Journal of Naval Architecture and Marine Engineering Dec., 2020 http://dx.doi.org/10.3329/jname.v17i2.44950 http://www.banglajol.info 1813-8535 (Print), 2070-8998 (Online) © 2020 ANAME Publication. All rights reserved. Received on: Jan., 2020 EFFECT OF GEOMETRICAL FEATURES ON HYDRODYNAMIC PERFORMANCES OF THE CONTRA-ROTATING PROPELLER F. Bouregba 1* , M. Belkadi 1 , M. Aounallah 1 and L. Adjlout 1 1 Laboratoire d'Aero-Hydrodynamique navale LAHN, USTO-MB, Oran, Algeria. * E-mail : fatimabouregba@hotmail.com, fatima.bouregba@univ-usto.dz Abstract : New contra-rotating four-bladed DTMB propeller configurations operating in open water are numerically studied to determine their hydrodynamic performances. The unsteady turbulent flow around propellers is modeled by RANS equations with SST k-ω turbulence model and solved by a CFD software. The computational domain is divided into two blocks linked with a rotating interface. The predicted results show that the thrust and efficiency of the contra-rotating propellers (CRPs) increase compared to the single propeller, leading to a significant reduction of the propeller diameter. The variation in axial spacing and angular displacement seems to have little effect on the CRPs efficiency. The results also show that the thrust can be further improved by adopting a moderate negative twist angle of the rear propeller. Keywords: Contra-rotating propellers (CRPs), axial spacing, angular spacing, twist angle, CFD. NOMENCLATURE D Propeller diameter u i Time average velocity J Advance coefficient j i u u   Reynolds stress K Q Total torque coefficient Z Blade number K T Total thrust coefficient Greek symbols L/D Axial spacing  Twist angle n Propeller rotational speed  Water density P Time average pressure  Dynamic viscosity Q Total torque 0  Propeller efficiency T Total thrust  Angular displacement t Time 1. Introduction The performance of marine propellers and in particular their propulsive efficiencies have not ceased to undergo spectacular progress since their invention. Several types of thrusters have been developed such as the contra- rotating propellers which the principle is based on the use of two propellers mounted on two coaxial shafts.The advantages of these propellers include the possibility to recover a part of the forward propeller rotational energy loss which leads to better efficiency and the possibility to use a lower rotational speed for the same diameter compared to a single propeller. Although on commercial vessels mechanical complications and high maintenance costs prevent the adoption of this system, some offshore vessels still use this technology. The application of CRPs to ships allows providing more power on the same engine without fearing the appearance of the cavitation phenomenon. As for its application to torpedoes, the torque compensation generated by the front propeller is insured by the second one, which facilitates the rectilinear trajectories without piloting. Among all the researchers who contributed to the performance study of contra-rotating propellers, it is obvious to mention first the work of Miller (1976) for his experimental investigation on the CRPs behavior in open water. He observed that for high advance coefficients, the thrust of the front propeller is greater than that of the