超臨界二氧化碳介質(zhì)箔片軸承彈流耦合研究
發(fā)布時間：2018-09-19 14:35
【摘要】：超臨界二氧化碳由于其特殊的傳熱以及壓縮特性,非常適合作為熱力循環(huán)的工質(zhì),近年來關(guān)于超臨界二氧化碳閉式布雷頓循環(huán)的研究正逐漸成為熱點,而由于高轉(zhuǎn)速與較高的溫度和壓力,該循環(huán)系統(tǒng)中的渦輪-電機-壓縮機共軸轉(zhuǎn)子的支承也面臨著一系列的問題。本文針對超臨界二氧化碳閉式布雷頓循環(huán)的支承系統(tǒng),采用理論推導與數(shù)值計算相結(jié)合的方法,對以超臨界二氧化碳為潤滑介質(zhì)的徑向箔片軸承和推力箔片軸承進行仿真研究。全文共分為三部分:第一部分,使用理論方法,從連續(xù)性方程和能量方程出發(fā),得到兩組適用于變粘度變密度工況的雷諾方程,在雷諾方程中加入隨雷諾數(shù)變化的半經(jīng)驗常數(shù),以此來考慮高轉(zhuǎn)速大雷諾數(shù)下潤滑介質(zhì)對軸承特性的影響。對兩個雷諾方程進行了無量綱處理,并建立合適的箔片變形模型,將潤滑膜厚度與壓力及箔片的變形相互耦合在一起,推導了基于有限差分法的顯式松弛迭代的穩(wěn)態(tài)雷諾方程求解推進格式。第二部分,使用基于MATLAB編寫的程序計算空氣介質(zhì)的箔片徑向和推力軸承的承載力與偏位角,并與文獻結(jié)果進行對比,結(jié)果表明數(shù)值計算準確可靠。接著結(jié)合物性計算工具使用該求解器仿真超臨界二氧化碳潤滑下的兩種軸承的靜特性,主要包括壓力、潤滑膜厚度和湍流潤滑系數(shù)分布、壓力峰值、偏位角、承載力和摩擦力矩等,并討論其與相同參數(shù)傳統(tǒng)空氣相比靜特性的區(qū)別,對于推力軸承還確定了最佳箔片數(shù)。第三部分,將變粘度變密度的瞬態(tài)雷諾方程中的壓力和潤滑膜厚度在平衡位置處基于小擾動法線性展開,按動態(tài)擾動量歸并后得到和靜參數(shù)相關(guān)的剛度和阻尼相互耦合的偏微分方程,將該方程與箔片變形方程耦合,求解軸承的動力學特性,并分析動力學系數(shù)隨軸承偏心率、間隙量、軸承數(shù)、箔片柔度、激振頻率的變化規(guī)律。本研究工作中針對兩種軸承不同雷諾方程所共有的結(jié)構(gòu)特點,提出一種顯式迭代求解雷諾方程的新思路,即將雷諾方程展開并化為標準形式,建立標準形式的通用迭代求解模塊,之后通過將不同雷諾方程化為標準型并調(diào)用通用模塊,可以大大簡化數(shù)值編程,并增加程序可靠性。在對超臨界二氧化碳物性進行計算時,通過建立物性映射表,并輔以等距分割快速查找算法,可以快速插值求取高精度的物性參數(shù),確保計算結(jié)果的準確。在軸承的動特性計算之中,基于穩(wěn)態(tài)雷諾方程,提出了一種適用于擾動頻率為0工況的新型動特性計算方法,該方法與靜壓計算程序結(jié)合能夠計算變物性的軸承特性。本文所使用的方法對于其它軸承仿真研究具有一定的借鑒作用,研究得到的一些規(guī)律和結(jié)論可用于超臨界二氧化碳箔片軸承的潤滑特性預測,對箔片軸承的設計具有一定的指導作用。
[Abstract]:Because of its special heat transfer and compression characteristics, supercritical carbon dioxide is very suitable as a working medium for thermal cycle. In recent years, the research on closed Brayton cycle of supercritical carbon dioxide is becoming a hot topic. Because of the high speed and high temperature and pressure, the support of the coaxial rotor of the turbo-motor-compressor is faced with a series of problems. In this paper, the radial foil bearing and thrust foil bearing with supercritical carbon dioxide as lubricating medium are simulated by combining theoretical derivation and numerical calculation for the supporting system of supercritical carbon dioxide closed Brayton cycle. The paper is divided into three parts: in the first part, two sets of Reynolds equations suitable for variable viscosity and variable density conditions are obtained by using the theoretical method and the energy equation. The semi-empirical constant with Reynolds number is added to the Reynolds equation. The influence of lubricating medium on bearing characteristics at high speed and large Reynolds number is considered. The two Reynolds equations are dimensionless and a suitable foil deformation model is established. The lubrication film thickness is coupled with the pressure and the deformation of the foil. Based on the finite difference method, an explicit relaxation iteration scheme for steady-state Reynolds equation is derived. In the second part, a program based on MATLAB is used to calculate the bearing capacity and offset angle of foil radial and thrust bearings in air media, and the results are compared with the results in literature. The results show that the numerical calculation is accurate and reliable. Then the static characteristics of two kinds of bearings under supercritical carbon dioxide lubrication are simulated by using the solver combined with physical property calculation tools, including pressure, thickness of lubricating film and distribution of turbulent lubricating coefficient, peak pressure, offset angle, and so on. The bearing capacity and friction moment are discussed, and the difference between static characteristics of thrust bearing and conventional air with the same parameters is discussed. The optimum foil number is also determined for thrust bearing. In the third part, the pressure and the thickness of the lubricating film in the transient Reynolds equation with variable viscosity and density are linearly expanded at the equilibrium position based on the small perturbation method. According to the partial differential equation of stiffness and damping coupling with static parameters, the dynamic characteristic of bearing is solved by coupling the equation with foil deformation equation, and the dynamic coefficient is analyzed with the eccentricity of bearing. Change law of clearance, bearing number, foil flexibility and exciting frequency. In this work, a new idea of solving Reynolds equation by explicit iteration is proposed, which is to expand the Reynolds equation and transform it into a standard form, according to the common structural characteristics of two different Reynolds equations of bearings. The general iterative solution module in standard form is established, and the numerical programming can be greatly simplified and the program reliability can be increased by converting the different Reynolds equations into the standard form and calling the general module. In the calculation of the physical properties of supercritical carbon dioxide, by establishing the physical property mapping table and adding the fast searching algorithm of equidistant segmentation, the high precision physical parameters can be obtained quickly, and the accuracy of the calculation results can be ensured. Based on the steady state Reynolds equation, a new method for calculating the dynamic characteristics of bearings is presented in this paper. The method is combined with the static pressure calculation program to calculate the characteristics of the bearings with variable physical properties. The method used in this paper can be used as a reference for the simulation of other bearings. The obtained laws and conclusions can be used to predict the lubrication characteristics of supercritical carbon dioxide foil bearings. It can guide the design of foil bearing.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TH133.3
