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The aerodynamic pressure transients caused by high-speed subway trains entering the tunnel can usually be simulated with high accuracy using three-dimensional compressible numerical simulation methods. However, these methods often require high computer resources, complex pre-processing and post-processing processes. For practical engineering design, it is difficult to use these methods to achieve fast and simple calculation. In this paper, a train wave signature method (TWS method) proposed by previous scholars in high-speed railroad tunnels was introduced, the principles of the method were explained in detail and a generalized computational method for predicting the pressure time history was established. Additionally, an improved TWS method based on the reflected waves from trains was proposed by analyzing the reflection mechanism of pressure waves encountering trains during the trains passing through the tunnel, and the calculation results were verified by using field measurements and three-dimensional numerical simulations. The results show that the improved TWS method has better accuracy compared to the TWS method. Furthermore, this paper presents a smoothing method to enhance the optimization of the improved TWS method and extends its feasibility for pressure gradient calculation. • A simple method for pressure prediction was proposed. • The existence of train reflected waves was clarified. • The applicability of the improved method under different conditions was analyzed. • A method for evaluating the similarity of pressure time-history curve was established. • A smoothing method was provided to extend the applicability of the improved method. [ABSTRACT FROM AUTHOR]

The paper presents the numerical results of the transverse flow around an infinite square beam based on the two-fluid turbulence model for the Reynolds number Re = 21400. This problem has a periodic solution, so the non-stationary system of equations of the turbulence model was solved. For the difference approximation of the initial equations, the control volume method and the computational grid arranged in a checkerboard pattern were used. Coarse, fine, and condensed computational grids were used in the work. Their influence on the numerical results is shown. The SIMPLE procedure was applied to correct the velocity through pressure. For the numerical implementation of the equations of the two-fluid model, the two-step Peaceman-Rachford scheme was used. In the work, instantaneous and averaged results for longitudinal and transverse velocities, pressure, pressure coefficient and turbulent stresses are obtained. These results are presented in the form of profiles, as well as in the form of dependences on time and distance in the longitudinal direction. The instantaneous and averaged flow patterns are also presented. The obtained numerical results are compared with the experimental data and the results of other known turbulent models. It is shown that the two-fluid model describes this turbulent flow well. • Please cite this article as: Malikov Z.M, Madaliev M.E. The paper presents the numerical results of the transverse flow around an infinite square beam based on the "two-fluid" turbulence model for the Reynolds number Re = 21400. This problem has a periodic solution, so the non-stationary system of equations of the turbulence model was solved. • For the difference approximation of the initial equations, the control volume method and the computational grid arranged in a checkerboard pattern were used. Coarse, fine, and condensed computational grids were used in the work. Their influence on the numerical results is shown. The SIMPLE procedure was applied to correct the velocity through pressure. For the numerical implementation of the equations of the "two-fluid" model, the two-step Peaceman-Rachford scheme was used. In the work, instantaneous and averaged results for longitudinal and transverse velocities, pressure, pressure coefficient and turbulent stresses are obtained. These results are presented in the form of profiles, as well as in the form of dependences on time and distance in the longitudinal direction. The instantaneous and averaged flow patterns are also presented. • The obtained numerical results are compared with the experimental data and the results of other known turbulent models. It is shown that the "two-fluid" model describes this turbulent flow well. [ABSTRACT FROM AUTHOR]

This paper presents the results of the application of the large eddy simulation (LES) numerical method with the aim of investigating static coefficients and nonstationary flutter derivatives for a common symmetric bridge deck section. The results are compared with those of the unsteady Reynolds-averaged Navier–Stokes (URANS) study. The results of the investigated numerical simulations are validated by force and pressure measurements from wind tunnel experiments. In addition to the commonly used representation of flutter derivatives based on the integrated forces, the paper uses cross-sectional representation by tracking the contributions of nonstationary coefficients around the bridge deck section. Besides providing a better insight into the physical mechanism, the cross-sectional representation seems to be a powerful tool for identifying deficiencies in visualizing the impact of flow separations on flutter derivatives. [ABSTRACT FROM AUTHOR]

