| As a new type of water jet technology,self-oscillating pulse cavitation jet is widely applied in industrial fields as large oil tank bottom mud cleaning,hull cleaning,lake oil cleaning,rock crushing,oil and gas mining,etc.However,in engineering applications,it is found that the nozzle structure directly affects the cleaning efficiency of the self-oscillating pulse cavitation jet.Therefore,on the basis of single chamber self-excited oscillation pulse nozzle,this paper proposes to establish a series double chamber self-excited oscillation pulse nozzle,optimizing its structural parameters by numerical simulation,in order to strengthen the degree of cavitation and the impact of jet and to improve the cleaning effect of tank bottom,hull and rust.Consequently,the topic selection and research of this paper is of important engineering application value and theoretical significance.Through numerical simulation of flow field in Helmholtz single chamber nozzle,organ pipe single chamber nozzle and double chamber nozzle,it is found that the cavitation degree and cleaning effect of double chamber nozzle are better than that of single chamber nozzle.So it is proposed to establish a new series-type double-chamber self-excited oscillation pulse nozzle by connecting the Helmholtz single-chamber structure nozzle and the organ pipe single-chamber structure nozzle in series.For the established tandem double chamber structure nozzle,firstly,the internal flow field numerical simulation is carried under different parameters such as Reynolds number,cavity length ratio and cavity diameter ratio.The results show that when the Reynolds number increases from Re1=2.98×105 to Re4=4.31×105,the degree of cavitation in the nozzle chamber increases first and then decreases;and when the cavity length ratio is Q=0.67 or the cavity diameter ratio is W=1.20,the degree of cavitation in the nozzle chamber is higher,meanwhile the velocity vortex ring with high symmetry inside the chamber can promote the occurrence of pulse cavitation.The turbulent kinetic energy in the chamber varies sharply when the distance between the back chamber and the cavity is l2=30 mm,which indicates a large amount of energy exchange.And when the diameter ratio of inlet and outlet is 0.32～0.75,the degree of cavitation in the chamber first increases and then decreases,and the change of diameter ratio has a strong influence on the pulse generation.When the chamber angle θ=60°,the turbulent kinetic energy in the chamber increases from 30 ms to 90 ms in a calculation cycle,which indicates that the energy exchange is intense,and the turbulent kinetic energy in 90 ms to 150 ms decreases and tends to be stable,which indicates that the spatiotemporal trend is stable.When the length of the chamber is 40 mm and the diameter of the chamber is 120 mm,the symmetry of the velocity vortex ring in the chamber is higher,which is beneficial to energy output.Then,the external flow field of the tandem double chamber nozzle is numerically simulated by changing inlet pressure,target distance and cavity length ratio.It is found that the velocity increases by 20～76 m/s for every doubling of the inlet incident pressure from 1.1 MPa to 4.4 MPa.With the increase of target distance from 100 mm to 400 mm,the degree of cavitation first increases and then decreases.The cleaning efficiency is the best when the target distance is 300 mm,but when the target distance is 400 mm,the bubble collapses in the air and cannot work on the cleaning surface.When the cavity length ratio Q=0.67 or the cavity diameter ratio W=1.20,a higher kinetic energy is generated on the surface of the cleaning material,so the cleaning effect is better.When the cavity distance l2=30 mm or the diameter ratio D=0.43,the surface velocity distribution of the cleaning material is more uniform and the cleaning effect is better.The angle of the chamber is equal to 60 degrees,the surface of the cleaning material has higher kinetic energy,so it has better cleaning ability;when the length of the chamber is 40 mm and the diameter of the chamber is 120 mm,the surface has greater impact force,so the cleaning effect is the best.The numerical simulation of the internal and external flow fields of the series double chamber nozzle offers the optimum parameters of the structure of the series double chamber nozzle,which not only strengthens the degree of nozzle cavitation and the impact of jet,improves the cleaning effect of tank bottom,hull and rust,but also provides a new method for the engineering application of self-excited oscillating pulsed cavitation jet. |
