A new high aspect ratio water channel facility to study the interaction between turbulent flow and complex surfaces

A novel water facility capable of sustaining a turbulent flow with Retau up to 2000 and an aspect-ratio of 20:1 was designed and manufactured. The water channel structure is modular so that it can be adapted or modified depending on the problem under study. In particular, the test section presents two removable plugs to accommodate different types of complex walls and the boundary conditions can thus be varied. The high versatility of the channel allows multiple measurement techniques: the drag variation induced by the complex wall is evaluated through differential pressure measurements along the central axes and flow visualisation is obtained through PIV. Optical access to the full height of the channel is provided by side windows and transparent plugs, allowing the use of alternative imaging techniques such as micro-PIV and LDV. The main purpose of the study is to investigate the interaction between turbulent flow and a complex surface, specifically liquid-infused surfaces (LIS). On one hand, the ability of the LIS to reduce drag when subjected to a turbulent flow is assessed and different types of failure (oil drainage, surfactants effect) are investigated; on the other hand, modified turbulent structures near the wall are observed and described.