基于有限元法的定向凝固過程溫度場(chǎng)數(shù)值模擬的研究
發(fā)布時(shí)間：2019-03-29 06:32
【摘要】：在航空航天領(lǐng)域中,主要采用定向凝固工藝生產(chǎn)渦輪葉片,而高性能的渦輪葉片一直是阻礙我國(guó)實(shí)現(xiàn)“大飛機(jī)”夢(mèng)的最大障礙。實(shí)際定向凝固過程是十分復(fù)雜的材料成形過程,而且需要特別考慮輻射換熱的影響。采用定向凝固溫度場(chǎng)模擬技術(shù),能夠?qū)﹁T件在凝固過程中的溫度場(chǎng)演變過程進(jìn)行有效的分析,預(yù)測(cè)可能出現(xiàn)的缺陷,為優(yōu)化定向凝固工藝提供理論指導(dǎo)。本文對(duì)有限元定向凝固溫度場(chǎng)數(shù)值模擬所涉及的各個(gè)方面進(jìn)行了深入研究,包括定向凝固溫度場(chǎng)數(shù)學(xué)建模、有限元數(shù)值求解、液態(tài)金屬冷卻液換熱處理和定向凝固溫度場(chǎng)分析判據(jù)等,開發(fā)了有限元定向凝固溫度場(chǎng)數(shù)值模擬系統(tǒng)。首先,由于輻射換熱在定向凝固溫度場(chǎng)數(shù)值模擬中需要重點(diǎn)考慮,采用射線追蹤法對(duì)其進(jìn)行處理,并結(jié)合計(jì)算機(jī)圖形學(xué)得到輻射換熱邊界條件的控制方程。通過對(duì)定向凝固過程進(jìn)行一系列相對(duì)合理的假設(shè)和簡(jiǎn)化,建立了定向凝固過程的溫度場(chǎng)模型,根據(jù)有限元數(shù)值計(jì)算理論,結(jié)合定向凝固過程溫度場(chǎng)的控制方程和邊界條件,詳細(xì)地推導(dǎo)出定向凝固過程溫度場(chǎng)數(shù)值模擬的有限元離散過程和求解方法。其次,采用等效比熱法和溫度校正方法共同處理鑄件潛熱,使其滿足能量守恒原則。針對(duì)定向凝固工藝的隨型型殼邊界,采用智能化查找型殼內(nèi)外表面的算法,自動(dòng)區(qū)分各材質(zhì)的內(nèi)外表面,避免用戶手動(dòng)選擇的繁瑣操作,并采用盒子樹法處理各個(gè)接觸表面的對(duì)流換熱邊界條件,能夠在不過多要求網(wǎng)格質(zhì)量的基礎(chǔ)上,較為合理地處理各材質(zhì)間的對(duì)流換熱邊界條件。由于LMC(Liquid Metal Cooling)工藝中型殼會(huì)逐漸浸入液態(tài)金屬冷卻液,為了避免直接求解所帶來(lái)的網(wǎng)格重新劃分難題,采用隨時(shí)間和溫度變化的等效換熱系數(shù)來(lái)處理型殼與冷卻液間的換熱。實(shí)際定向凝固過程中需要避免等軸晶即雜晶的出現(xiàn),為了對(duì)HRS(High Rate Solidification)和LMC定向凝固溫度場(chǎng)模擬結(jié)果進(jìn)行分析,采用G/L判據(jù)來(lái)預(yù)測(cè)鑄件可能出現(xiàn)雜晶的部位。同時(shí),為了保證有限元模擬系統(tǒng)的計(jì)算效率,提出局部矩陣的概念,在有限元程序處理過程中分開組裝各材質(zhì)的計(jì)算矩陣。通過實(shí)現(xiàn)上述各關(guān)鍵技術(shù),開發(fā)了有限元HRS和LMC定向凝固溫度場(chǎng)數(shù)值模擬系統(tǒng)。最后,分別采用溫度場(chǎng)數(shù)值模擬系統(tǒng)和通用化有限元平臺(tái)ANSYS計(jì)算典型工字件的空冷過程溫度場(chǎng),對(duì)比發(fā)現(xiàn)兩者的計(jì)算結(jié)果基本一致,驗(yàn)證了本文溫度場(chǎng)數(shù)值模擬系統(tǒng)中有限元算法的準(zhǔn)確性。采用溫度場(chǎng)數(shù)值模擬系統(tǒng)計(jì)算一組熔模鑄造工藝的溫度場(chǎng),其中初始方案由于閥蓋件中部散熱條件差,模擬結(jié)果預(yù)測(cè)其中部會(huì)出現(xiàn)縮孔縮松缺陷,通過實(shí)際生產(chǎn)得以驗(yàn)證。改進(jìn)工藝之后,加快了閥蓋件中部的降溫速率,消除了孔松缺陷,實(shí)際也生產(chǎn)出合格的閥蓋件,驗(yàn)證了溫度場(chǎng)數(shù)值模擬系統(tǒng)的實(shí)用性。采用定向凝固溫度場(chǎng)數(shù)值模擬系統(tǒng)對(duì)帶冠渦輪葉片分別進(jìn)行HRS和LMC工藝模擬,并通過設(shè)置不同的抽拉速度進(jìn)行多方案分析,模擬結(jié)果與實(shí)際過程相吻合,證明了本文的有限元定向凝固溫度場(chǎng)數(shù)值模擬系統(tǒng)的可靠性,能夠?yàn)閷?shí)際定向凝固生產(chǎn)提供科學(xué)指導(dǎo)。
[Abstract]:In the field of aeronautics and astronautics, a directional solidification process is used to produce turbine blades, while the high-performance turbine blades have been the biggest obstacle to the realization of the "a large plane" 's dream in our country. The actual directional solidification process is a very complicated material forming process, and it is necessary to take special consideration of the influence of radiation heat transfer. By adopting the directional solidification temperature field simulation technology, the temperature field evolution process in the solidification process of the casting can be effectively analyzed, the possible defects can be predicted, and the theoretical guidance is provided for optimizing the directional solidification process. In this paper, the numerical simulation of the finite element directional solidification temperature field is deeply studied, including the mathematical modeling of the directional solidification temperature field, the finite element numerical solution, the liquid metal cooling liquid heat treatment and the directional solidification temperature field analysis criterion, etc. The numerical simulation system of the finite element directional solidification temperature field is developed. First, because the radiation heat transfer needs to be taken into consideration in the numerical simulation of the directional solidification temperature field, the ray tracing method is adopted to deal with it, and the control equation of the radiation heat transfer boundary condition is obtained by computer graphics. The temperature field model of the