It’s official. Researchers are now directly measuring wall shear stress to help characterize turbulent boundary layers (University of Florida). Results were published in a recent Physical Review of Fluids journal paper (Pabon et al.), “Characteristics of turbulent boundary layer large scale motions using direct fluctuating wall shear stress measurements”. In the paper, a capacitive-based, floating element MEMS sensor was used for skin friction measurement. The goal was to further the understanding of wall shear stress dynamics, focusing on the large turbulent scales.
The study employed direct measurements of wall shear stress along with synchronous sampling of the streamwise velocity field using hot-wire anemometry. The UF capacitive shear stress sensor is a prototype version of the technology at the core of IC2's DirectShear™ sensor. In the published research, the UF sensor was used to measure a zero pressure gradient turbulent boundary layer over a flat plate model. The results from the UF sensor showed good agreement with existing velocity profile-based literature and direct numerical simulations (DNS).
The graduate student researcher, Rommel Pabon, also used IC2’s DirectShear™ sensor in his dissertation titled “Experimental Studies of Organized Motions in a Turbulent Boundary Layer and Their Imprint on Wall Shear Stress.” Additional publications from his dissertation work using the DirectShear™ sensor system are forthcoming.
Photograph of the IC2 DirectShear floating element head used in the UF dissertation (image courtesy of IC2/David Mills)
The DirectShear sensors provide both the spatial and temporal resolution needed to resolve turbulent structures in the flow over a body, while reducing measurement uncertainty. For more information on how IC2 DirectShear sensors can enhance your next data-set, click here.
Pabon, R. J., Ukeiley, L., Sheplak, M., & Keane, C. B. (2018). Characteristics of turbulent boundary layer large scale motions using direct fluctuating wall shear stress measurements. Physical Review Fluids, 3(11), 114604. https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.3.114604