The scale effect on aerodynamics determines, to some extent, the development trend and limitation of large vertical axis wind turbines (VAWTs). Among many factors, Reynolds number is an important one affected by such effects and is therefore often used as a criterion to distinguish between small-scale and large-scale wind turbines. In this paper, a dimensionless analysis was first conducted, and the results showed that scaling the wind turbine as a whole only led to a change in Reynolds number, while other key factors remained constant. Based on such understanding, a univariate analysis was then carried out to investigate the effect of Reynolds number variation due to scaling effects on the aerodynamic performance of VAWTs. In the study, a series of high-resolution numerical simulations were performed on a simplified single-bladed VAWT model. By directly scaling the model size, the operating Reynolds number of the wind turbine was made to vary in the range of 1 × 1 0 4 to 5 × 1 0 6 at a specific solidity and reduced frequency. The analysis shows that over the range of Reynolds number investigated, as the size of the wind turbine model increases, the flow separation nearby the blade decreases, the strength of the dynamic stall vortex becomes weaker, and the power coefficient of wind energy extraction generally tends to increase, thus indicating that large-scale wind turbine is generally beneficial aerodynamically. Specifically, when VAWTs operate in a Reynolds number ranging from 5 × 1 0 4 to 5 × 1 0 5 , the power coefficient increases significantly as the size of wind turbine increases, while when operating in the range of 5 × 1 0 5 ∼ 5 × 1 0 6 , the power coefficient still tends to increase, but in a decreasing increment ratio. • This paper verified the feasibility of large-scale wind turbines. • The power coefficient of vertical axis wind turbine increases as its scale enlarges. • The power coefficient of vertical axis wind turbine is sensitive to Reynolds number variation when the scale is small. • The vertical axis wind turbines are not suitable for very low Reynolds number conditions. [ABSTRACT FROM AUTHOR]

The slipstreams induced by high-speed trains under crosswind are studied in this paper by the detached-eddy simulation (DES) method. First, the formation and development of the slipstream induced by a train (5 cars) with a 4 m nose length are analysed in detail, including at different heights and widths on the windward side (WWS) and leeward side (LWS). Then, the slipstreams with and without crosswind are compared, and the differences are presented. Finally, by considering four different nose lengths (4, 7, 9, and 12 m) under crosswind, the differences in the slipstreams induced by different nose lengths are given and analysed. The results show that on the WWS at z = 0.5 m above the top of the rail (TOR), the slipstream velocity coefficient ' U ' decreases at the position of the nose due to a velocity cancellation and stagnation effect. On the LWS, from D = 0 m–145 m, where 'D' represents the distance from the nose point, at y = 1.9 m and 2.15 m beside the centre of rail (COR), there are two peak values at the position of the nose caused by the impact of the nose point and the strong disturbance of the bogie area. At y = 2.65 m and 3.65 m, the change in U is relatively complex due to the effect of vortexes on the LWS. The effect of crosswind on the slipstream velocity is different in different regions around the train. In the region close to the train side and the bottom, the value of U on the WWS is the smallest, followed by that in the no wind case, and that on the LWS is the largest. In other regions, the values of U on the WWS and LWS are larger than that in the no wind case. For different nose lengths, on the WWS, the change in U is smoother with increasing nose length due to more stable flow around the nose. On the LWS, the change in U with increasing nose length is relatively clear only at the positions around the nose of the head car and tail car. In the regions along the middle cars, the U values for trains with different nose lengths change with the same trends and vary intertwined. • The formation and development of the slipstream velocity induced by a high-speed train under crosswind are investigated. • The effects of nose length on the slipstream are concluded by considering four different nose lengths—4, 7, 9, and 12 ​m. • On the LWS, the change of slipstream with increasing nose length is relatively clear only at the position around the nose. [ABSTRACT FROM AUTHOR]

Wind-driven rain (WDR) is one of the main moisture sources of building external facades. WDR can apparently affect structural durability and hygrothermal performance. At present, most researches with WDR distribution characteristic emphasis on an isolated building rather than combination layout. In this paper, the applicability of the WDR simulation method with the Eulerian multiphase model is verified for two tandem layout buildings under the complex WDR field. With consideration of four factors including the front interfering building height, the distance between the buildings, rainfall intensity and wind velocity, the WDR distribution on the windward facade of the rear interfered building is simulated and compared with the isolated building to explore WDR variation law at both local area and global area due to aerodynamic interference. The results indicate that the WDR distribution on the windward facade of the rear interfered building is significantly affected by the front interfering building height and the local interference factor can well reflect the aerodynamic interference of the WDR distribution on the windward facade of the rear interfered building. • Eulerian multiphase model was adopted to simulate WDR on building facades. • Validation of WDR simulation for tandem layout building models was performed. • WDR simulations of building were conducted with four factors, respectively. • WDR distribution characteristics of the global and local interference factor were obtained and discussed. • Comparison of WDR distribution under different conditions have been conducted and analyzed. [ABSTRACT FROM AUTHOR]

Abstract Multi-hazard assessment is receiving increasing attention as often commonly occurring hazards may contain a second or even a third associated hazard. Generally, multi-hazards could be joint hazards (i.e. these hazards occur at the same time), for example, a hurricane usually comes with strong wind, storm surge, and heavy rainfall. They can also be one hazard preceding another, for example, an earthquake generating a tsunami. The jointly occurring hazards in some cases can be more devastating than a single hazard. This paper will describe the assessment of two jointly occurring hazards, wind and ice formation by using an advance numerical simulation. First, multivariate (hourly wind, temperature and precipitation) simulation for many years in the Midwestern US is undertaken. By setting a condition for freezing rain, these parameters were input into a simple ice-accretion model to estimate ice-thickness. A joint hazard curve for wind and ice was then constructed and compared to the existing prescribed treatment of these two hazards in design loading guidelines, such as ASCE 7 in the United States, ISO 12494 (International Standard); and the results from our previous model. Highlights • A new model (sophisticated model) to assess joint wind and ice hazard in US is proposed. • It is built from Markov Chain and Lag-one Markov generating process. • Comparing with the previous model (simple model), ASCE 7 and ISO 12494 was made. [ABSTRACT FROM AUTHOR]

