Wall roughness effects in turbulent flows using large-eddy simulation

Hydraulic installations can operate outside their nominal range, leading to accelerated wear and more frequent maintenance needs. It is established that the roughness of waterway surfaces in turbines and pump-turbines have a significant impact on the safety, performance, and efficiency of hydraulic machines, particularly by altering the turbulent flow structure and increasing pressure losses.

The prediction of these losses typically relies on an equivalent roughness height, which are not enough acccurate. The effects of roughness can be fully resolved using numerical simulation, but this approach requires very significant computational resources.  If one wishes to avoid using a mesh adapted to surface roughness, immersed boundary methods are a promising alternative, as they can handle complex geometries derived from scanned surfaces.

This thesis aims to contribute to the analysis of hydraulic flows near rough walls by performing high-fidelity simulations of representative configurations. A volume penalization method will be used to take into account the wall roughness. The following steps are proposed:
• Sep-up numerical simulations of rough walls on canonical configurations, whether regular or irregular, at moderate Reynolds numbers;
• Analyze the physical phenomena to feed roughness models and to improve the lifespan of these energy systems;
• Study roughness effects on the development of cavitation along an hydrofoil.

All generated data will be used to support the development and validation of wall models that account for roughness, which are being developed as part of another thesis at HES-SO (Sion, Switzerland). Comparisons with experimental data from this same thesis will also be implemented throughout the work. Finally, all results obtained from these two theses will be compiled into an open database for the scientific community.

The P’ Institute is a research laboratory in the fields of physical sciences and engineering sciences.

Its activities cover a wide range of topics, from materials physics to fluid mechanics, mechanical engineering, and energy. Its primary areas of focus are transportation and energy, with a particular emphasis on environmental considerations.

Master 2 or engineering degree in fluid mechanics. Knowledge on numerical methods, turbulence and  computer science (programming, processing of large volumes of data, high-performance computing) will be appreciated.