Wind Tunnel Experimental Data Research Articles

Integrating NSGA-II and CFD for enhanced urban airflow prediction: Recalibration of closure coefficients for a nonlinear eddy viscosity model

Accurately predicting urban environmental airflows using the Reynolds-averaged Navier‒Stokes (RANS) approach presents significant challenges due to unsolved closure issues. Previous attempts to address these limitations through coefficient adjustments were constrained by isotropic assumptions, resulting in limited generalizability and reliability, especially for complex building configurations. In this study, we proposed a recalibration approach within a multi-objective optimization framework. Nondominant sorting genetic algorithm-II (NSGA-II) and computational fluid dynamics (CFD) numerical computations were utilized to optimize the closure coefficients of a nonlinear eddy viscosity (NLEV) model, with a focus on improving the accuracy of the mean velocity, turbulent kinetic energy, and airflow characteristic predictions. To ensure the robustness of the model, appropriate objective functions were carefully defined. The proposed approach was evaluated using three-dimensional (3D) building cases related to urban prototypes, and the results demonstrated the necessity of multi-objective optimization. Our findings indicated that the trade-off solution on the Pareto front consistently outperformed the baseline and single-objective optimal versions across different types of urban airflow, demonstrating superior generalizability. The simulation results of this solution exhibited closer agreement with the wind tunnel experimental data and provided more accurate distributions of the time-averaged values and airflow characteristics. The normalized root mean square errors are reduced by about 33 %, 52 %, 35 % and 9 % in velocity, and 31 %, 25 %, 24 % and 11 % in turbulent kinetic energy, respectively. These results underscore the effectiveness of the multi-objective optimization framework in addressing closure issues and improving the prediction accuracy of complex urban environmental airflows.

Numerical investigation of evaporative cooling strategies on the aero-thermal performance of courtyard buildings in hot-dry climates

In hot and dry urban environments, courtyards help mitigate extreme heat and influence the urban microclimate. These structures not only provide light and private outdoor spaces but also aid in mitigating the urban heat island (UHI) effect through improved airflow and evapotranspiration. Courtyards, being central open-air areas enclosed by buildings, are crucial in creating opportunities for natural ventilation driven by wind and buoyancy-induced forces, thus serving as a microclimatic regulator. This study investigates the role of courtyards in modulating their microclimate and adjacent indoor areas by integrating evaporative cooling strategies to enhance cooling in these spaces. While numerous studies have been conducted on the role of water bodies in evaporative cooling, the aero-thermal impact on adjacent indoor spaces remains less understood. Addressing this gap, the present research explores the effect of an evaporative cooling system on the wind and thermal conditions within a courtyard and examines different natural ventilation modes, namely, single-sided and crossflow ventilation, in indoor spaces. A computational fluid dynamics (CFD) model, validated against wind tunnel experimental data, was employed to simulate various evaporative cooling water spray configurations. The results reveal complex courtyard microclimates with diverse cooling effects influenced by room orientation and floor level. Specifically, in single-sided ventilated courtyards, water sprays significantly improved the indoor thermal environment, with the average temperature across all rooms decreased by 2.06 °C, and humidity increased by 4.29 %. However, in cross-ventilated courtyards, water sprays' cooling and humidifying effects were relatively less effective. This research underscores the potential of evaporative cooling technology in improving the microclimate of courtyards, with practical applications extending to urban design and architecture. By tailoring cooling strategies to specific courtyard configurations, urban planners and architects significantly improve indoor comfort levels and energy efficiency.

Investigation of the integration of an oscillating aerofoil-based energy harvester into the building roof