Abstract Downburst produces strong winds near the ground and causes severe damage to buildings and people. The non-stationarity of downburst is characterized by moving downdraft and pulsed jet to the ground. In practice, both characteristics have often been observed simultaneously. These characteristics significantly affect the wind loads on buildings, particularly on low-rise buildings. However, the previous experimental studies of downbursts focused on each of these characteristics separately. No study has been made of their coupled effect. Therefore, we have developed a downburst simulator, which can generate a pulsed jet and a moving downdraft either separately or simultaneously. In the present paper, we have experimentally investigated the effects of non-stationary characteristics of downbursts on the wind field and wind loads on a flat-roofed low-rise building using this downburst simulator. The results may become a useful database for validating numerical simulation models of downbursts. Highlights • Effects of movement and impinging jet on the flow field of downburst is investigated. • Non-stationary flow fields of moving and pulsed jet are experimentally reproduced. • Downburst-induced pressure on a building is measured with a downburst simulator. • Downburst-induced wind forces are different from those by turbulent boundary layers. [ABSTRACT FROM AUTHOR]

Abstract Energy consumption due to the hydraulic resistance of a duct system accounts for approximately 30–50% of the total energy consumption in air conditioning systems. It is widely believed that the installation of a deflector on duct fittings under any operating conditions can reduce resistance and thus reduce energy consumption. This paper discusses the applicability of a deflector in ventilation and air conditioning duct tees through full-scale experiments and numerical simulations. The energy dissipation field was used to characterize the resistance field. The optimal deflector position under different flow ratios and tee forms was studied, and the influence of the deflectors on the energy dissipation field was analyzed. This study shows that five types of typical deflector placements in the tee can reduce the resistance when the velocity ratio between the branch duct and the main duct is less than 0.4, with a resistance reduction ranging from 5.2% to 38.4%. The optimal deflector position is not related to the type of tee. The deflector placement can effectively reduce the energy dissipation on the lower edge of the deflector. The calculated results are verified by a full-scale experiment and by previous studies, ensuring the accuracy of the present study. Highlights • The applicability of deflector in ventilation duct is analyzed. • The energy dissipation field is used to characterize the resistance field. • The optimal deflector position under different flow ratios and tee forms is studied. [ABSTRACT FROM AUTHOR]

Focus of this paper is the comparison of three different approaches to assess the aerodynamic stability of twin-box decks: experimental free-motion tests, numerical simulations using quasi-steady theory, and numerical simulations using flutter derivatives. To this end, these approaches are used to compare three deck configurations: a nominal twin-box deck configuration, a variation that includes a different walkway porosity, and a variation that consists in a different shape of the twin-box internal corner. Even though these configurations are geometrically very similar, their aeroelastic behaviour is quite different in terms of critical flutter speed, eigenvalue/eigenvector trend and static deformation as a function of wind speed. It is shown that free-motion tests provide the reference aeroelastic solution for each configuration, but do not provide any insight on the reason of the differences; simulations based on aerodynamic flutter derivative coefficients provide accurate results and insights, but only if unsteady coefficients are measured over all the mean angles of attack of interest; quasi-steady simulations, based on static coefficients slopes, can define quite precisely the aeroelastic behaviour in the nearby of flutter, provided that torsional aeroelastic damping is measured experimentally. Each method has therefore advantages and disadvantages that are highlighted and discussed throughout the paper. • Minor geometrical details of twin-box decks can have major effects on the aeroelastic behaviour. • Three approaches to assess the aerodynamic stability of twin-box decks are studied using a test-case. • Free-motion tests provide the reference aeroelastic solution, but any insight on the reason of the differences is given. • Quasi-steady simulations can define quite precisely the behaviour near flutter, if torsional aeroelastic damping is measured. • Unsteady simulations provide good results and insights, if coefficients are measured over the necessary angles of attack. [ABSTRACT FROM AUTHOR]

