The numerical model of the unsteady flow field of ducted propellers is based on CFD (computational fluid dynamics). By applying the numerical model, the unsteady hydrodynamic performance of the ducted propeller with the fracture at different positions of a certain blade is numerically analyzed under three different wake current fields. Based on regress analysis ,the relationships between the mean KQ、mean KT and the quantity of the blade fracture of ducted propellers are obtained; and the relationships between hydrodynamic coefficients Kp, KQ, KFy (Bearing force coefficient of the propeller) and wake current fields , the quantity of the blade fracture are respectively further analyzed. The results show that: (1) with the increase of the quantity of the blade fracture, the amplitude of bearing force periodic variation of propellers increases, while the thrust and torque reduce; (2) the bearing force of propellers is similarly sine-varying, and the frequency of its variation is unrelated to the normal variation frequency of the wake current field. The more non-uniform the wake current field is, the more the amplitude of its periodic variation is; (3) the thrust and torque of propeller are similarly sine-varying, and the frequencies of their variation are related to the normal variation frequency of the wake current field. And the frequencies equal the shaft frequency multiplied the normal variation frequency of the wake current field. The more non-uniform the wake current field is, the more the amplitude of their periodic variation is.

After a torpedo anchor is released into water during its installation, the directional stability of this anchor is an important factor for its penetration performance. In this paper, a CFD method is used to simulate the falling behavior of the anchor, and detailed parametric studies are conducted to analyze the effects of various parameters to the directional stability. The results show that some parameters like weight, gravity center, and aspect ratio of fin have significant influence on the directional stability.

Firstly, the calculated model was created in UG and GAMBIT, and then the Moving Mesh method was adopted to simulate thrust and torque of ducted propeller using FLUENT in the open water. The thrust, torque and bearing force of ducted propeller in three different wake fields were calculated. And the influence on the performance of ducted propeller by the wake fields was analyzed.

The numerical model of the unsteady flow field of ducted propellers is based on CFD (computational fluid dynamics). By applying the numerical model, the unsteady flow field of the ducted propeller with the fracture in different positions of a certain blade is simulated and its unsteady hydrodynamic performance is numerically analyzed. By extracting the fluctuating pressure data of the duct inner wall monitoring points,the fluctuating pressure-time oscillogram of ducted propellers is obtained, and then the spectrum is obtained by FFT transformation of the oscillogram. A blade fracture fault diagnosis technology of ducted propellers, which combines oscillogram analysis method with spectrum analysis method, is put forward by analyzing and studying the oscillogram and the spectrum.

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