Wind Tunnel Experimental Data Research Articles

Detached-eddy and large-eddy simulations of wind effects on a high-rise structure

Abstract In this study, detached-eddy simulations (DES) and large-eddy simulations (LES) of wind effect on a high-rise structure with elliptical shape are performed. The aim of this study is to examine the accuracy of the numerical simulations for wind flow around a complex high-rise structure and investigate the effects of surface roughness on the wind loading. In order to reproduce appropriate inflow turbulence, the improved recycling method combined with the weighted amplitude wave superposition (WAWS) method is used to generate the inflow turbulence in the streamwise direction. Also, to study the surface roughness effects on the wind loading, the rough wall boundary conditions are adopted in the DES models. Typical results including the mean and fluctuating pressure coefficients, force spectra, Reynolds stresses and wind-induced top-floor response are obtained and compared with the corresponding wind tunnel experimental data. Through the cross-comparisons, the numerical results by the DES and LES models are found to be comparable with the experimental results. Additionally, the surface roughness effects on the wind loading is well reproduced with the DES models, such as the slow pressure recovery in the separation regions and the increased mean drag force coefficients. It is demonstrated through the validations that the DES and LES models and the numerical treatments adopted in this study can provide reasonably good results.

Study on stall behavior of a straight-bladed vertical axis wind turbine with numerical and experimental investigations

This paper presents a straight-bladed vertical axis wind turbine (VAWT) model for the evaluation of the stall phenomenon associated with unsteady flow around the airfoil surface with numerical and experimental investigations. In wind tunnel experiments, in order to investigate flow visualization, light-weight tufts attached to the inner surface of blade are used to gain insight on the flow characteristics of VAWT during rotation in the low Reynolds numbers. In numerical analysis, a 2D computational investigation on the stall phenomenon and aerodynamic characteristics at the VAWT airfoil is associated with the standard κ−ε model and Shear Stress Transport κ−ω (SST κ−ω) turbulence model. And then, the stall behavior is validated according to compare the results of wind tunnel experiment and numerical analysis. From this study, it is concluded that the numerical simulation captures well the vortex-shedding predominated flow structure which is experimentally obtained and the results quantitatively agree well with the wind tunnel experimental data. Moreover, the flow separation behavior of the airfoil shows the importance of stall phenomenon and the interaction of the separated vortex with the blade as mechanisms in lift and drag coefficients.

Characteristics of unsteady flow around two successive rectangular ribs on floor of a wind tunnel

The presence of two or more mounted ribs in air duct or wind tunnel causes strong turbulence, affecting basic flow properties in mechanical or agricultural applications. The purpose of this work was the detailed analysis and visualization of turbulent flow around two successive ribs on the floor of a wind tunnel, with dynamic approximation. The statistical numerical results of flow parameters of the present numerical experiment were quantitatively compared with respective wind tunnel experimental data, in order to check the validity of the proposed mathematical model. Instantaneous values of both velocity components obtained from the direct solution of Navier–Stokes equations and the wind tunnel experiment were used to calculate the statistical data of turbulent flow, such as time-averaged stream and cross-wise velocities, turbulent intensities and turbulent kinetic energy. The validation of proposed model was confirmed by the satisfactory agreement between the numerical experiment and laboratory experiment with respect to turbulence statistics, such as averaged velocities, turbulence intensities and turbulent kinetic energy. The instantaneous streamlines around two successive rectangular ribs was presented for the first time, demonstrating the chaotic behavior of the flow. Intense variations of velocity components, were developing between the ribs and specifically at the beginning of the first roof to the second roof of ribs. The turbulence statistics showed that the maximum values of turbulent parameters were observed mainly over the two successive ribs. The direct simulation model overestimated the maximum values of turbulent parameters comparing to the corresponding experimental values.

LES of wind environments in urban residential areas based on an inflow turbulence generating approach

Wind environment in urban residential areas is an important index to consider when evaluating the living environment. However, due to the complexity of the flow field in residential areas, it is difficult to specify the correct inflow boundary conditions in the large eddy simulation (LES). In this paper, the weighted amplitude wave superposition (WAWS) is adopted to simulate the fluctuating velocity data, which satisfies the desired target wind field. The fluctuating velocity data are given to the inlet boundary of the LES by developing an UDF script, which is implemented into the FLUENT. Then, two numerical models - the empty numerical wind tunnel model and the numerical wind tunnel model with spires and roughness elements are established based on the wind tunnel experiment to verify the present method. Finally, the turbulence generation approach presented in this paper is used to carry out a numerical simulation on the wind environment in an urban residential area in Lisbon. The computational results are compared with the wind tunnel experimental data, showing that the numerical results in the LES have a good agreement with the experimental results, and the simulated flow field with the inlet fluctuations can generate a reasonable turbulent wind field. It also shows that strong wind velocities and turbulent kinetic energy occur at the passageways, which may affect the comfort of people in the residential neighborhood, and the small wind velocities and vortexes appear at the leeward corners of buildings, which may affect the spreading of the pollutants.