The increasing energy efficiency requirements have led to innovative renewable energy solutions being integrated into buildings. Several works have shown the potential of micro wind turbines on buildings. However, their implementations have been hindered by several challenges. Flow energy harvesting devices such as oscillating aerofoils provide potential, yet a literature gap exists regarding their integration into buildings. This study addresses this gap by investigating oscillating aerofoil wind energy harvesting system performance through numerical modelling. A coupled numerical model was introduced, integrating a novel computational approach using ANSYS Fluent with one degree of freedom in rotational motion. This methodology was introduced to analyze the dynamic behaviour and predict mechanical power output of the oscillating aerofoil wind energy harvesting system, which is a novel exploration in existing literature. Moreover, validation of the computational fluid dynamics model was conducted through using experimental wind tunnel data in the literature, and results demonstrated agreement between numerical and experimental results. To improve the wind energy harvesting system of a single oscillating aerofoil, it was integrated into building roof to take advantage of acceleration effects of building roof shape. The design improvement comprises of a novel wind energy harvesting system design of an oscillating aerofoil integrated into three different building roof including flat, pitched, and curved shapes to enhance energy efficiency. The numerical analysis demonstrated that integrating an oscillating NACA 0012 aerofoil into a curved roof resulted in the highest average power output. Specifically, the integration of the curved roof and the aerofoil yielded 18 watts, while the flat roof generated only 0.6 watts at a wind speed of 3 m/s. Integration into a pitched roof achieved 12 watts at 9 m/s. Comparatively, integrating the curved roof with the aerofoil increased power output by 50% compared to the pitched roof design at 9 m/s wind speed. Thus, variations in wind speed significantly impact performance. In addition, changes in wind direction from 0 to 10 degrees led to reduced efficiency and lower predicted power output. Lastly, the power spectral density for NACA 0012 integrated into the pitched and curved roof buildings revealed peaks at 5.8 Hz in 9 m/s wind speed conditions.

Numerical investigation on the effects of heel on the aerodynamic performance of wing sails

The utilization of wind-assisted propulsion technology could reduce ship fuel consumption and emission of pollutants. In the study, the effect of steady heel angles on the aerodynamic characteristics of wing sails was investigated. Full-scale three-dimensional simulations with the ship's superstructure were conducted at heel angles of 0°–15° in all apparent wind directions. The correctness of the numerical computations is verified by comparing them with the wind tunnel experimental data. Overall, the heel is detrimental to the capture of wind energy by the wing sails. The aerodynamic forces of the sail system decrease with increasing heel angles. Specifically, the average thrust performance is attenuated by 4.7%, 13.5% and 20.5%, respectively, at heel angles of 5°, 10°, and 15° compared to the upright condition. Due to changes in the airflow distribution around the sails, the aerodynamic force of sails in heeled to windward and heeled to leeward decreases by the reduced area of the low-pressure zone on the suction side and the high-pressure zone on the pressure side, respectively. Finally, a prediction scheme for assessing the effect of rolling motion on sail performance is proposed by steady heel results.

Machine Learning-Based Backpressure Unstart Prediction and Warning Method for Combined Cycle Engine Hypersonic Inlet-Oriented Wide Speed Range

Inlet unstart prediction and warning are strictly crucial to the operation of hypersonic engines, especially for combined cycle engines where implementation across a wide speed range poses significant challenges. This paper proposes a realization method that involves constructing the conditions of critical backpressure ratios for the inlet unstart and unstart warning states within a wide speed range and establishing the backpressure prediction models for each engine mode. The detection of the unstart and unstart warning states is achieved by predicting the backpressure ratio at the exit of the isolator and comparing it to the critical backpressure ratios. To achieve this, numerical simulations for a three-dimensional inward-turning multiducted hypersonic combined inlet at various Mach numbers and backpressure ratios are carried out to obtain the dataset of surface pressure. A 10-fold cross-validation support vector machine (10-CV SVM) is used to solve the unstart boundary of surface pressure, and an unstart margin is set to determine the unstart warning boundary. A back propagation (BP) neural network is constructed to estimate the critical backpressure ratios at each working point within a wide speed range. The data information of surface pressure on the boundaries is used as the input for the predictions. The overall average regression correlation coefficient approaches 0.99 on the test dataset at each working point. The backpressure prediction models are established by the one-dimensional convolutional neural network (1D-CNN). Only 2 to 4 measurement points of surface pressure are considered for cross-validation evaluation, and the mean absolute percentage error is between 4% and 8% with the average prediction time not exceeding 2 ms. Finally, the proposed method and prediction models are validated by wind tunnel experimental data.

