Wind Tunnel Test Results Research Articles

Dot-array porous medium model for windscreen and its simulation accuracy analysis

Porous medium models have long been prevalent numerical computation tools. Although they exhibit swift computational speed, their accuracy in simulating windscreen perforation structures is challenged. This paper introduces the innovative dot-array porous medium (DAPM) model, which accurately portrays the perforation structure and material characteristics of a windscreen by establishing virtual holes on the porous medium. Not only does it simplify modeling by eliminating complex perforation processes, but it also adeptly simulates the flow behavior of the windscreen. The comprehensive comparison between the DAPM model and the physical mesh model, traditional porous medium model, as well as wind tunnel test results, demonstrates that the DAPM model not only possesses rapid computational speed but also delivers outstanding precision in results. In terms of velocity distribution, vortex distribution, and flow intensity in the flow field, the model indicates a high level of accuracy, clearly exceeding that of the porous medium model. Moreover, the DAPM model showcases high versatility and adjustability in practical applications. By adjusting dimension parameters, it demonstrates the capability to precisely simulate any windscreen with holes arranged in a matrix pattern. This research provides an efficient and reliable tool for the numerical simulation of windscreens, with broad application prospects.

The mitigation of airframe noise using a Krueger flap as a leading-edge device in a high-lift configuration

High-lift device is a potent airframe noise contributor. The conventional slat, commonly used in a high-lift device, is known as one of the dominant noise sources. Here, we combine an experimental and a numerical approach to investigate the noise generation of a conventional slat and two Krueger flaps as leading-edge devices in a high-lift configuration. To reduce the computational cost, a short span of the entire high-lift device is selected as the focusing region for scale-resolving and acoustic computations using Improved Delayed Detached Eddy Simulation (IDDES) coupled with the Ffowcs-Williams and Hawkings (FWH) analogy. Simulation results show that turbulent cross flows induce slightly lower-level noise spectra at frequencies less than 300 Hz when the two spanwise sides of the FWH permeable integral surface are closed. Wind-tunnel test results show that the reference and optimal Krueger configurations effectively attenuate the dominant tone of the conventional slat by 4 and 6 dB, respectively. Besides, the optimal configuration is very effective in noise reduction in a wide frequency range. However, the reference Krueger configuration increases the noise level by 0 − 4 dB at frequencies exceeding 5, 500 Hz. Overall, the optimal Krueger configuration is a good choice for high-lift device noise mitigation.

A new controllable weak recycling inflow turbulence generator for evaluating wind effects on building in LES

The weak recycling method, known as the “rescaling-recycling” method, has been extended to simulate micro-scale turbulent atmospheric boundary layers (ABL) by employing staggered blocks in the developing section, replicating physical ABL wind tunnel setups. However, this method faces challenges, such as the need to re-evaluate the sizes and configurations of roughness elements when addressing different objective structures, computational domain sizes, or ground exposures. To address these issues, we propose a controllable weak recycling (CWR) method for generating turbulent ABL flows over rough surfaces in large eddy simulation (LES). This method can directly produce a turbulent boundary layer with arbitrary target characteristics in a single simulation, significantly enhancing generation efficiency and reducing computational resource consumption. Our refinement method incorporates a feedback proportional control algorithm into the “rescaling” procedure to minimize errors between simulated and targeted turbulence intensities. Besides, an existing drag model is utilized in the near-ground region to maintain horizontal homogeneous ABL flows over rough surfaces. The proposed CWR method is validated by simulating three turbulent ABL flows over various rough terrains using LES. Results confirm that the generated inflow turbulence adheres to prescribed mean velocities and turbulence intensities, demonstrating consistent self-sustainability along the flow direction. Furthermore, the generated wind spectra closely align with the anisotropic von-Kármán spectrum. When applying the extracted wind time histories at the main domain’s inlet, we find that the mean and fluctuating wind pressures on a high-rise building closely match specified wind tunnel test results.

