Structural Optimization Design Of Self-excited Pulse Nozzle Based On Coanda Effect

The self-excited pulse nozzle utilizes the principle of the Coanda effect to generate periodic oscillating pulse jets without the need for external forces and moving parts.It can be used in many fields such as oil drilling,industrial cleaning and flow measurement.In this paper,the flow field numerical simulation and structural optimization design of a deep well using self-excited pulse nozzle are studied,and the related mechanism and performance are explored.Firstly,the numerical simulation of the initial flow field in the nozzle is carried out by using the verified numerical simulation method,and the phenomenon and cause of the periodic oscillation pulse jet generated at the nozzle outlet are ascertained.Then,numerical simulation is carried out for the flow field in the nozzle with different structural parameters,and the influencing factors of the pressure fluctuation amplitude at the nozzle outlet are analyzed.The results show that the pressure pulsation amplitude increases first and then decreases with the increase of the diameter of the feedback channel.The angle increases and increases,and decreases as the diameter of the outlet increases.The pressure pulsation amplitude is the optimization target,and the nozzle size is optimized by the central composite response surface method:the feedback channel diameter is 16 mm,the attachment angle is 27°,and the outlet diameter is 14mm.Secondly,after adding an external flow field with a confining pressure of 30 MPa outside the nozzle,it was found that the pulse frequency was only related to the structural size and the inlet Reynolds number,and was independent of the external flow field.After the jet enters the external flow field,the pulse oscillation characteristic is maintained,and the maximum impact pressure point on the impact surface periodically oscillates on both sides of the center position.As the target distance increases,the stagnation pressure continues to decrease and gradually approaches ambient pressure.Through the numerical simulation of unidirectional fluid-solid coupling of jet impinging rock,the maximum equivalent stress on the rock is 30.80 MPa in one cycle,and the equivalent pressure pulsation amplitude at the center of the impact surface is 1.2 MPa.The pulsation impact effect is good.Finally,the impact performance of self-excited pulse nozzle is investigated and verified by visual impact experimental study.The experimental results can clearly observe the pulse jet phenomenon,and the experimental data show that the impact pressure and pressure pulsation amplitude of nozzle jet increase with the increase of flow rate,and when the nozzle inlet flow is 14 m~3/h,the impact pressure can reach 0.54MPa,and the pressure pulsation amplitude can reach 0.13 MPa.The relative error between the numerical simulation results and the experimental maximum impact pressure fitting value is 9.77,which verifies the reliability of the numerical simulation method.