Flow structures in the near wake of permeable circular cylinders in shallow water

Abstract

The flow structure in the wake of circular screen cylinders was investigated experimentally by dye visualization and high-image density Particle Image Velocimetry (PIV) technique in shallow water. The effect of permeability was analyzed for four permeability ratios across varying Reynolds numbers. Results showed that permeability significantly influences the wake flow dynamics. Jet-like flow structures and Kelvin-Helmholtz instabilities with pulsating behavior were observed at minimum permeability, i.e., β = 0.4. As permeability increases, these structures extend downstream (β = 0.5), weaken (β = 0.6), or completely disappear for β = 0.7. Velocity deficits were found to be highest at β = 0.4 and decreased with greater permeability values. Turbulent fluctuations are dominant along shear layers that diminish with increasing permeability. Two-point spatial correlations revealed strong vortical interactions for β ≤ 0.5 that diminish for β ≥ 0.6. These findings highlight the critical role of permeability in the wake characteristics of circular screen cylinders, providing insights for relevant engineering applications.