Abstract Orthopter-type Vertical Axis Wind Turbines (O-VAWT) are energy capturing devices which are suitable for micro-generation in urban areas. This paper aims to study the effect of number of blades (solidity), Aspect Ratio (AR), and wind speed on the performance of a small-scale O-VAWT using experimental and numerical techniques. Wind tunnel experiments were carried out to measure the torque of two-, three, and four-bladed turbine, each at a set of different wind speeds and blade aspect ratios. Increasing solidity was achieved by either decreasing the blade aspect ratio or increasing the number of blades, both resulting in a higher peak power coefficient (C p,max) of the VAWT. The startup characteristics of the O-VAWT were also examined at different aspect ratios, and showed its capability to start-up even at low wind speeds. In addition, numerical simulations were carried out using an unsteady three-dimensional Delayed Detached Eddy Simulation (DDES) with Spalart Allmaras model. Numerical results of power coefficient were validated by comparison against available experimental data. Moreover, velocity and vorticity contours for the two-, three-, and four-bladed turbines, and pressure contours at different span-wise locations were thoroughly analyzed to link the flow field aerodynamics to relevant changes in power coefficient for different rotor solidities. Highlights • The effect of solidity on the performance of an Orthopter-type vertical axis wind turbine is experimentally investigated. • A CFD approach is employed to analyze the 3D flow structures around turbines of different solidities. • The maximum power coefficient attained by the turbine increases with solidity. • Adding more blades results in attaining the maximum power coefficient at lower tip speed ratios. [ABSTRACT FROM AUTHOR]

Abstract The windless-air-induced added mass/mass moment of inertia (m a / I a) and damping (c a) effects on mechanical parameters of a vibrating bridge deck are usually ignored in wind tunnel tests. In this paper, for three typical deck sections, computational fluid dynamics simulations are carried out to study the vertical/torsional single degree-of-freedom forced vibration under windless conditions, and further to reveal the effects of m a , I a , and c a on the modal parameters. The influences of turbulence model, computational domain size, grid resolution, and time step size are analyzed. For the addressed issue, the Reynolds stress equation model (RSM) is found to be more suitable than the shear stress transportation (SST) k - ω model. A mathematical model for aerodynamic forces at zero wind speed is presented by using the dimensionless m a , I a , and c a , and they can be extracted by combining the motions and the numerically simulated aerodynamic forces using the least squares method. The numerically simulated results for an ideal plate under small amplitudes are very close to the theoretical values, and consequently verify their accuracy. The causes for the non-zero values of flutter derivatives H 4 ∗ and A 3 ∗ at zero wind speed are revealed. In the windless air, the added damping almost linearly increases with the vibration amplitude. Five existing long-span bridge deck models are taken as examples to investigate the effects of m a , I a , and c a on structural frequencies and damping ratios. Highlights • The CFD simulation is used to comprehensively study the bridge added mass and damping in windless air. • Compared to SST k-w, RSM turbulence model is verified to be more appropriate for the addressed issue. • The simulation accuracy is validated by using a thin plate with theoretical values. • The causes for the non-zero flutter derivatives H 4 ∗ and A 3 ∗ at zero wind speed are revealed. [ABSTRACT FROM AUTHOR]

Abstract This paper aims to systematically study the wind farm optimization with the continuous selection of wind turbine placement (using Cartesian coordinates) and wind turbine hub height (restrained among a predefined range). Two case studies are performed. The first case involves an ideal two-dimensional (i.e., flat terrain) wind farm, and the other is a three-dimensional wind farm with real terrain altitudes. The schemes of simultaneously optimizing the wind farm layout and wind turbine hub heights applying the simplified and augmented PARK wake model are established for the ideal and real wind farm cases, respectively. The results show that applying different wind turbine hub heights for the wind farm layout optimization yields significant improvement: up to a 0.2 MW increase in total power and a 2% increase of the wind farm efficiency for the ideal wind farm. However, for the real wind farm the effectiveness of applying different wind turbine hub heights varies depending on the number of turbines installed. With less number of turbines installed, the impact of varying hub heights is small. However, significant improvements can be achieved as the number of turbines increases. With 39 wind turbines, the wind farm cost of energy can be reduced by $15000 per megawatt and the wind farm efficiency can increase by up to 0.2%. Given the nameplate capacity and the lifespan of wind farm project, the resulting effect on total energy production can be significant and thus improve the competitiveness of wind power exploitation. Highlights • A combined optimization of wind turbine positions and hub heights is conducted with continuous variation. • A computationally-efficient method considering wake effect over non-flat terrain is applied. • Ideal wind farm yields 0.2 MW more power and 2% increase in efficiency with maximum hub height difference of 40 m. • Real wind farm reduces cost of energy by $15000 per megawatt with maximum hub height difference of 40 m. [ABSTRACT FROM AUTHOR]

