Numerical Study Of The Flow Field With Strong Disturbances, The Hydraulics And Separation Characteristics Of A Gas Centrifuge

This dissertation deals with three important issues in the theoretical study of centrifugation by means of numerical simulation: fluid flow simulation,centrifuge hydraulics,and separation characteristics.The first part of work in the dissertation is to solve the convergence problem of traditional iterative methods in the simulation of flow field in a gas centrifuge.Numerical simulation has so far become the most important method in the research for gas centrifuge flow and separation theory.However,in the presence of strong disturbances,a problem of sensitivity to initial value is usually encountered in solving the Navier-Stokes equations describing the fluid flow in a gas centrifuge by using classical iterative methods.It is very difficult for the iteration process to converge,seriously obstructing the numerical investigation of complex flow field in a gas centrifuge.Therefore,a homotopy method of a Predictor-Corrector type with much better convergence is proposed.In combination with an adaptive step strategy to ensure both efficiency and robustness of solution,the new method successfully solves the problem in the numerical simulation of flow field with strong disturbances.The stability and reliability of the homotopy method is adequately proved by various numerical simulation results.The new method lays a good foundation for the research of the hydraulics and separation performance of gas centrifuges.Based on the new numerical method,the second part of work is to study the hydraulics of gas centrifuges on two levels.Firstly,the numerical models for the hydraulic processes in gas centrifuges are established on the basis of the phenomena observed in experiments.Numerical simulation reveals the existence of two categories of centrifuges,classified according to the differences in the hydraulic characteristics,referred to as bidirectionally and unidirectionally connected centrifuges,respectively.The numerical results are confirmed by experiments,proving that the method presented in this study is able to correctly reveal the mechanisms of the actual hydraulic processes in gas centrifuges.The method can serve as a powerful tool in the study of hydraulics and separation problems in the centrifugation theory.Secondly,the influences of a gas centrifuge's main structural configuration and operational state on its hydraulic characteristics are investigated.Making use of the numerical solutions of the flow field in the centrifuge rotor,physical interpretations are also presented for better understanding the influential mechanisms.The last part of the dissertation's work is focused on the relationship between the separation performance of a centrifuge and its hydraulic characteristics.Both categories of centrifuges are investigated.It is found that the separation performance-hydraulic parameter relations are different for the two types of centrifuges.This discovery is also verified by both experiment observations and earlier studies in literature.Through the analysis of numerical results,the laws relating the overall separation factor to the feed flow rate and cut are obtained,which would be of great value to the optimization of gas centrifuges and cascades.The separation performance optimization methods for the two categories of centrifuges are studied.It is found that different types of hydraulic characteristics impose different constraints on decision parameters in the optimizations of separation performances,making it necessary to adopt different optimization methods.For a bidirectionally connected centrifuge,the hydraulic constraint is very weak,and its hydraulic parameters can be considered as independent decision variables.Traditional optimization method can be used in this case.However,for the optimization of unidirectionally connected centrifuges,the strong restriction imposed by hydraulic characteristics makes it inappropriate to treat hydraulic parameters as independent variables.Therefore,in optimizing unidirectionally connected centrifuges,the hydraulic constraint must be taken into account,and a method of optimization is proposed accordingly.The developed method is applied to the investigation of the influence of the waste scoop radius on the optimal separation power of a unidirectionally connected gas centrifuge,which gives valuable results for the experimental optimization of real gas centrifuges.