Theoretical And Experimental Study Of The Bionic Design Of Grooved Face Of A High Speed Dry Gas Seal

Centrifugal compressors, used to compress and transmit gas, are the key equipments in petrochemical and energy delivery industries. With the rapid development of large-diameter, high-speed and high-pressure centrifugal compressors, the dry gas seal(DGS) used to prevent leakage of gas in centrifugal compressors would be subjected to gas film instability, seal face wear and face deformation, which have a severe influence on the normal operation of centrifugal compressor and the whole production equipments. Clear that the Twelfth Five-Year plan to key development of high reliability mechanical seal and high performance non-contacting mechanical seal used for high-parameter centrifugal compressors. Hence, research and development of high-reliabitliy and high-performance DGS used for high-speed centrifugal compressors and realization the independent intellectual property rights, would not only have big significance to the long period stable operation of high-speed centrifugal compressors, but also have strategic significance to the national energy safety.The multi-factor coupling recursion order hierarchy model of the high speed wing is established from two aspects of marcoscopic configuration and wing structure of high-speed bird. Based on bionic method, the geometric model and structural parameter system of typical bionic bird wing grooved surface of a DGS are proposed and constructed. Based on statistical method and gas lubrication theory, the relationship between macroscopic configuration of a bird wing and grooved surface of a DGS is analyzed, and the feasibility of bionic design of face groove based on the geometric characteristics of bird wing outlines is demonstrated.Based on the theory of gas lubrication, the mathematical model of solving steady-state performance of a DGS is estabilished. Based on full factorical design, the preferred value ranges of structural parameters of spiral grooves are obtained, which provide the uniform baseline of the performance comparison of the DGS with bionic grooves. On the basis of the ratio of compressibility number to pressure, a characteristic parameter of comprehensive characterization of working conditions, is proposed, two typical bionic grooves with excellent comprehensive sealing performance, cluster bionic groove and multi-array bionic groove, are invented and optimized. The mechanism of maintain stiffer gas film and lower seal leakage of the two bionic groove DGSs(B-DGSs) under the condition of high-speed and low-pressure, compared to spiral groove DGS(S-DGS), is revealed by the numerical simulation analysis of pressure field and velocity field on the sealing gap of these three types of grooves. The influence of main geometric parameters of bionic grooves on the sealing performance is analyzed, and optimization of these geometric parameters is demonstrated.A special test rig has been built with adjustable spring pressure and measurable film thickness and leakage rate of a DGS for the purpose of validation. A new method of measuring film stiffness of a DGS is presented, the sealing performance of the two B-DGSs and S-DGS under the condition of high-speed and low-pressure have been tested, and the influence of main geometric parameters and operation parameters on the sealing performance of a DGS has also been analyzed. Experimental results show that the leakage and stiffness characteristics of the two BDGSs are superior to that of S-DGS under the condition of high-speed and low-pressure, with the increase ratio of 20% to 50% and decrease ratio of 20% to 40%, respectively. Both the film thickness and leakage rate increase significantly with an increase in seal pressure and groove depth, and with a decrease in spring pressure.Based on perturbation method and finite difference method, the mathematical model for the analysis of film dynamic characteristics of a DGS is estabilished by considering the axial disturbance, and the calculation expressions of stiffenss and damping coefficient of the gas film are derived. The correctness of the program and numerical method are verified by comparing with the numerical results in literature. A comparative study of the gas film dynamic characteristics between S-DGS and the convengent groove DGS imitated by the convengent wing of high-speed bird shows that the damping characteristics in low-frequency excitation improved dramatically by the convengent groove, which could avoid self-excited vibration. The gas film dynamic characteristics of the two B-DGSs and S-DGS are analyzed, and the influences of main geometric parameters on the film dynamic characteristics of the two B-DGSs have been studied. Results show that the damping characteristics in high-frequency excitation and the stiffness characteristics in low-frequency excitation of the two B-DGSs are superior to that of S-DGS, and the film dynamic characteristics of a DGS is significantly influenced by the geometric parameters of surface groove.A new method apply to judge the suitable operation range of different types of B-DGSs quickly is proposed based on the characteristic parameter, the ratio of compressibility number to pressure, and the fitting expressions of increment ratio of sealing performance with the ratio of compressibility number to pressure of the two B-DGSs are presented. An optimization model spectrum, enlightened by the reference model selection of centrifugal pump, of the main geometric parameters of the two B-DGSs under different operation conditions is proposed, for the purpose of solving the problem of optimization geometric parameters of surface groove change with operation condition which results in the difficulty in model selection of DGSs.The method and theory of bionic design of grooved surface of a high-speed DGS are proposed systematically in this thesis, which could provide a reference for the design and model selection of a high performance DGS used in high-speed rotating machine in engineering.