| The liquid-jet hammer has been successfully applied to oil and gas drilling due to its high drilling efficiency and unrestricted drilling depth.However,there are many problems remain to be solved,such as small single-shot impact and low impact frequency,and the premature failure of the fluidics amplifier.To solve the above problems,this paper conducts numerical simulation and experimental research on fluidics amplifierBased on the theory of confined space jet flow and the theory of the wall-attached jet,the flow-field of the fluidics amplifier switching process is studied;The wall-attachment and switching performance of the fluidics amplifier in the impactor are studied.It is concluded that the pressure recovery coefficient,the threshold velocity,the position of the attachment point and the switching time are important parameters for evaluating the performance of the fluidics amplifier;The key factors affecting the working characteristics of the fluidics amplifier are analyzed,which are the aspect ratio,the setback,the width of the control nozzle,the wall angle,the width of the vent,the height of the vent,the width of the output channel,of splitter to nozzle distance,and the input flow rate.The flow-field simulation of the fluidics amplifier was carried out by using the fluidics amplifier simulation model.It is found that when the jet achieves stable attachment,the flow attached to the wall is not the main jet,but the flows out from the supply nozzle;Aspect ratio,setback,wall angle,output channel width,and nozzle to splitter distance have influences on stable attachment of jet.When the aspect ratio is increased,the position of the attachment point is rising,and the stability of the attachment is increased;When the setback is increased,the position of the attachment point is lowered,and the stability attachment is decreased;When the wall angle is increased,the position of the attachment point is lowered,and the attachment stability is decreased;When the width of the output channel is increased,the position of the attachment point is lowered,and the stability of the attachment wall is decreased;When the nozzle to splitter distance is increased,the position of the attachment wall is rised,and the stability of the attachment is increased;The fluidics amplifier and the experimental device of the fluidics amplifier was designed and manufactured.The internal pressure of fluidics amplifiers with different structural parameters and under different input flow rates are measuredThrough experimental research,the variation law of the pressure recovery coefficient of the fluidics amplifier under different input flow rate and structural parameters is obtained.It is found that the pressure recovery coefficient of the fluidics amplifier is only affected by the structural parameters and hardly changes with the change of the input flow rate.That is to say,once the internal structural parameters of the fluidics amplifier are determined,the pressure recovery coefficient is also determined;The width and height of the vent and the width of the output channel have a great influence on the pressure recovery coefficient of the fluidics amplifier.The greater the width of the vent,the lower the pressure recovery coefficient of the fluidics amplifier;the higher the height of the vent,the lower the pressure recovery coefficient of the fluidics amplifier;the larger the width of the output channel,the higher the pressure recovery coefficient of the fluidics amplifier.Through experimental research,the variation law of the switching time of the fluidics amplifier under different input flow rate and structural parameters is obtained.It is found that for the structurally determined fluidic element,there is a specific input flow rate.When the input flow rate of the fluidic component is lower than the value,the switching time is longer.When the input flow rate is greater than the value,the switching time is shorter.The former is 4 to 6 times the latter.When the fluidics amplifier is in long switching time mode,its switching time is more susceptible to structural parameter changes;the setback,wall angle,supply nozzle,nozzle to splitter distance,and aspect ratio have a greater impact on the switching time of the fluidics amplifier:When in the low-speed switching state,these five structural parameters will affect the component switching time.When in the high-speed switching state,the switching time is only affected by the aspect ratio,and the width of nozzle.Through experimental research,the variation law of the threshold velocity of the fluidics amplifier under different structural parameters is obtained.It has been found that almost all structural parameter changes result in a change in the threshold velocity of the fluidics amplifier,and that when only one structural parameter is a variable,there must be a minimum threshold velocity of the fluidics amplifier. |
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