Numerical Investigation of the Automatic Air Intake Drag Reduction Strut Based on the Venturi Effect

Abstract

Drag reduction by injecting air is a promising engineering method for improving ship performance. A novel automatic air intake drag reduction strut structure based on the Venturi effect is proposed for the high-speed small water-plane area twin hull vessels in the present study. The drag reduction strut can achieve the function of automatic air intake when the vehicle is moving at high speed, and the air inhaled and the incoming flow form bubbly flows to cover the strut surface, effectively reducing the drag of the strut. Considering the longitudinal symmetry of the strut structure, a two-dimensional single-chip drag reduction strut structure is designed to facilitate analysis and a solution. The volume of fluid model is combined with the k-ω SST turbulence model, and a numerical simulation is carried out to investigate the variation of the air inflow, the air volume fraction in the bubbly flows of the strut and the drag reduction rate of the strut for different sailing speeds. The analysis result shows that when the proposed model reaches a certain speed, the external air is inhaled by the strut intake duct, and the bubbly flows are formed with the incoming flow covering the surface of the strut, thereby reducing the drag coefficient. Meanwhile, it is found that as the sailing speed increases, the drag reduction rate of the strut gradually rises and its maximum value reaches about 30%. For high sailing speeds, the drag reduction rate is affected by wave-making resistance so that it gradually declines.

Symmetry and Symmetry-Breaking in Fluid Dynamics

“…The last two papers [10,11] address propulsion in water, but in very different contexts: the first is a fundamental investigation of a surprising swimming mechanism; the second, an engineering design for reducing drag in high-speed vessels. Jean-Luc Thiffeault from the University of Wisconsin-Madison offers [10] a simple mechanical "toy" model for a micro swimmer, which shakes from side to side but nevertheless moves forward.…”

“…The effect depends on forcing that also exerts a torque and, crucially, on some form of friction. A numerical investigation of a drag-reducing mechanism for a surface ship is carried out in the concluding paper by a group of researchers from Harbin Engineering University led by Hai An [11]. The paper proposes a novel design of a partially submerged strut attached to the vehicle, with the air intake above the water line and air outlet below, producing a bubbly flow, which reduces skin friction.…”