Pressure Gradient Of Unsteady Flow Of Fluid In Eccentric Annulus With The Inner Cylinder Reciprocating Axially

During the process of oil production, the sucker rod is eccentric due to the depth of the. Therefore, the produced fluid unsteadily flows in eccentric annulus between the tube and the sucker rod reciprocating axially. Research on pressure gradient of such flow is of certain practical engineering significance for preventing eccentric wear and optimizing the working parameters of pumps in wells.In this paper, Newtonian fluid model is used to describe rheological properties of the produced fluid; equation of motion, initial condition and boundary conditions of the unsteady flow of Newtonian fluid in eccentric annulus with the inner cylinder reciprocating axially are given under the rectangular Cartesian coordinate system and bipolar coordinate system, respectively; governing equations of the flow are transformed using the method of undetermined coefficients and the expression of pressure gradient of the flow is obtained with the given flow rate; using water, the pressure gradient is numerically calculated by finite volume method; the influences of eccentricity of annulus, stroke and frequency of the inner cylinder on the pressure gradient of water flowing in eccentric annulus with the inner cylinder reciprocating axially are analyzed. The results show that instantaneous pressure gradient of the flow is obviously influenced by eccentricity, stroke and frequency of the inner cylinder, and time-average pressure gradient decreases with eccentricity, stoke and frequency of the inner cylinder increasing, respectively.