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Corresponding Author

Mostafa, Nabil

Subject Area

Mechanical Power Engineering

Article Type

Original Study

Abstract

An experimental analysis and numerical computation were conducted for flow around ship spoiler mounted at the bottom of the ship and subjected to air injection The air was injected beside the spoiler and at a distance equals the spoiler length to stabilize cavities behind spoilers. This system was proposed to control the roll, pitch motion and speed of the ship, with injecting exhaust gas behind spoilers. The forces and moments acting on the ship's bottom depend on spoilers' inclination, extensions and positions relative to the ship's center of mass. To improve the understanding of the parameters affecting the flow field aroundsuch spoiler, experimental images of bubble formation are triggered and compared with the computed flow field at different spoiler inclination angle, and air injection position. Two dimensional Navier-Stokes code is used to model the two-phase flow field around a ship spoiler with the free surface simulation in Piecewise Linear Interface Construction (PLIC) method. The governing equations are discretized on a structured grid using an upwind difference scheme. For different conditions, the bubbles shape, the two-dimensional flow field around the spoiler body and the pressure variation on the wake of the spoiler body are computed, Flow field and bubble formation around the spoiler are recorded experimentally at different condition and time sequence with scientific video camera The Froude number was about 1.6 based on spoiler length. The computational and experimental results show that there is a good matching of bubble formation in the spoiler with 90', but in the condition of 45° the experimental images show that bubble filled the space between the bubble and the body of the ship. This is may be due to the two-dimension computational model consideration. So, a water layer was isolated between the bubble and the ship body. In the case of spoiler with 45° inclination angle, the flow is circulated inside the bubble. The bubble shape is longer which gives more negative pressure on larger area. The moment around the 450 spoiler fixationpoint is seven times of that around the 90° spoiler. In double injection condition beside and at a distance equal the horizontal spoiler length downstream the spoiler, the bubbles are more stable and the moment is higher by 7.9 and 17.8 times after 1.2 and 2 seconds, respectively, than that around the 90° spoiler. Thus, changing inclination spoiler angle and position relative to injection angle will give different bubble shapes which give different forces to control the roll, pitch motion and speed of the ship.

Keywords

Ship; spoiler; Cavitation; Hydrofoils; Free surface; Two-Phase flows

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