Spectral representation method (SRM) is a widely-used tool for the simulation of fluctuating wind speed fields. To circumvent the computational challenges of the Cholesky decomposition involved in the spectral representation method, a wavenumber-frequency joint power spectrum based SRM was proposed recently. The method can be used for the efficient simulation of homogeneous and nonhomogeneous wind fields in one spatial dimension. In this paper, the wavenumber-frequency joint power spectrum based SRM is extended to simulate nonhomogeneous wind fields in two spatial dimensions. To this end, a closed-form evolutionary wavenumber-frequency joint spectrum is first derived, and integrated readily with the updated spectral representation method. To enhance the computational efficiency with respect to the threefold summation over the one-dimensional frequency domain and the two-dimensional wavenumber domain, two uneven-discretization strategies are proposed. They are associated with a tensor-product scheme and an acceptance-rejection criterion. For illustrative purposes, a numerical example of simulating a fluctuating wind speed field in two spatial dimensions associated with the rotating blades of a 5-MW wind turbine is considered. It is shown that both the proposed methods have good accuracy and efficiency, and the rejection-acceptance criterion based uneven discretization method is preferred to practical applications. [ABSTRACT FROM AUTHOR]

A consistent mesh refinement study, relating to the prediction of aerodynamic forces about an experimentally validated reference train geometry, is presented in this paper. The flow about a high-speed train has a multi-scale character which poses challenges for the design of computationally effective meshes. The purpose of this study is to assist in the development of guidelines for effective drag prediction of high-speed trains using numerical simulation. These guidelines should assist CFD practitioners by identifying the regions of the mesh that are critical for the correct estimation of drag as well as providing information on appropriate mesh characteristics, such as volume and surface element length scales. Numerical assessments are validated against an experimental drag measurement program and the extent to which RANS is sufficiently predictive for industrial design is discussed. The results obtained in the work suggest that the mesh about the train nose is essential for the proper assessment of the aerodynamic drag acting on the vehicle. [ABSTRACT FROM AUTHOR]

In recent years, governmental legislation and consumer demands are driving the development of more energy efficient road vehicles. One of the aspects considered when increasing efficiency is the aerodynamic performance of the vehicle. The focus of this paper is on wake effects for a vehicle with tapered rear extensions in side wind conditions. For this purpose, numerical simulations are analysed using post-processing techniques such as Proper Orthogonal Decomposition (POD) and Two-point correlation. The extensions protrude 150 mm from the perimeter of the base and are investigated in two configurations: with a smooth taper and with an added kick. The kick realigns the perimeter base flow to the vehicle's driving direction. As the oncoming flow angularity is increased, drag increases for the investigated angles. The smooth extensions provide the greatest drag improvement at 0° yaw while the extensions with a kick yield additional benefits at yaw, effectively reducing the vehicles drag sensitivity to side wind. A large scale twisting motion is present at yaw for the baseline and smooth extensions configurations which is reduced when adding a kick to the extension. [ABSTRACT FROM AUTHOR]

Air Cooled Heat Exchangers (ACHE)s are used for heat rejection in Liquefied Natural Gas (LNG) plants. Their thermal performance decreases under elevated ambient temperatures and windy conditions as exhaust air recirculates back into the ACHE units causing Hot Air Recirculation (HAR). This paper investigates the effect of various incident wind speed and directions on HAR. Understanding HAR helps to avoid undesirable work conditions. Three dimensional Computational Fluid Dynamics (CFD) studies were utilized to simulate the airflow around a full scale LNG plant. The simulations clearly captured HAR between parallel ACHE banks (Cross-HAR) and within a single ACHE unit (Self-HAR). Wind tunnel smoke visualization was used to qualitatively assess the CFD model. The impact of removing downstream ACHE protection screens on the HAR was computationally investigated showing an exhaust air temperature reduction of 5 °C. Different HAR mitigation methods were proposed using different configurations of side winglets. Horizontal winglets were shown to be more effective than vertical winglets as they decreased intake and exhaust air temperatures by about 5 °C and 8 °C respectively and increased exhaust air velocity by 1.2 m/s. This work provides a thorough understanding of HAR around ACHEs and proposes mitigation methods to reduce its effects on plant production. [ABSTRACT FROM AUTHOR]

The Dual Vertical Axis Wind Turbine (D-VAWT) is an innovative turbine proposed to improve the aerodynamic efficiency of small Vertical Axis Wind Turbines (VAWTs). The D-VAWT has two axes, allowing the blades to move in an oval shaped path to extend the region of maximum power generation of a typical VAWT. The aim of this paper is to perform a parametric study on the D-VAWT variables as a previous investigation aimed only to prove its concept. The current study is performed through 2D unsteady simulations using computational fluid dynamics. Advanced moving mesh techniques are used to prescribe the motion of the blades, combining the sliding and dynamic mesh techniques as well as re-meshing for multi-blade simulations. A turbine with a single blade is first investigated to determine the relation between the tip speed ratio (TSR) and power coefficient. The investigation continues with the study of the turbine sensitivity to different incoming wind angles, turbine axes spacing, number of blades, airfoil profile and blade mounting point. It was found that the D-VAWT has a low sensitivity to TSR, allowing the turbine to operate efficiently for a wide range of TSRs. [ABSTRACT FROM AUTHOR]