Aerodynamic Analysis of Fixed-Wing Unmanned Aerial Vehicles Moving in Swarm

This paper presents a close-formation flight of two unmanned aerial vehicles (UAVs) and the aim of the study is to improve the understanding of the vortex effects between fixed-wing UAVs in a swarm using computational fluid dynamics (CFD) tools. To validate the numerical method, results of a variable-density wind tunnel test from the literature were used. This numerical CFD analysis was used to determine the lift coefficient (CL) and the drag coefficient (CD) values for a single UAV at various angles of attack. When examining the aerodynamic impact areas behind the UAV, the longitudinal distance between the two UAVs is not particularly effective for close flight. Therefore, CFD analyses were carried out on the two UAVs for both vertical and lateral distances. The optimum position for close-formation flight was identified using CL/CD ratios. The results of the analysis indicate that the most effective flights, across all lateral positions, occur when the two UAVs are vertically at the same height. In terms of aerodynamic efficiency, the most effective points for close-formation flight for wingspan b are at lateral distances of 0.875 b and 1 b. At these positions, flight efficiency can be increased by approximately 11.5%.

Assessment of computational fluid dynamic as a design tool for estimation of wind loads on unconventional skyscrapers in urban environment

AbstractComputational fluid dynamic (CFD) has not been widely accepted as a design tool in current wind‐resistant structural design practices due to its contentious accuracy. To promote the application of CFD in wind‐resistant structural design, the accuracy of CFD should be comprehensively validated. However, most previous validation studies were focused on isolated generic or regular‐shaped buildings. This paper evaluates the accuracy of large eddy simulation (LES) in predicting the wind loads on a 600‐m‐high supertall building with a complex appearance in a realistic urban area against wind tunnel test results. The aerodynamic characteristics obtained from the LES and the wind tunnel test are compared and analyzed in detail, including wind pressure and force coefficients, wind force spectra, base moments, and correlations of the wind loads. This study aims to assess the performance and potential as well as the strengths and weaknesses of CFD in predicting wind loads on high‐rise buildings in an urban environment and promote its application to the wind‐resistant design of skyscrapers.

Inflow turbulence generator for large eddy simulation based on a novel block‐vorticity vortex method: Application on a tall building wind effect

AbstractAccurately simulating turbulent wind fields is a significant challenge in wind engineering. This study proposes a novel block‐vorticity method aimed at overcoming the limitations of traditional turbulence generation methods. By superimposing a blocked vortex field at the inlet boundary of large eddy simulation (LES), the proposed method enables the generation of highly precise and anisotropic turbulent wind fields. To validate the effectiveness of the proposed method, the study investigates wind pressures on a high‐rise building structure and performs a comparative analysis with LES narrowband synthesis random flow generator (NSRFG), traditional LES, and SST k‐ω turbulence inlet models. The results demonstrate that the proposed method can effectively simulate turbulence characteristics of atmospheric boundary layer flow, including vortex structure and stochastic fluctuating wind field. Compared to traditional methods, the wind field characteristics of turbulence intensity, instantaneous vorticity, and turbulence self‐equilibrium had obvious advantages over traditional methods. Moreover, the LES vortex method is more accurate in simulating the mean wind pressure and fluctuating wind pressure of the high‐rise building compared to traditional models and is closer to the wind tunnel test results. The proposed method provides an effective approach for generating turbulent wind fields with anisotropic characteristics and can be used to predict the wind‐induced response of civil engineering structures.

Research on Aerodynamic Performance Optimization and Drag Reduction of mid-sized SUV on CFD

With the increase of vehicle ownership, the environment and energy issues are highlighted, and reducing vehicle wind resistance has become the key to improving fuel economy. Based on the theory of fluid mechanics and project development experience, this paper develops a medium-sized SUV model for wind resistance reduction. Through the simulation modeling of the vehicle's external flow field, the proportion model wind tunnel test and the optimization scheme research of the exterior shape, the bottom of the vehicle and the engine room, the wind resistance is significantly reduced. Combined with the wind tunnel test results, the actual contribution of each local optimization scheme is verified, and the EGO algorithm is used for further optimization to further reduce the wind resistance coefficient. This paper summarizes the key parts and regularity experience of the aerodynamic drag reduction of the medium-sized SUV model, providing guidance for the development of high-precision vehicle performance in the future. The research methods and results of this paper are of great significance for improving the aerodynamic performance and fuel economy of vehicles.

