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CONTENTS
Volume 33, Number 6, December 2021
 


Abstract
Although existing algorithms can predict wind speed using historical observation data, for engineering feasibility, most use moment methods and probability density functions to estimate fitted parameters. However, extreme wind speed prediction accuracy for long-term return periods is not always dependent on how the optimized frequency distribution curves are obtained; long-term return periods emphasize general distribution effects rather than marginal distributions, which are closely related to potential extreme values. Moreover, there are different wind speed parent sample types; how to theoretically select the proper extreme value distribution is uncertain. The influence of different sampling time intervals has not been evaluated in the fitting process. To overcome these shortcomings, updated steps are introduced, involving parameter sensitivity analysis for different sampling time intervals. The extreme value prediction accuracy of unknown parent samples is also discussed. Probability analysis of mean wind is combined with estimation of the probability plot correlation coefficient and the maximum likelihood method; an iterative estimation algorithm is proposed. With the updated steps and comparison using a Monte Carlo simulation, a fitting policy suitable for different parent distributions is proposed; its feasibility is demonstrated in extreme wind speed evaluations at Longhua and Chuansha meteorological stations in Shanghai, China.

Key Words
distribution of extreme value; maximum likelihood estimation; mean wind; Monte Carlo simulation; parent sample distribution; probability plot correlation coefficient

Address
Lin Zhao:State Key Lab of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China/ Key Laboratory of Transport Industry of Wind Resistant Technology for Bridge Structures, Tongji University, Shanghai 200092, China

Xiaonong Hu:State Key Lab of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China

Yaojun Ge:State Key Lab of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China/ Key Laboratory of Transport Industry of Wind Resistant Technology for Bridge Structures, Tongji University, Shanghai 200092, China

Abstract
As wind turbine rotors increase, the overall loads and dynamic response become an important issue. This problem is augmented by the exposure of wind turbines to severe atmospheric events with unconventional flows such as tornadoes, which need specific designs not included in standards and codes at present. An experimental study was conducted to analyze the loads induced by a tornado-like vortex (TLV) on horizontal-axis wind turbines (HAWT). A large-scale tornado simulation developed in The Wind Engineering, Energy and Environment (WindEEE) Dome at Western University in Canada, the so-called Mode B Tornado, was employed as the TLV flow acting on a rigid wind turbine model under two rotor operational conditions (idling and parked) for five radial distances. It was observed that the overall forces and moments depend on the location and orientation of the wind turbine system with respect to the tornado vortex centre, as TLV are three-dimensional flows with velocity gradients in the radial, vertical, and tangential direction. The mean bending moment at the tower base was the most important in terms of magnitude and variation in relation to the position of the HAWT with respect to the core radius of the tornado, and it was highly dependent on the rotor Tip Speed Ratio (TSR).

Key Words
experimental test; HAWT; tornadoes; wind loads; wind turbine; WindEEE dome

Address
Juan P. Lopez:Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario, Canada

Horia Hangan:Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario, Canada/ Department of Mechanical Engineering, Ontario Tech University, Oshawa, Ontario, Canada

Ashraf El Damatty:Department of Civil and Environmental Engineering, University of Western Ontario, London, Ontario, Canada

Abstract
High spatial and temporal surface pressure measurements were carried out in the state-of-the-art tornado simulator, the Wind Engineering, Energy and Environment (WindEEE) Dome, to explore the characteristics of stationary and translating tornado-like vortices (TLV) for a wide range of swirl ratios (S=0.21 to 1.03). The translational speed of the TLV and the surface roughness were varied to examine their effects on tornado ground pressures, wandering, and vortex structure. It was found that wandering is more pronounced at low swirl ratios and has a substantial effect on the peak pressure magnitude for stationary TLV (error percentage≤35%). A new method for removing wandering was proposed which is applicable for a wide range of swirl ratios. For translating TLV, the near-surface part lagged behind the top of the vortex, resulting in a tilt of the tornado vertical axis at higher translating speeds. Also, a veering motion of the tornado base towards the left of the direction of the translation was observed. Wandering was less pronounced for higher translation speeds. Increasing the surface roughness caused an analogous effect as lowering the swirl ratio.

