Numerical Study Of The Hydrodynamic Performance Of Podded Propulsor

As a new type of electric propulsion device, the podded propulsor has been usedin commercial and naval ships more and more widely. Meanwhile, with the advancesin CFD techniques, numerical simulation methods are also becoming more and moredeveloped for predicting the hydrodynamic performance of podded propulsor inviscous flow. In this thesis, the hydrodynamic performance of podded propulsor isstudied by RANS method using the commercial software FLUENT.Firstly, the computation model is studied. With the comparison of calculation andtest results and y+distributions, an appropriate first-layer thickness of boundary layergrids is confirmed. The numerical results for three kinds of k-ε turbulence models andtwo kinds of wall functions are compared, which show that the calculation resultswith RNG k-ε model and non-equilibrium wall functions agree better with test results.In the comparison of different models for simulating rotational motion, it is found thatnumerical results from the MRF model are closer to those from the sliding meshmodel. In addition, using the MRF model the propeller blades at different angularpositions are calculated, and the results are compared with the unsteady results of thesliding mesh model, which show that the thrust and torque with MRF model are closeto the unsteady results, but the errors of lateral forces are large. Calculation with MRFmodel cannot completely replace unsteady calculation, but MRF model can be usedappropriately according to the actual need, in order to save calculation time.Then the effects of strut gap and hub gap on podded propulsor hydrodynamicperformance are studied. Numerical results indicate that the strut gap has littleinfluence on propeller blade and propulsor unit thrust and torque. Therefore it is quitesafe to neglect the streamlined body and the end-plate in CFD simulations. The hubgap has little influence on the hydrodynamic forces of the propulsor unit and propellerblades; the pressure on the downstream face of hub acts as thrust, and the magnitudeof which is about2%~3%of the blade thrust; and when the distance between the downstream face of hub and the propeller trailing edge is kept constant, the hub gappressure decreases with increasing gap width.The scale effect on podded propulsor performance are also studied. The modelscale and full scale models are calculated, and the results show that compared to themodel scale propulsor, the propeller thrust in full scale increases, the resistances ofpod and strut decrease, therefore the unit thrust increases, but the propeller torquedecreases. And these variations are mainly caused by the changes in viscous forces.From velocity distributions around podded propulsor, it can be seen that the relativethickness of the boundary layer around model scale propulsor is larger, but theinfluence of propeller wake on full scale propulsor is more obvious.Finally, the podded propulsor hydrodynamic performances under steeringconditions are calculated. The calculation results about the variation of poddedpropulsor hydrodynamic performance with steering angle are consistent withexperimental results. As the steering angle increases, the thrust and torque of propellerand the lateral force of propulsion unit increase, while the thrust coefficient ofpropulsion unit decreases. And on the lateral force, the contribution from propellerblades is dominantly large in the ship hull coordinates, which indicates that on thesteering condition, the turning moment of the ship mainly comes from the propeller.