the significance of investigating neuronal communication between the subiculum and pathways promoting both sleep and wakefulness. [ABSTRACT FROM AUTHOR]

Flow around a cylinder is an important research problem in fluid mechanics. However, studies on traveling wave wall (TWW) flow control for the wake generated by the flow around a 3D cylinder remain limited. This study performs large eddy simulation (LES) to investigate the wake characteristics of flow around a three-dimensional (3D) circular cylinder with the TWW. The influence of the main control parameters of TWW on the aerodynamic forces and wake of the 3D cylinder is analyzed. The wake characteristics of the 3D cylinder at Re = 4 × 104 are obtained, and the traveling wave propagating downstream is achieved on the rear surface of the 3D cylinder using dynamic mesh. The control effects of wave amplitude, number of waves, and wave velocity of the traveling wave on the aerodynamic forces of the cylinder are analyzed, and the optimal control parameter combination is determined. The results demonstrate that the TWW control method completely eliminates the spanwise 3D flow characteristics of the cylinder when the amplitude ratio, number of waves, and velocity ratio are 0.02, 4, and 1.5, respectively. Moreover, it effectively suppresses the flow separation on the cylinder surface, eliminates the wake vortex, and suppresses vortex-induced vibration (VIV). [ABSTRACT FROM AUTHOR]

Static axial induction control and tilt control are two strategies that have the potential to increase power production in wind farms, mitigating wake effects and increasing the available power for downstream turbines. In this study, wind tunnel experiments are performed to evaluate the efficiency of these two techniques. First, the axial induction of upstream turbines in wind farms comprising two, three, and five turbines is modified through the tip-speed ratio. This strategy is found to be ineffective in increasing power extraction. Next, the power extraction and flow through a two-turbine wind farm are evaluated, considering different tilt angles for the upstream turbine, under two levels of incoming flow turbulence intensities and turbine spacing distances. It is shown that forward tilting increases the overall power extraction by deflecting the wake downwards and promoting the entrainment of high-speed fluid in the upper shear layer, regardless of the turbine spacing distance and turbulence intensity level. Also, the wake is seen to recover faster due to the increased shear between the wake and the outer flow. Tilting a turbine backward deflects the wake upwards and pulls low-speed flow from under the turbine into the wake space, increasing the available power for downstream turbines, but it is not enough to increase global power extraction. Moreover, since the wake deflection under backward tilting is not limited by ground blockage, it leads to larger secondary steering compared with forward tilting. Finally, it is demonstrated that the secondary steering of the downstream turbine's wake influences the flow encountered by a turbine positioned farther downstream. [ABSTRACT FROM AUTHOR]

In order to explore the wake interference effect of the wind farm and quantitatively predict the overall output efficiency under different wind farm layouts, the mathematical model and prediction program of the wake interference effect was constructed. The newly established model originates from the Jensen model, which was the most commonly used to predict the wake effect of a single wind turbine, and was based on the shadowing effect and shadowing mode of the upstream wind turbine on the downstream one in the wind farm layout. The variation of wind farm overall output efficiency with wind farm scale, row/ column spacing and wind direction angle in homogeneous arrangement mode, and with dislocation spacing and wind direction angle in staggered arrangement mode were studied. The results show that the overall output efficiency increases with the increase of row/ column spacing under different wind farm scales, and decreases with the increase of wind farm scales under different row/ column spacing. There are obvious differences in the overall output efficiency of the wind farm under different dislocation spacing and wind direction angle. It is necessary to reasonably arrange the row/ column spacing of wind turbines according to the wind direction where the wind farm is located, to maximize the overall output efficiency. Research can provide guidance for the prediction of wake interference effect under any wind farm layout and rational design of wind farm layout. [ABSTRACT FROM AUTHOR]

The free surface and pycnocline wake characteristics of SUBOFF were studied by simulations and experiments in a two-layer ocean. The experimental results showed that the simulation method accurately calculated the wake characteristics of the scaling model, and the simulation method was expanded to full-scale prototypes. When typical Froude numbers of flow is from 0.05 to 2.7, the submerged body velocity can influence the wake characteristics of the free surface and pycnocline interface. The wake system of the free surface would transform into a Kelvin wake, and the angles of the V-shaped divergent waves of the pycnocline interface would be reduced with the increasing Froude number. [ABSTRACT FROM AUTHOR]

This article presents the jet mixing characteristics of sonic under expanded co-flowing jet by means of varying the lip thickness between the primary and secondary nozzle. The lip thicknesses between the nozzles chosen were 0.3Dp and 1.5Dp and their jet mixing characteristics is studied numerically for the nozzle pressure ratio of 5. The jet mixing effectiveness in the axial and radial directions were analysed by the total pressure decay plots and contours of Mach number, density gradient and turbulent kinetic energy. The results exhibit that, for the reduced lip thickness of 0.3Dp, the core of the primary jet is increased due to the encasing given by the surrounding jet. For the dominant lip thickness of 1.5Dp, the primary jet core is reduced due to the strong interaction between the primary and co-flowing jet. The various jet mixing phenomenon like shear layer between surrounding jet and atmosphere, recirculation zone and Mach disk were also analysed from the contour plots. [ABSTRACT FROM AUTHOR]