Quantification of three-dimensional added turbulence intensity for the horizontal-axis wind turbine considering the wake anisotropy

The accurate evaluation of wake turbulence intensity (TI) is of great significance for the layout optimization of wind farms and research on control strategies. However, the existing engineering wake models still have many shortcomings in evaluating the TI in the wake of horizontal-axis wind turbines (HAWTs), especially in the near wake region. In response to this, this article proposed an analytical model based on the double-Gaussian ellipse function that can describe the three-dimensional added TI distribution in the entire wake region. Firstly, the anisotropy of wake expansion is taken into account in both the horizontal and vertical directions, assuming that the added TI distribution downstream of the HAWT is a double-Gaussian elliptical shape. Secondly, taking into account the self-similarity characteristics of flow TI, the maximum added TI and its position in the entire wake region are evaluated. In addition, considering the influence of the ground effect, the vertical turbulence distribution was corrected. Finally, the proposed added turbulence model was validated and relative error analysis was conducted using large eddy simulation (LES) data, wind field measurement data, and wind tunnel experimental data. The results show that the model had good prediction accuracy in the entire wake region, and its prediction performance was significantly improved compared to traditional models, especially in the near wake region, with the lowest even relative error of 3.66%. This model has significant advantages such as low computational cost, wide applicability, and high accuracy. It can reduce energy losses in wind farms, improve wind energy utilization efficiency, and has great potential for widespread application in large-scale wind farms.

Design and Analysis of UAV Profile for Agriculture and Surveying Application

This study represents the aerodynamic design of an Unmanned aerial vehicle intended for surveillance or agriculture with a maximum take weight of 125 kg. Weight estimation and constraint analysis were done based on the Mission profile. Design of Computer-Aided Design (CAD) models were generated for three different configurations using CATIA V5R20 as a high wing, mid-wing, and low wing. Flow analysis was done for the above configurations at various angles of attack. ANSYS 15 was used for the flow Analysis. A Tetrahedron element meshed the model with the minimum required orthogonal quality. Five microns were given to the initial layer height of the prism mesh. Spalart Allmaras model is used as the Turbulence model in the solver. The aerodynamic characteristics of the above configuration obtained from Computational Fluid Dynamics (CFD) results were compared with the DATCOM program and validated with the wind tunnel experimental test data. The open-circuited suction-type Subsonic wind tunnel was employed for the test. The aerodynamic properties for the angle of attack in the range of -2° to 14° angle of attack are calculated using a six-component balance. The study aims to find the Unmanned Aerial Vehicle (UAV) configuration based on the aerodynamic characteristics obtained from the CFD and DATCOM results. High-wing UAVs have better aerodynamic efficiency than the other two configurations.

Multiscale coupling simulation of surface catalytic effect on hypersonic aerothermodynamic environment

The complicated heat and mass transfer at the high-temperature gas-solid interface of a thermal protection material under highly non-equilibrium conditions is of high importance to hypersonic flows. Surface catalysis, an exothermic reaction that refers to the recombination of dissociated atoms at the surface, and its effect on the aerothermodynamic environment has been investigated by researchers, especially focusing on oxygen recombination process. To further identify the nitrogen recombination mechanism, a hybrid CFD-RMD multiscale simulation method is employed in this work to qualitatively investigate its effect on aerothermodynamic environment prediction under hyperthermal non-equilibrium condition. Taking carbon-based phenolic resin (PR) composite as a typical material with 300 K, the nitrogen recombination coefficient obtained from atomistic-scale RMD simulation is coupled with the continuum two-temperature Navier-Stokes model to capture the catalytic effects and the heat / mass transfer at high temperature: A catalytic benchmark simulation is conducted under a Mach number of 9.7, and the heat flux distribution along the surface coupled with the RMD-derived nitrogen recombination coefficient of 0.0704 is obtained, which result is comparable with the published wind tunnel experimental data and the finite-rate catalytic result is 10 %∼30 % lower than the fully catalytic assumption result. The nitrogen recombination coefficient of PR is theoretically found to increase with thermal dissociation fraction of the free stream and decrease with the wall temperature due to the catalysis-ablation competitive mechanism. The influence of the recombination coefficient on the heat transfer at the surface is also quantitatively analyzed for evaluating the surface catalysis effect on aerothermodynamic heating.

