Search Results (61)

The wake behavior of wind turbines in complex terrain is influenced by the combined effects of atmospheric turbulence and terrain features, which brings challenges to wind farm power production and safety. Despite extensive studies, there remains a gap in understanding the combined impact of turbulent inflows and terrain slopes on turbine wake behaviors. To address this, the current study conducted systematic wind tunnel experiments, using scaled wind turbines and terrain models featured both gentle and steep slopes. In the experiments, different turbulent inflows were generated and the wake characteristics of turbines located at different locations were analyzed. The results demonstrated that higher turbulence intensity accelerates wake recovery, and that steep slopes introduce distinctive wake patterns, including multi-peak added turbulence intensity profiles. Moreover, turbines on hilltops exhibited a more rapid wake recovery compared to those positioned in front of hills, a phenomenon attributed to the influence of adverse pressure gradients. This study provides pivotal experimental insights into the evolution laws of wind turbine wake over terrains under different turbulent inflow conditions, which are instrumental in wind turbine siting in complex terrains. Full article

In this study, a particle image velocimetry (PIV) system was used in a large circulating water tank to investigate the wake of a horizontal-axis tidal turbine model, focusing on minor blockage effects and scale influence. A wake map of the turbine was constructed based on PIV measurements, using velocity deficit, turbulence intensity (TI), and turbulence kinetic energy (TKE) as key indicators. The results showed that TKE developed later than TI, forming a plateau-like shape. This plateau was considered the decay region, with the transition and far-wake regions located before and after it, respectively. Additionally, the power law exponent of TI decreased from −0.731 in the decay region to −0.765 in the far wake, indicating a steeper decay further downstream. Overall, the wake map of the tidal stream turbine model exhibited similarities to that of a previously reported wind turbine model. Full article

In this paper, we compare three mathematical models for the mean velocity and Reynolds stress profiles for fully developed pressure-driven turbulent channel flow with the aim of assessing the level of accuracy of each model. Each model is valid over the whole boundary layer thickness (0 $\le y\le$ $\delta$), and it is formulated in terms of a law of the wall and a law of the wake. To calibrate the mathematical models, we use data obtained by direct numerical simulations (DNS) of pressure-driven turbulent channel flow in the range 182 $\le {Re}_{\tau }\le$10,049. The models selected for performance evaluation are two models (Musker’s and AL84) originally developed based on high Reynolds boundary layer experimental data and Luchini’s model, which was developed when some DNS data were also available for wall-bounded turbulent flows. Differences are quantified in terms of local relative or absolute errors. Luchini’s model outperforms the other two models in the “low” and “intermediate” Reynolds number cases (${Re}_{\tau }=$ 182 to 5186). However, for the “high” Reynolds number cases (${Re}_{\tau }=$ 8016 and ${Re}_{\tau }=$ 10,049). Luchini’s model exhibits larger errors than the other two models. Both Musker’s and AL84 models exhibit comparable accuracy levels when compared with the DNS datasets, and their performance improves as the Reynolds number increases. Full article

The change in the composite lay-up method affects the blade stiffness, which in turn affects the structural dynamic and aerodynamic characteristics, but the influence law is not yet clear. In this paper, two-way fluid–structure coupling is used to study wind turbine blades with different numbers of lay-up layers. The analysis results show the following: (1) With the increase in the number of pavement layers, the maximum deformation of the blade tip decreases, the magnitude of the decrease also decreases gradually, and the growth trend of deformation along the blade spreading direction is gradually flattened. (2) The maximum stress–strain of the root of the blade gradually decreases, the tip of the blade is the opposite of the blade, the unevenness of the distribution of the stress–strain of the surface of the blade is gradually slowed down, and the concentration area is shifted back. (3) The different numbers of pavement layers affect the turbulence intensity of the blade in the flow field space. Herein, the spatial distribution trend of turbulence intensity in the flow field of wind turbine blades with different numbers of layers is basically the same, and the trend of turbulence intensity changes is gentle when the number of layers is increased. (4) The amount of the tip vortex in the wake stream of the wind turbine decreases, and the decay rate of the center vortex increases. A reasonable lay-up scheme can improve the deformation and stress of the blade, extend the service life of the blade, promote airflow mixing, and enhance the energy conversion efficiency. Full article

