Issue34

J. He et alii, Frattura ed Integrità Strutturale, 34 (2015) 564-573; DOI: 10.3221/IGF-ESIS.34.62 565 However, the performance life of a fluidic amplifier is still unsatisfactory in oil and gas drilling engineering [5]. As shown in Fig. 1, the heavy wear or erosion of fluidic amplifier is derived from the incision of drilling muds with high speed and pressure [6]. Large particles in drilling muds serve as abrasive grain beam to washout the fluidic amplifier, which accelerates the failure of hydraulic hammers in drilling process, thus the service life of fluidic amplifiers is reduced. The average performance life of each fluidic amplifier in oil and gas wells drilling is appropriately 30 hours, whereby the minimum service life of a fluidic amplifier is 15 hours, and the maximum service life is 113 hours, which has huge improvements on service life in subsequent optimization [7, 8]. In previous researches, the service life of a fluidic amplifier has been studied by drilling crews and researchers. W.T. Li have analyzed the effect of material of fluidic amplifier on its service life time, and numerical models of the damage mechanism of fluidic amplifiers are established [9]. In order to improve the actual service life of a fluidic amplifier, the processing technique of a fluidic amplifier in hydraulic hammers has also been discussed in his work. Meanwhile, series of experiments on fluids flow distribution in fluidic amplifiers have been conducted by J.J. Chen on the basis of Particle Image Velocimetry (PIV), which contributes to improving the service life of hydraulic hammers with a fluidic amplifier [10]. Some other related work has been finished with different experiments and apparatuses in order to study the service life of a fluidic amplifier in various performance conditions [11, 12]. Since 1980s, the numerical modelling technique in drilling engineering has been popularized throughout the world [13]. Bai Yalei and Ming Xiao established a model to investigate the pressure distribution of the flow inside the fluidic amplifier, and the deflection of induced main jet is obtained by numerical simulation [14]. In the meantime, the grain movement of abrasive water jet is analyzed by Dong Xing, and the friction between the mixture of water and abrasive grains has been acquired by numerical simulation [15]. Moreover, the erosion characteristics of typical materials in abrasive water jet (AWJ) were numerically simulated by Y.Z. Song, and valid results have been obtained according his research [16]. Thus simulation of drilling muds on anti-erosion property of a fluidic amplifier can be effectively conducted, which is a successful approach to reduce the experiments cost and test time in the design of fluidic amplifiers. Figure 1 : Failure of a fluidic amplifier before and after erosion by drilling muds. The study of drilling muds on anti-erosion property of a fluidic amplifier is another efficient way to improve the service life time of hydraulic hammer. In this paper, numerical models of fluidic amplifier have been established with several groups of drilling muds, and different fluid velocity, grain sizes as well as solid contents of drilling muds have utilized to the simulation. In end, the erosion rate and fluid velocity in a fluidic amplifier has been obtained by Computational Fluid Dynamics (CFD), which promotes the improvement of service life time of hydraulic hammers with a fluidic amplifier. T HEORY AND M ETHODOLOGY here are conclusively 3 theories suited for the erosion of a fluidic amplifier in hydraulic hammers, and they are elasto-plastic deformation theory, micro-cutting theory and the secondary erosion theory. T