Research On Simulation Computation And Experiment Of Liquid Jet Hammer

Since 1990s, enormously potential drilling demands in new areas like oil and gas drilling, ocean and continental scientific drilling, geothermal drilling, anchor construction, water well drilling, rock-embedded pile hole construction, trenchless guided boring and so on have promoted research of liquid jet hammer to much higher level. Particularly in oil and gas drilling area, structure and properties of liquid jet hammer needed to be developed urgently. Slight increase of drilling efficiency will generate significant economic benefits, so it is of great economic and social significance to develop liquid jet hammer of large impact energy , reasonable impact frequency, long working life and application in oil and gas drilling area widely as soon as possible, which will benefit to raise China's oil and gas drilling technology, reduce drilling cost and increase China's oil drilling enterprises' competition in both domestic and international market.Based on the Continental Scientific Drilling Engineering Center project "Development application of liquid-jet hammer for SSCD" and "Development of high efficient rock-breaking hammer" -hi-tech research and development of china (863 program), this thesis puts emphases on simulation and computation of dynamic flow field for liquid jet hammer, which combines inner flow of jet element with piston motion to analyse and shows inner flow law of impact system. Advanced particle image velocimetry was applied to measure work cavity's velocity of jet element exploringly. According to the results of computational fluid dynamics analysis and experimental and extempore application, design methods of new jet element and piston cylinder are put forward.Following conclusions and innovations can be concluded from this research of paper:(1) The Finite Volume Method (FVM ) is available in computing the inner flow field of liquid jet hammer, relatively exact computing results can acquire by simple supposition and computing mode for this paper. It's known that better precision is guaranteed by using following settings in comparing with experimental results: SIMPLE velocity-pressure coupling arithmetic. First order upwind difference discretization; standard k—εturbulent model. Applying layering mesh methods to control cylinder's volume change up and down, program of piston motion control equation conducting mesh's dynamic changing better. No sliding wall condition comparing with relatively internal boundary's mesh set for all kinds of walls of jet element's flow passages, with standard wall functions applied for near-wall treatment.(2) By analyzing of entire process for one hammer with pump volume 320L/min, stroke 75mm, piston diameter 50mm, diameter rod 30mm and piston-quality 25Kg , conclusions can be drawn as follow:1) Piston speed of return process increases but the rate of increase is getting smaller and smaller and more stable while forces on piston of process of stroke suffered more, which make piston move faster with the biggest impact end velocity-3.29m/s. During return process, top and bottom cylinder pressure are stable, on the other hand, during stroke process, pressure of top cylinder becomes smaller and smaller while pressure of down cylinder gets larger and larger, at the end of stroke process, pressure of top cylinder is bigger than that of down cylinder.2) After piston rebounding of return, major factor for switching wall-attached jet is the high speed flow in signal passage near down cylinder, and major factor for switch wall-attached jet after piston rebounding of stroke is in high pressure and high speed flow.3) Impact System exists 'differential circuit' and backwater in discharge passage.4) When jet element works well, the shear stress at the wedge tip, side wall and the endxtrance of discharging passage change with wall-attached jet's alternating switch.5) Piston was impelled to moves upward due to pressure during return process. During stroke process which impact because of direct transmission of momentum for wall-attached jet.once wall-attached jet forms that will be stable to attach wall.6) lock vortex forms after jet switch from the area of low pressure near wall-attached jet.(3) Following conclusions are drawn from orthogonal test:1) All kinds parameter's primary and secondary relation effecting impacting ending velocity is from diameter to pump discharge, then stroke, piston and clash hammer mass, the piston's diameter effects impacting ending velocity more significantly.2) All kinds parameter's primary and secondary relation effect impacting frequency is from stroke to pump discharge ,then piston diameter and piston and clash hammer mass, the piston's stroke effects impacting frequency more significantly.(4 ) Following conclusions are drawn by single factor test:1) With pump volume increasing, the impact energy, the impact frequency and the impact end velocity increase linearly , the energy usage reduces and the flux usage increases, and pump pressure increases linearly.2) With piston diameter increasing, the impact energy, the impact frequency and the impact velocity reduces, and the energy usage reduces and the flux usage increases with the pump pressure gradually increasing.3) With piston stroke increasing, the impact energy and the impact velocity increases. Wwhile the impact frequency reduces, energy usage reduces after increasing at first moment with the flux and pump pressure increasing gradually.4) With the quality of the piston-hammer increasing, the impact energy increases, while the impact frequency and impact end velocity reduces, energy usage increases, the flux usage pump pressure reduces.(5 ) Introducing advanced laser particle image velocity to measure velocity for inner flow of jet element, after image data processing, it is found that the testing velocity is close to the results of CFD .During piston's moving, we find that large pump output volume is benefit to form leaping pressure . Meanwhile large pump output is propitious to increase impacting frequency.(6 ) After lengthening exporting passage, the apart hammer still work well.(7) Through CFD computing, experimental and field application analysis, improving methods of the structural design and processing technology for liquid jet hammer is put forward.Dynamic flow field characteristics for liquid jet hammer impacting system is acquired by applying dynamic mesh technique to simulate impacting system. There is a great breakthrough comparing to early research, but it still need to be improved, such as model building, mesh meshing and flow field parameter set. In order to simulate impacting system more reasonably, experiment and CFD computing results should be combined to study in simulating more accurately. And the PFV technique is applied to vision and measure inner flow field of jet element elementarily, the range measure is limited, the measure precision and image distinguishing system need to be promoted ulteriorly and pressure measure system with high sample and strong antijamming also need to be developed.