CBET-EPSRC: Wall Similarity of 2D and 3D Non-Equilibrium Rough Wall Boundary Layers

About This Grant

Predicting the flow of air or water over a vehicle or other device is key to making engineering improvements. When a rough surface is exposed to the flow, it is assumed that the only effect of the roughness is to increase the friction without otherwise changing details about the flow. However, this assumption is unproven in all but the simplest situations. The purpose of this project is to definitively resolve this issue, using the novel approach of comparing flows over different surfaces that generate the same friction. This work will enable more reliable analysis and design of many systems and vehicles. The project will engage and train researchers at postdoctoral, doctorate, undergraduate, and high-school levels, enable interdisciplinary international exchanges, and provide unique research experiences for hundreds of undergraduate engineers. The approach will combine state-of-the-art experimental capabilities and experience at Virginia Tech with leading edge computational expertise at the University of Cambridge. The goal is to reveal the limits and mechanisms of rough wall similarity, by comparing the properties and mechanics of non-equilibrium boundary layers generated over rough walls with different geometry but with the same effective sand-grain roughness. This comparison will be conducted for a systematic set of two- and three-dimensional flow geometries that include many of the non-equilibrium complexities found in practical applications. At Virginia Tech, experiments performed in the Stability Tunnel will include detailed mean flow and turbulence measurements at friction Reynolds numbers up to 20,000. Coordinated and complementary scale-resolving simulations at Cambridge will provide intricately detailed views of the turbulence dynamics that mediate the critical relationship between the roughness layer and outer region. The project will form the focus of post-doctoral training at the University of Cambridge and doctoral-student training at Virginia Tech. In addition, the project includes a series of sub-projects to be conducted by groups of undergraduate and high school students drawn from the Southwest Virginia Governor’s School. Furthermore, wind tunnel tests will be integrated with required undergraduate laboratory courses in Aerospace and Ocean Engineering and Mechanical Engineering, providing substantive research experiences to large numbers of undergraduate students annually. This project is jointly funded by the U.S. National Science Foundation Fluid Dynamics program and the UK Research and Innovation (UKRI)/ Engineering and Physical Sciences Research Council (EPSRC) under the NSF Directorate for Engineering – UKRI Engineering and Physical Science Research Council Lead Agency Opportunity. 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.