H Ghasemi۱ - Associated Professor of Amirkabir University of Technology,Tehran
A Imantalab - ۲M.Sc .student of Hydromechanics at Amirkabir University of Technology,Tehran
E Rajabiani - M.Sc .in Naval Architecture, S.V.G .Research Center, Tehran
M Rostami - M.Sc .in NavalArchitecture, S.V.G .Research Center, Tehran

Design of the nozzle profile and the nozzle length depends seriously on requirements with respect to efficiency, danger of flow separation on the nozzle, and critical cavitation indexes on nozzle and propeller. In heavy load conditions flow separation occurrence is inevitable .It is clear that the drag of the nozzle will increase sharply in case of flow separation occurrence on the interior or exterior surface of the nozzle, furthermore, the propeller will be operating in a highly irregular flow if separation occurs on the interior surface of the nozzle )something which usually occurs in accelerating nozzle types.(In any case, the efficiency of the system would begin to decrease .Therefore, cares must be taken to prevent flow separation on the nozzle surface .In order to examination, the maximum loading of the nozzle without separation, the flow around the nozzle profile can be assumed to be two-dimensional .From the two-dimensional airfoil flow, the approximation that flow separation occurs if the lift coefficient,

Flow Separation, Accelerating Marine Ducts, Vortex Representative Method