Effects of Gurney Flaps on the Performance of a Horizontal Axis Ocean Current Turbine

Gurney flaps can enhance the hydrodynamic efficiency of airfoils, and they are currently used in several applications, including racing cars and wind turbines. However, there is a lack of studies in the literature on the application of Gurney flaps on the Horizontal Axis Ocean Current Turbine (HAOCT). The influence of Gurney flaps on the hydrodynamic efficiency of the HAOCT is evaluated through numerical analysis. The effect of the Gurney flaps on the turbine is evaluated after the validation of the utilized numerical method is completed using the wind tunnel experimental data of the two-dimensional NACA 63415 airfoil and the water tunnel experimental data of the NACA 638xx series rotor on the clean blade. By calculating the velocity and pressure fields of the 2D airfoil by CFD, it was possible to analyze the lift improvement with the addition of the Gurney flaps by evaluating the pressure difference between the pressure surface and the negative pressure surface, and the drag improvement was due to the Gurney flaps obstructing the chordal flow of the fluid in the wake. For the 2D NACA-63415 airfoil, the drag coefficient increases with the increase in the head angle, while the lift coefficient increases and then decreases. The flap height divided by the local chord length of the Gurney flaps is 0.01, and the lift-to-drag ratio is the highest when the head angle is 4°. For the NACA-638xx turbine, the addition of Gurney flaps significantly increases the axial thrust coefficient. At lower tip speed ratios, the effect of the Gurney flaps on the rotor’s power coefficient is limited, with the greatest increase in the power coefficient at a tip speed ratio of 6 and a decrease in the power coefficient increase as the tip speed ratio increases. Increasing the height of the Gurney flaps can increase the peak power coefficient, but the power performance decreases at high tip speed ratios. The Gurney flaps distributed at the root of the rotor have less effect on the power performance. A 0.4 local radius spread of the Gurney flaps increases the peak turbine power coefficient by only 0.34%, while full-length Gurney flaps can increase the peaked blade power coefficient by 10.68%, indicating that Gurney flaps can be used to design a new HAOCT.

On the characteristics of the wake of a wind turbine undergoing large motions caused by a floating structure: an insight based on experiments and multi-fidelity simulations from the OC6 project Phase III

Abstract. This study reports the results of the second round of analyses of the Offshore Code Comparison, Collaboration, Continued, with Correlation and unCertainty (OC6) project Phase III. While the first round investigated rotor aerodynamic loading, here, focus is given to the wake behavior of a floating wind turbine under large motion. Wind tunnel experimental data from the UNsteady Aerodynamics for FLOating Wind (UNAFLOW) project are compared with the results of simulations provided by participants with methods and codes of different levels of fidelity. The effect of platform motion on both the near and the far wake is investigated. More specifically, the behavior of tip vortices in the near wake is evaluated through multiple metrics, such as streamwise position, core radius, convection velocity, and circulation. Additionally, the onset of velocity oscillations in the far wake is analyzed because this can have a negative effect on stability and loading of downstream rotors. Results in the near wake for unsteady cases confirm that simulations and experiments tend to diverge from the expected linearized quasi-steady behavior when the rotor reduced frequency increases over 0.5. Additionally, differences across the simulations become significant, suggesting that further efforts are required to tune the currently available methodologies in order to correctly evaluate the aerodynamic response of a floating wind turbine in unsteady conditions. Regarding the far wake, it is seen that, in some conditions, numerical methods overpredict the impact of platform motion on the velocity fluctuations. Moreover, results suggest that the effect of platform motion on the far wake, differently from original expectations about a faster wake recovery in a floating wind turbine, seems to be limited or even oriented to the generation of a wake less prone to dissipation.