Wind flow in urban areas is strongly affected by the urban geometry. In the last decades most of the geometries used to reproduce urban areas, both in wind-tunnel (WT) tests and Computational Fluid Dynamics (CFD) simulations, were simplified compared to reality in order to limit experimental effort and computational costs. However, it is unclear to which extent these geometrical simplifications can affect the reliability of the numerical and experimental results. The goal of this paper is to quantify the deviations caused by geometrical simplifications. The case under study is the district of Livorno city (Italy), called “Quartiere La Venezia”. The 3D steady Reynolds-averaged Navier-Stokes (RANS) simulations are solved, first for a single block of the district, then for the whole district. The CFD simulations are validated with WT tests at scale 1:300. Comparisons are made of mean wind velocity profiles between WT tests and CFD simulations, and the agreement is quantified using four validation metrics ( FB , NMSE , R and FAC1.3 ). The results show that the most detailed geometry provides improved performance, especially for wind direction α = 240° (22% difference in terms of FAC1.3 ). [ABSTRACT FROM AUTHOR]

Through numerical simulation investigation, a twin-winglet system is used as an aerodynamic affiliated facility to increase the flutter stability of a box-girder suspension bridge. Its flutter suppression effect can be greatly enhanced when the winglet rotation is feedback-controlled in real-time, depending on the deck motion. Since the control algorithm was previously examined by a self-consistent mathematical model, the control process is realized through computational fluid dynamics simulation in this paper to check the applicability of the device. Moreover, the non-interference assumption used in the control algorithm is analyzed carefully, with several cases of different distance between a deck and winglets. The results verify the effectiveness and robustness of the control algorithm, and also provide a quantitative conclusion about the influence effect, which can be used in the design of a twin-winglet system. In addition, the advantages of this twin-winglet facility are revealed by investigations of the flutter control mechanism. [ABSTRACT FROM AUTHOR]

This paper reports the first aero-elastic test conducted under a scaled downburst wind field at the WindEEE dome facility at the University of Western Ontario, Canada. The main purpose of the test is to assess the dynamic response of a multi-span transmission line. The study starts by providing a characterization of the downburst wind field produced in WindEEE including a comparison with results of previously conducted numerical simulations. A number of test configurations, involving different locations of the downburst relative to the line, is considered. A decomposition approach is developed to separate between the resonant and the background components of the response. The results are presented in the form of a dynamic magnification factor that relates the peak response including the dynamic effect to the maximum quasi-static response. The test results show that the resonance contribution ranges between 5% and 10% of the peak response for the tower. They also show that the dynamic response of the conductors can reach up to 30% and 12% of the peak response at low and high downburst speeds, respectively. [ABSTRACT FROM AUTHOR]

Horizontal axis wind turbines (HAWTs) are being widely used for green energy generation. Hence, aerodynamic performance enhancement of these machines is a key point for their overall performances. This paper numerically investigates effects of a passive flow control method on aerodynamic performance of a HAWT by splitting its blades along the span. First, 2-D simulations are conducted on S809 airfoil in order to study effects of split width and Reynolds. Later, original blade (without split) and two split blades are simulated, and effects of split location on power coefficient, low speed shaft torque and flow patterns are investigated at different tip speed ratios. The results reveal that for an attached flow, torque value are sensitively dependent upon split location and injected flow angle. This is because injected flow triggers an early separation and reduces aerodynamic performance. For a partially separated case, results show that split location may impose either positive or negative effects on torque generation. Finally, for highly separated/stall situations, blade aerodynamic performance becomes less sensitive to the location of split. Also, torque per unit span analysis shows that as tip speed ratio decreases the split part of the blade generates a higher share of the total power. [ABSTRACT FROM AUTHOR]

Due to the increasing windage area of container ships, wind loads are playing a more important role in navigating the ship at open sea and especially through harbor areas. This paper presents 3D steady RANS CFD simulations of wind loads on a container ship, validation with wind-tunnel measurements and an analysis of the impact of geometrical simplifications. For the validation, CFD simulations are performed in a narrow computational domain resembling the cross-section of the wind tunnel. Blockage effects caused by the domain boundaries are studied by comparing CFD results in the wind tunnel domain and a larger domain. The average absolute difference in numerically simulated and measured total wind load on the ship ranges from 37.9% for a simple box-shaped representation of the ship to only 5.9% for the most detailed model. Modeling the spaces in-between containers on the deck shows a 10.4% average decrease in total wind load on the ship. Modeling a more slender ship hull while keeping the projected front and side area of the ship similar, yields an average decrease in total wind load of 5.9%. Blockage correction following the approach of the Engineering Sciences Date Unit underestimates the maximum lateral wind load up to 17.5%. [ABSTRACT FROM AUTHOR]