Typhoon- and temperature-induced responses of a cable-stayed bridge

Long-span bridges are subjected to wind and temperature actions. Wind action is generally the governing load of long-span bridges in design, while temperature action is also significant. Accurate separation of typhoon- and temperature-induced responses is thus necessary for in-depth investigation of their effects and comprehensive evaluation of structural performance. This paper separates the temperature- and typhoon-induced responses of the Qingzhou Bridge by using a unified global analysis approach. The field-monitored meteorological data and structural responses collected from the structural health monitoring system installed on the bridge are analyzed in detail, with emphasis on the comparison of those during typhoon Higos (Signal No. 9) and a typical sunny day after the typhoon. Results show that the quasi-static variation of displacement and stress responses are higher on a typical sunny day than those during the typhoon period, which is out of intuition. Through the unified analysis, the temperature-induced responses are calculated, and the typhoon-induced responses can be separated. The temperature- and typhoon-induced longitudinal displacement, mid-span deflection, and stress of the girder are compared. The temperature-induced response accounts for a large part of the total quasi-static recording either on a typical sunny day or during the typhoon period, whereas typhoon caused significant dynamic responses. The typhoon-induced quasi-static and dynamic responses are also in good agreement with the wind tunnel test results. This case study demonstrates the effectiveness of the unified global analysis in separating the temperature effect.

Theoretical and experimental study of the spanwise effect of turbulence on the aerodynamic lift on a wing with different aspect ratios

In this paper, a combined theoretical and experimental study is carried out to investigate the spanwise effect of turbulence on the aerodynamic lift on a wing with different aspect ratios. The ratio of the mean square variance of the aerodynamic lift calculated by the commonly used strip theory and the two-wavenumber buffeting theory is analyzed comprehensively for the wings with different aspect ratios in turbulence with various integral scales. To validate the theoretical analysis and achieve a deeper understanding of the spanwise effects of turbulence, wind tunnel experiments are performed on National Advisory Committee for Aeronautics 0015 airfoils in grid-generated turbulent flows with different integral scales. The results demonstrate that it is essential to use the two-wavenumber buffeting theory to account for the spanwise effect of turbulence when calculating the aerodynamic lifts on wings with small aspect ratios, especially when in small-scale turbulence. The deviations between the equivalent two-wavenumber coherence function and the spanwise effect influence function at low reduced streamwise wavenumbers are the underlying causes for spanwise effects of turbulence. To achieve reliable wind tunnel testing results, appropriate simulations of the ratio of the turbulence integral scale to the chord are very important in the measurements of aerodynamic lifts on finite-span wing sections, especially for those with small aspect ratios.

Simulation and prediction of vortex-induced vibration of a long suspension bridge using SHM-based digital twin technology

Although wind tunnel tests have already become a design basis for improving the stability of long-span bridges under the action of wind loads, vortex-induced vibration (VIV) events of in-service long-span bridges have still been frequently reported in recent years. The reasons behind this could be attributed to the limitations and uncertainties involved in wind tunnel tests as well as the changes and degradations of in-service bridges. In consideration that most long-span bridges have now been equipped with long-term structural health monitoring (SHM) systems and that digital twins could provide a new solution for simulating and predicting the reality, this study aims at developing a digital twin for VIV of a long suspension bridge to simulate and predict its VIV. The design document-based finite element (FE) model of the bridge is first updated using the measured dynamic characteristics. The numerical model for VIV of the bridge is then established using the vortex-induced force (VIF) model established based on wind tunnel test results. The numerical model together with the VIF model are finally updated against the measured vortex-induced responses (VIR) to produce a digital twin for VIV of the bridge. The relationships between the parameters in the VIF model and wind characteristics are further investigated to enable the digital twin to predict future VIV events. The accuracy of the digital twin for predicting the future VIV and the influence of the VIF parameters obtained from wind tunnel tests on the prediction accuracy both are confirmed through comparisons between the predicted and measured results.