In order to investigate the transport law of an unsteady wake in a downstream cascade channel in a turbine stage environment, this study was based on a self-designed unsteady wake generator, and a low-pressure turbine cascade was the research object. The research was carried out through a combination of experiments and numerical simulation. The results show that in the range of −50° to 20° inflow incidence, there is no separation on the blade suction surface, the total pressure loss coefficient is low, and the cascade has good adaptability to the inflow incidence. When the incoming flow is at a negative incidence, the transport of the unsteady upstream wake to the downstream unsteady wake is basically the same; the same holds for a non-negative incidence. When the upstream unsteady wake is transported downstream in the cascade channel, the wake near the cascade suction surface follows a detour and barely interacts with the mainstream fluid. The total pressure loss fluctuation value obtained via numerical calculation shows good periodicity; therefore, the unsteady cascade effect under the action of upstream wake sweeping becomes very obvious. Full article

In urban settings, buildings create complex turbulent conditions, affecting helicopter flight performance during missions and increasing safety risks during takeoff and landing. A numerical study on rotor–building coupled flow field is carried out to address rotor aerodynamic performance under building interferences in natural atmospheric conditions. A high-fidelity atmospheric boundary layer (ABL) model described by an exponential law is established herein. The solution of the coupled flow field is based on the Reynolds-averaged Navier–Stokes (RANS) equations, with the rotor’s rotation achieved through the overset grid method. Based on the dominant wind features, the building flow field is distributed into four regions, where the updraft along the headwind side impacts the rotor, bringing about a 76% increase in pitching moment. On the lateral side of the building, distorted rotor wake squeezed upward into the rotor disk, leading to severe blade–vortex interaction (BVI). During low-altitude hovering over rooftops, the mixing of building shed vortices with forward flow wakes causes the formation of a circulation region on the rotor’s windward side, resulting in a thrust loss of approximately 7.8%. Meanwhile, the flow environment on the leeward side of the buildings is more stable. Therefore, it is recommended that helicopters adopt a headwind approach during rooftop operations. However, an 11.4% loss in the average hover figure of merit is observed due to consistent thrust losses caused by the recirculation region. Full article

In 2019, a noise complaint from a new, white resident of Shaw, a historically Black neighborhood of Washington, DC, led a local MetroPCS store to mute the go-go music that the storefront had played on its outdoor speakers for decades. The cultural and social implications of muting go-go music, a DC-originated genre of music that has played a central role in DC Black culture, inspired a viral hashtag, #dontmutedc, on social media, as well as a series of high-profile public protests against the muting. The #dontmutedc protests highlighted the increasing impact of gentrification on DC’s Black communities, and connected gentrification to several other important social issues affecting Black DC residents. In the wake of the #dontmutedc incident, several DC-area activist organizations have integrated go-go music into major, public-facing racial justice projects. The first part of this article presents a brief history of go-go music and race in DC community life, mainstream media, and law enforcement in order to contextualize the work of go-go-centered activist work in the aftermath of the #dontmutedc protests. The second part of this article highlights the go-go-centered activist work of three organizations: the Don’t Mute DC movement, Long Live Go-Go, and the Go-Go Museum and Café. These movements’ projects will be used to categorize three distinct approaches to go-go-centered racial justice activism in the Washington, DC, area. Full article

Our ability to reliably and efficiently predict complex high-Reynolds-number ($Re$) turbulent flows is essential for dealing with a large variety of problems of practical relevance. However, experiments as well as computational methods such as direct numerical simulation (DNS) and large eddy simulation (LES) face serious questions regarding their applicability to high $Re$ turbulent flows. The most promising option to create reliable guidelines for experimental and computational studies is the use of analytical conclusions. An essential criterion for the reliability of such analytical conclusions is the inclusion of a physically plausible explanation of the asymptotic turbulence regime at infinite $Re$ in consistency with observed physical requirements. Corresponding analytical results are reported here for three canonical wall-bounded turbulent flows: channel flow, pipe flow, and the zero-pressure gradient turbulent boundary layer. The asymptotic structure of the mean velocity and characteristic turbulence velocity, length, and time scales is analytically determined. In outer scaling, a stable asymptotic mean velocity distribution is found corresponding to a linear probability density function of mean velocities along the wall-normal direction, which is modified through wake effects. Turbulence tends to decay in this regime. In inner scaling, the mean velocity is governed by a universal log-law. Turbulence does survive in an infinitesimally thin layer very close to the wall. Full article