This paper presents a study on the generation mechanism of wind-induced vibration of suspenders of suspension bridges in the wake of bridge towers. The computational fluid dynamics (CFD) simulation is carried out to characterize the wind flow in the wake of bridge towers at different wind directions. The time series of force coefficients of suspenders are determined which clearly show the dominant frequency component associated with the vortex-shedding from the towers. A wind tunnel test program is also implemented to measure wind-induced vibration of suspenders at different wind speeds and directions. Results show that vortex-shedding from bridge towers has a strong influence on the aerodynamic forces of suspenders at a wide range of wind directions. The suspenders vibrate in both longitudinal and transverse directions. The large-amplitude vibration of suspenders is observed when the vortex-shedding frequency from the towers coincides with the frequency of the suspenders. [ABSTRACT FROM AUTHOR]

In this paper, three-dimensional wind flow patterns over a star dune under a longitudinal (W, 270°) and transverse airflow (ENE, 70°) were examined using computational fluid dynamics (CFD) simulations. New surveying techniques of airborne LiDAR and DGPS allow for establishment of the realistic digital model of the star dune. Simulation results were then validated by field measurement using three-dimensional (3D) ultrasonic anemometers combined with arrays of HOBO cup anemometers. Results show that incident flow conditions (longitudinal or transverse airflow) controlled by the angle between incident flow and dune crestline exert great impact on wind flow patterns over the star dune. In periods of longitudinal airflow, a marked feature of wind flow pattern was flow deflection. Wind erosion occurs on both sides of WNW and S sides during W wind and its main effect was to prolong the star dune longitudinally. However, leeside flow separation and reversal were obvious under transverse airflow. The main effect of ENE wind was to promote the upward growth of the star dune. The CFD simulation of 3D wind flows over complex dune system presents great potential for geomorphological research, enabling new insights into complex dune geomorphology and dynamics. [ABSTRACT FROM AUTHOR]

This paper addresses the interference effects of high-rise building caused by either an upstream or downstream adjacent building. During the study, aeroelastic vibration tests and high-frequency force balance tests are conducted for two identical square prism models of buildings with an aspect ratio of 8 in a turbulent boundary layer flow. Later, critical locations for interfering buildings are identified by examining interfered force spectral characteristics and various patterns of response trajectories. Finally, an idealized 2D numerical simulation of CFD is tried for the simulations of some critical cases. Although the absolute values from CFD results cannot be perfectly compared with the experimental results, the simulated vorticity movement generated from the existence of both buildings provides an intuitive way for the enhancement of the downstream interference mechanism. [ABSTRACT FROM AUTHOR]

Wind-driven rain (WDR) has significantly unfavorable effects on the performance and durability of the enclosure systems of low-rise buildings. Therefore, a field measurement facility for the WDR on a gable-roofed low-rise building with overhang has been established and implemented in a typhoon-prone region of China. This paper presents and analyzes the field measurements of the WDR on the facades of the full-scale building during a typhoon in 2018. In addition, numerical simulations of the WDR on the instrumented building are performed using the Eulerian Multiphase model and validated based on the field measured WDR results. Then, a detailed parametric study of numerical simulation is carried out to examine the influences of roof overhang, wind speed, wind direction and horizontal rainfall intensity on the WDR amounts on the building facades. Next, the WDR on the low-rise building during a super typhoon are numerically reproduced and investigated. The measurement techniques and numerical simulation methodologies, analyzed results and conclusions presented in this paper would be useful to understand and evaluate the WDR on building facades so as to improve the serviceability of low-rise building envelopes. • Establish measurement facility of wind driven rain (WDR) on a low-rise building. • Analyze measurements of WDR on the full-scale building during a typhoon. • Verify the numerical simulation results based on the field measurements. • Examine effects of key parameters on WDR by a detailed parametric study. • Further investigate WDR on the building under extreme weather condition. [ABSTRACT FROM AUTHOR]

In this paper, the DDES (Delayed Detached Eddy Simulation) is applied to study the spanwise suction control effect on wind-induced effect of a static bridge deck. Isolated suction holes are arranged on the lower surface of the test model in spanwise direction, and based on previous studies of similar bluff body, a proper distance of spanwise suction was chosen to trigger or amplify the most unstable secondary instability (i.e. Mode A) in wake. The simulation results show that the suction arranged close to the wake has the best control effect on reducing the fluctuating aerodynamic forces. Due to the mean-velocity modification by isolated spanwise suction, the virtual aerodynamic shape modification is generated, which could act as spanwise perturbation to suppress spanwise vortexes. The results indicate that the spanwise suction could trigger or amplify the Mode A instability, and hence lead to the dislocation of the spanwsie vortex or even completely suppress the spanwise vortex. In addition, the spanwise suction control can surpress spanwise vortex shedding in a wide Re range. [ABSTRACT FROM AUTHOR]