Flow morphology of a supersonic gravitating sphere

ABSTRACT Stars and planets move supersonically in a gaseous medium during planetary engulfment, stellar interactions, and within protoplanetary discs. For a nearly uniform medium, the relevant parameters are the Mach number and the size of the body, R, relative to its accretion radius, RA. Over many decades, numerical and analytical work has characterized the flow, the drag on the body, and the possible suite of instabilities. Only a limited amount of work has treated the stellar boundary as it is in many of these astrophysical settings, a hard sphere at R. Thus, we present new 3D athena++ hydrodynamic calculations for a large range of parameters. For RA ≪ R, the results are as expected for pure hydrodynamics with minimal impact from gravity, which we verify by comparing to experimental wind tunnel data in air. When RA ≈ R, a hydrostatically supported separation bubble forms behind the gravitating body, exerting significant pressure on the sphere and driving a recompression shock, which intersects with the bow shock. For RA ≫ R, the bubble transitions into an isentropic, spherically symmetric halo, as seen in earlier works. These two distinct regimes of flow morphology may be treated separately in terms of their shock stand-off distance and drag coefficients. Most importantly for astrophysical applications, we propose a new formula for the dynamical friction, which depends on the ratio of the shock stand-off distance to RA. That exploration also reveals the minimum size of the simulation domain needed to accurately capture the deflection of incoming streamlines due to gravity.

Investigating and Analyzing the Potential for Regenerating Excess Energy in a Helicopter UAV

Energy consumption is a critical parameter in the development of helicopter Unmanned Aerial Vehicles (UAVs). Today, helicopter UAVs are playing an increasingly pivotal role in various applications, from surveillance and reconnaissance to package delivery and search and rescue missions. However, their energy efficiency remains a pressing issue, as it directly impacts their operational duration and payload capacity. One of the key challenges in optimizing energy consumption is the existence of excess power during flight, arising from the intricate interplay between helicopter aerodynamic behavior and safety design. Typically, this excess energy is dissipated, resulting in a suboptimal performance and efficiency. This study investigated the behavior of excess power in a helicopter Unmanned Aerial Vehicle (UAV). Typically, this excess energy is wasted in conventional helicopters and helicopter UAVs. A dual-method approach, encompassing numerical and experimental methodologies, was employed to provide comprehensive insights into the helicopter UAV’s performance under various conditions. Computational fluid dynamics (CFD) simulations were performed to analyze the UAV’s aerodynamics. The simulations were validated by comparing the lift force with wind tunnel experimental data, resulting in acceptable deviations. The experimental analysis was conducted using a wind tunnel and a small-sized helicopter UAV. The experiments were designed to examine the excess power behavior of the UAV under two distinct flight conditions: hover and forward flight. The power output from the generator and power input from the battery were measured under various angular velocities and pitch angles. The results revealed a maximum excess power of 6.84% for hover conditions and 9.83% for forward flight conditions. This indicates that the maximum excess power percentage attributable to the helicopter UAV’s safety measure is 6.84% and that resulting from aerodynamics is 2.99%. The findings of this study contribute valuable knowledge to the optimization of helicopter UAV performance and the potential for harnessing excess power during flight operations. When this excess energy is harnessed, it can contribute significantly to the overall performance and efficiency of the UAV, potentially extending its flight duration or accommodating additional payload capacity that could potentially pave the way for the development of hybrid helicopter UAV models in the future.

Stochastic determination of thermal reaction rate coefficients for air plasmas.

This work deals with the stochastic inference of gas-phase chemical reaction rates in high temperature air flows from plasma wind tunnel experimental data. First, a Bayesian approach is developed to include not only measurements but also additional information related to how the experiment is performed. To cope with the resulting computationally demanding likelihood, we use the Morris screening method to find the reactions that influence the solution to the stochastic inverse problem from a mechanism comprising 21 different reactions for an air mixture with seven species: O2, N2, NO, NO+, O, N, e-. A set of six reactions, mainly involving nitrogen dissociation and exchange, are the ones identified to impact the solution the most. As such, they are assumed to be uncertain and estimated along with the boundary conditions of the experiment and the catalytic recombination parameters of the materials involved in the testing. The remaining 15 reactions are set to their nominal values. The posterior distribution is then propagated through the proposed boundary layer model to produce the posterior predictive distributions of the temperature and mass fraction profiles along the boundary layer stagnation line. It is identified that NO concentrations have the largest increase in uncertainty levels compared to cases where the inference problem is carried out for fixed chemical model parameter values. This allows us to inform a new experimental campaign targeting the reduction of uncertainties affecting the chemical models.