A Comparative Study on Turbulence Models for Simulation of Flow Past NACA 0015 Airfoil Using OpenFOAM

An implementation of C++ language open source code software, OpenFOAM, for simulation of flow past NACA 0015 airfoil was performed to access a suitable turbulence model. Three various turbulence models were selected which comprised of Spalart-Allmaras model, RNG k-e model and Menter SST k-ω model, respectively. The SIMPLE algorithm and Upwind method was used to solve the governing equation to achieve flow solutions of computational fluid dynamic (CFD) models. The flow simulation obtained lift coefficient (C L ) and drag coefficient (C D ) to compare with the wind tunnel experiment data at Reynolds number (Re) of 160,000 and 360,000 with the large range airfoil angle of attack (AOA) from 0 to 20 degree. The suitable CFD model was the Menter SST k-ω model which obtained an average error of C L and C D less than 10.96% and 22.21%, respectively.

Trailing-edge flow control for wind turbine performance and load control

This paper reports an investigation into the performance of trailing-edge flow control devices on horizontal axis wind turbines by solving the three dimensional Reynolds averaged Navier-Stokes equations in the rotational framework. The validation case selected for this work is the NREL Phase VI blade with wind tunnel experimental data. The trailing-edge flow control devices studied include microtabs and microjets installed near the trailing-edge of the rotating blade. The divergent trailing-edge is also included in the study as a passive flow control device due to its practical interest. These trailing-edge devices are implemented on the fixed-pitch NREL Phase VI blade, using the original performance and flow characteristics as a benchmark. Both 2D and 3D simulations are carried out in order to investigate the suitability of the 2D blade sectional design analysis and control for the actual 3D rotating blades.

Large-Eddy Simulation of Atmospheric Boundary-Layer Flow Through a Wind Farm Sited on Topography

Large-eddy simulation (LES) has recently been well validated and applied in the context of wind turbines over flat terrain; however, to date its accuracy has not been tested systematically in the case of turbine-wake flows over topography. Here, we investigate the wake flow in a wind farm situated on hilly terrain using LES for a case where wind-tunnel experimental data are available. To this end, first boundary-layer flow is simulated over a two-dimensional hill in order to characterize the spatial distribution of the mean velocity and the turbulence statistics. A flow simulation is then performed through a wind farm consisting of five horizontal-axis wind turbines sited over the same hill in an aligned layout. The resulting flow characteristics are compared with the former case, i.e., without wind turbines. To assess the validity of the simulations, the results are compared with the wind-tunnel measurements. It is found that LES can reproduce the flow field effectively, and, specifically, the speed-up over the hilltop and the velocity deficit and turbulence intensity enhancement induced by the turbines are well captured by the simulations. Besides, the vertical profiles of the mean velocity and turbulence intensity at different streamwise positions match well those for the experiment. In addition, another numerical experiment is carried out to show how higher (and more realistic) thrust coefficients of the turbines lead to stronger wakes and, at the same time, higher turbulence intensities.

Multi-Zone Ice Accretion and Roughness Models for Aircraft Icing Numerical Simulation

AbstractA mathematical multi-zone ice accretion model used in the numerical simulation of icing on airfoil surface based on three water states, namely, continuous film, rivulets and beads is studied in this paper. An improved multi-zone roughness model is proposed. According to the flow state of liquid water and film flow, rivulets flow governing equations are established to calculate film mass distribution, film velocity, rivulet wetness factor and rivulet mass distribution. Force equilibrium equations of droplet are used to establish the critical conditions of water film broken into rivulets and rivulets broken into beads. The temperature conduction inside the water layer and ice layer is considered. Using the proposed model ice accretion on a NACA0012 airfoil profile with a 4° angle of attack under different icing conditions is simulated. Different ice shapes like glaze ice, mixed ice and rime ice are obtained, and the results agree well with icing wind tunnel experiment data. It can be seen that, water films are formed on the surface, and heights of the films vary with icing time and locations. This results in spatially-temporally varying surface roughness and heat transfer process, ultimately affects the ice prediction. Model simulations indicate that the process of water film formation and evolution cannot be ignored, especially under glaze ice condition.