本文編號：2250419
[Abstract]:Because of its special heat transfer and compression characteristics, supercritical carbon dioxide is very suitable as a working medium for thermal cycle. In recent years, the research on closed Brayton cycle of supercritical carbon dioxide is becoming a hot topic. Because of the high speed and high temperature and pressure, the support of the coaxial rotor of the turbo-motor-compressor is faced with a series of problems. In this paper, the radial foil bearing and thrust foil bearing with supercritical carbon dioxide as lubricating medium are simulated by combining theoretical derivation and numerical calculation for the supporting system of supercritical carbon dioxide closed Brayton cycle. The paper is divided into three parts: in the first part, two sets of Reynolds equations suitable for variable viscosity and variable density conditions are obtained by using the theoretical method and the energy equation. The semi-empirical constant with Reynolds number is added to the Reynolds equation. The influence of lubricating medium on bearing characteristics at high speed and large Reynolds number is considered. The two Reynolds equations are dimensionless and a suitable foil deformation model is established. The lubrication film thickness is coupled with the pressure and the deformation of the foil. Based on the finite difference method, an explicit relaxation iteration scheme for steady-state Reynolds equation is derived. In the second part, a program based on MATLAB is used to calculate the bearing capacity and offset angle of foil radial and thrust bearings in air media, and the results are compared with the results in literature. The results show that the numerical calculation is accurate and reliable. Then the static characteristics of two kinds of bearings under supercritical carbon dioxide lubrication are simulated by using the solver combined with physical property calculation tools, including pressure, thickness of lubricating film and distribution of turbulent lubricating coefficient, peak pressure, offset angle, and so on. The bearing capacity and friction moment are discussed, and the difference between static characteristics of thrust bearing and conventional air with the same parameters is discussed. The optimum foil number is also determined for thrust bearing. In the third part, the pressure and the thickness of the lubricating film in the transient Reynolds equation with variable viscosity and density are linearly expanded at the equilibrium position based on the small perturbation method. According to the partial differential equation of stiffness and damping coupling with static parameters, the dynamic characteristic of bearing is solved by coupling the equation with foil deformation equation, and the dynamic coefficient is analyzed with the eccentricity of bearing. Change law of clearance, bearing number, foil flexibility and exciting frequency. In this work, a new idea of solving Reynolds equation by explicit iteration is proposed, which is to expand the Reynolds equation and transform it into a standard form, according to the common structural characteristics of two different Reynolds equations of bearings. The general iterative solution module in standard form is established, and the numerical programming can be greatly simplified and the program reliability can be increased by converting the different Reynolds equations into the standard form and calling the general module. In the calculation of the physical properties of supercritical carbon dioxide, by establishing the physical property mapping table and adding the fast searching algorithm of equidistant segmentation, the high precision physical parameters can be obtained quickly, and the accuracy of the calculation results can be ensured. Based on the steady state Reynolds equation, a new method for calculating the dynamic characteristics of bearings is presented in this paper. The method is combined with the static pressure calculation program to calculate the characteristics of the bearings with variable physical properties. The method used in this paper can be used as a reference for the simulation of other bearings. The obtained laws and conclusions can be used to predict the lubrication characteristics of supercritical carbon dioxide foil bearings. It can guide the design of foil bearing.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TH133.3
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