Wind Tunnel Experimental Data Research Articles

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.

Influence of relative thickness on static and dynamic stall characteristics and prediction of airfoils

A study was conducted to investigate the effects of relative thickness on the static and dynamic characteristics of airfoils. A series of NACA symmetric airfoils with relative thickness ratios ranging from 12% to 30% have undertaken a series of sinusoid pitching motion simulations and these airfoils' Glasgow wind tunnel experiment data were analyzed. It was found that the relative thickness of airfoils would affect the stall onset angle of attack (AOA), the severity of the stall, and the dynamic stall model parameters. As the relative thickness of airfoils increases, static and dynamic stall onset AOA decrease and stall occurs earlier. At the static AOA, the thickest airfoil shows a very large reverse flow region. At the dynamic stall onset AOA, the thinner airfoil exhibits a more obvious burst of the laminar separation bubble. When the relative thickness of the airfoil is smaller, a dynamic stall occurs with more severity. On the one hand, the aerodynamic characteristic curve and suction surface pressure curve of airfoils change are more complicated. And the severity of the dynamic stall was quantitatively compared by extracting the difference of lift coefficients corresponding to the same AOA in the upstroke and downstroke stages. On the other hand, vortex occurrence, convection and shedding on the suction surface of the airfoil are more frequent and complicated. This paper also gives a method to solve the problem of the lack of the dynamic stall model parameters of blades section airfoils when predicting the wind turbine's unsteady force.

Effect of Reynolds number on the wake of a Next-Generation High-Speed Train using CFD analysis

Improvement to the next-generation high-speed train (NG-HST) is ongoing particularly in achieving a higher operating speed. Consequently, the aerodynamic effect of the train will be more critical as it affects the development of a wake flow characterized by complex and unsteady structures. Although the effect of Reynolds number (Re) on aerodynamic forces is negligible, its effect on the wake of NG-HSTs is unknown. In this study, the Re ranging from 7.42 × 105 to 1.62 × 106 was used to examine the characteristics of vortex structures, streamline distributions, velocity characteristics, and pressure characteristics in the wake region of an NG-HST. The Delayed Detached Eddy Simulation (DDES) is used as the turbulence model. In addition, the simulation results were compared with the previous wind tunnel experimental data. The results indicated no significant changes in the overall wake flow structure when Re was increased. According to power spectral density analysis, increasing the Reynolds number increased the turbulence intensity of the wake which gradually dissipated as the distance from the train increased. The findings of the study could be used to better understand the flow characteristics at the wake of NG-HSTs for future development.

An Intelligent Algorithm for Aerodynamic Parameters Calibration of Wind Tunnel Experiment at a High Angle of Attack

In this paper, an intelligent algorithm for the aerodynamic parameter calibration of wind tunnel experiments of advanced layout aircraft at a high angle of attack is proposed. The proposed algorithm is based on a homologous comparison and tuning algorithm, and it can effectively improve the accuracy of the wind tunnel experiment model. First, based on the analysis of large oscillation wind tunnel experimental data of an advanced layout scaled aircraft, the high angle of attack wind tunnel experimental model composed of static derivative, dynamic derivative, and rotating balance derivative is established. Second, to improve the accuracy of the wind tunnel experimental model effectively, the idea of combing layered calibration and intelligent algorithm for high angle of attack homologous comparison correction is proposed. The proposed method solves the problems of complex structure, a large amount of data, and poor accuracy in homologous comparison of high angle of attack aerodynamic models of advanced layout aircraft. Finally, the homologous comparison interface software is designed based on MATLAB GUI, which integrates the proposed methods and ideas and realizes effective adjustment of aerodynamic parameters of high angle of attack simulation flight wind tunnel test of an advanced layout aircraft. This study provides a reliable engineering and technical means for subsequent high angle of attack flight test verification of the advanced layout aircraft.

The Influence of Rotor Overlapping Azimuth on Compound Coaxial Helicopter Performance Based on Unsteady CFD Simulation

In this paper, a computational fluid dynamics simulation method is developed to study the influence of the rotor overlapping azimuth on the aerodynamic performance of compound coaxial helicopter. The simulation method is verified by comparing the numerical simulation results with the wind tunnel experiment data of the NASA coaxial rotor. Two overlapping azimuths of the upper and lower blades are considered, and the aerodynamic performance of the isolated rotor and the compound coaxial helicopter in hover and forward are analyzed respectively. State 1 means the upper and lower blades overlap at azimuth 0/180° or 90/270°, state 2 means the upper and lower blades overlap at azimuth 45/225° or 135/315°. It is found that the performance of isolated rotors is not affected by rotor overlapping azimuth in hover, but the total thrust fluctuation amplitude of isolated rotors in state 2 is 76.3% smaller than that in state 1 in forward. In the hovering flight of compound coaxial helicopter, compared with state 1, the fluctuation amplitude of the lift of the wing in state 2 is 42.7% smaller; the lift fluctuation amplitude of the flat tail in state 2 is 52.4% smaller. In the forward flight of compound coaxial helicopter, compared with state 1, the total thrust fluctuation amplitude in state 2 is 83.5% smaller; the fluctuation amplitude of the lift of the wing in state 2 is 61.2% smaller. It can be concluded that the compound coaxial helicopter working in state 2 has better aerodynamic performance than the compound coaxial helicopter working in state 1; changing the rotor overlapping azimuth of the upper and lower rotors has a high engineering application value, which can increase aerodynamic stability and reduce lift fluctuations.