Summary: The sleep disorder narcolepsy, a hypocretin deficiency disorder thought to be due to degeneration of hypothalamic hypocretin/orexin neurons, is currently treated symptomatically. We evaluated the efficacy of two small molecule hypocretin/orexin receptor‐2 (HCRTR2) agonists in narcoleptic male orexin/tTA; TetO‐DTA mice. TAK‐925 (1–10 mg/kg, s.c.) and ARN‐776 (1–10 mg/kg, i.p.) were injected 15 min before dark onset in a repeated measures design. EEG, EMG, subcutaneous temperature (Tsc) and activity were recorded by telemetry; recordings for the first 6 h of the dark period were scored for sleep/wake and cataplexy. At all doses tested, TAK‐925 and ARN‐776 caused continuous wakefulness and eliminated sleep for the first hour. Both TAK‐925 and ARN‐776 caused dose‐related delays in NREM sleep onset. All doses of TAK‐925 and all but the lowest dose of ARN‐776 eliminated cataplexy during the first hour after treatment; the anti‐cataplectic effect of TAK‐925 persisted into the second hour for the highest dose. TAK‐925 and ARN‐776 also reduced the cumulative amount of cataplexy during the 6 h post‐dosing period. The acute increase in wakefulness produced by both HCRTR2 agonists was characterised by increased spectral power in the gamma EEG band. Although neither compound provoked a NREM sleep rebound, both compounds affected NREM EEG during the second hour post‐dosing. TAK‐925 and ARN‐776 also increased gross motor activity, running wheel activity, and Tsc, suggesting that the wake‐promoting and sleep‐suppressing activities of these compounds could be a consequence of hyperactivity. Nonetheless, the anti‐cataplectic activity of TAK‐925 and ARN‐776 is encouraging for the development of HCRTR2 agonists. [ABSTRACT FROM AUTHOR]

High physical activity levels during wake are beneficial for health, while high movement levels during sleep are detrimental to health. Our aim was to compare the associations of accelerometer-assessed physical activity and sleep disruption with adiposity and fitness using standardized and individualized wake and sleep windows. People (N = 609) with type 2 diabetes wore an accelerometer for up to 8 days. Waist circumference, body fat percentage, Short Physical Performance Battery (SPPB) test score, sit-to-stands, and resting heart rate were assessed. Physical activity was assessed via the average acceleration and intensity distribution (intensity gradient) over standardized (most active 16 continuous hours (M16h)) and individualized wake windows. Sleep disruption was assessed via the average acceleration over standardized (least active 8 continuous hours (L8h)) and individualized sleep windows. Average acceleration and intensity distribution during the wake window were beneficially associated with adiposity and fitness, while average acceleration during the sleep window was detrimentally associated with adiposity and fitness. Point estimates for the associations were slightly stronger for the standardized than for individualized wake/sleep windows. In conclusion, standardized wake and sleep windows may have stronger associations with health due to capturing variations in sleep durations across individuals, while individualized windows represent a purer measure of wake/sleep behaviors. [ABSTRACT FROM AUTHOR]

Through direct numerical simulations, the transition from pure mode A to mode B in the near wake of a circular cylinder is studied with no effect of vortex dislocations. The Reynolds number is computed from 100 to 330 with the computational spanwise length of 4 diameters. In the present part, fluid forces are analyzed. The results show that mode swapping still exists in the range of Reynolds numbers from 230 to 240. In this range, fluid forces with low and high levels occur intermittently. Moreover, when the critical Reynolds number of 193 ( ± 0.5) is exceeded, with the increase of the Reynolds number, the vortex-shedding frequency gradually shifts from a single low frequency, high and low frequency coexistence to a single high frequency. [ABSTRACT FROM AUTHOR]

Understanding the unsteady characteristics of the mid-to-far wake and comprehension of the aerodynamic performance of floating offshore wind turbines is essential for the further development of offshore wind farms. In this perspective, a developed Actuator line model is utilized to analyze an offshore turbine on four different platforms. The model reliability was examined through three sets of validations involving turbine output in fixed and floating conditions and wake expansion in terms of size and rate. The affected relative velocity by the platform motion contributes to the wake deformation and temporal effects on induced velocity. Angular platform motions produce a non-axisymmetric helical wake that raises the chance of meandering wake patterns. It was founded although platform movement generally can boost the recovery of mean velocity value, it may amplify the amplitude of velocity deficit fluctuation at further downstream by encouraging interactions and merging vortex rings. Consequently, the wake propagates into a form of stronger circles whose period, strength, and center are functions of turbine movement and operation conditions. By providing a computationally efficient tool, the findings emphasize the importance of wake propagation in designing and assessing farm layouts that operate in the presence of significant multi-motions of floating offshore wind turbines. [ABSTRACT FROM AUTHOR]

Astrocytes mediate many important aspects of neural homeostasis, but until recently, their role in sleep was largely unknown. The situation has dramatically changed in the last decade. The use of transgenic animals, optogenetics, chemogenetics, brain imaging and sophisticated molecular assays has led to exciting discoveries. Astrocytes dynamically change their activity across the sleep–wake cycle and may encode sleep need via changes in intracellular signalling pathways. Astrocytes also exocytose/secrete sleep‐inducing molecules which modulate brain activity, sleep architecture and sleep regulation. Many of these observations have been made in mice and Drosophila melanogaster, indicating that astroglial sleep mechanisms are evolutionarily conserved. We review recent findings and discuss future directions. [ABSTRACT FROM AUTHOR]

To live in the wake of slavery is to be vulnerable to violence known and unknown to ourselves and to always have those violent possibilities legally and scientifically justified. This research asks in what ways do Black people communicate care for each other while living in structures of racial oppression? I look to the Black performative arena, specifically hip-hop, to explore the ways Black hip-hop lyrics provides an avenue to care for lost Black lives in ways not possible by state-institutions. This research uses ethnographic content analysis of posthumous released songs about Nipsey Hussle to explore the ways he has been engaged in the wake of his death. I argue that in the wake of Nipsey's passing hip-hop served as a form of wake-work praxis and has cared for Nipsey by keeping his voice alive, changing the discursive contours of contemporary hip-hop using his brand, and named him in ways that challenge how the state-institutions position Black subjectivity. [ABSTRACT FROM AUTHOR]

