International Journal of Civil and Structural Engineering Research ISSN 2348-7607 (Online) Vol. 9, Issue 2, pp: (16-26), Month: October 2021 - March 2022, Available at: www.researchpublish.com
Wind Mill Reliability: Determining TornadoWind Force Coefficients for Thin-Cylinder Structures with Computer Modeling Quentin S. Ragan1, R. Panneer Selvam2 1
Graduate Student, 2University Professor of Civil Engineering University of Arkansas, Fayetteville, Arkansas
Abstract: A two-dimensional (2D), Computational Fluid Dynamics (CFD) model was used to study tornado-wind force interaction with a smooth, thin-cylinder structure having a radius less than the tornado radius and little roof area. They are widely used as wind turbine support towers in tornado-prone areas. The Navier-Stokes equations were approximated with a Finite-Difference method. Simulations were performed to determine the minimum required grid resolution to prevent divergence of the program, replicate known straight-wind force coefficients, and determine tornado-wind force coefficients. The ratio of the core, forced-vortex tornado radius to the cylinder diameter (rcore/D) was increased with constant tornado and translation velocities to determine the tornado drag and lift force coefficients (Cd and Cl). The rotational velocity strength (Vtan) and rcore were then simultaneously increased to determine their effects on Cd and Cl. Tornado-wind force coefficients Cd and Cl were corrected for velocity and combined to determine a single tornado-wind force coefficient (C). The combined coefficient was compared to published force coefficients, including ASCE 7, for straight-wind. Force coefficients for tornados approached constant values when rcore exceeded 15D. Tornado-wind force coefficients were 2-3 times the published values for straight-wind. Keywords: Tornado Wind, Force Coefficient, CFD, Thin-Cylinder.
I. INTRODUCTION Catastrophic forces of nature from rain, wind, wave, hail, and earthquake have produced challenges in the stability of the built environment. The Insurance Information Institute (III) reported that up to 80% of insured, inflation-adjusted monetary losses were due to hurricanes, tropical storms, and convective events (severe storm, hail, tornado, flash flood, and lightning). Events including tornadoes comprised 40% of losses, with an increasing trend in cost . Understanding the effects of these forces clearly benefits the built environment and can save lives. Wind-generated energy is viewed as a cleaner, viable alternative to fossil-fuel produced energy. However, as shown in Fig. 1 below, wind turbines are located in states with the highest vulnerability to tornados precisely because of the wind conditions in those states. Since safe electricity production is a necessary requirement for modern life and for national security during catastrophic events such as tornados, design of wind-generated energy facilities for tornado winds would help provide consistent, clean energy during normal times and after catastrophic events. The primary structural component of a wind-turbine facility is the support tower, which as shown in Fig. 2 below is a thin-cylinder structure. Thin-cylinder structures are absent appreciable roof area. The design of thin-cylinder structures for wind requires an understanding of the force coefficient in the basic fluid-structure interaction equation F=Cf*(1/2ρV2A). Force coefficients (Cf) reflect the variation of wind force with respect to the type of object. The density of the air (ρ), tornado-wind velocity (V), and cross-sectional area (A) of the structure are generally known, leaving Cf to be determined. Force coefficients for straight-wind interaction with a thin-cylinder has been reasonably understood for many decades. Force coefficients for tornado-wind interaction with a thin-cylinder have only recently been studied. This paper
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