Study On Optimization Of Key Structures And Parameters Of Fluidic Oscillator Of Down-the-hole High Energy Fluidic Hammer

The DTH(down-the-hole)fluidic hammer has been developed since the 1970 s and has become one of the most efficient DTH power tools in the field of hard rock drilling.With its simple structure,few vulnerable parts,high drilling efficiency,long service life,strong adaptability to complex formations,and good inclusiveness of various drilling fluids,it has played an important role in geological drilling,mineral exploitation,water conservancy and hydropower,and foundation construction.With the increasing demand in the energy market,the requirements for the performance of DTH drilling tools are also continuously improving.To improve impact energy,extend service life,and adapt to the more difficult dry hot rock formations with high temperature,high hardness,and strong abrasiveness,a new generation of DTH high energy fluidic hammer has been developed and introduced.In recent years,researchers have made continuous breakthroughs in the optimization of DTH high energy fluidic hammer.The use of integral cemented carbide fluidic oscillator has greatly improved the erosion resistance.The improvement of cemented carbide piston rods and cylinder liners has significantly improved the working life of the impact system.The design of the return buffer mechanism and chopping gasket group can protect the fluidic oscillator from being damaged by impact.The improved DTH hammer bit replaces traditional cone and PDC bit,the strength and service life of the drill bit have been significantly improved.Laboratory and engineering field practices have proven that DTH high energy fluidic hammer can have significant advantages in drilling deep and high temperature hard rock formations.To expand the application of DTH high energy fluidic hammer,further structural innovation and parameter optimization of existing products have important engineering and economic significance.However,there are still some problems with DTH high energy fluidic hammer.Firstly,the traditional single feedback channel fluidic oscillator(SFO)is unstable in operation,often causing the piston to pause,which is difficult to meet the needs of DTH high energy fluidic hammer.And,the new generation of high-performance lateral feedback channel fluidic oscillator(LFO)can only be processed by electrical discharge machining due to its special structure,which takes a long time and costs more than 10 times as much as ordinary fluidic oscillator,greatly increasing the production cost.It is particularly urgent to develop new fluidic oscillator with good performance and low cost.Secondly,based on engineering feedback,there is still a significant gap in drilling efficiency between DTH high energy fluidic hammer and pneumatic DTH hammer,as well as internationally leading fluidic DTH hammers.There is still a large room for improvement in impact frequency and impact power.However,the optimization of the impact performance of DTH high energy fluidic hammer was mainly aimed at improving the impact system in the past,and the research on structural parameters of the impact system is mature,without systematic research on key parameters of fluidic oscillator.As the core control component of the DTH high energy fluidic hammer,the fluidic oscillator determines the attachment and switching of the main jet,thereby controlling the high-frequency reciprocating motion of the piston,and playing a crucial role in the output performance of the DTH high energy fluidic hammer.However,there is little data to support the impact of structural parameters of fluidic oscillator on the output performance of DTH high energy fluidic hammer.Optimizing key parameters of fluidic oscillator has great potential and feasibility for further improving the output efficiency of DTH high energy fluidic hammer.This paper takes the SC86 H DTH high energy fluidic hammer as the research object,and the main content is divided into three parts:(1)Through computer aided design and fluid dynamics(CFD)technology,combined with bench experiments,a new type of double feedback channel fluidic oscillator(DFO)has been studied,which can be produced using a low-cost processing method while maintaining the efficiency and stability of impact performance.At the same time,the dynamic analysis of the piston motion is carried out using a hammer full-stroke laser measurement system,and the feasibility of the new signal feedback channel structure is confirmed through experiments.(2)Based on the existing symmetrical LFO with the best performance,a systematic study was conducted on the key structural parameters that have a significant impact on output performance.New structures such as deflector,straight wall splitter,and double sidewalls structures were proposed.The orthogonal test method was used to optimize their main structural parameters to obtain the optimal combination of structural parameters.The experimental results showed that the impact frequency and impact energy of the fluidic oscillator was significantly improved.(3)Based on the optimized symmetric fluidic oscillator,combined with the differences in the flow field during backward stroke and forward stroke of the piston,a new type of asymmetric fluidic oscillator is proposed.The influence of key parameters of both sides on the piston backward stroke performance and forward stroke performance is analyzed,and the optimal combination of asymmetric key parameters is obtained through orthogonal experimental calculations,and verified by bench experiments.Compared to the original LFO,the latest asymmetric fluidic oscillator has an average impact frequency increase of 28.7%,an average single impact energy increase of 12.4%,and an average output power increase of 44.6%.The main conclusions obtained in this paper are as follows:(1)By studying the influence rule of signal feedback channel structural parameters on the wall attachment and switching property of the main jet,and analyzing the flow field and output performance of the fluidic oscillator cavity with different forms and intensities of signal flows,it is concluded that: When the supply flow is 200L/min,the peak intensity of signal flow increases first and then decreases with the increase of the width of signal feedback channel,while the average flow of signal feedback channel increases with the increase of the width of signal feedback channel.During the main jet switching,the higher the signal flow intensity,the more conducive it is to the rapid deflection of the main jet.However,during the backward stroke and forward stroke,when the main jet is attached to the sidewall,excessive signal flow intensity can lead to instability of the main jet wall attachment.The optimal value of the signal feedback channel width needs to be determined comprehensively based on the main jet switching property and output performance.