The unsteady aerodynamic characteristics and interference effects of floating offshore wind turbine (FOWT) are mainly affected by the pitch motion of the ocean platform. Based on computational fluid dynamics (CFD) and advanced overset grid technology, the aerodynamic performance and wake characteristics of a fully configured wind turbine with rotating blades, nacelle , and tower are studied in this paper. The effects of the amplitude and frequency of pitch motion on the wind turbine aerodynamic loads and flow field are investigated herein in detail. The power and thrust between numerical simulation and experiment are compared. The results show that the grid and simulation parameters used in this study can accurately capture the aerodynamic characteristics and the flow field around wind turbines. The influence of the pitch amplitude and frequency on the performance of wind turbines is discussed. The complex flow interaction between the tip vortex, tower shedding vortex, and the turbulent wake was observed. The present results indicate that the pitch motion amplitude and frequency have a great influence on the power, thrust, and wake characteristics. [ABSTRACT FROM AUTHOR]

Due to aerodynamic resistance, aerodynamic noise, and other problems, the further development of traditional high-speed electric multiple units (EMUs) on the open line has been seriously restricted, and the construction of a vacuum pipeline high-speed train system has become a new solution. In this paper, the Improved Detached Eddy Simulation (IDDES) is used to analyze the turbulent characteristics of the near wake region of EMU in vacuum pipes, so as to establish the important relationship between the turbulent boundary layer, wake, and aerodynamic drag energy consumption. The results show that there is a strong vortex in the wake near the tail, which is concentrated at the lower end of the nose near the ground and falls off from the tail. In the process of downstream propagation, it shows symmetrical distribution and develops laterally on both sides. The vortex structure far from the tail car is increasing gradually, but the strength of the vortex is decreasing gradually from the speed characterization. This study can provide guidance for the aerodynamic shape optimization design of the rear of the vacuum EMU train in the future and provide certain reference significance for improving the comfort of passengers and saving the energy consumption caused by the speed increase and length of the train. [ABSTRACT FROM AUTHOR]

The aim of this essay is to interrogate the possibility of a wake in historiographical practice, especially in written form, by juxtaposing reflections on the theory and philosophy of history at the close of the first quarter of the twenty-first century with the avant-garde movement of the early twentieth. To this end, I establish a dialogue between the Dada and Surrealist artistic avant-gardes' experiments with writing and reflections on narrative constructivism and the possibility of conceiving a postmodern historical discipline. What are the implications of considering certain well-known historiographical or classic works of the discipline as artifacts of writing that generate effects highly similar to what the Dada avant-gardes called Readymades and the Surrealists objet trouvé? My answer unfolds in two parts. First, I demonstrate the situated nature of historical knowledge about the past (be that past distant or recent) to articulate and evaluate intersections between the artistic avant-garde, poststructuralist academic reflections on historical practice, the institution of academic history, the historiographical operation and, above all, the writing of history as a heuristic in order to access any other bygone period. Secondly, I argue that all historians who emerge from such reflections must be independent as well as firm in their ways of conceiving and rendering concrete their own historiographical gesture. The context for all this is a present in which written formats and platforms on the past as history are exploding and multiplying exponentially. Through the fabrication of an object – a 'work of history' – given an aesthetic and reflexive value through the use of the elements, their positioning, and the hierarchy and meanings granted to them, it becomes possible to generate a bi-directional historiographical operation that can incorporate both the audience and a historian-performer, starting from the premise that all writing of history does not end in a single time or in a single paradigm. [ABSTRACT FROM AUTHOR]

Yuan, H.; Li, F.; Yan, Q.; Zhang, W., and Hu, J., 2023. Investigating pressure fluctuations on marine vessel rudders: Numerical results from propeller–rudder–hull interactions. Journal of Coastal Research, 39(2), 284–295. Charlotte (North Carolina), ISSN 0749-0208. Severe pressure fluctuations induced by propeller wake enhance rudder vibrations. In the present study, the pressure fluctuations on the rudder are numerically investigated by using k-ω Menter's shear stress transport turbulence model. The pressure fluctuations on the port and starboard sides of the rudder are compared in time and frequency domains. Furthermore, the impact of the advance coefficient on the displacement of propeller wake and pressure fluctuations is also discussed. The numerical results indicate that the propeller wake displacement is oriented upward and downward at the port and starboard sides, respectively. The most intense pressure fluctuation occurs at the propeller blade passage frequency. As a result of vortex displacement, the suction-side fluctuations are weaker than those on the pressure side at frequencies of 100–300 Hz over an advance coefficient range of J = 0.75–0.925. The displacement of the propeller wake weakens when the advance coefficient decreases. [ABSTRACT FROM AUTHOR]

Recently, wind turbine research has switched focus to vertical axis wind turbines due to the extensive research that has been performed on horizontal axis wind turbines and the potential of vertical axis wind turbines in built-up areas. This study aims to analyse the performance of a small-scale hybrid vertical axis wind turbine that can switch from functioning as a Darrieus (lift) turbine to a Savonius (drag) turbine by rotating the blades. The turbine was analysed using 3D computational fluid dynamics (CFD) simulations in ANSYS Fluent as the primary method, and the findings were verified using wind tunnel experiments. During the analysis, design parameters such as the blade length, diameter, and number of blades were varied to determine if the design had room for improvement. It was found that the current design of the turbine has an optimal efficiency of 12.5% in the Darrieus configuration, which was found to increase when the diameter or blade length was increased. The Savonius configuration was found to be more efficient at low tip-speed ratios (<0.14), and its efficiency could be increased by adding more blades. The experiments found similar trends to the simulations; however, the efficiencies obtained were on average a tenfold increase from the simulation. Implementing the changes that increased efficiency leads to an increased wake recovery distance, making it less suitable for use in a wind farm. [ABSTRACT FROM AUTHOR]

We study the compression of spatial and temporal features in fluid flow data using multimedia compression techniques. The efficacy of spatial compression techniques, including JPEG and JPEG2000 (JP2), and spatiotemporal video compression techniques, namely H.264, H.265, and AV1, in limiting the introduction of compression artifacts and preserving underlying flow physics are considered for laminar periodic wake around a cylinder, two-dimensional turbulence, and turbulent channel flow. These compression techniques significantly compress flow data while maintaining dominant flow features with negligible error. AV1 and H.265 compressions present the best performance across a variety of canonical flow regimes and outperform traditional techniques such as proper orthogonal decomposition in some cases. These image and video compression algorithms are flexible, scalable, and generalizable holding potential for a wide range of applications in fluid dynamics in the context of data storage and transfer. [ABSTRACT FROM AUTHOR]