Evaluation of a micro-scale wind model’s performance over realistic building clusters using wind tunnel experiments

The simulation performance over complex building clusters of a wind simulation model (Wind Information Field Fast Analysis model, WIFFA) in a micro-scale air pollutant dispersion model system (Urban Microscale Air Pollution dispersion Simulation model, UMAPS) is evaluated using various wind tunnel experimental data including the CEDVAL (Compilation of Experimental Data for Validation of Micro-Scale Dispersion Models) wind tunnel experiment data and the NJU-FZ experiment data (Nanjing University-Fang Zhuang neighborhood wind tunnel experiment data). The results show that the wind model can reproduce the vortexes triggered by urban buildings well, and the flow patterns in urban street canyons and building clusters can also be represented. Due to the complex shapes of buildings and their distributions, the simulation deviations/discrepancies from the measurements are usually caused by the simplification of the building shapes and the determination of the key zone sizes. The computational efficiencies of different cases are also discussed in this paper. The model has a high computational efficiency compared to traditional numerical models that solve the Navier–Stokes equations, and can produce very high-resolution (1–5 m) wind fields of a complex neighborhood scale urban building canopy (~ 1 km ×1 km) in less than 3 min when run on a personal computer.

Numerical Simulation and Reduced-Order Aerodynamic Modeling of a Lambda Wing Configuration

This work is a contribution to the North Atlantic Treaty Organization Science and Technology Organization Task Group AVT-201 on stability and control estimation methods. Specifically, this study uses the Cobalt and Kestrel computational fluid dynamics flow solvers to predict and create reduced-order models for the aerodynamic force and moment coefficients of a generic uninhabited combat air vehicle under static and dynamic conditions and compare them with wind tunnel data. The particular reduced-order method investigated in this work is based on response functions. The geometry under investigation is known as DLR-F19, which is a lambda-wing configuration with a 53 deg angle of sweep at the leading edge. Each wing has two control surfaces on the trailing edge, hinged along the 75% chord line. Two different gridding strategies are employed: one uses an overset grid method for simulation of control-surface deflections without the need for regridding, and the other is to create a new grid for each control-surface deflection. The simulation results of these grids are compared in order to identify the effect of gaps present in the overset method. A grid is also created to study the presence of the sting geometry as tested in the experiments. Validation results are shown for different turbulence models at selected flight conditions. Overall, a good agreement between computational results and the wind tunnel experimental data for total force coefficients is achieved. However, delayed detached eddy simulations are required for angles of attack greater than 20 deg. The reduced-order modeling results show that predictions from a nonlinear model match quite well with full-order data of small amplitude motions. Small discrepancies can be seen in the plots of large-amplitude motions as well. The model predictions get worse when the belly sting geometry is included in simulations because of the nonlinear hysteresis behavior of a wake formed behind the sting.

Large-eddy simulation of flow and scalar dispersion in rural-to-urban transition regions

Large-eddy simulations (LES) are performed to simulate the flow and scalar transport in rural-to-urban transition regions. The LES framework is first validated with wind-tunnel experimental data of scalar dispersion within and above a staggered array of cubes. It is then used to simulate the scalar dispersion in transition regions from a flat homogeneous terrain to uniform arrays of cubes with height h. Staggered cube arrays with five different plan area densities, equal to 0.028, 0.063, 0.111, 0.174 and 0.250, and two incoming wind directions (α), equal to 0° and 27° are considered. Above the cube array, self-similar profiles for the mean scalar concentration are found and a scalar internal boundary layer is identified in all the cases. For all the cases tested, larger internal boundary layer thickness is found for α = 27° compared with that of α = 0°, which is related to the higher effective surface roughness in the cases of α = 27°. Within the urban canopies, the scalar concentration is found to adjust quickly within the cube array, which leads to a similar scalar concentration distribution pattern after the second row of cubes. Comparing the cases of the two different α, similar scalar concentration and adjustment pattern are found when the density is low. However, when the density is higher, higher scalar concentration is found in the cases of α=27∘ compared with those of α=0∘.

