FLOW INDUCED VIBRATION IN SQUARE CYLINDER OF VARIOUS ANGLES OF ATTACK

An experimental study was carried out to identify the effect of angle of attack on flow-induced vibration (FIV) of square cylinders. The experiment was conducted at the Aeronautical and Wind Engineering Laboratory (AEROLAB), UTM Kuala Lumpur using a wind tunnel that was free from external wind conditions. A supporting structure was designed and fabricated to conduct this experiment. The importance of this support structure was to enable the rigid cylinder to suspend and vibrate freely upon excitation of wind speed. The results were analysed through the response of amplitude and frequency of the rigid cylinder over a velocity range of 0.5m/s to 4.0m/s. The results showed that for a square cylinder of ?=0°, vortex-induced vibration (VIV) occurred at low reduced velocity (UR) in range of 5 ? UR ? 10 and galloping occurred at higher reduced velocity which started at UR=15. A tranquil zone was found between VIV and galloping in the reduced velocity range of 10 ? UR ? 15. As for ?=22.5° and 45°, only VIV response was found at low reduced velocity in range of 4? UR ? 9. ABSTRAK: Satu kajian eksperimentasi telah dilakukan bagi mengenal pasti pengaruh sudut serangan oleh getaran cetusan-aliran (FIV) dalam silinder persegi. Eksperimen ini dijalankan di Makmal Kejuruteraan Aeronautika dan Angin (AEROLAB), UTM Kuala Lumpur dengan menggunakan terowong angin yang bebas dari pengaruh angin luar. Struktur sokongan telah direka dan difabrikasi bagi tujuan eksperimen ini. Ini penting bagi membolehkan silinder pegun tergantung dan bergetar dengan bebas semasa ujian kelajuan angin. Dapatan kajian dianalisis melalui tindak balas amplitud dan frekuensi silinder pegun pada kadar halaju 0.5m/s sehingga 4.0m/s. Hasil kajian menunjukkan bahawa bagi silinder persegi ? = 0 °, getaran pengaruh-vorteks (VIV) berlaku pada halaju rendah (UR) dalam julat 5 ? UR ? 10 dan getaran lebih teruk telah ketara berlaku pada kadar halaju berkurang iaitu bermula pada UR = 15. Zon tenang dijumpai antara VIV dan getaran teruk pada kadar halaju berkurang 10 ? UR ? 15. Adapun pada ? = 22.5° dan 45°, hanya tindak balas VIV dijumpai pada halaju rendah dalam kadar 4? UR ? 9.