It is very likely to bring safety hazards to the aircraft in the takeoff and climb or approach and landing phase for low-level wind shear in aviation flight. In severe cases, it can lead to aircraft stall or even crash. Low-altitude wind shear often also has a short duration, small scale, sudden and strong characteristics. Therefore, it is of great significance and practical value to strengthen the numerical simulation and research on aircraft encountering low-altitude wind shear in the context of the rapid development of China's civil aviation and general aviation industry. The SST model and FLUENT were used to calculate the wake vortex evolution. ANSYS FLUENT user defined function(UDF) was applied to compile seven cases with different environmental side winds for numerical simulation of the wake vortex dissipation mechanism by constructing a two-dimensional model of H-B wake vortex dissipation. It is found that the superposition of side wind and vortex-induced velocity under the influence of nonlinear vertical shear will lead to asymmetric pressure distribution around the vortex, causing the vortex pair to tilt by comparing the vortex detected in the field at Chengdu Shuangliu Airport. [ABSTRACT FROM AUTHOR]

In the present study, numerical simulations are performed to identify the role of Reynolds number (Re), Richardson number (Ri) and free-stream orientations (α) on flow structures, aerodynamic parameters and heat transfer characteristics for the conditions (20 ≤ Re ≤ 120, 0° ≤ α ≤ 90° and 0 ≤ Ri ≤ 1.6). Prandtl number (Pr) and cylinder orientation (ϕ) are kept fixed at 0.71 and 0°. The Oberbeck–Boussinesq approximation is used to account for buoyancy effects. The governing equations of continuity, momentum and energy are discretized on a colocated body-fitted grid by employing a finite difference method. A viscous implicit pressure correction scheme is employed to advance the discrete solution in time. Contour maps of mean/steady drag coefficient and Nusselt number on (α-Ri) plane are plotted for 20 ≤ Re ≤ 120. From these contour maps, it is possible to identify the ranges of parameters (α, Ri) that can yield a relatively high mean/steady heat transfer rate accompanied by relatively low values of mean/steady drag coefficient. For [70° ≤ α ≤ 90°, 0 ≤ Ri ≤ 1.6], such a scenario is possible for any Re ∈ [20, 120]. The Strouhal number is observed to be maximum for Re = 120 at α = 45° and Ri = 1.2. Mean or steady coefficient of lift for any free-stream orientation (α ≠ 0°) is found to be highest at Re = 20 and Ri = 1.6. Sensitivity of (C D)Ri = 0.0 to α is observed to be minimum for Re = 20 and maximum for Re = 120. Sensitivity of the ratio C D(Ri,α)/ C D(0,α) to Re is observed to be lower for unsteady flows than for steady flows, and it decreases with an increase in Re at a fixed value of Ri. Mean Nusselt number (Nu) in the forced flow regime increases significantly with an increase in Re at a fixed α. The Nusselt number is observed to be more sensitive to Ri for steady flows than for unsteady flows. The percentage increase in the ratio Nu (Ri,α)/ Nu (0,α) for the entire range of Re is found to be 14.07%, 14.13%, 11.74% and 10.62% at α = 30°, 45°, 60° and 90°. At a fixed Ri, the Nusselt number ratio is found to decrease with an increase in Re for the entire range of α except for α = 90°. It is observed that the rate of heat transfer from the faces of the cylinder increases with an increase in Re for the entire ranges of α and Ri. [ABSTRACT FROM AUTHOR]

Excessive daytime sleepiness (EDS) is a complex symptom characterized by a strong urge to sleep during daytime accompanied by problems such as attention deficits, anxiety, and lower cognitive performance. The efficacy of treatments for EDS is determined by their ability to decrease sleepiness, and less attention has been given to the effects these compounds have on the quality of the wake itself. Hypocretin (HCRT; orexin) signalling is implicated in narcolepsy, and hypocretin receptor 2 (HCRTR2) agonists are in clinical trials for treating EDS in narcolepsy. Here, we review preclinical research to determine how HCRTR2 agonists may affect attention and anxiety compared with other EDS treatment strategies. We conclude that such compounds may improve not only the quantity but also the quality of wake, and we hope that they will create opportunities for more nuanced treatment strategies in narcolepsy. Targeting hypocretin (HCRT) for the treatment of excessive daytime sleepiness (EDS) provides new opportunities to improve the quality of wake in patients with narcolepsy. HCRT signalling is implicated in maintenance of wakefulness and also in important aspects of the quality of wake, such as attention and anxiety. Hypocretin receptor 2 (HCRTR2) agonists may be at least as effective in decreasing sleepiness as currently approved EDS treatments such as modafinil, solriamfetol, and pitolisant. HCRTR2 agonists may be similarly effective in improving attention compared with currently approved EDS treatments. Although pitolisant and solriamfetol have risks of increasing anxiety, preclinical research suggests that targeting HCRT signalling with HCRTR2 agonists may decrease anxiety. [ABSTRACT FROM AUTHOR]

Savonius vertical axis wind turbines have simple structures, can self-start in environments with low wind speed and strong turbulence intensity, and can be installed at low costs. Therefore, installation is possible in urban centers with low wind speeds, which may contribute to the construction of a decentralized power system. Savonius wind turbines are operated by drag force, with the blades moving in the same direction as the flow current providing the thrust force and those moving in the opposite direction of the wind being rotated by the drag force. In this study, the Savonius wind turbine design was examined to develop a stable wind turbine for use in urban centers at low wind speeds. The Savonius rotor design variables (aspect and overlap ratios) and blade forms (semi-circular, Bach, and elliptical type) were examined using computational fluid dynamics analysis. Moreover, a rotor capable of providing the target output was designed and maximum rotor efficiency of 18% was realized. Further, changes to the flow corresponding with various turbine layouts were analyzed to determine the arrangement that would maximize turbine performance. The results showed that the maximum efficiency of the turbines was in the 17–19% range and without significant variation. [ABSTRACT FROM AUTHOR]