directional solidification process is established by a series of relative reasonable assumptions and simplification to the directional solidification process, and the control equation and the boundary condition of the temperature field of the directional solidification process are combined according to the finite element numerical calculation theory. The finite element discrete process and the method for solving the numerical simulation of the temperature field in the directional solidification process are derived in detail. Secondly, the latent heat of the casting is treated by using the equivalent specific method and the temperature correction method so as to satisfy the energy conservation principle. aiming at the along-the-type shell boundary of the directional solidification process, an intelligent searching type shell inner and outer surface algorithm is adopted, the inner and outer surfaces of each material are automatically distinguished, the tedious operation of the manual selection of the user is avoided, and the convection heat exchange boundary conditions of each contact surface are treated by adopting a box tree method, And the convection heat exchange boundary conditions between the materials can be more reasonably processed on the basis of more demanding the grid quality. As the medium shell of the LMC (Liquid Metal Cooling) process is gradually immersed in the liquid metal cooling liquid, the heat exchange between the shell and the cooling liquid is treated by the equivalent heat exchange coefficient which is changed with time and temperature in order to avoid the problem of re-partitioning the grid brought by the direct solution. In order to analyze the simulation results of HRS (High Rate Solid) and LMC directional solidification temperature field, the G/ L criterion is used to predict the potential of the casting. At the same time, in order to ensure the calculation efficiency of the finite element simulation system, the concept of the local matrix is put forward, and the calculation matrix of each material is assembled separately during the process of the finite element program. The numerical simulation system of the directional solidification temperature field of the finite element HRS and the LMC was developed by the key techniques. In the end, the temperature field of the air-cooling process of the typical I-piece is calculated by using the temperature field numerical simulation system and the general-purpose finite element platform ANSYS, and the results of the comparison are basically the same, and the accuracy of the finite element algorithm in the numerical simulation system of the temperature field is verified. The temperature field of a set of investment casting process is calculated by the temperature field numerical simulation system, and the initial scheme is due to the poor heat dissipation condition of the middle part of the valve cover. After the improvement process, the cooling rate of the middle part of the valve cover is accelerated, the defect of the hole is eliminated, the qualified valve cover is actually produced, and the practicability of the temperature field numerical simulation system is verified. By adopting the directional solidification temperature field numerical simulation system, the HRS and the LMC process simulation are respectively carried out on the crown turbine blades, and the multi-scheme analysis is carried out by setting different drawing speeds, and the simulation results are consistent with the actual process, The reliability of the numerical simulation system of the finite element directional solidification temperature field is proved, and the scientific guidance can be provided for the actual directional solidification production.
