Study On Erosion Wear Behavior And Performance Enhancement Of Fluidic Oscillator For High-energy Fluidic Down-the-hole Hammer

High-energy fluidic down-the-hole（DTH）hammer has a good application prospect in hard rock drilling due to its advantages of high penetration rate,low drilling cost and great driven media adaptability.The characteristic of the fluidic hammer is only with one moving part,which brings the advantage that the fluidic hammer has less wear and better structural stability.However,the erosion of fluidic oscillator（FO）is serious in the drilling mud containing solid particles due to the high internal flow velocity.FO is the core component of the fluidic hammer,which controls the reciprocating motion of the impact body.The erosion of FO will cause the working performance of hammer to gradually decline until it stops working.Therefore,it is necessary to study the erosion problem of FO and optimize its anti-erosion ability to improve their service life and work efficiency.This article has conducted the following research:（1）Based on the discrete phase model（DPM）and dynamic grid method in computational fluid dynamics（CFD）,the erosion prediction of FO for the fluidic hammer was established.We comprehensively considered the coupling effect of jet component erosion and hammer motion,analyzed the erosion characteristics of jet components during the working process of the down-hole hammer,and conducted experimental verification.The erosion mechanism of FO was revealed by analysing the flow field and particle motion.Then,the influence of flow rate,particle mass content,particle diameter and flow characteristics of drilling fluids on the erosion of FO was studied through this method.The results showed that the numerical simulation results are in good agreement with the experimental results.The main erosion areas in the FO were the splitter,attachment walls,control nozzles and cover plate.The erosion in the FO was asymmetric.Different working conditions had different effects on the periodic erosion amount,erosion asymmetry and erosion rate of FO.（2）The influence of the FO erosion on the performance of fluidic hammers was studied deeply.The effects of the erosion amount and asymmetry of each main erosion region on the maximum impact velocity(₈（6）),impact frequency（1）),single-impact energy(₄8)（6（8））,and output power（）of the fluidic hammer were analyzed in detail.The variations of velocity and pressure fields in the FO were analyzed to reveal and the effect mechanism of erosion on the performance of fluidic hammer.The results showed that the erosion of splitter has the most significant impact on the performance of fluidic hammer.As the erosion depth of splitter increased from 0 to 0.8 mm,₈（6）and1)decreased by 11.1%and 23.6%,respectively.The fluidic hammer stopped working as the erosion depth of splitter increased to 1 mm.When the erosion of splitter was asymmetric,the working performance decreased further.The erosion of splitter was not conducive to the development of hinder vortex,reducing the pressure and flow recovery of FO.The erosion of attachment wall also had significant influence on the working performance of fluidic hammer.As the erosion depth of attachment wall increased from0 to 1 mm,₈（6）decreased by 3.7%.However,as the erosion depth of attachment wall increased,1)andfirst increased and then decreased,and reached the maximum at0.4 mm.The working performance decreased further when the erosion of attachment wall was asymmetric.The erosion of attachment wall enhanced the stability of the attachment of supply jet,resulting that the pressure recovery of FO increased in the backward stroke and the flow rate recovery decreased in the forward stroke.The erosion of the signal channel had a small impact on₈（6）and1).While,it would increase the sensitivity of jet switching.The erosion of the cover plate reduced the working performance of fluidic hammer continuously.As the erosion depth of cover plate increased from 0 to 1mm,₈（6）and1)of the fluidic hammer decreased by 1.8%and4.1%respectively.The erosion of the cover plate provided an additional channel for flow from the supply jet to the non-attachment side,reducing the flow into the outlet channel in the attachment side.（3）The erosion wear performance of four grades of PDCs with different diamond gains 2-3,5,10,and 25μm was studied by the modified erosion experimental device based on submerged abrasive water jet.The influence of different erosion conditions on the erosion rate of PDC was analyzed.The erosion surface of PDC was observed by scanning electron microscopy（SEM）to analyze the erosion mechanism of PDC with different grain sizes under different erosion conditions.The erosion process of PDC could be divided into cobalt removal stage and steady-state erosion stage.The quality loss of PDC during cobalt removal stage was mainly caused by the removal of cobalt;the mass loss of PDC in the steady-state erosion stage was mainly caused by the breakage or overall pullout of diamond grains.The erosion resistance of PDC was superior to that of cemented carbide.When the jet velocity was 100 m/s,the erosion rate of PDC was only 1/192～1/43 of YG8.The erosion rate of PDC increased with the rise of jet velocity,impact angle,erosion particle size and erosion particle hardness.The erosion resistance of PDC was related to the diamond grain size.Among the four grades of PDCs with different grain sizes,PDC2-3 has the worst erosion resistance,while the erosion resistance of other PDCs decreased with the rise of diamond grain size.The erosion mechanisms of PDC at high impact angle were mainly the partial breakage and overall pullout of diamond particles.While,the erosion mechanisms at low impact angles had not only the breakage and detachment of diamonds,but also the ploughing of erosion particles.（4）The anti-erosion FO was designed by enhancing the splitter with PDC.The rapid erosion experiment for the anti-erosion FO was carried out under harsh conditions for 2 h.The experimental results showed that the erosion rate of PDC splitter is 0.15mm/h.While,the erosion rate of cemented carbide splitter is 0.76 mm/h.Therefore,the strengthening measures of erosion resistance could increase the service life of FO by more than 5 times.The fluidic hammer controlled by the anti-erosion FO could continue to work normally after 2 h of erosion test,while the other one controlled by the carbide FO stopped working after 1.6 h of erosion test.