The flow around roughened circular cylinders and the wake behind them were studied in a wind tunnel flow using the Particle Image Velocimetry (PIV) method. The Reynolds number ranged from 5140 to 11800, and the real diameter of the cylinders including surface roughness ranged from 15.06 to 17.34 mm. The flow properties and forces around the roughened cylinders was evaluated by means of Strouhal number and coefficient of drag. The wake was analysed by means of mean velocities along the cylinder centreline, its width and the Proper Orthogonal Decomposition (POD) method. The added surface roughness was found to decrease the wake length and increase the wake width at lower Reynolds numbers. At higher Reynolds numbers, the added surface roughness did not decrease the wake length, but did increase the wake width, although with less effect. The POD analysis showed changes in the higher modes of the flow. The kinetic energy of the first two modes covers up to 50% of the total kinetic energy; the first two modes in the case of the smooth cylinder have the lowest kinetic energy, whereas the first two modes in the case of the roughest cylinder have the highest kinetic energy. The similarity between the POD modes of the smooth and roughened cylinders might be due the fact that the actual Reynolds number range was below the transitional one. • Added surface roughness decreases the wake length and increases the wake width at lower Reynolds numbers. • Added surface roughness decreases the Strouhal numbers at lower Reynolds numbers. • The cylinder drag was increased at higher surface roughnesses. • The kinetic energy of the first two POD modes cover up to 50% of the total kinetic energy. • The absolute kinetic energy is increasing with increasing surface roughness. [ABSTRACT FROM AUTHOR]

Ducted turbines have the potential to generate large-scale electricity when placed in tidal farms. Understanding the fluid-duct interaction would provide vital information for tidal farm projects. This paper describes flume experiments to investigate the performance and far wake impact on flanged duct turbines in bi-directional tidal flows. Results showed that ducted turbines generate 40% more power per rotor unit area than bare turbines. The turbines underperformed for each device in tandem configurations. However, ducted turbines outperformed bare turbines by 15%. The decreasing range of wake velocities and increasing turbulence intensities of the devices were shown to be greater in the ducted turbines. The drop in wake velocity is caused by kinetic energy extraction, and duct and rotor blockage effects. For the isolated bare and ducted turbines, full flow recovery occurs at around 13 and 20 rotor diameters, respectively. In tandem arrangements, while the bare turbine operated as if it was in isolation from 24 rotor diameters downstream, the wake flow in the ducted turbines persisted beyond. However, in terms of power output per rotor unit area, the deployment of additional ducted turbines may be advantageous. Though in the present state of development, precise economic estimates of energy costs are unavailable. • Performance and far wake impact on flanged duct turbine are experimentally studied. • Flanged duct turbines outperform the bare turbine both in isolation and within an array. • Decreasing range of wake velocities is greater in ducted turbines than in bare turbines. • Increasing range of turbulence intensities is greater in ducted turbines than in bare turbines. • The proposed flanged duct shape may well perform in both flood and ebb current flows. [ABSTRACT FROM AUTHOR]

Sasha Huber's Shooting Back-Reflections on Haitian Roots portraits (2004) and the Haïti chérie ('Haiti, my beloved', 2010) performance are multi-sensorial works which voice an incessantly reverberating call for justice and solidarity with the absent and silenced victims of past, and ongoing, violences; from Columbus's 1492 'discovery' and landing on Hispaniola; the Duvaliers' dictatorship in Haiti; and the 12 of January 2010 earthquake that became a disaster. Taking Huber's works as the starting point, the article explores the ways in which these wakeful pieces gesture towards an ambivalent repair and perform a form of justice against legal, epistemic and representational regimes of 'un-visibility'. With each tak-tak-tak of the staple gun, the shining staples, or the contour of a snow angel, these works conjure a space of defiant care and Afro-diasporic solidarity, protest and presence, creating an alternative 'archive of affect'. [ABSTRACT FROM AUTHOR]

Renewable energy has received a lot of attention. In recent years, offshore wind power has received particular attention among renewable energies. Fixed-type offshore wind turbines are now the most popular. However, because of the deep seas surrounding Japan, floating types are more preferable. The floating system is one of the factors that raises the cost of floating wind turbines. Vertical axis wind turbines (VAWT) have a low center of gravity and can tilt their rotors. As a result, a smaller floating body and a lower cost are expected. A mechanism called a floating axis wind turbine (FAWT) is expected to further reduce the cost. FAWT actively employs the features of VAWT in order to specialize itself in the area of offshore floating-type wind turbines. The lifting line theory simulation was used in this study to discuss the performance of the FAWT under the tilted conditions and its wake field. The results show that a tilted VAWT recovers faster than an upright VAWT. This suggests that FAWTs can be deployed in high density and efficiently generate energy as an offshore wind farm using VAWTs. [ABSTRACT FROM AUTHOR]