Research into how fish and other aquatic organisms propel themselves offers valuable natural references for enhancing technology related to underwater devices like vehicles, propellers, and biomimetic robotics. Additionally, such research provides insights into fish evolution and ecological dynamics. This work carried out a numerical investigation of the most relevant dimensionless parameters in a fish swimming environment (Reynolds $Re$, Strouhal $St$, and $Slip$ numbers) to provide valuable knowledge in terms of biomechanics behavior. Thus, a three-dimensional numerical study of the fish-like lambari, a BCF swimmer with carangiform kinematics, was conducted using the URANS approach with the k-$\omega$-SST transition turbulence closure model in the OpenFOAM software. In this study, we initially reported the equilibrium Strouhal number, which is represented by $S{t}^{\ast }$, and its dependence on the Reynolds number, denoted as $Re$. This was performed following a power–law relationship of $St\propto R{e}^{(-\alpha )}$. We also conducted a comprehensive analysis of the hydrodynamic forces and the effect of body undulation in fish on the production of swimming drag and thrust. Additionally, we computed propulsive and quasi-propulsive efficiencies, as well as examined the influence of the Reynolds number and $Slip$ number on fish performance. Finally, we performed a vortex dynamics analysis, in which different wake configurations were revealed under variations of the dimensionless parameters $St$, $Re$, and $Slip$. Furthermore, we explored the relationship between the generation of a leading-edge vortex via the caudal fin and the peak thrust production within the motion cycle. Full article

To study the hose-and-drogue system’s motion under bow waves, this paper established a dynamic model of the hose-and-drogue system based on the multibody dynamics theory and the rigid ball-and-rod model. The wake of a tanker aircraft was taken into account in the simulation. The simulation results conformed to the general laws and verified the model’s accuracy. The equilibrium positions of the hose-and-drogue system were computed by the linear superposition of the bow waves and wake. The motion of the hose-and-drogue system was simulated and analyzed when a receiver aircraft moved at a constant speed or accelerated relative to the tanker aircraft. Since the receiver aircraft would not immediately stop after docking, the pulling force changes on the hose with and without a reel were compared. The present results are essential for improving the success rate of aerial refueling and ensuring the safety and stability of the hose-and-drogue system. Full article

Carrier-based aircraft landing involves complex system engineering characterised by strong nonlinearity, significant coupling and susceptibility to environmental disturbances, and autonomous landing of carrier-based aircraft under fault states is even more challenging and riskier. To address the control-system problems of loss of efficiency and performance due to actuator faults and performance degradation due to various unknown disturbances, presented here is fault-tolerant control for carrier-based aircraft based on adaptive fuzzy sliding-mode fault-tolerant control (AFSMFTC). First, three models are built (the carrier-based aircraft fault model, the carrier air wake model and the deck motion model), and the control framework of the autonomous landing control system is introduced. Next, a longitudinal and lateral flight channel controller comprising an adaptive fuzzy network, adaptive laws and a sliding-mode controller is designed using the AFSMFTC method. The adaptive fuzzy network implements fuzzy approximation for the sliding-mode switching terms to further offset errors induced by unknown disturbances, the adaptive laws compensate for actuator faults, and the sliding-mode controller ensures tracking of the overall flight path. Furthermore, the stability of the fault-tolerant method is demonstrated using the Lyapunov function. Finally, simulation and comparative experiments show that the proposed fault-tolerant method has outstanding control performance and strong fault-tolerant capability, thereby providing an effective and feasible solution for designing an autonomous landing system for carrier-based aircraft under fault states. Full article

