3D Numerical simulations around roughness elements
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hdl:2117/401152
Document typeMaster thesis
Date2023
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Abstract
In the field of hydraulic engineering, computational fluid dynamics (CFD) has emerged as a potent and valuable instrument in recent years. It empowers researchers with valuable insights into intricate flow phenomena occurring in rivers and streams. Numerical simulations provide a cost-effective and efficient approach to study diverse flow conditions, encompassing lowland rivers with moderate flow velocities to steep rivers characterized by high velocities and the presence of roughness elements, like boulders. The comprehension of flow behavior in these varied environments holds utmost importance in predicting flow hydrodynamics, sediment transport, and riverbed stability.
One of the key challenges in numerical simulations is accurately modeling flows near solid boundaries, particularly those attached to the wall. Near-wall flows exhibit complex velocity profiles and turbulence structures, which are critical in determining flow resistance and sediment transport.
However, resolving these small-scale turbulent structures requires computationally expensive approaches like Large-Eddy Simulations (LES). As a result, Reynolds-Averaged Navier-Stokes (RANS) simulations have been commonly used due to their computational efficiency. Nonetheless, RANS models often fail to capture the dynamics of large-scale turbulence accurately, leading to potential inaccuracies in flow predictions.
To overcome the limitations of RANS and LES, the focus is on employing a wall-modeling approach to study flows attached to roughness elements, such as boulders, in steep rivers. The primary objective of this project is to develop a comparison the flow fields for simulations of detaching flow with and without wall-model as well as finding out if the wall-model is applicable to the detached flow case. All by using two different modeling techniques, Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Detached Eddy Simulations (DES).
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