EAGER: Towards a Universal Roughness Model

Flows over rough boundaries arise in many scientific and engineering disciplines including urban and vegetation canopies, maritime biofouling, additive manufacturing of flow passages, pipe transport and others. This research explores a new, accurate, general, physics-inclusive, and computationally efficient modeling framework for these flows, based on space/time averaging and attendant modeling of the Navier-Stokes governing equations. This research is enabled by proposed large scale Direct Numerical Simulations of these rough wall systems, which provide near-exact space/time distributions of model terms, thereby enabling uncertainty quantification of model accuracy. A broadly applicable Distributed Element Roughness Model, as proposed here, would be a disruptive contribution to fluid dynamics communities involved in a wide range of disciplines, including aero/hydrodynamics, atmospheric science, bio-fluid dynamics, and energy science. Also, considering that progress in machine learning has placed an ever-increasing premium on large data sets, the proposed database of Direct Numerical Simulations will enable new physics discoveries, new turbulence models, and, importantly, a significant increase in validation data, for the fluids engineering and science communities. Also, the proposed research activities will train a new generation of graduate students with experience in high performance computing, computational fluid dynamics, and turbulence modeling.The goal of the project to explore Double-Averaged Navier-Stokes closure as a universal roughness modeling paradigm. Existing rough-wall models parameterize surface geometry/structure and are empirical correlations between these parameters and hydrodynamic/aerodynamic properties. There, physical processes responsible for the momentum loss and transport are not explicitly modeled, so these models do not generalize well to roughness geometries outside of their correlation basis. By contrast, the horizontally and temporally averaged governing equations include terms representing all physical processes present in the roughness-occupied layer, and these can each be explicitly modeled. This approach, a Distributed Element Roughness Model, is a necessary and sufficient framework for the development of a universally applicable roughness model. In this approach, models are required for the Reynolds stress, the dispersive stress, and the forces at fluid-material interfaces. In the proposed research, the PIs will explore development of such a complete roughness model, based on modeling these closure terms in the Double-Averaged Navier-Stokes equations. The ultimate goal of the proposed research is a universal modeling paradigm, and a universal rough wall model.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.