Key Words
roughness; surface pressure; swirl ratio; tilting; tornado-like vortices; translation speed; veering; wandering

Address
Aya Kassab:WindEEE Research Institute, Western University, 2535 Advanced Ave., London, ON, Canada, N6M 0E2

Chowdhury Jubayer:WindEEE Research Institute, Western University, 2535 Advanced Ave., London, ON, Canada, N6M 0E2

Arash Ashrafi:WindEEE Research Institute, Western University, 2535 Advanced Ave., London, ON, Canada, N6M 0E2

Horia Hangan:WindEEE Research Institute, Western University, 2535 Advanced Ave., London, ON, Canada, N6M 0E2

Abstract
This study investigates the aerodynamic characteristics of NACA series airfoil by altering the trailing edge in the form of extended and serrated sections. This contemporary advent examined NACA 0020 airfoil experimentally at the angle of attack ranging from 0° to 45° and for the Reynolds number of 2.46 x 105. To figure out the flow behaviour, the standard average pressure distribution over the airfoil surface is estimated with 50 pressure taps. The time series surface pressure is recorded for 700 Hz of sampling frequency. The extended trailing edge of 0.1 c, 0.2 c and 0.3 c are attached to the base airfoil. Further, the triangular serration is introduced with the base length of 2 cm, 4 cm and 6 cm. Each base length with three different amplitudes of 0.1 c, 0.2 c and 0.3 c were designed and equipped with the baseline case at the trailing edge and tested. The aerodynamic force coefficient, as well as pressure coefficient are presented. The obtained data advises that modification in the trailing edge will reflect the aerodynamic characteristics and the flow behaviour over the section of a wing. Resultantly, the extended trailing edge as a thin elongated surface attached to a base airfoil without revising the main airfoil favors good lift increment. The serrated trailing edge acts as a flow control device by altering the flow pattern results to delay the stall phenomenon. Besides it, improves lift co-efficient with less amount of additional drag. This extended and serrated trailing edge approach can support for designing the future smart airfoil.

Key Words
extended trailing edge; flow control technique; pressure distribution; serrated trailing edge; stall delay; wind tunnel experiment

Address
Livya Ethiraj:Turbulence and Flow Control Lab, School of Mechanical Engineering, SASTRA Deemed University, Thanjavur, TamilNadu, India – 613401

Subramania Nadaraja Pillai:Turbulence and Flow Control Lab, School of Mechanical Engineering, SASTRA Deemed University, Thanjavur, TamilNadu, India – 613401

Abstract
This present paper leads to investigation of blade-fluid interactions of cambered blade H-Darrieus rotor having EN0005 airfoil blades using comprehensive Computational Fluid Dynamics (CFD) analysis to understand its performance in low wind streams. For several blade azimuthal angle positions, the effects of three different low wind speeds are studied regarding their influence on the blade-fluid interactions of the EN0005 blade rotor. In the prevailing studies by various researchers, such CFD analysis of H-Darrieus rotors are very less, hence it is needed to improve their steady-state performance in low wind velocities. Such a study is also important to obtain important performance insights of such thin cambered blade rotor in its complete rotational cycle. It has been seen that the vortex generated at the suction side of the EN0005 blade rolls back to its leading edge due to the camber of the blade and thus a peak velocity occurs near to the nose position of this blade at its leading edge, which leads to peak performance of this rotor. Again, in the returning phase of the blade, a secondary recirculating vortex is generated that acts on the pressure side of EN0005 blade rotor that increases the performance of this cambered EN0005 blade rotor in its downstream position as well. Here, the aerodynamic performances have been compared considering Standard k-ω and SST k-ω models to check the better suited turbulence model for the cambered EN0005 blade H-Darrieus rotor in low tip speed ratios.

Key Words
blade-fluid interaction; CFD simulation; H-Darrieus rotor; lift coefficient; power coefficient

Address
Anal Ranjan Sengupta:Department of Mechanical Engineering, JIS College of Engineering, Kalyani, WB-741235, India

Agnimitra Biswas:Department of Mechanical Engineering, NIT Silchar, Assam-788010, India

Rajat Gupta:Department of Mechanical Engineering, NIT Mizoram, Mizoram-796012, India


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