Numerical and experimental study of stern flaps impact on resistance and propulsion of high–speed displacement ships

Abstract

This study investigates hydrodynamic interactions between a high-speed displacement ship and various stern flap configurations. It combines towing tank model tests and advanced Computational Fluid Dynamics (CFD) simulations to explore hydrodynamics and energy-saving potential. Sixteen flap combinations were tested across Froude numbers (Fn) from 0.198 to 0.452 to understand post-installation hydrodynamics and energy-saving potential. The alignment between model tests and CFD simulations reinforces the potential of stern flaps to enhance efficiency and environmental friendliness in high-speed displacement vessels with transom sterns. CFD enhanced visualisation of flow, pressure, and other hydrodynamic parameters. The study reveals that the stern flaps reduce resistance and effective power, saving energy across all the combinations. However, the effectiveness of the flaps is limited at lower speeds (Fn < 0.198), where increasing flap angles incur higher resistance penalties. The greatest decrease in resistance is noted when the Froude number (Fn) is at 0.367, with a subsequent reduction after that. Stern flaps influence trim, sinkage, and hydrodynamic length, reducing wave-making resistance without increasing friction. Increased wake fraction and reduced thrust deduction enhance propulsion efficiency, while stern flaps suppress waves, lowering overall resistance. A reduction of effective power by 6% was observed in the present study. This research provides valuable insights into stern flap hydrodynamics and energy-saving potential, guiding ship design and operation.