Numerical study of the wall boundary condition in large-eddy simulation of the flow past a sharp-edged bluff body

Based on the fact that the drag coefficient is relatively insensitive to the Reynolds number in many experiments on the flow past a sharp-edged bluff body (SEBB) at high Reynolds numbers, it is speculated that the effect of the wall viscosity on the aerodynamics of the SEBB can be neglected to some extent. To validate this hypothesis for the large-eddy simulation (LES), the slip-wall boundary condition was applied to the SEBB, and this LES was termed slip-wall LES (SWLES). The flow past a square cylinder was chosen to validate the SWLES. The aerodynamic parameters, such as the drag coefficient and Strouhal number, agreed well with the experimental data and those of the traditional wall-resolved LES (WRLES). The surface pressure distributions and energy spectra were close to those of the WRLES. The Kelvin–Helmholtz instability structures, flow separation, and von Kármán vortex shedding were captured accurately by the SWLES. The computational cost was compared with that of the WRLES. An interpretation of the SWLES was discussed based on flow visualizations. After the validation, the SWLES was applied to the flow past a photovoltaic system. The wind loads of the system were compared with the wind tunnel experimental data at different incident angles. The surface pressure distributions, flow structures, and wake were analyzed. The present study demonstrated that the SWLES has potential applications for the flow around an SEBB with a much lower cost than that of the WRLES.

An Evaluation of Inflow Profiles for CFD Modeling of Neutral ABL and Turbulent Airflow over a Hill Model

The implementation of the wind turbine is a major issue in the wind engineering sector. However, the presence of wind turbines in the lower part of the atmospheric boundary layer (ABL) requires an appropriate study for the simulation of turbulent airflow in the wind farm situated on hilly terrain. The use of precise Computational Fluid Dynamics (CFD) simulations for the ABL flow is vital for numerous applications, such as wind energy, building, urban planning, etc. To achieve accurate results, it is imperative that the inlet boundary conditions produce vertical profiles that keep a uniform horizontal distribution (with no streamwise gradients) in the upstream region of the computational domain for all important parameters. A development approach is proposed herein, focused on the imposition of two different inlet profiles when used in combination with the rough z0-type scalable wall function. The horizontal homogeneity of these profiles has been verified by 2D Reynolds averaged Navier-Stokes (RANS) through the examination of a neutral ABL in an empty computational domain using the k-ε turbulence model. The findings indicate that the use of this modeling approach can yield relatively consistent homogeneity of neutral ABL for both inlet boundary conditions. Subsequently, sensitivity analyses were performed on the inflow profiles to forecast the evolution of the bottom half of an idealized truly-neutral ABL and to accurately capture the complex dynamics of atmospheric flows over hilly terrain. This study compares the results with the CRIACIV (Inter-University Research Centre on Building Aerodynamics and Wind Engineering) boundary layer wind tunnel experimental data, showing that the inflow profiles and the presence of topographic complex have a significant impact on air velocity, turbulent kinetic energy and turbulence intensity in the x-direction. The results obtained are in good correlation with published experimental data in the presence of the hill surface.

Numerical simulation of the boundary layer development behind a single quarter elliptic-wedge spire

For decades wind tunnel has been utilized to generate a quasi-atmospheric boundary layer to observe the wake flow around objects submerged within the Atmospheric Boundary Layer. The quarter elliptic-wedge spire is the most commonly used as a vortex generator among other passive devices. However, despite numerous past studies that utilize rows of spires to generate deep quasi-ABL, only a few researchers targeted spires as the main subject of their investigation. Hence, the present work originally aims to investigate the wake flow structure behind a single quarter elliptic-wedge spire and its aerodynamic interaction with a smooth wall boundary layer. A computational fluid dynamics simulation predicting the wake flow structure behind a single quarter elliptic-wedge spire was conducted using the OpenFOAM® software. The computational domain consists a smooth flat plate, and a single quarter elliptic-wedge spire. A comparison of two Reynolds-Averaged Navier–Stokes turbulence models, namely the k-ɛ model and the SST k-ω model, was conducted. A SIMPLE algorithm was used as the solver in the simulation iteration and ParaFOAM® was used as the post-processing software. The development of the boundary layer height from streamwise x0=0.5S to downwind x0=20S was observed. The mean vertical velocity profiles predicted by both turbulence models are in good agreement with the previous wind tunnel experimental results. However, the results obtained with the k-ɛ model were overpredicted compared to the results of the SST k-ω model causing deviation of the boundary layer height from the wind tunnel experimental data. This anomaly might be caused by the velocity deficit recovery above the boundary layer height region where the turbulence is low.