Study on the Wind-induced Interference Effect of a Large-span Roof Structure Building Group

The wind-induced interference effects existing during the construction of a building group were studied in the context of the Zhangjiakou Olympic Sports Center project. Based on CFD numerical simulations, 120 and 96 different working conditions during construction of a swimming pool and speed skating hall were simulated and analyzed respectively, and the numerical simulation results were found to be in high agreement with the wind tunnel test results, which verified the accuracy and feasibility of the numerical simulation. By comparing the wind-induced interference effects of the surrounding buildings on the swimming pool and the speed skating hall during different construction periods, it was found that the swimming pool was more affected by the interference of the surrounding buildings than the speed skating hall, and the wall area was more affected by the interference than the roof area. The wind-induced response of the swimming pool structure during different construction periods was analyzed, and it was found that the interference effect under some working conditions had a greater impact on the structural stress, and it was suggested that the wind interference effect brought about by the construction of the building should not be ignored in such projects.

Vortex-Induced Force Identification of a Long-Span Bridge Based on Field Measurement Data

Vortex-induced force (VIF) identification and modelling of a long-span bridge are often conducted in terms of aeroelastic sectional model tests in wind tunnels. However, there are uncertainties inherent in wind tunnel model tests so that vortex-induced vibration (VIV) still occurs in real long-span bridges designed according to wind tunnel test results. This paper presents a framework for VIF identification of a long-span bridge based on field-measured wind and acceleration data. The framework is composed of the four steps: (1) decompose field-measured acceleration response time histories using variational mode decomposition (VMD) method; (2) obtain velocity and displacement response time histories using frequency domain integration (FDI) method; (3) establish and update the finite element model and identify the generalized VIF time histories of the bridge; and (4) identify the parameters in the polynomial VIF models and decide the most suitable VIF model. The proposed framework is finally applied to a real suspension bridge with a recent VIV event. The results show that the proposed framework can accurately identify the generalized VIF acting on the bridge from the field-measured acceleration and wind data, and the derived most suitable VIF model can produce almost the same vortex-induced response (VIR) as the measured ones.

Comparison of Aerodynamics and Flight Performance of Fixed Wing Solar Powered Unmanned Aerial Vehicle When Separate Lift and Thrust Vertical Take-Off and Landing System is Installed

The objective of this research paper is to analyze the effects of installing a separate Lift and Thrust vertical takeoff system for fixed-wing solar powered UAVs in terms of flight performance changes. This research article uses a prototype aircraft in this study, which is a fixed-wing aircraft powered by an electrical system and equipped with a solar system. There are 2 types of designs, namely the type with installation and without installation of the Vertical Take-Off and Landing system which the vertical take-off and landing aircraft compared to the normal configuration will weigh 42.48% more and have a zero-lift drag coefficient of 67.1% more. The initial step involves creating an aircraft model in the XFLR5 software to assess the lift and drag coefficients and compare them with the wind tunnel test results. Subsequently, the software analysis findings are used to evaluate the flight performance of both aircraft configuration, as well as to identify the performance changes that occur when the VTOL system is installed. The outcomes align with expectations, installing a VTOL system leads to a significant reduce in flight performance, In particular, the Endurance and maximum range of vertical take-off aircraft are only 41.55% and 43.43% of normal aircraft and for solar-powered systems. The vertical takeoff has the Endurance and range is 31.46% and 32.06% of normal aircraft equipped with solar systems. which can be distinctly contrasted with the performance of aircraft in various aspects. However, these compromises are made in exchange for the capability to take off and land vertically.

