Investigação numérica da força de impacto e do coeficiente de descarga em bocais ejetores de brocas de perfuração

Abstract

The exact determination of the discharge coefficient value and the jet impact force are important factors in drilling operations because they optimize the rate of penetration and the cleaning efficiency of the downhole. This paper shows a numerical study that determines these values with different volumetric flow rates, density, dynamic viscosity and the nozzle jet's diameter. All the fluids in this study are Newtonian fluids. The geometry developed is composed of a circular pipe with a sudden contraction and an annulus pipe for the return of the fluid. The fluid flows beyond the contraction and is ejected against a wall, after that, the fluid returns in an annulus pipe. The discharge coefficient is determined by the pressures drop caused in the contraction, and the impact force by the fluid’s pressure in the impacted wall. This paper also presents a methodology to extract results provided by ANSYS CFX, a computational dynamics fluid program. Method was developed a method so that the results were not affected by the mesh size or incorrect numerical parameters; for that a mesh test and three numerical validations were carried out. The results agree with the literature on the independence of viscosity, density and volumetric flow rate in the discharge coefficient, and the linear dependence on the nozzle diameter. It was also evidenced the independence of the viscosity in the impact force and the dependence of the density, volumetric flow rate and the nozzle diameter.