In a compressor, the periodic wake is an inherently unsteady phenomenon that affects the downstream flow conditions and loading distribution. Thus, understanding the physical mechanisms of these unsteady effects is important for eliminating flow losses and improving compressor performance, particularly at low Reynolds numbers. To understand the influence of the upstream wake on the downstream flow field structure, this paper describes numerical simulations of a one-stage high-pressure compressor at altitudes of 10–20 km. The influence of the wake on rotor flow blockage at different Reynolds numbers is analyzed, and the unsteady interaction between the upstream wake and boundary layer or tip leakage flow is discussed. The results indicate that the wake has a beneficial effect on the efficiency of the rotor at high Reynolds numbers, but this weakens and becomes negative as the Reynolds number decreases. The wake can reduce the flow blockage in the mainflow region. Due to the wake, the length of the laminar separation bubble at high Reynolds numbers decreases and that at low Reynolds numbers increases. In addition, the unsteadiness of the wake causes separation bubbles to appear periodically at high Reynolds numbers and induces an open separation bubble at low Reynolds numbers. The Kelvin–Helmholtz instability can dominate the transition process of the boundary layer, which is also affected by the disturbance vortex induced by the wake. Regarding the tip leakage flow, the wake can reduce the flow blockage at high Reynolds numbers but increase the flow blockage at low Reynolds numbers. The interaction at low Reynolds numbers causes a double-leakage flow, which finally leads to the large-scale separation of the suction surface boundary layer. The large-scale separation causes flow blockage in the tip region and prevents the rotor wake from propagating downstream. On the contrary, the unsteady wake can pass through the tip clearance vortex and inhibit the separation of the suction boundary layer at high Reynolds numbers, which is reflected in a larger amplitude of one blade passage frequency. Therefore, the flow loss in the downstream flow field at high Reynolds numbers is significantly reduced at high Reynolds numbers. [ABSTRACT FROM AUTHOR]

The lowest input voltage for a single-inductor switched-inductor (SL) boost charger to draw power is critical for energy-harvesting applications. When a battery is fully discharged, the charger solely relies on the millivolt input-source voltage vS to wake the system. When the charger is awake and operates in static mode, it needs to draw power from low voltage vS efficiently. Thus, the major contribution of this article is theorizing the fundamental limits of SL converters, and experimentally validating the lowest vS possible for a single-inductor boost to operate, both in wake and static mode. This article derives closed-form design expressions for all circuit components and validates the design theory with a 1.6-μm CMOS prototype. When source resistance is 350 Ω, this prototype validates that the lowest-possible vS for SLs in wake mode is 225–285 mV. In static mode, the lowest-possible vS for SLs is 40 mV. Despite recent literature shows that switched-capacitors (SCs) can wake with lower vS, theorizing and experimentally validating the lowest vS possible for SL converters can prove the fundamental limits of SL chargers. Moreover, since this article also validates that SLs operate with lower vS than SCs in static mode, thus, SC-SL hybrids are the best system. [ABSTRACT FROM AUTHOR]

Sleep is a necessity for our survival, but its regulation remains incompletely understood. Here, we used a human sleep duration gene to identify a population of cells in the peri-tegmental reticular nucleus (pTRNADRB1) that regulate sleep-wake, uncovering a role for a poorly understood brain area. Although initial ablation in mice led to increased wakefulness, further validation revealed that pTRNADRB1 neuron stimulation strongly promotes wakefulness, even after stimulation offset. Using combinatorial genetics, we found that excitatory pTRNADRB1 neurons promote wakefulness. pTRN neurons can be characterized as anterior- or posterior-projecting neurons based on multiplexed analysis of projections by sequencing (MAPseq) analysis. Finally, we found that pTRNADRB1 neurons promote wakefulness, in part, through projections to the lateral hypothalamus. Thus, human genetic information from a human sleep trait allowed us to identify a role for the pTRN in sleep-wake regulation. [ABSTRACT FROM AUTHOR]

Memory consolidation is promoted by sleep. However, there is also evidence for consolidation into long-term memory during wakefulness via processes that preferentially affect nonhippocampal representations. We compared, in rats, the effects of 2-h postencoding periods of sleep and wakefulness on the formation of long-term memory for objects and their associated environmental contexts. We employed a novel-object recognition (NOR) task, using object exploration and exploratory rearing as behavioral indicators of these memories. Remote recall testing (after 1 wk) confirmed significant long-term NOR memory under both conditions, with NOR memory after sleep predicted by the occurrence of EEG spindle-slow oscillation coupling. Rats in the sleep group decreased their exploratory rearing at recall testing, revealing successful recall of the environmental context. By contrast, rats that stayed awake after encoding showed equally high levels of rearing upon remote testing as during encoding, indicating that context memory was lost. Disruption of hippocampal function during the postencoding interval (by muscimol administration) suppressed long-term NOR memory together with context memory formation when animals slept, but enhanced NOR memory when they were awake during this interval. Testing remote recall in a context different from that during encoding impaired NOR memory in the sleep condition, while exploratory rearing was increased. By contrast, NOR memory in the wake rats was preserved and actually superior to that after sleep. Our findings indicate two distinct modes of long-term memory formation: Sleep consolidation is hippocampus dependent and implicates event-context binding, whereas wake consolidation is impaired by hippocampal activation and strengthens context-independent representations. [ABSTRACT FROM AUTHOR]

The results of high fidelity aerodynamic and acoustic computations of thick flatback airfoils are reported in the present paper. The studies are conducted on a flatback airfoil having a relative thickness of 30% with the blunt trailing edge thickness of 10% relative to chord. Delayed Detached‐Eddy Simulation (DDES) approaches in combination with high order (5th) flux discretization WENO (Weighted Essentially Non‐Oscillatory) and l2Roe$l^{2}Roe$ Riemann solver are employed. Two variants of the DES length scale calculation methods are compared. The results are validated against experimental data with good accuracy. The studies provide guideline on the mesh and turbulence modeling selection for flatback airfoil simulations. The results indicate that the wake breakdown is strongly influenced by the spanwise resolution of the mesh, which directly contributes to the prediction accuracy especially for drag force and noise emission. The Reynolds normal stress u′u′¯$\overline{u^{\prime }u^{\prime }}$ and the u′v′¯$\overline{u^{\prime }v^{\prime }}$ Reynolds stress component have the largest contributions on the mixing process, while the contribution of the u′w′¯$\overline{u^{\prime }w^{\prime }}$ component is minimal. Proper orthogonal decomposition is further performed to gain deeper insights into the wake characteristics. [ABSTRACT FROM AUTHOR]