In this paper, the flow around a rectangular cylinder with aspect ratio 5:1 is studied at three attack angles by means of both LES and URANS simulations. Despite its geometric simplicity, such a rectangular shape is characterized by many aerodynamic phenomena typical of reattached flows around bluff bodies and has been recently widely studied as a prototype of flows encountered around shapes of technical interest like, for example, bridge deck sections. The present study is aimed at providing insight in the modifications occurring in the flow at small incidence angles, by comparing the accuracy of the two aforementioned simulation strategies in reproducing them. Some recurring biases observed in URANS simulations are illustrated and their origin discussed. Results are presented in terms of flow bulk parameters and pressure distributions and systematic comparison with available experimental data is provided. Finally, the effects of small incidence angles on along span flow correlations are investigated and Covariance Proper Transformation is used in order to further characterize the flow dynamic behavior. [ABSTRACT FROM AUTHOR]

Multi-source fires burning is a fundamental process involved with the development from group fire to regional fire. However, there is great difference for the burning characteristics between the multiple fire sources and one single fire source, which has not been paid much attention in the previous study. In this paper, small-scale tests and numerical simulations have been conducted to investigate the fire characteristics at the case of simultaneous occurrence of two corridor fire sources. Both the experiment and simulation results indicated that obvious tilted flame and the phenomenon of moving closer to each other had been observed between the two fire sources. The simulation results predicted the velocity distribution in some sections always subjected to Gaussian profile for subsection. Besides, in the experiments, with the increase of fire size at the corner, the time for the peak ceiling temperature between two fires arrived earlier, and the distribution of vertical temperature was in a good agreement with Gaussian profile under different sizes of middle fires. [ABSTRACT FROM AUTHOR]

The practice of reproducing wind tunnel tests by means of CFD numerical simulations, which is known as numerical wind tunnel (NWT), is becoming quite common in many research fields of wind engineering. Wind tunnel tests can provide the indispensable validation data needed for CFD numerical simulations; at the same time, CFD can be considered a complementary support for wind tunnel tests in order to obtain a more comprehensive description of the flow field. In the present paper, NWT technique is applied to study the flow around and inside a multi-stage vertical-axis wind turbine (VAWT) surrounded by stator vanes. At first, the flow field has been studied in the wind tunnel by means of experimental tests. Then the experimental results have been used to validate a CFD model. The numerical model has finally been used to study and describe how the results obtained by means of the physical model can be extended to more general conditions. [ABSTRACT FROM AUTHOR]

The increasing human activity in forested regions requires a better understanding of the wind conditions. This paper aims to improve the wind simulation in forested regions of complex terrain, and thereby to investigate the effect of forest on wind characteristics. Considering the complexity of the surface, simulations were carried out covering different parameterization schemes sets using Weather Research and Forecasting model (WRF). The results indicate that Noah-MP scheme and YSU scheme are recommended for a mesoscale wind simulation in forested regions of complex terrain. Moreover, due to the complexities of land surface with seasonally-varied roughness length (RL) and leaf area index (LAI), localized LAIs and RLs would significantly improve wind field simulation. Comparisons demonstrated that the modified RLs, which can reshape the wind speed distribution, have greater impact than LAI on the wind field simulation in the near-surface level. The findings can be further exploited in the wind damage assessment for the infrastructures, as well as wind power assessment in forested regions. • WRF simulation is conducted to study surface wind field in forested regions. • Roughness length and LAI are modified to better represent forest canopy. • Combination of Noah-MP, YSU scheme and modified roughness and LAI produces optimum. [ABSTRACT FROM AUTHOR]

Unbalanced snow distribution is one of the main reasons for the collapse of multi-span arch roofs due to excessive snow loads in the valley and leeward areas. The formation of uneven snowdrifts is closely related to the shape of the building as it seriously affects the turbulent structure and snow drifting process. This study aims to investigate the snowdrift characteristics of multi-span arch roofs based on a multiphase snowdrift approach. Firstly, the prediction accuracy of the flow field is tested to select a reasonable turbulence model. Then, the reliability of this multiphase approach is validated by comparing the results with a wind tunnel experiment of snowdrifts on a multi-span arch roof. The result preliminarily proves that this approach could well reproduce the unbalanced snowdrift on each span roof and at the trough. The snowdrift characteristics of multi-span arch roofs are investigated under different rise/span ratio and span number conditions based on the validated approach. The formation mechanism and characteristics of snowdrifts on different roofs are clarified by analysis. Finally, several typical distribution patterns are derived based on the statistical analysis of results. It is found that the middle-span roof bears a larger snow load than the roofs at both ends. • The paper proposes a multiphase approach that could accurately predict the snowdrifts on arch roofs. • The multiphase approach could well reproduce the snow drifting process and the sliding effect at roof edge. • Two kinds of unbalanced triangular snow loads are formed on the single-span arch roof according to the rise/span ratio. • The stacking snow load at the trough of the multi-span roof is about twice the peak snow load of the single-span roof. • The middle-span arch roof bears a larger snow load than the roofs at both ends of the multi-span building. [ABSTRACT FROM AUTHOR]