Stability and Control Investigations of Generic 53 Degree Swept Wing with Control Surfaces

A contribution for the assessment of the static and dynamic aerodynamic behavior of a generic unmanned combat air vehicle configuration with control devices using computational fluid dynamics methods is given. For the study, various computational approaches have been used to predict stability and control parameters for aircraft undergoing nonlinear flight conditions. For the computational fluid dynamics simulations, three different computational fluid dynamics solvers are used: the unstructured grid-based solvers DLR TAU code and USM3D from NASA, as well as the structured grid-based National Aerospace Laboratory/NLR solver ENSOLV. The numerical methods are verified by experimental wind-tunnel data. The correlations with experimental data are made for static longitudinal/lateral sweeps and at varying frequencies of prescribed roll/pitch/yaw sinusoidal motions for the vehicle operating with and without control surface deflections. Furthermore, the investigations should support the understanding of the flow physics around the trailing-edge control devices of highly swept configurations with a vortex-dominated flowfield. Design requirements should be drawn by analyzing the interaction between the vortical flow and the control devices. The present work is part of the North Atlantic Treaty Organization’s Science and Technology Organization/ Applied Vehicle Technology Task Group AVT-201 on stability and control prediction methods.

Aerodynamic characteristics of a spinning projectile with elastic deformation

The elastic deformation of a spinning projectile with a large slenderness ratio influences its flight stability and maneuverability. Unsteady time-accurate simulation based on a dual-time stepping method and the dynamic mesh method were used to solve the unsteady Reynolds-averaged Navier–Stokes (URANS) equations and obtain the aerodynamic characteristics of a spinning projectile given continuously elastic deformation. Archival wind tunnel experimental data were used, and grid resolution and time independence studies were carried out for numerical validation at angles of attack ranging from 2.09° to 10.4°. The aerodynamic coefficients induced by spin and elastic deformation were compared to the effect of movement frequency, deformation component, Mach number and angle of attack using Fourier transform. Numerical simulations indicate that the time-averaged values and the fluctuation amplitudes of the aerodynamic coefficients increase with movement frequency; two aerodynamic components are induced by elastic deformation, one opposite and one perpendicular to the direction of deformation; nose and body deformation have different effects on the aerodynamic characteristics; and the effective angle of attack induced by elastic deformation and rolling movement decreases as the Mach number increases, thus weakening the influence of movement on the aerodynamic forces.

Large-Eddy Simulation of Turbulent Flow Around a Finite-Height Wall-Mounted Square Cylinder Within a Thin Boundary Layer

In this paper, large-eddy simulation (LES) has been performed to investigate the turbulent wake behind a wall-mounted square cylinder. The flow features a relatively high cylinder aspect ratio of 4, a Reynolds number of 12,000 (based on the free-stream velocity and cylinder side length), and a thin developing boundary layer with a thickness of only 18 % of the obstacle height. These characteristics of the flow impose challenges to LES for accurate simulation of large energetic eddies induced by the cylinder and their intense interactions with the thin developing boundary layer. The coherent flow structures around the cylinder have been studied based on the instantaneous and time-averaged resolved velocity and pressure fields. The local kinetic energy transfer between the resolved and subgrid scales and the streamwise evolution of the subgrid-scale viscosity have been investigated to provide physical insights into the subgrid-scale dynamics. The LES predictions of the flow statistics have been validated against a set of recently reported wind-tunnel experimental data.

Base Flow of Circular Cylinder at Hypersonic Speeds

The paper presents a computational and an experimental investigation of base flow of a circular cylinder at hypersonic speeds. Effects of chemistry and wall temperature on the flow in the base region, at low to high enthalpies, are discussed. The experiments were conducted in a shock tunnel at a nominal Mach number of 10. Freestream Reynolds numbers based on cylinder diameter were and , respectively, and the total specific enthalpies were 13.35 and , respectively. The test gas was air. The surface pressure and heat flux were measured using a cold wall model. Equilibrium and thermal as well as chemical nonequilibrium numerical simulations were performed using a Navier–Stokes equations-based computational fluid dynamics code. Both a cold wall and adiabatic wall were considered. Particular emphasis was placed on the wake structure, vorticity distribution, wake centerline aerothermodynamic properties, and surface data. The existing low-enthalpy cold hypersonic wind-tunnel experimental data are included for comparison. The simulations predicted the effect of chemistry on the near wake to be negligible for the low-enthalpy, high Reynolds number flow but more significant for the high-enthalpy, low Reynolds number flow.

Influence of Turbulence Model for Wind Turbine Simulation in Low Reynolds Number

In designing a wind turbine, the validation of the mathematical model’s result is normally carried out by comparison with wind tunnel experiment data. However, the Reynolds number of the wind tunnel experiment is low, and the flow does not match fully developed turbulence on the leading edge of a wind turbine blade. Therefore, the transition area from laminar to turbulent flow becomes wide under these conditions, and the separation point is difficult to predict using turbulence models. The prediction precision decreases dramatically when working with tip speed ratios less than the maximum power point. This study carries out a steadiness calculation with turbulence model and an unsteadiness calculation with laminar model for a three-blade horizontal axis wind turbine. The validation of the calculations is performed by comparing with experimental results. The power coefficients calculated without turbulence models are in agreement with the experimental data for a tip speed ratio greater than 5.

