By Yolanda Zhou, VI Form

Inverted Airfoils’ Abilities to Prevent Wind Storm Roof Destruction

Student-Submitted Note: This paper investigates a new way to reduce aerodynamic lift created around houses’ roofs in extreme windstorms. Three test models were created in computer modeling software OnShape and simulated in CFD using OpenFOAM. This project was inspired by the concept of “downforce” used to stabilize Formula One race cars. This paper was written for submission to the High School Science Symposium (HiSci) in May 2023 as part of the STEM Fellowship.

Abstract

As severe windstorms increase in frequency and intensity, more residential houses are predicted to be vulnerable to structural damage by severe windstorms towards the end of the 21st century. Wind around the roof exerts a negative pressure that lifts the roof up and threatens the structural integrity of houses. In this paper, a novel method of mitigating lift using inverted airfoils was explored through CFD simulations. The performance of the model was assessed through three criteria: net lift coefficient, effectiveness under different wind directions, and manufacturability. Visual representations of pressure and velocity distribution of the airflow over the model were analyzed to validate simulation data. Single inverted airfoils and round airfoil-shaped roofs were tested for the first prototype. A further iteration of the prototypes improved the model performance. All roof configurations were able to reduce the overall lift of the system when compared to the control group. Single airfoil roof setup was most effective at reducing net lift, while round roof setup was effective in a wider range of wind direction conditions. Rectangular Roof setup combines the advantages of both setups and reduces more net lift than the Revolved Airfoil setup.

Introduction

As global climate change accelerates, the intensity and frequency of wind disasters, such as tropical cyclones and tornadoes, are predicted to increase significantly by the end of 21st century [8]. The increase in the intensity of tropical cyclones is found to be correlated to the rise of Sea Surface Temperatures [8]. Furthermore, Category 4 and 5 tropical cyclone activities, which have wind speeds that exceed 150 miles per hour, are likely to increase in the late 21st century [10]. Such tropical cyclones, although very rare, are catastrophic and account for around half of the economic damage done by all tropical cyclones in the US [6]. In 2013, an EF-5 category tornado hit Moore, Oklahoma. Reaching a speed of over 200 miles per hour, type EF-5 tornadoes are the rarest and most destructive type of tornado on Earth. The tornado caused 24 deaths, more than 200 injuries, and billions of dollars for repairing the destroyed houses and facilities [3]. Overall, tropical cyclone frequencies, intensities, and damages are projected to increase as the global climate continues to get warmer [10]. High School Science Symposium 2022