Ice-phobic properties of MoS2-loaded rice straw biogas residue biochar-based photothermal and anti-corrosion coating with low oxygen to carbon ratio

Icing of wind turbine blades will seriously hinder the development of the wind power industry, and the use of biomass resources to solve the icing problem is conducive to promoting the synergistic development of biomass and wind energy. In this study, ice-phobic coatings with photothermal and anti-corrosion properties were prepared by surface modification pyrolysis and hydrothermal reaction with rice straw biogas residue as raw material. The erosion of KOH and the surface modification of MoS2 produced a rough structure of the material, and the high-temperature pyrolysis and hydrothermal reaction promoted the dehydrogenation and decarboxylation reactions, which reduced the number of oxygen-containing functional groups and decreased the surface energy of the material. The ice-phobic coating has superhydrophobic properties with a contact angle of 158.32°. Due to the small surface area in contact with water, the coating was able to significantly reduce the icing adhesion strength to 53.23 kPa. The icing wind tunnel test results showed that the icing area and mass were reduced by 10.54% and 30.08%, respectively, when the wind speed was 10 m s−1 and the temperature was − 10 °C. Photothermal performance tests showed that the MoS2-loaded material had light absorption properties, and the coating could rapidly warm up to 58.3 ℃ under xenon lamp irradiation with photothermal cycle stability. The loading of MoS2 acts as a physical barrier, reducing the contact of corrosive media with the substrate, thus improving the anti-corrosion of the coating. This study has practical application value and significance for the development of the anti-icing field under complex environmental conditions.Graphical

On the anti-rolling performance of a train using a vortex generator array

Vortex generators (VGs) have shown the potential to mitigate the train's operational instability issues caused by strong wind. Numerical simulations are used to predict the flow structures around a train with VGs of different heights. The improved delayed detached eddy simulation (IDDES) hybrid modeling method is adopted to predict the trailing vortices on the leeward field. The numerical method is validated by reproducing wind tunnel test results. The study results reveal that VGs are capable of reducing the rolling moment coefficient around the leeward rail of a train by about 5% ∼ 15% while keeping the drag of the train still lower than its operational drag without crosswind. The control mechanism lies on that the streamwise vortices generated by VGs are attracted to the large-scale trailing vortices, resulting in the pressure on the leeward wall rising. The differences in the domain frequencies between VGs and Baseline cases in POD modes indicate that the VGs changed the periodicity and symmetry of the vorticity fluctuation. This study provides a new method to improve the safety of trains under crosswinds.

Experimental studies of airliner aerodynamic characteristics at overcritical angles of attack

PurposeThe main purpose of this study was to determine the basic aerodynamic characteristics of the airliner Tu-154M at the wide range of the overcritical angles of attack and sideslip angles, i.e. α = −900° ÷ 900° and β = −900° ÷ 900°.Design/methodology/approachWind tunnel tests of the Tu-154M aircraft model at the scale 1:20 were performed in a low-speed wind tunnel T-3 by using a six-component internal aerodynamic balance. Several model configurations were also investigated.FindingsThe results of the presented studies showed that at the wide range of the overcritical angles of attack and sideslip angles, i.e. α = −900° ÷ 900° and β = −900° ÷ 900°, the Tu-154M aircraft flap deflection affected the values of the drag and lift coefficients and generally had no major effect on the values of the side force and pitching moment coefficients.Research limitations/implicationsThe model vibration which was the result of flow separation at high angles of attack was the wind tunnel test limitation.Practical implicationsStudies of the airliner aerodynamic characteristics at the wide range of the overcritical angles of attack and sideslip angles allow assessment of the aircraft aerodynamic properties during possible unexpected situations when the passenger aircraft is found to have gone beyond the conventional flight envelope.Social implicationsThere are no social implications of this study to report.Originality/valueThe presented wind tunnel test results of the airliner aerodynamic characteristics at overcritical angles of attack and sideslip angles is an original contribution to the existing not-too-extensive database available in the literature.

Spraying performance of umbrella wind-field-type atomization and its application to parameter optimization.

