Investigation On The Coupling Characteristics Of The Propeller And Shaft In Non-uniform Inflow

With the magnificent change of the ship technology,modern ship is gradually to large-scale,fast and quiet.Some severe challenges are putted forward to the vibration and noise performances of the ship.The measuremental results in the real ship show that the total sound pressure levels are too higher,the main reason is that the sound pressure levels are too higher at 1/3 octave sound pressure spectrum and some frequency band or frequency points of the line spectrum,and these are mainly in the low frequency band.Several line spectrums or narrowband spectrums at low frequency are the main characteristics of the ship radiated noise.This characteristics are closely realted to the unsteady characteristics of propeller in non-uniform flow field caused by the ship stern.Therefore,based on the summary about the present research,the method on the numerical simulation and model test are used to investigate the unsteady vibration charactersitics of the propeller-shaft system and the dynamics strain of the balde under no excitation and external ones.The main research contents are as follows.In the second chapter,the control equations are given on the unsteady numerical simulation of the propeller.The basic principle of the dynamic mesh method and sliding mesh method are peresented in details.And the RANS turbulence model commonly used in the unsteady numerical simulations of the propeller is summarized.Moreover,the dynamic mesh method and sliding mesh method are developed to calculate the unsteady characteristics of the propeller in nine-order non-uniform flow fields.The applicability of the dynamic mesh method in the unsteady numerical simulation of the propeller is verified by the comparsion of the results of two viscous flow method,the potential flow method and the experiments.The calculation results show that,for the dynamic mesh method and sliding mesh method,the main differences exist in the interface about the simulation of the propeller flow field.However,for the unsteady bearing forces,the results of the two viscous flow methods are better than the potential flow method.Therefore,a reliable calculation model is established for the unsteady numerical simulation of the propeller.In the third chapter,the dynamics mesh method and SST k-? turbulence model are employed to calculate the unsteady characteristics of the propeller under external axial-excitation and external transverse-excitation.The numerical results show that,a new response component will appear in the frequency-domain of the unsteady forces of the propeller under the action of the external axial-excitation.The frequency is always consistent with the excitation frequency.The amplitude of the response frequency increases with the increasing of the excitation frequency.And there exists a quadratic function relationship between them.Under several external axial-excitation with the same frequency,the amplitude of the new response frequency increases with the growth of the excitation amplitude.And a proportional relationship exists between them.When the external transverse-excitation acts on the propeller-shaft system,a new significant response component also appears in the frequency-domain of the unsteady forces of the propeller.However,the frequency of this response component is found permanently to be double of the excitation frequency.The amplitude shows a gradual increaseing trend with the growth of the excitation frequency.If the exciation frequency keeps constant,then the amplitude of the response increases with increasing of the excitation amplitude,showing a power-law relationship.For the interface mechanical characteristics of the propeller and flow fields,the pressure distribution on three different disk,as well as the pressure coefficients in the blades and the vorticity will happen the obvious changes under the actions of the external axial-excitation and external transverse-excitation.And these changes become more and more obvious with increase of the excitation frequency or the excitation amplitude.In the fourth chapter,based on the gravity circulation water tunnel,the unsteady vibration characteristics of the propeller-shaft system are measured by using the micro acceleration sensor under the condition of non-uniform.Meanwihle,the dynamic strain characteristics of the blade are investigated by the strain gauge and underwater data acquisition instrument.The experimental results show that,the shaft frequency and the first-order blade passing frequency can be obviously reflected in the frequency spectrum of the unsteady vibration characteristics of the propeller-shaft system.Moreover,when the angular frequency number of non-uniform inflow is equal to the blades number or its euploid number,the first-order blade passing frequency will be enhanced.When the external axial-excitation act on the propeller-shafting,a new response component will appear in the frequency-domain of the unsteady vibration of the propeller-shaft system,and the frequency is consistent with the excitation frequency.When the excitation frequency aggrandizes,the amplitude of the response frequency will increase.When the external axial-excitation with different amplitude acts on the propeller-shaft system,the amplitude of the response frequency will increase with the growth of the excitation amplitude,showing a proportional relationship.Moreover,the amplitude of the response frequency increases with the increasing of the rotational speed.For the dynamic strain of the blade,the frequency-domain characteristics can obviously reflect the coupled vibration peculiarity between the non-uniform flow field and the propeller.There exsit obviously peaks in the shaft and harmonic frequencies for the dynamic strain,and the amplitudes of the dynamic strain are the most obvious at 0.6R.When an external axial-excitation is loaded at the propeller-shaft system,then a new response frequency can appear in the frequency spectrum of the dynamic strain of the blades.This response frequency keeps consistent with the excitation frequency.