American Journal of Mechanical Engineering, 2016, Vol. 4, No. 6, 218-225 Available online at http://pubs.sciepub.com/ajme/4/6/3 ©Science and Education Publishing DOI:10.12691/ajme-4-6-3 A Combined Method to Design of the Twin-Waterjet Propulsion System for the High-Speed Craft Hassan Ghassemi * , Hamid Forouzan Department of Maritime Engineering, Amirkabir University of Technology, Hafez Ave, No 424, P.O. Box 15875-4413, Tehran, Iran *Corresponding author: gasemi@aut.ac.ir Abstract This paper is presented a combined method to design of the twin-waterjet propulsion system for high- speed craft (HSC). First, a practical approach employed to obtain the main data of the geometry of waterjet system. Thrust of the system is calculated by the momentum theory. Next, RANS solver is performed with the realizable ε − k turbulence model. The numerical results of the pressure distribution coefficient, thrust coefficient and the flow field inside the duct are presented and discussed. Keywords: twin-waterjet, practical and numerical method, pressure and thrust coefficients Cite This Article: Hassan Ghassemi, and Hamid Forouzan, “A Combined Method to Design of the Twin- Waterjet Propulsion System for the High-Speed Craft.” American Journal of Mechanical Engineering, vol. 4, no. 6 (2016): 218-225. doi: 10.12691/ajme-4-6-3. 1. Introduction The use of conventional propellers for HSC is not practical due to the high-speed of the craft relative to the water. The high water speed results in cavitation on the propeller with a resulting loss of thrust and efficiency. Waterjet propulsion systems overcome this problem by using an intake to slow the water relative to the craft and reduce the likelihood of cavitation before delivering it to the rotor. Figure 1 show the schematic of the marine vehicle using waterjet propulsion system. Most of researches on the waterjet propulsion have been carried out by experiments for last decades [1]. Levy presented a brief description of the water-jet propulsion system as applied to hydrofoil craft, and a discussion of the salient hydrodynamic aspects of the problem of fitting the main propulsion system to the specified thrust-versus-speed requirements [2]. An example of predicted vessel performance regarding speed, power and propulsor RPM is presented which includes engine characteristics and BHP versus RPM [3]. Ghassemi & Mazinani carried out the practical method to obtain the geometry data of the waterjet system for a HSC in order to generate the required thrust [4]. A comprehensive formula based on the momentum theory studied by Allison [5]. General jet efficiency formulae are obtained based on many parameters. The application of CFD is continuously increased by virtue of the advancement of numerical algorithms and computer hardware. Nevertheless, CFD works are mostly devoted to the intake duct and a few applications to waterjet pump were accomplished [6]. Most of them did not solve whole system of waterjet propulsion, consisting of intake duct, rotor, stator, and discharge nozzle. Recently, Park et al. [7] did waterjet performance using RANS code and analyzed the flow in the duct including full elements. A comparative study between a computation and an experiment has been conducted to predict the performance of a Pod type waterjet for an amphibious wheeled vehicle carried out by Kim et al [8]. Lam et al [9] presented time-averaged velocity and turbulence intensity at the initial plane from a ship′s propeller using a computational fluid dynamics (CFD) approach. Also, CFD analysis is applied to free surface flow around a waterjet propelled ship by Hino and Ohashi [10]. A series of self-propulsion tests of a catamaran design at medium- speeds is proposed to study the influence of the hydrodynamics at medium-speeds on the waterjet propulsor [11]. In the paper two original dimensionless numerical procedures, one referred to jet units for naval applications and the other more suitable for planing boats, are presented [12]. Experiments and simulations are carried out to investigate the reactive thrust and the conversion efficiency of cylindrical nozzles, conical nozzles and optimized nozzles [13]. Tokai et al was performed to investigate the capability of a URANS flow solver for the accurate simulation of waterjet propelled ships [14]. This paper has two parts, the first part is to find the geometry of system for the special craft by the practical method and next to analyze the flow field and the performance of the waterjet propulsion system by the CFD code. The following sections are organized as follows. Practical method is described in Section 2. The governing equations of the CFD and its numerical method explained in Section 3. The numerical results are presented in Section 4, and Section 5 is given for the conclusions. 2. Practical Approach to Design the Waterjet Before going ahead to analyze the waterjet system by CFD, it is needed to estimate the geometry and size of the