Compressible flow past a heated circular cylinder at subcritical Reynolds number of 3900 is numerically investigated by using the large-eddy simulation method. Rigorous validations of the numerical model are carefully performed under isothermal conditions on the basis of available experimental data. The calculated mean flow and Reynolds stresses show good agreement with the published experimental data. The effects of temperature difference between the cylinder surface and the freestream on the flow statistics and thermal characteristics are further studied in detail by setting two kinds of wall temperature boundary conditions. It is manifested that increasing the wall temperature leads to the augmentation of skin friction drag, suppression of turbulent intensity, enhancement of flow mixing and extension of recirculation zone. In addition, it is found that the variations of thermo-physical properties pose a slight effect on the wall heat flux before the boundary layer separates from the cylinder surface. It is worth noting that the recirculation bubble length can be used as a distance scaling parameter to weaken the temperature dependence of the flow and thermal statistics. These results provide a more detailed insight into the statistical difference in the wake region of cylinder when the temperature effect is taken into account. [ABSTRACT FROM AUTHOR]

This study examines the wake of a porous disk that generates a velocity deficit equivalent to that of a wind turbine. Three‐dimensional unsteady numerical simulations based on the finite volume method are performed. The URANS‐SST (k–ω) model is applied for the turbulence closure. Two investigations are carried out in this study: (i) the influence of the disk porosity on the wake, for porosities values (p) ranging from 0 to 0.55 in the case of a perpendicular flow; and (ii) the influence of the yaw angle on the wake deviation, for yaw angles ranging from 5° to 30°. Good agreements with the available experimental data are obtained for the mean x‐velocity component. The results confirm that wake length increases as porosity decreases. For nonporous disks, most part of the fluid is deflected toward the mast and above the disk. The y‐velocity contours highlight two contra‐rotating vortices in the vicinity of the disk. In both cases (nonporous and porous disks), a high turbulent kinetic energy is obtained near the disk area, with a higher maximum value for the nonporous disk. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the wake behind an oscillating airfoil at a various angle of incidence and Reynolds number in a deep dynamic stall condition. Design/methodology/approach: NACA 0012 airfoil is allowed to undergo harmonic pitching motion about the quarter chord axis at Reynolds numbers of 0.5 * 105, 1.17 * 105, 1.7 * 105 and 2.12 * 105, and the reduced frequency of 0.1. The experiments are conducted at a set of mean and amplitude angle of attack that covered the angle of incidence from −5° to 25°. The wake rake is placed at a distance of one chord from the trailing edge of the airfoil. Findings: The hysteresis of the flow during the upstroke and the downstroke motion are captured. The huge growth in the velocity defect and the wake thickness beyond the angle of attack of 15° explicate the appearance of the strong unsteady effects on the wake. The results also show that at the reduced frequency of 0.1, the wake structure is of drag producing type due to the momentum deficit. Originality/value: Streamwise velocity profile and the turbulent intensity profiles are presented to show the effects of Reynolds number and angle of incidence on the wake behind the oscillating airfoil at the reduced frequency of 0.1, and in the intermediate range of Reynolds number is the novelty of the study. [ABSTRACT FROM AUTHOR]

Most wind turbines are installed inside wind farms, where they often operate under wake-affected inflow conditions. New methods are required to evaluate the power performance of a wind turbine in wake, as the International Electrotechnical Commission (IEC) standard procedure is applicable only to wake-free turbines. In this work, we investigate the accuracy of a multivariate power curve acquired through a polynomial regression, whose input variables are wind speed and turbulence measurements retrieved upstream of the turbine's rotor. For this purpose, we use measurements from the SpinnerLidar, a continuous-wave, scanning Doppler lidar measuring the turbine inflow. The SpinnerLidar was mounted in the spinner of a Neg Micon 80 wind turbine located within an onshore wind farm in western Denmark. The input variables are selected among the available lidar measurements with a feature-selection algorithm, resulting in seven input variables, distributed in different locations along the rotor area: six wind speed and one turbulence measurements. The multivariate power curve is tested and compared with IEC-similar power curves under both wake-affected and wake-free conditions. Results show that the multivariate power curve estimates the turbine's power output more accurately than the IEC-similar power curves, with error reductions up to 66.5% and 34.2% under wake-affected and wake-free conditions, respectively. Furthermore, the multivariate power curve estimates have an accuracy of the same order under both wake-affected and wake-free conditions. Finally, we show that the multivariate model accurately predicts the power even when a simple measuring geometry is used, such as circular scanning pattern with a diameter equal to 90% of the rotor. • Measurements from a spinner-mounted lidar under wake conditions. • Wind speed and turbulence retrieved from lidar Doppler radial velocity spectra. • Wind turbine power curves modelled as multivariable polynomial regressions. • The multivariate power curves are more accurate than the IEC binning method. • The multivariate power curves are as accurate in wake as in wake-free conditions. [ABSTRACT FROM AUTHOR]

It is well known that a shroud placed around a wind turbine can increase its power coefficient, but it brings complex mechanisms by which the shroud alters the flow passing through the rotor. Such mechanisms impose numerical challenges, as the shrouded turbines present nonlinear behavior in the wake. This paper deals with a comprehensive analysis of tip vortex trajectory in shrouded wind turbines using Reynolds Averaged Navier–Stokes numerical solutions. The analysis includes aerodynamic performance and vortex characteristics of the whole wind turbine. The Multiple Reference Frame is used on a high-order unstructured compressible solver to study both, isolated and shrouded rotor. The NREL Phase VI Unsteady Aerodynamic Experiment rotor is used as a test case. The accuracy of results for wind speeds between 7 and 25 m s − 1 is discussed. Overall, good agreement is achieved between the computed pressure distributions and the experimental reference values. At stalled blade, more efforts are needed to improve numerical solutions, especially for integrated load quantities. The vortex structure is examined, showing that shroud impacts tip vortex trajectory by the increase of the axial induced velocity at the rotor plane. This result, demonstrates that the classical Prandtl tip loss is not accurate for shrouded turbine analysis, and modern finite blade functions are needed. The influence of the flow conditions on the tip vortex trajectory, flow separation and shroud interaction are also discussed. • Tip vortex trajectory of the NREL Phase Vi. • Use of a simplified Multiple Reference Frame model with open-source high-order CFD solver, avoiding conformal interface complexities and enabling efficient shrouded turbine simulation. • Accurate and efficient computation of the integrated loads on the wind turbine. • Unprecedented perspective into profoundly altered tip vortex trajectory behavior within shrouded turbines using validated higher-order framework. • Study of the interaction between the tip vortex and shroud's boundary layer. [ABSTRACT FROM AUTHOR]

