A Numerical Study On Shock Wave And Sound By A Pulsed Positive Streamer Discharge In Water

Whether in military or civilian spheres,the demand for underwater sound sources is getting higher and higher,especially the current low-frequency sound sources and bulky and have poor adaptability.In the underwater plasma discharge process,low-frequency sound waves are generated,which can be used to design the new underwater sound sources.However,the experiment is difficult due to the very short discharge last time and very strong shock pressure,and the theoretical analysis is hard because the shock waves belong to non-linear problems.In this thesis,the shock wave and sound generated by underwater streamer discharge are analyzed and studied by using numerical simulation technology,which has shown certain engineering significance.Firstly,we discuss the generation and evolution of the streamer,and speculate the cause of shock wave.Then the calculation method is given,which is the hybrid method of Computational Fluid Dynamics and Computational Aero Acoustics,which decouples the solving of the flow field and the sound field,ensuring accuracy while reducing the amount of computation.Secondly,we use CFD and Dynamic Meshes to realize the motion of the streamer.The results of the streamer moving straightly or periodically are showed respectively,which are not consistent with the phenomena in the experiment photos.It is considered that the actual streamer evolution is not the above two cases.Subsequently,the question mentioned above are discussed,and the motion of the streamer is reset.Then,one point or five shock wave points on the streamer are simulated respectively.The results are in good agreement with the experimental results.It shows that the numerical calculation method used is suitable for analyzing the phenomena of the discharge.At the same time,it proves one possibility of a real motion of the streamer,which can help figure out the evolution of the shock waves in the discharge.Thirdly,we use CAA to calculate the sound results though reasonable integral surfaces by using FW-H equation and the CFD results.The frequency domain information is obtained by the fast Fourier transform.The results show that the shock wave sound field of underwater streamer discharge has the characteristics of low-frequency and high directivity,which means it can be suitable as a new type of underwater sound source.Meanwhile,it is feasible to analyze the physical phenomena of the discharge by using the hybrid method of CFD and CAA.