Heat transfer in ground-elevated roughness elements

Over the years, extensive research has been developed on momentum and heat transfer characteristics for turbulent boundary layers over k-type and d-type roughness elements. Interestingly, a relatively unexplored new class of surface roughness, referred to here as ground-elevated roughness (or e-type roughness), has emerged in numerous engineering applications (e.g., solar energy), where roughness elements (i.e., solar panels) are mounted at a certain height above the ground. As a result, in flow over e-type roughness, it is hypothesized that a new relevant length scale is to be introduced associated with the distance from the ground. In this study, Large Eddy Simulations (LES) will be employed to investigate both heated and non-heated e-type roughness configurations, using Uintah MPMICE, a fluid-structure interaction computational fluid dynamics platform. The e-type roughness elements are systematically organized in rows oriented either perpendicular or parallel to the mean flow, thereby introducing organized streamwise and spanwise heterogeneity. The first one generates Kelvin-Helmholtz instabilities that trigger spanwise rollers, while the latter creates secondary circulations arising from the anisotropy of Reynolds stress terms and the buoyancy torque. This work builds on recent studies that have explored the effect of roughness interspacing and alignment with the mean flow in canonical tree elements to understand the confluence of streamwise and spanwise heterogeneity in developing k-type or d-type flow, as well as roughness or topographic response. However, the present study aims to isolate the flow response to e-type roughness by independently introducing streamwise and spanwise heterogeneity with thermal effects. Specifically, the first objective is to determine whether elevated roughness exhibits distinct fluid behavior compared to classical k-type or d-type roughness by systematically varying the streamwise spacing between roughness rows in non-heated cases with streamwise heterogeneity. The second goal is to analyze the thermal transport by comparing heated streamwise and spanwise heterogeneous configurations to determine whether spanwise rollers or secondary circulations more effectively enhance heat transfer over elevated roughness arrays.