Experimental and numerical investigation of bow wave and wake flows around towed surface-piercing cylinders

Abstract

An investigation was conducted to study the flow characteristics around towed surface-piercing cylinders and understand the mechanisms behind the bow wave and wake region formation. The experiments took place in a towing tank using three different cylinder models, covering a range of Froude numbers based on cylinder diameter from 0.28 to 1.73. Three-cylinder models are considered M1 is circular, M2 is semicircular ellipse and M3 is elliptical. Numerical simulations were performed using the OpenFOAM framework, considering turbulence effects through the unsteady Reynolds-Averaged Navier Stokes equations with the Shear Stress Transport k-ω turbulence model. The numerical results matched well with the experimental data. The bow wave's general features were similar across all cylinder models, with the height increasing as the Froude number rose. Froude numbers between 0.28 and 0.58 displayed a smooth surge surface, transitioning to a rough surface with roll-up initiation between 0.87 and 1.15. At Froude numbers 1.44 to 1.73, a fountain-like bow wave formed. Models M1 and M2 had the same average bow wave height, approximately 15% higher than that of Model M3. The depression depth or air ventilation at the trailing edge of the cylinders increased with the Froude number. Model M1 exhibited a greater depression depth than Models M2 and M3 at Froude number 1.15, and this difference further increased at Froude number 1.73 due to high vorticity and adverse pressure gradient generated by Model M1. Vortex coherent structures visualization revealed that at a low Froude number of 0.58, only the Karman vortex at the trailing edge was observed. At Froude number 1.15, the deep wake region maintained predominantly two-dimensional vortex structures, while the free surface displayed pronounced three-dimensional vortex structures. Model M1 had a drag coefficient approximately 40% higher than Model M3. These findings are valuable for engineering applications, particularly in the design of submarine masts.