In this paper, the coupling effect of multiphysical fields of droplet migration is deeply studied by constructing a physical model of droplet migration with multiphysical fields. Digital holographic interferometry and particle image velocimetry are used to simultaneously measure the temperature and velocity fields of the mother liquor in the process of droplet migration for the first time. Due to the advancements of measuring, the zero-velocity region is also in the region where the thermal wake appears, four vortexes appear in the droplet migration and the off-axis behavior of double-droplet migration is found. The aim of this work is to analyze the coupling relationship of multiphysical fields, so as to reveal the physical laws of thermocapillary migration of single droplet and multiple droplets with the same phase and heterophase and to study the driving mechanism of the thermocapillary force and the flow of the mother liquor. Full article

Offshore wind farms (OWFs) generate large-scale wind wakes, which might lead to upwelling/downwelling. Understanding the vertical marine response to the wake effects is crucial for assessing the ecological impacts of OWFs and optimizing their co-deployments with mariculture. In this study, we employ a high-resolution ocean model to investigate the spatiotemporal variations of upwelling and downwelling induced by the wind wakes of OWFs through idealized numerical experiments. We have two main findings. First, the wind-wake-induced upwelling and downwelling are not balanced in the north–south direction, resulting in a net effect of thermocline rising. Second, the thermocline depth changes caused by wind wakes develop nonlinearly over time. Specifically, when the elevated thermocline approaches the sea surface, the upwelling slows down significantly. The spatially asymmetric pattern of the upwelling is attributed to horizontal Ekman transport, while its temporal nonlinear evolution is caused by stratification changes. By utilizing the simulated change law of thermocline depth, we calculate the ocean response of OWF wakes in China’s adjacent waters. The results suggest that baroclinic theory overestimates the ocean response in the Bohai Sea, the Yellow Sea, and the nearshore waters of the East China Sea. However, in the open seas and the South China Shelf, the upwelling/downwelling is expected to be close to the theoretical calculations. This study provides a foundation for conducting regional simulations with high resolutions in areas where OWFs will be constructed. Full article

In response to the challenges posed by rapid development, the wide-ranging disaster impact, and the untimely warning of debris flow resulting from tailing dam failure, it is of great significance to study the mechanism of dam failure as well as the evolution law and affected area of debris flow for effective disaster prediction and risk assessment. We developed a 1:150 physical model for testing tailing dam failure and combined it with RAMMS (V1.7.0) debris flow software to investigate the mechanisms of tailing dam failure and the evolutionary patterns of rock flows in complex environments. Through the analysis and comparison of experimental data, we comprehensively summarized the consequences of disaster risk resulting from dam failure. The results show that the grain size distribution of the model sand should be moderate; the composition of the particle size distribution has a significant impact on the collapse morphology of the dam after failure. The saturation line is the lifeline for the stability of the wake reservoir, and its level determines the degree of saturation of the wake in the reservoir. The breach was at the midpoint of the crest of the dam. The inflow volume at the time of the breach was 0.313 m³. According to the flow ratio relationship, the inflow volume at breach occurrence was equivalent to 1.78 times the total amount of a 1000-year flood and 1.19 times the total amount of a probable maximum flood (PMF). Analysis of the surface flow field revealed that the region with the highest flow velocity extended from the toe of the dam to Shangdi village; the impact on the village of Shizhou was limited to the backflow of the dam break and the gradual sedimentation of the tailings. Full article

Low-fidelity engineering wake models are often combined with linear superposition laws to predict wake velocities across wind farms under steady atmospheric conditions. While convenient for wind farm planning and long-term performance evaluation, such models are unable to capture the time-varying nature of the waked velocity field, as they are agnostic to the complex aerodynamic interactions among wind turbines and the effects of atmospheric boundary layer turbulence. To account for such effects while remaining amenable to conventional system-theoretic tools for flow estimation and control, we propose a new class of data-enhanced physics-based models for the dynamics of wind farm flow fluctuations. Our approach relies on the predictive capability of the stochastically forced linearized Navier–Stokes equations around static base flow profiles provided by conventional engineering wake models. We identify the stochastic forcing into the linearized dynamics via convex optimization to ensure statistical consistency with higher-fidelity models or experimental measurements while preserving model parsimony. We demonstrate the utility of our approach in completing the statistical signature of wake turbulence in accordance with large-eddy simulations of turbulent flow over a cascade of yawed wind turbines. Our numerical experiments provide insight into the significance of spatially distributed field measurements in recovering the statistical signature of wind farm turbulence and training stochastic linear models for short-term wind forecasting. Full article