(2)Due to the operation of the SFO in practical applications,it is known from numerical simulation results that the main reason is that the signal flow has asymmetric ejection patterns and low intensity.Asymmetric signal flow can lead to unsynchronized switching of the main jet.The side with higher signal flow intensity deflects faster,while the smaller side deflects slower,which can lead to an incomplete deflection of the main jet and confusion in the flow field,resulting in piston pause.Due to the high cost of the LFO,the DFO have been studied.With the same signal feedback channel size,the DFO operates smoothly,providing high performance similar to that of the LFO,but the cost is almost the same as that of the SFO.(3)The structural parameters of the existing symmetrical LFO were optimized,and a new internal structure of the fluidic oscillator,the deflector,was proposed.The distribution pattern of the main jet and locking vortex is limited by means of solid blocking,and the wall attachment ability and flow field stability of the main jet are improved.At the same time,the structural parameters of the deflector are optimized,the optimal parameter combination is proposed,processed,and verified by bench experiments.The results show that compared to the original structure without a deflector,the average impact frequency of the deflector structure is increased by 5.8%,the average single impact energy is increased by 7.5%,and the impact power is increased by 13.75%.(4)A curved wall splitter was improved to a straight wall splitter in order to reduce the radial flow of the main jet at the tip of the splitter,reduce the difficulty of the main jet entering the output channel,and improve flow recovery.The experimental results show that the structure has a gain effect,with an increase in impact frequency of 2.93%,an increase in average single impact energy of 1.5%,and an increase in average output power of 4.48%.It is proposed to improve the single sidewall to a double sidewalls structure that combines a long sidewall and a short sidewall,which can not only ensure the wall attachment stability of the main jet,but also further improve the flow recovery and reduce the backward stroke time.However,the structure will have a negative impact on the forward stroke.but overall,the optimization effect on the impact frequency is obvious.In the experiment,the average impact frequency of the double sidewalls fluidic oscillator is 10.56% higher than that of the single sidewall.(5)According to the difference of the flow field between the backward stroke and the forward stroke,the concept of an asymmetric fluidic oscillator is proposed.The purpose is to further optimize the fluidic oscillator and improve the impact performance by studying the influence law of the structural parameters of the backward stroke side and the forward stroke side on the piston backward and forward strokes performance respectively.An asymmetric deflector is proposed.During the forward stroke,the wall attachment of the main jet is better than that of the backward stroke,and the requirement for locking vortex strength is lower than that of the backward stroke.Therefore,the reflux flow at the splitter can also be less.So the width of the deflector on the forward stroke side should be appropriately increased to reduce the split distance at the splitter,which is more conducive to improving flow recovery.Compared to the symmetric deflector,the average impact frequency of the asymmetric deflector increased by 1.93%,the impact energy increased by 1.86%,and the average impact power increased by3.83%.(6)The asymmetric sidewalls were proposed.Enlarge the separation vortex space by increasing the potential difference of the long sidewall on the backward stroke side.At the same time,reduce the opening angle of the long sidewall to ensure the stability of the main jet attachment to the wall.Increase the opening angle of the short sidewall and continue to divert the main jet to the backward stroke side,improving the flow recovery of the output channel.The design of the long sidewall on the forward stroke side is in the form of "small potential difference and large opening angle" compared to the backward stroke side.The volume of the separated vortex on the forward stroke side is small,and the requirement for the strength of the locking vortex is low.The main design direction is to completely clear obstacles for the main jet.Reducing the opening angle of the short sidewall on the forward stroke side and reducing fluid flow from the discharge channel on the forward stroke side can help to improve the impact velocity of the piston.The position and size of the discharge channel need to be adjusted according to the sidewalls.It is known that the best design method to maintain stable pressure in the cavity and improve stroke impact performance is to appropriately reduce the distance between the splitter and the discharge channel of the forward stroke side,but maintain the same width and size of the discharge channels on both sides.Based on comprehensive experimental analysis,compared to the optimal parameters of symmetric fluidic oscillator,the average impact frequency of asymmetric fluidic oscillator can be increased by 6.9%,the average impact energy increased by 4%,and the average impact power increased by 10.98%.