Machine learning based surrogate model to analyze wind tunnel experiment data of Darrieus wind turbines

Wind tunnel experiment is one of the most common research methods of wind turbines. However, the processing of experiment data towards Vertical Axis Wind Turbines (VAWT) are inefficient. In this work, a data-driven surrogated model based on Artificial Neural Networks (ANN), Support Vector Regression (SVR), Gaussian Process Regression (GPR) and Decision Tree Regression (DTR) is proposed to regress the experimental data of aerodynamic forces. Meanwhile, a novel U-typed Darrieus Wind Turbine (UDWT) and two H-typed VAWTs are manufactured in this work. A measurement system combining the magnetic remanence brake, six force sensor, and data processing subsystem is assembled to investigate the aerodynamic forces of wind turbines. A Spin-Down measurement procedure is adopted to collect experiment data in various operating conditions. Results showed that SVM- and GPR-based regression models feature the better fitting ability with R2 larger than 0.99, which can regress the experiment data accurately. ANN-based surrogated model can reproduce the fluctuation of experiment data because of the best learning ability. Aerodynamic forces of UDWT outperform H-type wind turbines at azimuth angle of 90° and 270°.

Equivalent oscillator approach to model vortex induced vibrations on a circular cylinder

The paper presents a numerical model, based on the equivalent oscillator approach, able to simulate vortex induced vibrations on a circular cylinder. This model consists of a single degree of freedom mechanical system characterized by non-linear parameters that reproduce the fluid-structure interaction in time domain. A genetic algorithm approach was used in order to identify the characteristic parameters of the equivalent oscillator: obtained results are discussed and compared with wind tunnel experimental data and with a previous version of the numerical model. Comparison is performed both in terms of aerodynamic forces and oscillation amplitudes and both in steady and transient conditions.

Fourth High-Lift Prediction/Third Geometry and Mesh Generation Workshops: Overview and Summary

The Fourth AIAA Computational Fluid Dynamics (CFD) High Lift Prediction Workshop and the Third Geometry and Mesh Generation Workshop were held collaboratively with the common goal of assessing the numerical prediction capability of current-generation computational fluid dynamics technology for swept medium-/high-aspect-ratio wings in high-lift configurations. A key aspect of this joint endeavor was the use of technology focus groups: an innovative new approach for workshops involving close collaboration between participants. These groups, which included both mesh-generation and flow-solver experts, worked to accelerate advancements for their particular methodologies by addressing key questions of importance before the workshop. The high-lift version of the NASA Common Research Model (CRM-HL) configuration was the focus of this workshop. Measured experimental wind-tunnel data were available for comparison. The workshop also included a two-dimensional turbulence model verification exercise based on the CRM-HL wing shape. Altogether, 44 participants submitted a total of 184 datasets of CFD results. This paper provides a high-level summary of the results and conclusions from the workshop. Like at past workshops, fixed-grid Reynolds-averaged Navier–Stokes methods continued to be inaccurate and inconsistent for predicting high-lift flow physics near maximum lift conditions. However, mesh adaptation definitively brought more consistency. Scale-resolving methods appeared most promising for predicting high-lift flow physics near maximum lift.

A simplified semi-empirical model for long-range low-frequency noise propagation in the turbulent atmosphere

We present a semi-empirical long-range low-frequency acoustic propagation model, which accounts for atmospheric turbulence. Ostashev and Wilson’s scattering model is combined with a ray-theory based refraction model to account for turbulent scattering and refraction via a turbulent absorption coefficient. The coefficient is ascertained via integration of scattered energy. The model is formulated, calibrated, and validated via corresponding experiments conducted within the National Science Foundation Boundary Layer Wind Tunnel. The predictions of the newly proposed ‘bridging model’ match the wind tunnel experimental data with an average error of 11.9%. Example predictions are shown to quantify the effect of turbulent kinetic energy and turbulent integral length scale on long-range infrasound propagation. To demonstrate the approach, we present predictions of the propagation of noise from a tornado and a nonlinear wave.