Aerodynamic performance simulation of three selected airfoils

This work presents the lift and drag coefficient curves, as functions of the angle of attack, for the NACA0012, S809 and SG6043 airfoils in turbulent flow conditions. The objective is to identify the airfoil with the best aerodynamic performance under conditions that are descriptive of small scale wind turbine. With the use of OpenFOAM, an analysis was done by numerical simulation. In the case of the NACA0012 airfoil, it was found that the performance is insensitive to the changes in turbulence and the Reynold number. The aerodynamic response of the S809 airfoil is to increase both the drag and lift as the turbulence increases. The SG6043 airfoil responds the best out of the three in turbulent flow, given that the lift curves mostly increase with the turbulence. The curves reported in this work are new and not found in previous literature. Keywords: aerodynamics, lift, drag, turbulence References [1]R. Madriz-Vargas, A. Bruce, M. Watt, L. G. Mogollón and H. R. Álvarez, «Community renewable energy in Panama: a sustainability assessment of the “Bocade Lura” PV-Wind-Battery hybrid power system,» Renewable Energy and Environmental Sustainability, vol. 2, nº 18, pp. 1-7, 2017. https://doi.org/10.1051/rees/2017040. [2]S. Mertenes, «Wind Energy in the Built Environment, » Ph.D. dissertation. Multi-Science, Brentwood, 2006. [3]P. Giguere and M. S. Selig, «New airfoils for small horizontal axis wind turbines,» Journal of Solar Energy Engineering-transactions, vol. 120, pp. 108-114, 1988. https://doi.org/10.1115/1.2888052. [4]A. K. Wright and D. H. Wood, «The starting and low wind speed behaviour of a small horizontal axis wind turbine,» Journal of wind engineering and industrial aerodynamics, vol. 92, nº 14-15, pp. 1265-1279, 2004. https://doi.org/10.1016/j.jweia.2004.08.003. [5]G. Richmond-Navarro, M. Montenegro-Montero and C. Otárola, «Revisión de los perfiles aerodinámicos apropiados para turbinas eólicas de eje horizontal y de pequeña escala en zonas boscosas,» Revista Lasallista de Investigación, vol. 17, nº 1, pp. 233-251, 2020. https://doi.org/10.22507/rli.v17n1a22. [6]A. Tummala, R. K. Velamati, D. K. Sinha, V. Indraja and V. H. Krishna, «A review on small scale wind turbines, » Renewable and Sustainable Energy Reviews,vol. 56, pp. 1351-1371, 2016. https://doi.org/10.1016/j.rser.2015.12.027. [7]L. Pagnini, M. Burlando and M. Repetto, «Experimental power curve of small-size wind turbines in turbulent urban environment,» Applied Energy, vol. 154,pp. 112-121, 2015. https://doi.org/10.1016/j.apenergy. 2015.04.117. [8]W. D. Lubitz, «Impact of ambient turbulence on performance of a small wind turbine,» Renewable Energy, vol. 61, pp. 69-73, 2014. https://doi.org/10.1016/j.renene.2012.08.015. [9]P. Devinant, T. Laverne and J. Hureau, «Experimental study of wind-turbine airfoil aerodynamics in high turbulence, » Journal of Wind Engineering and Industrial Aerodynamics, vol. 90, nº 6, pp. 689-707, 2002. https://doi.org/10.1016/S0167-6105(02)00162-9. [10]C. Sicot, P. Devinant, S. Loyer and J. Hureau, «Rotational and turbulence effects on a wind turbine blade. Investigation of the stall mechanisms,» Journal ofwind engineering and industrial aerodynamics, vol. 96, nº 8-9, pp. 1320-1331, 2008. https://doi.org/10.1016/j.jweia.2008.01.013. [11]C. R. Chu and P. H. Chiang, «Turbulence effects on the wake flow and power production of a horizontal-axis wind turbine,» Journal of Wind Engineering and Industrial Aerodynamics, vol. 124, pp. 82-89, 2014. https://doi.org/10.1016/j.jweia.2013.11.001. [12]Y. Kamada, T. Maeda, J. Murata and Y. Nishida, «Visualization of the flow field and aerodynamic force on a Horizontal Axis Wind Turbine in turbulent inflows,» Energy, vol. 111, pp. 57-67, 2016. https://doi.org/10.1016/j.energy.2016.05.098. [13]Q. A. Li, J. Murata, M. Endo, T. Maeda and Y. Kamada, «Experimental and numerical investigation of the effect of turbulent inflow on a Horizontal Axis WindTurbine (Part I: Power performance),» Energy, vol.113, pp. 713-722, 2016. https://doi.org/10.1016/j.energy.2016.06.138. [14]S. W. Li, S. Wang, J. P. Wang and J. Mi, «Effect of turbulence intensity on airfoil flow: Numerical simulations and experimental measurements,» Applied Mathematics and Mechanics, vol. 32, nº 8, pp. 1029-1038, 2011. https://doi.org/10.1007/s10483-011-1478-8. [15]S. Wang, Y. Zhou, M. M. Alam and H. Yang, «Turbulent intensity and Reynolds number effects on an airfoil at low Reynolds numbers,» Physics of Fluids, vol. 26, nº11, p. 115107, 2014. https://doi.org/10.1063/1.4901969. [16]M. Lin and H. Sarlak, «A comparative study on the flow over an airfoil using transitional turbulence models, » AIP Conference Proceedings, vol. 1738, p.030050, 2016. https://doi.org/10.1063/1.4951806. [17]Langley Research Center, «Turbulence Modelling Resource,» NASA, [Online]. Available: https://turbmodels.larc.nasa.gov/langtrymenter_4eqn.html. [Last access: 08 03 2021].

A Performance-Based Wind Engineering Framework for Engineered Building Systems Subject to Hurricanes

