Evaluation of turbulence models for estimating the wake region of artificial reefs using particle image velocimetry and computational fluid dynamics

Abstract

Many studies have evaluated the performance of turbulence models used for computational fluid dynamics (CFD) analysis of artificial reefs (ARs), but an optimal model remains elusive, particularly in terms of wake length and areal estimation. Only a few models were used in previous studies and no report has yet investigated wake shape. We compared five turbulence models and verified the CFD results using particle image velocimetry (PIV). A standard k-epsilon model, renormalization group k-epsilon model, k-omega model, shear stress transportation k-omega model, and Reynolds stress model (RSM) were used. A down-scaled half-ball-type AR was devised and CFD and PIV analyses were performed. Three different inlet velocities (three Reynolds numbers, Re) were considered in each model, and the CFD and PIV results were compared. Wake lengths obtained in the PIV experiments were 1.05 L (Re = 2632), 0.90 L (Re = 5655) and 0.85 L (Re = 8782), respectively. The RSM well-reflected this, especially when Re = 2632 (difference +1%) and Re = 5655 (difference -2%). PIV revealed that all wake regions had unique shapes, reflecting flow divergence (local upwelling) from the end of the wake. Considering such divergent flow, the RSM optimally predicted the overall characteristics of the wake region.