We designed an umbrella wind-field-type anti-drift spraying device to improve droplet deposit in the fruit tree canopy, reduce spray drift between fruit tree rows, and avoid uneven droplet deposit in the canopy. We used Computational Fluid Dynamics combined with wind field tests to optimize the parameters of the anti-drift spray device, and the results showed that airflow velocity at the outlet of the device after optimization was 24.5 m s-1 , which is 48% higher than that before optimization (16.5 m s-1 ) airflow velocity. We designed wind tunnel tests and field tests to analyze the anti-drift characteristics of the anti-drift spraying device. Wind tunnel test results showed that the side airflow velocity, outlet diameter, spray distance, and spray drift ratio were correlated. The mathematical models established by vertical and horizontal multifactor orthogonal tests were significant (P < 0.05, R2 0.947, 0.878, respectively). The results of the field tests showed that side airflow, velocity spray pressure and outlet diameter had significant effects on the droplet deposit characteristics (in descending order: the side airflow velocity, spray pressure, and outlet diameter). The maximum droplet deposit was 6.34 μL cm-2 when the side airflow velocity was 2 m s-1 , the spray pressure was 0.4 MPa, and the outlet diameter was 70 mm2 . When the side airflow velocity exceeded 2 m s-1 , the outlet diameter and spray pressure had to be reduced to ensure better droplet deposit. The results indicated that the umbrella wind field could reduce spray drift and ineffective deposit in off-target areas and provides a reference for the comprehensive analysis of the spray drift deposit law. © 2023 Society of Chemical Industry.

Aerodynamic Characteristics of Corrugated Features for Ahmed Model

The numerical simulation method is used to mimic the outflow field of 30 ° Ahmed model. The accuracy of the simulation method is verified by comparing with the wind tunnel test results. Based on the aerodynamic characteristics of the wind tunnel model, the impact of Ahmed on the structure is explored by combining the numerical simulation method of Ahmed model. The results show that the fold structure has more significant effect on lift and less effect on aerodynamic resistance.

Acceleration and Reynolds effects of crosswind flow fields in gorge terrains

A significant acceleration generated in the gorge terrain poses a serious threat to the operational safety of the transportation facilities downstream of the gorge. To determine the formation mechanism of the acceleration effect, this paper compares the results of wind tunnel tests with the improved delayed detached eddy simulation in terms of the spatial distribution, turbulence, and spectrum of the flow field on the gorge topography under crosswinds. The effect of the Reynolds number on the results is discussed in terms of the characteristic wind speed of flow field and the scaling ratio. Recurrent neural networks are used to attempt to get signals from unknown measurement points and to repair damaged signals. The results show that when the mountain spacing in the experimental and the computational fluid dynamics models is zero, the most dramatic acceleration reaches 1.28–1.4 times the incoming wind speed. In the wind tunnel tests, the peak of the power spectra density (1.065 × 10−2) at the downstream of the center of the gorge with a mountain spacing of zero is 3.37 and 14.77 times higher than the corresponding values (3.16 × 10−3 and 7.21 × 10−4) in the gorge topography with the mountain spacing of 0.01 and 0.02 m, respectively. The maximum difference of mean wind velocities in the leeward of the gorge is 6.4% when the Reynolds number ranges from 2.03 × 105 to 1.03 × 107. The results are expected to provide a reference for the design of windproof facilities in gorge terrains.

Wind Tunnel Study of a Grid Fin Stabilized Guided Projectile

There is a need for methods/techniques to analyze the aerodynamics of grid fins at high angle of attack. The existing methods to predict or compute the aerodynamic parameters for grid fins are inadequate at high angles of attack. The present study attempts to extend the understanding of the complex aerodynamics associated with grid fins. The analysis draws its conclusion from wind tunnel test results of five basic grid fin configurations. A vortex lattice solution was used to model the aerodynamics of the chosen grid fins. Next the analytical and empirical relations as discussed in open literature were applied to model grid fin aerodynamics at high angle of attack. The aerodynamic coefficients were computed. These coefficients were then compared with the experimental results obtained using the five grid fin configurations. To improve the matching at high angle of attack a proposed approach using Kirchoff’s theory along with vortex lattice method was applied. The results show that this approach can be a starting tool to model lattice/grid fin aerodynamics.