Over the past decade, significant research efforts have been dedicated to the development of performance-based wind engineering (PBWE). Notwithstanding these efforts, frameworks that integrate the damage assessment of the structural and envelope system are still lacking. In response to this need, the authors have recently proposed a PBWE framework that holistically treats envelope and structural damages through progressive multi-demand fragility models that capture the inherent coupling in the demands and damages. Similar to other PBWE methodologies, this framework is based on describing the hurricane hazard through a nominal straight and stationary wind event with constant rainfall and one-hour duration. This study aims to develop a PBWE framework based on a full description of the hurricane hazard in which the entire evolution of the storm track and time-dependent wind/rain fields is simulated. Hurricane-induced pressures impacting the building envelope are captured through the introduction of a non-stationary/-straight/-Gaussian wind pressure model. Time-dependent wind-driven rain is modeled through a computational fluid dynamics Eulerian multiphase framework with interpolation schemes for the rapid computation of wind-driven rain intensities over the building surface. Through the development of a conditional stochastic simulation algorithm, the envelope performance is efficiently characterized through probabilistic metrics associated with rare events of design interest. The framework is demonstrated through analyzing a 45-story archetype building located in Miami, FL, for which the envelope performance is estimated in terms of a suite of probabilistic damage and loss metrics. A comparative study is carried out in order to provide insights into the differences that can occur due to the use of nominal hurricane models.

Heuristic Feature Selection for Wind Power Anomaly Events Study

Wind power ramp events are typical harmful anomaly events in wind engineering, which bring new threat to the safety operation of power systems. To in-depth understand ramps and mitigate their harms, suitable ramp characteristics are crucial in many studies, e.g., ramp definition, classification, prediction and so on. However, due to ramps’ specificity on event feature, more profound characteristics are needed besides basic ramp morphological characteristics. In this paper, an approach for extracting and selecting ramp characteristics is proposed for ramp study. First, according to ramps’ causation on energy change, wavelet transformation is introduced to analyze ramp categories, and used to extract ramp energy characteristics. Then, heuristic feature selection methods are proposed to select ramp characteristics based on specific ramp application contexts. The objective of feature selection is to remove redundant characteristics, and to improve ramp studies’ performance. Finally, combining basic ramp characteristics and wavelet characteristics, ramp studies on category classification and prediction of appointed characteristics are implemented on industrial data. The computational results validate the usefulness of wavelet characteristics, the feasibility of the proposed approach, and that performance of ramp study could be improved by using ramp characteristics in this paper.

Role of dynamic water rivulets in the excitation of rain–wind-induced cable vibration: A critical review

It has been more than 30 years since Hikami Y and Shiraishi N (1988) Rain–wind-induced vibrations of cable-stayed bridges. Journal of Wind Engineering and Industrial Aerodynamics 29: 409–418 first reported the rain–wind-induced vibration (RWIV) of stay cables in the construction stage of Meikonishi Bridge, Japan. After that, considerable research efforts have been devoted to understanding the RWIV of stay cables, and the role of the upper rivulet has been gradually realized and studied. This study presents a selective review on recent progress of RWIV and its controversial excitation mechanism. The available knowledge and up-to-date understanding of this complex fluid-structure interaction are presented in some detail. The formation, dynamics of water rivulet, and its role in affecting the near-wall boundary layer properties and in the excitation scenario of RWIV are of particular interest in this study. Finally, some limitations of previous studies are concluded, with some perspective suggestions for further study of excitation mechanism of RWIV.

Extracting Time-Varying Mean Component of Non-Stationary Winds Utilizing Vondrak Filter and Genetic Algorithm: A Wind Engineering Perspective

The time-varying mean (TVM) component plays a vital role in the characterization of non-stationary winds, whereas it is difficult to extract the TVM accurately or to validate it quantitively. To deal with this problem, this paper first develops two additional conditions for the TVM extraction from the perspective of structural wind-induced vibration response, then presents an approach, based on the combination of Vondrak filter and genetic algorithm (Vondrak-G), to derive the optimal TVM from non-stationary wind speed records as well as its turbulence characteristics (i.e. gust factor, turbulence intensity, and turbulence integral length scale). Furthermore, the wind characteristics obtained by the Vondrak-G approach are compared with those by a conventional approach derived for stationary winds, demonstrating that the results by the Vondrak-G approach are evidently more accurate. This paper aims to provide an effective method for accurately extracting the TVM and then evaluating wind characteristics of the non-stationary wind.

Aerodynamic Architectural Features to Mitigate Peak Pressures over Low-Rise Buildings

A number of aerodynamic devices to perturb or modify the flow over low-rise buildings are proposed. The purpose of these devices is to reduce the adverse effects of wind over low-rise buildings and to mitigate the pressures on the roofs to lower vacuum levels. Pressure measurements were performed on a scaled down model of the well-known TTU experimental building of the Wind Engineering Research Facility (WERFL) at TTU University. Different results were obtained: reduction of average peek vacuum, smoothing of windward pressure distribution on the roof and narrowing and localizing of the suction pressure zones on the roof. Results that may be of interest to other disciplines such as heat transfer are also reported.