Effect of tornado near-ground winds on aerodynamic characteristics of the high-speed railway viaduct

The tornado is in direct contact with the underlying surface, which causes damage and indicates the vortex structure close to the ground. Accordingly, the maximum wind velocity generally could occur near the ground, potentially exposing the infrastructure to higher wind loads. However, one of the biggest challenges facing tornado research is characterizing the wind structure very near the surface due to the limitation of the data by using Doppler weather Radar. Considering the advantage of the high-fidelity computational fluid dynamics (CFD) models, this study aims to investigate the aerodynamic characteristics of a high-speed railway viaduct under tornado near-surface winds. More specifically, in light of limited full-scale data to arrive at a consensus on quantifying key parameters characterizing the tornado flow and near-surface winds, firstly. Secondly, tornado radar-measured data and a theoretical analysis model were utilized to validate the accuracy of the numerical method adopted in this study. Thirdly, the wind pressure distribution on the bridge is validated using the wind tunnel experimental data in Central South University(CSU), and the comparison between the simulational bridge and the measured data under crosswind was satisfactory. Finally, a comprehensive modeling strategy comprehensively investigates the aerodynamic characteristics of a high-speed railway viaduct under a tornado near-surface wind.

Computational Fluid Dynamics Study of Aircraft Wing with Winglet Performance at High Subsonic Speeds

Most commercial aircraft use winglets, which are structures that reduce drag generated by tip vortices and improve fuel efficiency. At high speeds, the tip vortices will be stronger, which increases induced drag. So, analysis of the aerodynamic performance of the winglet is essential. For that, a wing with a winglet using the NACA 2213 airfoil has been designed in the SolidWorks software, and its CFD study had performed at high subsonic speeds in the Ansys software. The simulation has performed at four different angles of attack and two different subsonic speeds (0.7 and 0.8 Mach). The obtained results, including the lift-to-drag ratio and coefficient of lift and drag, have been compared to NASA wind tunnel experiment data. A CFD analysis of a wing without a winglet was carried out to determine the benefits of winglets over them. In comparison to a wing without winglets, a wing with winglets produces less drag. Winglets also increase the lift-to-drag ratio of the wing at high subsonic speeds.

Feasibility analysis using a porous media model to simulate the wind protection effect of windbreak forests

AbstractThe porous media model theory has been applied to the study of soil wind erosion, and the accuracy of simulation test results using the resistance source term instead of the windbreak geometry model has received much attention. A common shrub windbreak was used as the research object, and a porous media model with a similar shape was established to synthetically compare the wind tunnel experimental data with the results of computational fluid dynamics numerical simulations, analyze its feasibility for windbreak research instead of wind tunnel experiments, and try to elaborate the causes of errors arising from numerical simulations. The relative standard deviation of more than 80% of the sampling points in the porous media model and wind tunnel experimental results was less than 5%, and the wind speed difference at the maximum relative standard deviation was only 0.257 m s−1; the difference in wind speed variation was most obvious on the leeward side of the lower part of the vegetation canopy, but this error does not affect the wind speed recovery trend of the Caragana shrub/forest belt array. The combination of numerical simulations and wind tunnel experiments gives a reference for the accuracy of porous media models used to simulate plant wind protection.

Aerodynamic and aeroacoustic performance assessment of a vertical axis wind turbine by synergistic effect of blowing and suction

The power efficiency of Darrieus wind turbines significantly deteriorates during rotation caused by periodic dynamic stall at low tip speed ratios. This leads to a strong fluctuation in torque and a reduction in energy acquisition. This paper aims to improve the aerodynamic performance of an H-type Darrieus wind turbine using an innovative fluidic flow control technique based on the synergistic effect of blowing and suction. The aeroacoustic noise emissions accomplished with this enhancement are evaluated. The Improved Delayed Detached Eddy Simulation turbulence model and the Ffowcs Williams-Hawkings acoustic analogy method are adopted to simulate the instantaneous flow field and predict the far field noise. Following validation of the numerical approach using wind tunnel experimental data on a static airfoil, an orthogonal experimental design method was used to analyze and optimize the operating factors. The factors include suction position relative to leading-edge (Ls), blowing position relative to trailing-edge (Lb) and jet coefficient (Cμ). The results indicate that Cμ plays crucial role in determining the airfoil performance, while the role of Lb is almost negligible. Furthermore, the impact of optimal combination of these factors was analyzed based on three different control strategies. It is found that appropriate application of the active control solution can eliminate the wind turbine’s negative torque, avoid excessive alternating load on the rotor and improve the energy extraction efficiency. The aeroacoustic noise estimation shows that the active device can reduce the noise emission by moderating pressure fluctuation, stabilizing the flow field and influencing the vortex shedding. Similarly, the proposed active control solution can reduce the wind turbine noise level by up to 6.56 dB by modifying the sound pressure spectra at frequencies between 100 and 1000 Hz.