A microscale model for air pollutant dispersion simulation in urban areas: Presentation of the model and performance over a single building

A microscale air pollutant dispersion model system is developed for emergency response purposes. The model includes a diagnostic wind field model to simulate the wind field and a random-walk air pollutant dispersion model to simulate the pollutant concentration through consideration of the influence of urban buildings. Numerical experiments are designed to evaluate the model’s performance, using CEDVAL (Compilation of Experimental Data for Validation of Microscale Dispersion Models) wind tunnel experiment data, including wind fields and air pollutant dispersion around a single building. The results show that the wind model can reproduce the vortexes triggered by urban buildings and the dispersion model simulates the pollutant concentration around buildings well. Typically, the simulation errors come from the determination of the key zones around a building or building cluster. This model has the potential for multiple applications; for example, the prediction of air pollutant dispersion and the evaluation of environmental impacts in emergency situations; urban planning scenarios; and the assessment of microscale air quality in urban areas.

Study of a fogging system using a computational fluid dynamics simulation

Fogging is one of the most effective methods for lowering the air temperature in rooms and greenhouses. It also has many industrial applications, especially in gas turbines where this method presents great advantages over others in terms of achieving better turbine performance in hot weather conditions.With this in mind, a numerical study was performed in STAR-CCM+ to investigate mist dynamics at a turbine's inlet duct, specifically measuring: (i) residence time of water droplets; (ii) mass transfer between water and air; (iii) coalescence and agglomeration of the water droplets; and (iv) changes in air density and temperature inside the duct. The results were compared against the same variables taken from experimental wind tunnel data and found to be similar with respect to the behavior of temperature and relative humidity.Therefore, it was possible to conclude that the results obtained in the simulation were close to those reported experimentally with differences from 3 to 6%. Based on the profiles and contour graphs obtained, it was also found that the best mass and energy transfer occurs when an atomizing diameter of 20 µm is used with the lowest relative humidity possible. Working with this humidity and droplet diameter, it is possible to avoid water runoff on duct walls.

Self-starting aerodynamics analysis of vertical axis wind turbine

Vertical axis wind turbine is a special type of wind-force electric generator which is capable of working in the complicated wind environment. The self-starting aerodynamics is one of the most important considerations for this kind of turbine. This article aims at providing a systematic synthesis on the self-starting aerodynamic characteristics of vertical axis wind turbine based on the numerical analysis approach. First, the physical model of vertical axis wind turbine and its parameter definitions are presented. Secondary, the interaction model between the vertical axis wind turbine and fluid is developed by using the weak coupling approach; the numerical data of this model are then compared with the wind tunnel experimental data to show its feasibility. Third, the effects of solidity and fixed pitch angle on the self-starting aerodynamic characteristics of the vertical axis wind turbine are analyzed systematically. Finally, the quantification effects of the solidity and fixed pitch angle on the self-starting performance of the turbine can be obtained. The analysis in this study will provide straightforward physical insight into the self-starting aerodynamic characteristics of vertical axis wind turbine.

Multi-dimensional interrelation theory for hypersonic wind-tunnel experimental data and its correlation algorithm

The progress on the ground to flight data correlation of aerodynamic forces and heat transfer for hypersonic vehicles is reviewed in this paper. The research approach and its limitation of the existing correlation methods are examined and discussed. In order to improve the performance of the data correlation, a new universal method so called the multi-dimensioanl interrelation theory, is proposed from which the nature of the wind-tunnel experimental data is revealed. Based on this theory, a correlation algorithm based on functional optimization is also developed to detect the inherent relations that, underly the multi-dimensional wind-tunnel experimental data. The practicability of the multi-dimensional interrelation theory, the capability of the proposed correlation algorithm and the accuracy of the obtained correlation fanctions are then examined and demonstrated respectively, with several typical test cases. These research results indicate that the multi-dimensional interrelation theory agrees well with physical phenomena, and its correlation algorithm can make use of hypersonic wind-tunnel experimental data effectively and the correlation function is capable of representing the underlying law of the experimental data in an analytical form. With the proposed theory and algorithm, one can expect to find a reliable correlation function with high accuracy for a given set of wind-tunnel experimental data. And such the progress on the ground to flight data correlation is of significant importance for developing advanced hypersonic vehicles.