Research On Fine Flow Field And Noise Prediction Method Of Highly Skewed Propeller Based On LES

Due to the development of modern military technology,there are higher requirements for underwater vehicle noise.The propeller noise is a very important part of the underwater vehicle noise,and the study of the fine flow field and noise prediction methods under the uniform and non-uniform incoming flow conditions is an interdisciplinary problem involving fluid mechanics and acoustics,which has important academic research significance and engineering application value.The accurate flow field information,especially the wake vortex structure capture,is the most critical aspect when the propeller noise is simulated by computational fluid dynamics technology.In this paper,we use the large eddy simulation method combined with FW-H acoustic analogy theory to numerically study the tail flow velocity and pressure characteristics,vortex volume and turbulent kinetic energy evolution,tail flow spectrum characteristics and noise attenuation characteristics of E1619 seven-blade large side-slope propeller under open water conditions with different inlet coefficients,and compare the fine flow field of the propeller tail flow with that of the open water conditions under the propeller coupling conditions..Firstly,the flow field and hydrodynamic properties of the propeller under different inlet speed coefficients in open water conditions were calculated by using a slip grid method based on large eddy simulation combined with three sets of different number of grids.Through the verification of the hydrodynamic coefficients and experimental results and the analysis of vortex structure capture,a grid scheme of 20.77 million grids was determined as the grid scheme for the subsequent analysis.Then,on the basis of this grid scheme,the fine-grained flow field characteristics such as wake velocity and pressure characteristics,vortex volume and turbulent energy evolution,wake spectral characteristics under different inlet coefficients of propeller open-water operation are analyzed,and the results show that the propeller wake instability is caused by the mutual induction effect between tip vortices and the induction between tip vortices and follow-side vortices,and the turbulent energy is influenced by the tip vortices and hub vortices and the velocity pulsation in its vortex core.The turbulent energy is influenced by the tip vortex and hub vortex and is related to the velocity pulsation in the vortex core,and the tail flow non-constant characteristics change quantitatively from low to medium load and qualitatively from medium to high load.Then,based on the accurate solution of the flow field,the propeller noise was calculated by using the FW-H model,and the results showed that the load noise in the axial direction decayed with a slope of 1/r~2 in the near field and 1/r in the far field,while the thickness noise decayed with a slope of 1/r~2 in the full path.In the radial direction,the load noise and thickness noise in the near field decay law is closely related to the number of propellers,which is caused by the mutual interference between the noise generated by the rotating propeller blades in the near field,and the decay slope in the far field both converge to 1/r,the difference is that the load noise decays with a slope of 1/r~2 during the propagation from the near field to the far field.Finally,a comparative analysis of the fine flow field of a fully attached SUBOFF submarine with E1619 propeller based on a 30.54 million grid with the open water condition at the specified advance coefficient shows that the non-uniform incoming turbulent structure interferes with the tip vortex,leading to earlier triggering of the tip vortex instability,and makes turbulence around the boundary layer of the propeller blade,interfering with the boundary layer flow,leading to a decrease in turbulent kinetic energy at the trailing edge of the blade,especially at the root of the blade,and its interaction with the blade makes the hydrodynamic power spectral density curve produce peaks at the blade frequency and second order harmonics indicating that the non-uniform incoming flow makes the non-constant characteristics of the propeller wake flow field change quantitatively.In this paper,the tail flow velocity and pressure characteristics,vortex and turbulent kinetic energy evolution,tail flow spectrum characteristics and noise characteristics of a seven-bladed large side-slope propeller under different operating conditions are analyzed in detail using a large eddy simulation method,which provides a certain reference for propeller design and noise prediction and optimization.