Volumetric characterization of spatially organized features of Reynolds stress anisotropy in the vicinity of submerged model boulders

Authors: WYSSMANN, MICAH - University Of Missouri; CODER, JAMES - Pennsylvania State University; SCHWARTZ, JOHN - University Of Tennessee; Papanicolaou, Athanasios

Submitted to: Physics of Fluids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Understanding flow patterns around objects such as boulders in rivers and vegetation patches in landscapes can provide unique information of the level of turbulence and friction characteristics within the vicinity of these objects. The focus of this study is, using new technology that involves laser techniques and imaging analysis to describe the patterns of turbulence around objects (here the application is boulders). For large size objects that typically protrude through the water surface turbulent patterns that match the shape of a horseshoe have been identified. Horseshoe patterns spiral down in front of the objects affecting pressure distribution and velocity with implications to soil erosion and deposition in front of the objects. The same phenomenon has been observed in overland flows in front of vegetation patch. In the latter case horseshoe patterns affect soil moisture levels as well as radiation levels. This research provides biosystem engineers, research ecosystem scientists, as well as water researchers, potential mechanisms for future studies aiming to quantify turbulence effects on soil attributes such as moisture and radiation for landscapes with vegetation and no vegetative cover.

Technical Abstract: Experimental characterization of Reynolds stress anisotropy in flows of engineering relevance is important for improving understanding of flow physics and providing validation data for numerical models. Recently, techniques enabling spatial visualizations of anisotropy have been developed, but they have been minimally utilized to experimentally examine spatially distributed characteristics of anisotropy. This study reports a characterization of anisotropy based on laboratory volumetric particle image velocimetry (PIV) data obtained in the vicinity of submerged model boulders (i.e., wall-mounted obstacles atop a rough, permeable bed in open-channel flow). Reynolds stress anisotropy was analyzed using 2D and 3D visualization methods that are mathematically connected with the Lumley triangle to investigate the hypothesis that anisotropy exhibited spatial organization in this three-dimensional flow field. Multi-planar visualization results depicted spatially organized features in the boulder vicinity via distinct color bands. Some of the anisotropy color bands appeared to originate upstream, wrap around the boulder, detach at the boulder flank, and then extend downstream into the wake. In the upstream region, these specific features corresponded with an approach to two-component turbulence due to the suppression of boulder-normal turbulence. The wake was generally characterized by banded anisotropy regions that originated in the near wake, had a predominantly streamwise orientation, and whose signatures were still visible in the far wake. The complex organization of these bands was investigated via transverse-vertical planes in the wake. In addition, strongly anisotropic behavior was observed via both 2D and 3D visualizations near the expected tip vortex location for a wall-mounted cylinder.