Effects of bidirectional deformation on colony-scale flow around a reticulate sea fan

Reticulate sea fans such as Gorgonia ventalina exhibit whole colony flexibility in habitats experiencing moderate to high flow currents. The entire colony can undergo unidirectional and bidirectional deformation (oscillatory motion) depending on the environmental flow conditions. While unidirectional deformation benefits attachment by reducing drag and feeding by influencing local flow, the impact of bidirectional deformation on filtration and drag forces remains unclear. To investigate this, PIV experiments and numerical simulations were conducted on an artificial stiffened model of G. ventalina under varying oscillation parameters (angular amplitude, frequency) with and without continuous background flow. Findings suggest that bidirectional deformation induces flow recirculation and fluid displacement across the downstream and upstream sides of the colony. Increased angular amplitude results in generating more vorticity, retaining particles within the vicinity for further encounters. Vorticity production is enhanced at lower frequencies. The effect of the unsteady pressure fields on drag generation during bidirectional deformation will be presented.