The flow around a surface-mounted cube has been investigated for decades, yet the fundamentals of the mean flow have not been updated to reflect the latest advances regarding the flow around surface-mounted finite-height square prisms in general. One of the main gaps is the flow field very near the cube walls, especially the sides, and its relationship to the near wake. To investigate these features, large-eddy simulations of the flow around a surface-mounted cube were carried out at a Reynolds number Re = 1 × 1 0 4 . Two boundary layers were considered: a thin and laminar boundary layer and a thick and turbulent one, to provide an overview of the flow around the cube for contrasting boundary layers. The major flow structures in the mean wake were the horseshoe vortex, the arch vortex and the dipole structures, with other regions of vorticity also present. The time-averaged flow fields presented similar flow features for both boundary layers, but the thicker and turbulent one caused the horseshoe vortex to be located closer to the cube, the wake to become narrower and shorter, the coherent structures and downwash to weaken, the pressure to decrease around the sides and top of the cube, the drag force coefficient to decrease, the normal force coefficient to increase, and the trailing edge vortices to weaken. Intermittent flow reattachment on the top and side faces of the cube, as well as corner vortices, were found for both boundary layers, while the side and free end vortices were found exclusively with the thicker boundary layer, yielding a headband vortex. The three-dimensional flow structures and features were related to the near-wall flow field on the cube and ground plane surfaces, giving a complete and updated description of the mean flow characteristics. [Display omitted] • The mean flow around a surface-mounted cube was studied via large-eddy simulation. • The three-dimensional flow field is characterized for different boundary layers. • Dipole structures, horseshoe vortex and near wake vorticity regions are analyzed. • Besides corner vortices, a headband vortex formed for the thick boundary layer. • The flow on the sides of the cube may interfere with formation of dipole structures. [ABSTRACT FROM AUTHOR]

The "whitewater zone" represents a critical maritime feature intimately tied to ship identification and stealth capabilities. In this study, the large eddy simulation method is employed to analyze wake fields under varying operational conditions, and the influence of propeller turbulence and bubble wakes on the "whitewater zone" is investigated in conjunction with a self-built optical testing platform. The results indicate that an increase in propeller speed serves to stabilize the vortex structure but also results in a unimodal signal waveform. Moreover, the behavior of bubbles exerts a significant impact on the flow field structure. The coalescence and division of large bubbles play a primary role in altering the flow field structure of the "whitewater zone," consequently accelerating the mixing and diffusion of the "whitewater." The smaller bubbles exhibit prolonged retention times and a broader disturbance area within the surrounding flow field. The research conclusion has certain reference significance for the future development of ocean exploration technology. • An optical test platform for identifying the "whitewater area" is constructed. • Details on the "whitewater area" flow field characteristics is elucidated. • The effect of the "whitewater area" on the laser transmission signal is examined. [ABSTRACT FROM AUTHOR]

This study utilized a Convolutional Neural Network (CNN) trained via computational fluid dynamics (CFD) data that was further processed with continuous wavelet transform (CWT). The goal was to examine whether a deep learning algorithm could learn the features left in a flow by upstream bluff bodies. The study aimed to understand whether the trained algorithm could deduce the geometry of an upstream bluff body by analyzing downstream flow data. The scope of the work also included exploring the potential of the trained CNN to understand how turbulent flow develops in the wake of these bluff bodies. We investigated three bluff bodies (a circular cylinder, a square prism, and a triangular prism) by employing large-eddy simulations to produce a time series of velocities and analyzing them using CWT to create two-dimensional contours, representing the velocity data's time and frequency domain. These contours were used to train our adapted GoogLeNet while we optimized hyperparameters via Bayesian Optimization per each training. Training occurred in the near wake. The model accurately identified the bluff body within this region when tested with unknown data. The study reveals that features the model identifies in the near wake of a square-shaped bluff body persist into the far and mid wake. However, as flow transitions from a circle's near wake to its far wake, its features change and become more similar to those identified in the square's wake. The flow downwind of the triangle experiences similar developments, but transformations are less severe than in the circle. • Convolutional neural network was trained using scalograms of velocity time series. • A trained CNN can detect unknown upstream bluff bodies by analyzing downstream flow. • Sharp edges and flow separation make it easier for the neural network to learn. • Features identified in the near wake of squares do not evolve, contrary to circles. • Features identified in the near wake of circles evolve to those identified squares' wake. [ABSTRACT FROM AUTHOR]

Data driven approaches are utilized for optimal sensor placement as well as for velocity prediction of wind turbine wakes. In this work, several methods are investigated for suitability in the clustering analysis and for predicting the time history of the flow field. The studies start by applying a proper orthogonal decomposition (POD) technique to extract the dynamics of the flow. This is followed by evaluations of different hyperparameters of the clustering and machine learning algorithms as well as their impacts on the prediction accuracy. Two test cases are considered: (1) the wake of a cylinder and (2) the wake of a rotating wind turbine rotor exposed to complex flow conditions. The training and test data for both cases are obtained from high fidelity CFD approaches. The studies reveal that the combination of a classification-based machine learning algorithm for optimal sensor placement and Bi-LSTM is sufficient for predicting periodic signals, but a more advanced technique is required for the highly complex data of the turbine near wake. This is done by exploiting the dynamics of the wake from the set of POD modes for flow field reconstruction. A satisfactory accuracy is achieved for an appropriately chosen prediction horizon of the Bi-LSTM networks. The obtained results show that data-driven approaches for wind turbine wake prediction can offer an alternative to conventional prediction approaches. [ABSTRACT FROM AUTHOR]