| Due to the operation mechanism of the beam pumping unit and the connection between the outlet of the downhole cyclone and the inlet of the downhole pump.The liquid flow at the inlet of the cyclone will fluctuate in the form of pulsation at a certain frequency.This instability will affect the separation performance of the cyclone and will further cause pollution to the environment and waste of resources.For the sake of solving the problem of low separation efficiency of downhole oil-water cyclone separators caused by intermittent fluid supply of beam-type pumping units,a steady-flow oil-water cyclone separator suitable for flow pulsation is designed in the dissertation.The flow field characteristics and separation performance under pulsating inlet conditions are studied using a combination of computational fluid dynamics methods and laboratory experiments,providing a certain method for predicting the separation performance of the oil-water cyclone separator.It is of great significance to improve the downhole oil-water separation efficiency.Under the conditions of pulsating flow and constant flow,the flow field characteristics of conventional cyclones were numerically simulated and analyzed.It was found that the separation efficiency changes sharply due to the influence of pulsating flow on the internal flow field of cyclone,which hindered the separation of oil-water two phase.For the sake of improving the separation efficiency of conventional cyclone under the condition of flow fluctuation,a new type of oil-water cyclone separator was designed,which can separate oil-water two phases for many times in the cyclone chamber.At the same time,a vortex stabilizer was added inside to make it suitable for flow pulsation conditions,forming a steady flow oil-water cyclone separator,which can improve the convergence and lifting capacity of the flow field to the central oil core.And its separation efficiency was 23.6%higher than that of conventional cyclones.When the inlet flow rate of the cyclone was constant and pulsating,the addition of vortex stabilizer can promote the separation performance of oil-water cyclone.According to the simulation results,the characteristics of the flow field under the pulsating inlet condition were studied,and the relationship between separation efficiency and flow rate and swirl intensity was derived.The structural parameters of the vortex stabilizer in the steady flow oil-water cyclone were optimized by the response surface method.And the Box-Behnken experimental design（BBD）method was selected.The linear regression equations of the diameter of large end of cone section D1,diameter of small end of cone D2,cone height L1 and column height L2 were obtained.The significance test was carried out by variance analysis,and the optimal structure size parameters were obtained.The operation parameters of the stable flow oil-water cyclone after structure optimization were optimized,and the simulation analysis showed that the optimal working conditions of the cyclone were as follows:the oil phase volume content was 3%,the overflow diversion ratio was 25%,the pulsation frequency was 0.5Hz,and the pulsation amplitude was 0.5m/s.For the sake of examining the separation performance of the steady-flow oil-water cyclone,the optimized cyclone prototype was processed.And the prototype experiments were conducted indoors to analyze its separation performance.By using a combination of computational fluid dynamics method and prototype experiments,the simulated values of the separation efficiency of the steady-flow oil-water cyclone were compared and analyzed with the experimental values under the conditions of variable operating parameters.The rationality of the structure design of the cyclone and the accuracy of the numerical simulation results were verified. |
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