1. Scanning PIV of turbulent flows over and through rough porous beds using refractive index matching
- Author
-
Gauthier Rousseau and Christophe Ancey
- Subjects
velocity ,wall permeability ,Materials science ,010504 meteorology & atmospheric sciences ,Flow (psychology) ,Computational Mechanics ,General Physics and Astronomy ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,resistance ,symbols.namesake ,0103 physical sciences ,open-channel flow ,Porosity ,fluid-flow ,0105 earth and related environmental sciences ,Fluid Flow and Transfer Processes ,boundary-conditions ,Turbulence ,layer ,bedload transport ,Reynolds number ,Mechanics ,Velocimetry ,simulation ,Boundary layer ,Mechanics of Materials ,Representative elementary volume ,symbols ,Refractive index - Abstract
This paper presents image velocimetry measurements on turbulent flows adjacent to a permeable bed made of randomly packed glass particles. For measuring flow velocities inside the bed, the refractive index of the glass particles was matched with that of the fluid. By continuously scanning in the transverse direction, we measured the streamwise and vertical velocity components within a three-dimensional domain (3D2C-PIV), including first- and second-order turbulent statistics. We established how the scanning travel speed is associated with the laser sheet thickness and the space-time velocity fluctuations for collecting reliable measurements. The methodology was applied to free-surface flows over a sloping bed under low relative submergence and supercritical conditions. Space- and time-averaged profiles were obtained in a representative elementary volume as defined by thedouble-averagingprocedure (Nikora et al. in J Hydraulic Eng.127(2):123–133, 2001). A turbulent boundary layer over the rough bed was observed when experiments were run at intermediate Reynolds numbers Re =$$O(1000)$$O(1000). Apart from measuring subsurface velocities, this method shed light on the part played by the rough bed in the overall flow dynamics: the roughness layer was a buffer region within which porosity varied sharply and turbulent stress was rapidly dampened.Graphic abstract
- Published
- 2020