Pressure and drag influences due to tunnels in high-speed planing craft

Article type: Research Article

Authors: Subramanian, V. Anantha | Subramanyam, P.V.V. | Ali, N. Sulficker

Affiliations: Department of Ocean Engineering, Indian Institute of Technology Madras, Chennai 60036, India

Note: [] Corresponding author. Tel.: +91 44 22574812; E-mail: subru@iitm.ac.in.

Abstract: Tunnels or ‘propeller pockets’ are often a necessity in planing crafts, in order to accommodate propellers and minimize the shaft angle. Computational Fluid Dynamics (CFD) is increasingly being used as a design tool for the purpose of modelling ship flows. This is due to advances in computational methods together with improvement in performance and affordability of computers. Qualitative information to decide the relative merits of aspects, such as flow alteration in and around the ship hull, can be usefully deduced from careful CFD based analysis. In this paper, work has been undertaken to assess the pressures and resistance characteristics of a single chine high speed planing hull. A relatively full sized tunnel has been introduced in the numerical model. Using k−ε turbulence model in FLUENT, combining the predicted trim angle from equilibrium considerations and an iterative process, the stable equilibrium flow conditions have been modelled. The dynamic pressures have been evaluated and by integration, they have been matched with the total weight of the vessel. Single phase flow has been used to obtain the dynamic pressures in the underwater hull region. The numerical model predicts more favourable trim and qualitatively reduced resistance. Experiments conducted in a towing tank, using a model with and without the tunnel, confirm that by providing the tunnel there is improvement in the resistance by appreciable reduction. Pressure measurements confirm the validity of the numerical predictions obtained from CFD. It is quantitatively established that tunnels may be designed with beneficial effects for resistance.

Keywords: High speed planing craft, tunnels, resistance, extrapolation methods, pressure distribution, CFD studies

Journal: International Shipbuilding Progress, vol. 54, no. 1, pp. 25-44, 2007