Study On Vortex Shedding And Coupled Vibrato Of Two-dimensional Hydrofoil

Propeller singing is a special noise phenomenon.When the singing occurs,the noise level of the propeller will increase by 8-10 decibels,and this increase interval is mostly at a frequency of several hundred to 2000 Hz.This frequency is the most sensitive frequency band for underwater acoustic equipment monitoring,so it will greatly affect the acoustic stealth capability of military ships and increase the risk of ships being monitored.Another feature of the singing phenomenon is its strong concealment,which is usually difficult to find at the design stage.It is often found that there is a singing phenomenon after being put into use,which increases the cost of returning the propeller to the field and has an impact on the economy of the ship.At present,the solution to the phenomenon of singing is to cut the edges of the propeller,but the theory of this method is not clear,and sometimes the blades with the edges cannot suppress the generation of singing.Therefore,it is of research significance to analyze the production mechanism of singing voice linearity,and to find methods that can predict and suppress the production of singing voice.According to previous researches,the production of singing is closely related to the phenomenon of blade vortex shedding.The vortex shedding motion is a local detail flow,and its simulation requires extremely high mesh quality.Therefore,through simplification,the research object of the blade is transformed into the two-dimensional profile of the blade to obtain the law of vortex motion more clearly.First,the vortex shedding at the trailing edge of the rigid profile is simulated,and the law of the vortex shedding itself with flow field velocity,profile length,and angle of attack is studied.And further study the change of the vortex shedding frequency under the corresponding velocity and angle of attack after the trailing edge is chamfered.This part of the study found that beveling the trailing edge can have a significant effect on reducing the shedding frequency,and the relationship between the vortex shedding frequency and the flow field velocity is approximately a linear function.Further study the resonance phenomenon between shedding vortex and elastic hydrofoil.This part of the research shows the change of the curve oscillation law in the process when the vortex shedding frequency approaches the natural frequency of the solid,and the law of the shedding frequency changing with the flow field is obtained.The study obtained the coupling-decoupling process when the vortex shedding frequency is close to the natural frequency of the elastic hydrofoil.The production analysis of the working conditions in the process shows that the sound field will increase suddenly at the coupling frequency,which proves that the singing phenomenon is caused by the coupling resonance.