Large Eddy Simulation Of Flow Around A Seal Whisker

In cognitive robot design,tactile sensing systems have received wide application due to their stability.At present,the design of the touch sensor is mostly inspired by the mammal's whiskers.Seal whiskers produce violent vibrations in the wake of the prey,making it a major source of inspiration for underwater sensor design.Based on the researches of the seal whisker,the effect of whiskers on the flow field is studied by calculating different flow fields.Efforts are also made to explain the detection principle of seal whiskers and provide theoretical guidance for the design of seal whiskers sensor.Based on the numerical method of large eddy simulation,the flow around the whisker under different conditions has been calculated,including the whisker in uniform flow and wake and that at different angles of attack.The motion response of whisker was analyzed through the force and the flow characteristics in the field.In the uniform flow,the flow field around the whisker and the cylinder at the Reynolds number Re=3000 has been compared and analyzed.The results show that the fluctuation of lift and drag coefficients on the whisker surface is very small.Meanwhile,the fluctuating lift coefficient is one-twentieth of that of the cylinder.Unlike the two-dimensional characteristics of flow around the cylinder,the pressure and velocity distribution around the whisker vary with the different axial positions.Moreover,the shedding directions of boundary layers at different cross-sections are also different.This asynchronous vortex shedding reduces the fluctuation of the force on the whisker,which thus suppresses the vortex-induced vibration.The effects of angle of attack on the flow field around the whisker has been studied in the present study.The flow fields around the whisker with four angles of attack,0,30,60,and 90,are calculated.With the increase of angle of attack,the fluctuation of surface force of whiskers increases gradually.The fluctuation of lift and drag coefficient of whiskers remains in a very small range at small angle of attack.When the angle of attack exceeds a certain range,the fluctuation of force on whiskers will increase sharply which indicates that under this condition suppression to vortex-induced vibration will disappear in the whisker.The three-dimensional characteristics of the whisker flow field at the small angle of attack still exist.However,when the angle of attack is 60 degrees and 90 degrees,the difference between the cross-sections of the flow field almost disappears,accompanied by the change of the flow pattern to two-dimensional flow and the appearance of the classical Karman vortex street in the wake area of the whisker.When the whisker is in the wake,its vortex-induced vibration is extremely strong.We find that the fluctuation value of lift coefficient is 71 times that of uniform flow,while the cylinder's fluctuation value of lift coefficient increases only 1.6 times.The whisker's fluctuation value of drag coefficient also increases substantially due to the influence of wake.Through analyzing the flow field,it is found that the whisker will affect the wake.For example,the vortices in the flow are separated on the whisker surface.The kinetic energy in the vortices is absorbed on the whisker surface,which is shown by the fluctuation of force.In the cylinder,the vortices pass around the cylinder and do not transfer energy.This study not only helps to understand the mechanism of harbor seal to detect the change of the flow direction and surrounding environment,but also provides theoretical guidance for the optimization design of biomimetic sensors based on the harbor seal whisker.