Investigation of Scour Caused by Twin-Propeller Jet

This study investigated twin-propeller-induced scour on sandy seabeds with varying grain sizes (d50 = 0.11, 0.5, and 0.95 mm) through a series of laboratory experiments. The effects of propeller rotation speed (rpm), offset height (y0), propeller diameter (Dp), and sediment grain size (d50) on scour development were examined. Results indicated that sediment grain size significantly influences scour patterns. A key objective was to develop predictive expressions for primary scour characteristics at equilibrium: maximum scour depth (Smax), scour hole length (Lmax), and maximum scour width (Bmax). Using a nonlinear regression approach, the proposed expressions demonstrated strong predictive performance. Findings show that equilibrium scour depth increases with higher Froude numbers (F0) but decreases with larger sediment size (d50) and higher propeller offset (y0). Additionally, empirical equations were formulated to predict the temporal evolution of scour depth, achieving high correlations with experimental data (R2 > 0.97). These results enhance understanding of scour induced by unconfined twin-propeller jets in harbors or navigation channels and provide valuable data for the design and protection of harbor basins.