The present study experimentally and numerically investigates the feasibility of applying multiple dielectric barrier discharge (multi-DBD) plasma actuators to reduce wind loads and modify local flow field on the roofs of low-rise buildings. Four arrangements of multi-DBD plasma actuators are placed on the roofs and induce four directions of wall jets. The results show that mean and peak negative pressure coefficients are negative no matter the plasma actuation is on or off. These wall jets decrease the absolute values of these pressure coefficients in different roof regions and succeed in modifying the local flow around the roof. The wall jet blowing from the trailing edge to the leading edge has the best effect on wind loads, since the absolute values of mean and peak negative pressure coefficients are respectively reduced by about 20% and 12% near the leading edge. The different variations of wind loads and the local flow for all arrangements are due to the compact of the directionality of the wall jets. The wall jet produces a strong suction region at the beginning of the wall jet, which leads to an obvious enhancement of wind loads in this region. Meanwhile, the wall jet induces a strong pressure region at the back of the wall jet, resulting in an apparent decline of wind loads.
This paper presents the study of the pulsating characteristics of three adjacent high-rise buildings A, B, and C under typhoon ‘Moranti’ (2016) based on the measurement of the actual top wind speed. The studied pulsating characteristics included mean wind speed and direction, turbulence intensity, gust factor, turbulence integral scale, wind speed spectrum and correlation. The relationships between each pulsating parameter and the relationship between the pulsating parameter and gust duration have been investigated. Results show that the mean wind speed and wind direction of three buildings are close. When U ≥ 10 m/s in three different sites at the same time, the turbulence intensity variation of three buildings is consistent and decreases when mean wind speed increases. Once only two locations are acquired simultaneously and the wind angle between 35° and 45°, the mean values of the along-wind and cross-wind turbulence of building A and building C are close. The along-wind turbulence of the three buildings is greater than the predicted Chinese codes for various terrains. The turbulence intensity and gust factors obtained through the analysis of the samples with the mean wind speed U ≥ 10 m/s are reasonable. The turbulence integral scales of buildings A and C are equal to the predicted values of ASCE-7 and AIJ-2004, whereas the turbulent integral scale of building B is evidently small. The gust factors of three buildings increase when the turbulence intensity increases; these two characteristics have a linear relationship. At the same time interval, building B has the maximum along-wind turbulence intensity and gust factors during the low wind speed period and building C achieves the minimum values. Building A acquires the maximum and building C obtains the minimum values in the high wind speed period. The turbulence intensity and gust factors of building B show a certain pulsation. Results show that turbulence intensity and gust factors are mainly affected by the short-term fluctuation of wind. The longitudinal wind speed spectrum of three buildings conforms well to the von Karman model. The correlation of along-wind speed depends on the wind speed, whereas the correlation of cross-wind direction is independent of wind speeds. The measured data and statistical parameters provide useful information for the wind resistance design of high-rise buildings in typhoon-prone areas.
This paper simultaneously measures the characteristics of wind on the roof and the acceleration responses of the 10th, 18th, 25th, 32nd and 41st floors of a high-rise building in Wenzhou during the passing of typhoons between 2014 and 2016. This paper also analyses the dynamic characteristics and wind-induced response of buildings by using Welch and improved Natural Excitation Technique-Eigensystem Realisation Algorithm methods. The results show that the typhoons that affected Wenzhou are dominated by wind from the east, northeast and northwest. The acceleration response probability densities of different floors during Typhoons Chan-hom and Dujuan are similar to the Gaussian distribution. The first-order natural frequencies of the two wind directions of the test building are 0.390 and 0.409, which are in good agreement with Tamura's prediction results. The relevant amplitude and frequency characteristics of the first three modes are investigated in detail according to the nonlinear characteristics of the measured building. The first-, second-and third-order damping ratios of the structure during Typhoons Chan-hom and Dujuan increased with the peak acceleration, whereas the damping during Typhoon Fung-wong remained almost unchanged. The root mean square of the acceleration response of the building structure during Typhoons Chan-hom and Dujuan increased with the wind speed. However, the increase rate of Typhoon Chan-hom was small, possibly because the angle between the incoming flow and the building is 45 • , and the acceleration response in the downwind and crosswind directions is not apparent. The measured results show that the working environment of the staff at the top of the building under the influence of the typhoon also meets comfort requirements. The measured data and statistical parameters provide a valuable reference for the wind-resistant design of high-rise buildings in typhoon-prone areas.Appl. Sci. 2019, 9, 2180 2 of 31 damping ratios [1-9]. However, comprehensively measuring the wind-induced response of high-rise buildings during the passing of a typhoon is difficult due to the high cost, uncertain landing trajectory and long test period. Therefore, an on-site measurement of high-rise buildings during typhoons is crucial to a wind-resistant design of high-rise buildings in typhoon-prone areas.At present, research on the damping ratio of high-rise building structures is mainly based on field measurements, and the influence analysis on the aerodynamic damping ratio is mainly conducted in wind tunnel tests. However, the structure and aerodynamic damping ratio of the actual structure under a strong wind excitation are inseparable. Aeroelastic models, which simulate the amplitude-dependent damping characteristics of high-rise buildings and are designed in wind tunnel tests, are not considered. Many scholars have conducted various studies on the relationship of the damping ratio and vibration amplitude. Vickery and Steckley [10] and Kareem and Gurley [11] proposed that aeroelastic effects, especially aero...
The present research aims to explore, by large-eddy simulation (LES), the potentiality and mechanism of multiple surface dielectric barrier discharge (multi-SDBD) plasma actuators to manipulate mean and fluctuating wind loads on a low-rise building. Three actuator configurations are located on the roof to induce directional wall jets in different directions. The effects of these configurations on flow structure and wind loads are studied in absence and presence of approaching flow. Results show that all subgrid-scale models can obtain accurate roof pressure, and for the diffusion and convection terms, the bounded central differencing scheme can provide more accurate predictions for the roof pressure. The control impact of active actuators gradually weakens with the increase of the approaching flow velocity. The direction of the wall jet can determine the position of the limited roof region with the reduced mean pressure coefficient. The multi-SDBD actuators continue to absorb the upstream flow and blow this flow downstream, meaning the wall jet exerts strong pressure on the local roof area at the end of the jet, which results in a significant reduction of the mean pressure coefficient. Furthermore, the counter-rotating vortices caused by the wall jet restrain the size and strength of the vortex shedding, thereby achieving the purpose of reducing the fluctuating pressure coefficient. Further analysis of the instantaneous vorticity fields indicates that the intensity and size of streamwise shedding vortices can be restrained by small-scale spanwise vortices induced by the plasma actuators. Under the action of the wall jet blowing from the trailing edge to the leading edge, the fluctuating lift and drag coefficients can be reduced by over 15% and the fluctuating pressure coefficient can be reduced by about 20% from the no actuation situation.
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