CAREER: Flow Physics of Transient Rooftop Vortices at High Reynolds Numbers and Bio-Inspired Flow Control Strategies to Mitigate Wind Hazards

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This Faculty Early Career Development (CAREER) grant will advance scientific knowledge of the flow physics of rooftop vortices from hurricane-type strong winds on low-rise buildings and develop bio-inspired flow control strategies to attenuate the damaging effects of roof suctions on building resilience. Dramatic damage repeatedly occurs on low-rise building roofs during windstorms, as observed in recent hurricanes Matthew (2016), Maria (2017), and Michael (2018). Building roof failure often starts at the windward roof edges and corners, where extreme peak suctions are induced by flow separation and unsteady vortices. Improved understanding of vortex dynamics governing the worst roof suction and smart flow control strategies by learning from nature will contribute towards more accurate wind load prediction, enhanced wind design provisions, and reduction of wind-induced damage and economic and life losses, and thus advance post-windstorm national welfare and prosperity. The bio-inspiration approach will not only produce cost-effective, high-performance mitigation strategies for low-rise buildings, but will also motivate new thinking in broader engineering fields. This research will use the Natural Hazards Engineering Research Infrastructure (NHERI) Wall of Wind (WOW) facility at Florida International University (FIU). Experimental datasets will be archived in the NHERI Data Depot (https://www.DesignSafe-ci.org) and be made publicly available for validation of computational fluid dynamics (CFD) models. To strengthen the persistence of engineering students, first-year undergraduate students will be engaged in a new learning community by integrating scientific questions into team-based, early research experiences, as well as weekly open workshops and invited seminars. The learning community program will improve the STEM infrastructure, broaden underrepresented groups’ participation in engineering, and build a pipeline for the engineering workforce. This project will support the investigator's long-term career vision focused on fundamental research on wind-structure interaction and bio-inspired flow control to increase the wind resilience of civil infrastructure that contributes to community resilience and sustainability. This award contributes to the National Science Foundation's role in the National Windstorm Impact Reduction Program (NWIRP). The specific research objectives are the following: (1) quantify three-dimensional, transient rooftop vortices from hurricane-type high winds of high Reynolds numbers, (2) correlate the unsteady vortices with roof peak pressures, and (3) utilize bio-inspiration as an innovation tool to create cost-effective wind mitigation devices, ultimately enhancing the wind resiliency of low-rise buildings. A series of well-controlled wind tunnel experiments with unsteady flow and pressure over a scaled low-rise building model will be conducted at Cleveland State University and the FIU WOW facility. Systematic measurements of the unsteady three-dimensional vortical flow at high Reynolds numbers will also be beneficial to the broader fluid mechanics community to advance understanding, modeling, and control of a wide class of vortex flow phenomena. The research will result in (1) vortex flow mechanisms governing the peak roof suctions at high Reynolds numbers, and (2) bio-inspired, cost-effective mitigation strategies (porous fractal parapets) to manipulate vortex formation, applicable to new and retrofit of existing low-rise buildings.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.