Particle image velocimetry analysis of plane flow field induced by drill string planetary motion based on superposition principle

To study the law of a fluid plane flow induced by the planetary motion of the drill string and solve the practical engineering problems, such as improving the cutting-carrying capacity of a drilling fluid and reducing the flow pressure loss or damage to the drill string by whirling, a method based on the superposition principle is proposed. The flow field induced by the planetary motion is decomposed into a centrifugal force field through an equal angle rotation of the drill string and wellbore, and a flow field induced by through the simultaneous rotation of the drill string and wellbore. To analyze the latter, an experimental device was designed to measure the plane flow field of a fluid induced by the rotation of the internal rod and outer cylinder, and a particle image velocimetry experiment was performed. The results are as follows: the velocity of the plane flow field induced by the rotation of the internal rod and outer cylinder has an approximately symmetrical distribution, with the line connecting the cross section centers of the outer cylinder and inner rod as the axis of symmetry; when the outer cylinder is motionless and the inner rod rotates eccentrically, there is a critical value of the eccentricity upon which the secondary flow occurs and it is 0.7, moreover, the secondary flow occurs in a place far away from the inner rod and near the wall of the outer cylinder; when the inner rod and outer cylinder rotate in the same direction, the occurrence of the secondary flow is related to the eccentricity, and the area of distribution of the secondary flow expands with the increase in the eccentricity, for example, when the inner rod and outer cylinder rotate in the same direction with the speed of 60 r/min and 120 r/min respectively, the secondary flow occurs only when the eccentricity exceeds 0.4, and the area of the secondary flow becomes larger and larger with the increase of the eccentricity; when the inner rod and outer cylinder rotate in the same direction, the occurrence of the secondary flow is related to the difference in rotation speed between the inner rod and outer cylinder, and the area of distribution of the secondary flow expands with the increase in this difference, for example, when the eccentricity is 0.4, the secondary flow disappears or does not occur on the rotating speed difference being 0, and the area of distribution of the secondary flow expands with the rotating speed difference increasing from 60 r/min to 120r/min; when the inner rod and outer cylinder rotate in opposite directions, for example, when both of them rotate at speed of 60 r/min and the eccentricity of 0.2, the secondary flow occurs, the distribution of the secondary flow is approximately symmetrical and shaped like a crescent moon, and the area of distribution expands with the increase in the rotation speed of the inner rod or outer cylinder and the increase in eccentricity.