Numerical Prediction Analysis Of Propeller Exciting Force Under Propeller-ice Interaction

In recent years,with the international community on the Arctic waterways and polar resources concern rising,the research of ice-ship receives more attention and has made considerable developments.The multi-operating condition of ice-ship cause the working environment of its propulsion device is very greatly different from conventional ships.Especially in the ice-breaking sailing condition,the ice frequently soaks to the ship’s bottom surface,skids to the flow field in front of the propeller,produces extreme loads on propeller blade,influents on hydrodynamic performance of propeller.Because the existence of ice results in the nonuniform flow field,the propeller exciting force sharply increases,and even causes serious noise,vibration and cavitation problems.In this paper,the ice class propeller Icepropeller Ⅰ was set as resaersh object.The hydrodynamic performance of IcepropellerⅠ in multiple working conditions was calculated by using CFD numerical simulation.Through comparing the calculation results with test results,the calculation method is proved to be feasible and accurate.In this numerical simulation method,the exiciting force in ice blocked flow of IcepropellerⅠ was calculated in multiple working conditions.The working conditions include in different advance coefficients and different relative locations of ice and propeller.The time domain data of propeller unsteady bearing force and fluctuating pressure was obtained.Through Fast Fourier Transform,the time domain data is transformed to frequency domain date in order to analyze the frequency domain characteristics of propeller exciting force.At last,the propeller exciting force changing was analyzed and summarized.With the increase of advance coefficient,the fluctuating amplitudes of bearing force gradually increase,but the fluctuating amplitudes of fluctuating pressure decrease in ice blocked flow.In order to calculate the propeller cavitation excitiong force in ice blocked flow,the unsteady calculation method of propeller cavitation was established.The propeller E779 A was set as calculation object,and its cavitation form and hydrodynamic performance were calculated.The numerical simulation results agree well with test results,so the accuracy of cavitation calculation method was certified.Based on this method,the cavitation performance of IcepropellerⅠ was simulated.The calculation results include in the cavation form on the surface of blade and propeller cavitation exciting force results.Through the propeller cavitation exciting force was compared with non-cavitation exciting force,the influence of cavitation to propeller exciting force was analyzed.At last,blade pressure distribution and flow field distribution around propeller was predicted,and used to analyze exciting force.In ice blocked flow,cavitation area of blade in ice interference region obviously increases.Thehydrodynamic performance of propeller is worse,and the pulsation of cavitation exciting force is stronger than non-cavitation exciting force.The STAR-CCM+ software was used to calculate propeller exciting force in milling condition in this paper,because the overlapping grids can be generated in STAR-CCM+software.Trimmed Grid is used in the entire calculation domain,and the overlapping grid method was used for the information transfer between propeller rotation calculation domain and the ice surface caculation domain.And the gap of ice and propeller was made partial grid refinement processing,as to ensure the accuracy of flow field in detail.Based on this method,the propeller exciting force and flow field distribution in milling condition was predicted and analyzed.The pulsation of bearing force is strong,and fluctuating amplitudes in high-order blade frequency are still not ignored,but the periodicity of fluctualting pressure becomes weak.In order to simulate the actual situation of propeller-ice interaction,the propeller exciting force was made a preliminary exploration when the ice block was in the state of motion.The ice block was set a relative velocity,and was gradually closed to the propeller.In this process,the propeller exciting force was monitored,and the flow field distribution was predicted to analyze exciting force changing.It was found that time-average value and pulsating range of bearing force increased when the ice block was gragually closed to the propeller,but it had a little influence to fluctuating pressure.