Investigation into the Aerodynamic Performance of a Vertical Axis Wind Turbine with Endplate Design

For the past decade, research on vertical axis wind turbines (VAWTs) has garnered immense interest due to their omnidirectional characteristic, especially the lift-type VAWT. The H-rotor Darrieus VAWT operates based on the lift generated by aerofoil blades and typically possesses higher efficiency than the drag-type Savonius VAWT. However, the open-ended blades generate tip loss effects that reduce the power output. Wingtip devices such as winglets and endplates are commonly used in aerofoil design to increase performance by reducing tip losses. In this study, a CFD simulation is conducted using the sliding mesh method and the k-ω SST turbulence model on a two-bladed NACA0018 VAWT. The aerodynamic performance of a VAWT with offset, symmetric V, asymmetric and triangular endplates are presented and compared against the baseline turbine. The simulation was first validated with the wind tunnel experimental data published in the literature. The simulation showed that the endplates reduced the swirling vortex and improved the pressure distribution along the blade span, especially at the blade tip. The relationship between TSR regimes and the tip loss effect is also reported in the paper. Increasing VAWT performance by using endplates to minimise tip loss is a simple yet effective solution. However, the improvement of the power coefficient is not remarkable as the power degradation only involves a small section of the blades.

Investigation on transition correlation of conical boundary layer in hypersonic wind tunnel experiments

The wind tunnel experiment is an important approach to studying boundary layer transition. In this study, the effects of bluntness, unit Reynolds number, and wall temperature ratio on hypersonic conical boundary layer transition were studied using numerical simulations and linear stability analyses based on the wind tunnel experimental data. Through the flow similarity principle, the treatment of the bluntness-varying problem was determined. Combining the experimental transition data and theoretical analysis results of sharp and blunt cones at home and abroad, the relation between the transition factor Ntr and the unit Reynolds number before ‘N factor reversal’, as well as the relation between the transition value Rtr and the unit Reynolds number from ‘N factor reversal’ to ‘transition reversal’ were determined too. Finally, according to the wind tunnel test data of China Aerodynamics Research and Development Center, the effect of wall temperature ratio on the receptivity of blunt-cone boundary layer was stated out, and the correlation of transition Reynolds number under different wall temperature ratios was determined. The influence law of parameters in this correlation was also determined.

Three-dimensional modeling and investigation of the flow around a troposkein vertical axis wind turbine at different operating conditions

Vertical axis wind turbines of troposkein architecture are among the most attractive technologies for harvesting wind energy off-shore. In this paper, a high-fidelity Computational Fluid-Dynamics model of the flow around troposkein rotors is presented, experimentally validated, and applied to analyze the complex aerodynamics of this machine considering both operation and design aspects. At first, a set of two-dimensional simulations of the machine equatorial section was carried out to compare multiple spatial resolutions and three eddy-viscosity turbulence models, including Spalart–Allmaras, k-ω SST, and k-ω SST in low-Reynolds formulation, using as reference wind-tunnel experimental data. Then, the results of fully three-dimensional simulations for peak power and high TSR conditions are discussed, to further assess the models against experiments and to investigate the turbine aerodynamics and its spanwise variability, the flow around and downstream of the rotor, with particular emphasis on the peculiar character of troposkein rotor wake and the related tip vortices. Finally, the paper proposes an analysis about the impact of blade design on the machine aerodynamics, showing that rotors obtained with the simplest and most economic blade bending procedure outperforms configurations obtained by manufacturing the blades with plane airfoil sections along the troposkein curve.

Ship Air-Wake Identification from Experimental Data for Automatic Deck Landing and Takeoff

Ship air-wake modeling is a critical task needed to support the design and validation of algorithms that can assist a helicopter’s pilot during shipboard launch and recovery operations. In fact, these operations are often carried out in challenging conditions and impose a significant workload on the pilot. In this framework, the paper presents an air-wake model applicable for flight mechanics analyses and real-time simulations. The definition of the model is based on system identification methodologies applied to wind-tunnel experimental data. The main innovation of the approach consists of the definition of a modular structure of the model that allows setting up a multistep identification strategy and exploiting the most suitable technique for the estimation of each set of the model’s parameters. The validation of the obtained model highlighted a good capability to reproduce the air-wake flowfield in several flow conditions. The model was applied to test trajectory generation and tracking algorithms for helicopter automatic takeoff and landing on a ship deck.