| Ship noise will not only damage the health of crew,but also affect some equipment.At the same time,some special ships need to control noise to meet their stealth performance.The aerodynamic noise of pipeline system is an important part of ship noise,and its influence cannot be ignored.As a typical pipeline structure,the internal flow of exhaust ejector has the characteristics of high speed and large flow.It is necessary to study it.Taking the marine gas turbine exhaust injection as the research object,the flow field and sound field characteristics are studied by numerical simulation.The specific research contents are as follows:Firstly,the simulation calculation of two typical research objects is carried out,and the subsequent research method of aerodynamic noise is determined by comparing the simulation results with the experimental results: the characteristics of aerodynamic sound source inside the injection are studied by Lighthill acoustic analogy and M?hring acoustic analogy,and the jet noise outside the injection is simulated by SNGR method.Then,the three-dimensional flow field of the exhaust injection is simulated.The simulation results show that there is little difference in the distribution law of the flow field in the exhaust injection under different working conditions,and the turbulent kinetic energy inside the mainstream nozzle of the injection and its subsequent mainstream flow is large.The turbulent kinetic energy peak of the jet outside the injection is located in the outlet area of the injection;Through the simulation calculation of the tab injection,it is found that the tab will cause more vortices in the subsequent flow field.These vortices can accelerate the mixing of the main flow and the secondary flow,and hinder the development of the original vortex;At the same time,due to the improvement of the uniformity of air velocity at the outlet of the injection,the potential flow core of the jet outside the tab injection is longer and the peak value of turbulent kinetic energy is smaller.Finally,three acoustic calculation methods are used to study the aerodynamic noise of the injection.The results show that the sound source inside the injection presents the distribution characteristics of "large distribution range of low-frequency sound source,high energy,small distribution range of high-frequency sound source and low energy";Comparing the spectrum curves of near-field monitoring points,it is found that the spectrum curve trend and later amplitude difference of different monitoring points are small,and the curve difference is mainly in the low frequency band.The tab structure can reduce the sound pressure level of the internal sound source acting on the far-field monitoring point,and the noise reduction amplitude can reach more than 2d B;The SNGR method is used to calculate the external jet noise of the injection.The calculation results show that there is no obvious peak value in the external jet noise curve,and the change trend conforms to the characteristics of air flow mixing noise.The reduction of working conditions will reduce the peak frequency of jet noise.The tab structure can reduce the jet noise of the injection.The noise reduction amplitude of the five-tab injection is 2.56 d B and the eight one is 2.27 d B,but the introduction of the tab will not significantly change the change trend of the spectrum curve. |
PDF Full Text Request