NSF Award
2301453
The turbulent flow over two roughness elements in close proximity on an otherwise relatively smooth surface is encountered in environmental and engineering applications (e.g., two dunes in close proximity and two protrusions in close succession on an engineered surface). The interactions between the upstream wake and the downstream wake govern important flow features including drag and turbulence. This project aims to quantify and understand the wake interactions between two roughness elements in close proximity under incoming turbulent flow. For this purpose, flow measurements will be made for a wide range of configurations using state-of-the-art instrumentation. The project will be performed at an undergraduate institution providing foundation for engineering research and enhancing undergraduate research training. The project will provide engaging research experiences for undergraduate students who will gain valuable research training and mentoring while working alongside faculty.<br/><br/>High-speed volumetric particle image velocimetry, a non-intrusive laser-diagnostic flow measurement technique, will be used to measure the flow over two cylindrical roughness elements positioned in close proximity and immersed in a turbulent boundary layer. The cylinders will be positioned at various configurations to vary the degree by which the upstream cylinder shelters the downstream cylinder from the incoming high-momentum flow. The experiments will allow for the characterization of rich flow physics: the interaction of two 3D shear layers in the lower portion of a turbulent boundary layer. The objectives are to 1) quantify the flow interactions between the wakes of the two cylindrical roughness elements; 2) characterize the vortical structures shed from isolated cylindrical roughness elements and identify the modifications to these structures due to the introduction of an upstream cylinder; 3) investigate the effects of additional upstream elements (i.e., sheltering by 2, 3, and 4 upstream elements) on the captured flow physics, 4) quantify the roughness-induced perturbation to the boundary layer and its coherent structures; and 5) distill a spatiotemporally-resolved flow description that illustrates sheltering flow physics across a wide range of arrangements. The spatially- and temporally-resolved measurements will aid in addressing a gap in the literature on the flow over two roughness elements in close proximity, offer insight into the rich flow physics involved, and provide benchmark results to aid other researchers in their modeling and validation efforts.<br/><br/>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.