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：V261.31
本文編號(hào)：2449252
[Abstract]:In the field of aeronautics and astronautics, a directional solidification process is used to produce turbine blades, while the high-performance turbine blades have been the biggest obstacle to the realization of the "a large plane" 's dream in our country. The actual directional solidification process is a very complicated material forming process, and it is necessary to take special consideration of the influence of radiation heat transfer. By adopting the directional solidification temperature field simulation technology, the temperature field evolution process in the solidification process of the casting can be effectively analyzed, the possible defects can be predicted, and the theoretical guidance is provided for optimizing the directional solidification process. In this paper, the numerical simulation of the finite element directional solidification temperature field is deeply studied, including the mathematical modeling of the directional solidification temperature field, the finite element numerical solution, the liquid metal cooling liquid heat treatment and the directional solidification temperature field analysis criterion, etc. The numerical simulation system of the finite element directional solidification temperature field is developed. First, because the radiation heat transfer needs to be taken into consideration in the numerical simulation of the directional solidification temperature field, the ray tracing method is adopted to deal with it, and the control equation of the radiation heat transfer boundary condition is obtained by computer graphics. The temperature field model of the directional solidification process is established by a series of relative reasonable assumptions and simplification to the directional solidification process, and the control equation and the boundary condition of the temperature field of the directional solidification process are combined according to the finite element numerical calculation theory. The finite element discrete process and the method for solving the numerical simulation of the temperature field in the directional solidification process are derived in detail. Secondly, the latent heat of the casting is treated by using the equivalent specific method and the temperature correction method so as to satisfy the energy conservation principle. aiming at the along-the-type shell boundary of the directional solidification process, an intelligent searching type shell inner and outer surface algorithm is adopted, the inner and outer surfaces of each material are automatically distinguished, the tedious operation of the manual selection of the user is avoided, and the convection heat exchange boundary conditions of each contact surface are treated by adopting a box tree method, And the convection heat exchange boundary conditions between the materials can be more reasonably processed on the basis of more demanding the grid quality. As the medium shell of the LMC (Liquid Metal Cooling) process is gradually immersed in the liquid metal cooling liquid, the heat exchange between the shell and the cooling liquid is treated by the equivalent heat exchange coefficient which is changed with time and temperature in order to avoid the problem of re-partitioning the grid brought by the direct solution. In order to analyze the simulation results of HRS (High Rate Solid) and LMC directional solidification temperature field, the G/ L criterion is used to predict the potential of the casting. At the same time, in order to ensure the calculation efficiency of the finite element simulation system, the concept of the local matrix is put forward, and the calculation matrix of each material is assembled separately during the process of the finite element program. The numerical simulation system of the directional solidification temperature field of the finite element HRS and the LMC was developed by the key techniques. In the end, the temperature field of the air-cooling process of the typical I-piece is calculated by using the temperature field numerical simulation system and the general-purpose finite element platform ANSYS, and the results of the comparison are basically the same, and the accuracy of the finite element algorithm in the numerical simulation system of the temperature field is verified. The temperature field of a set of investment casting process is calculated by the temperature field numerical simulation system, and the initial scheme is due to the poor heat dissipation condition of the middle part of the valve cover. After the improvement process, the cooling rate of the middle part of the valve cover is accelerated, the defect of the hole is eliminated, the qualified valve cover is actually produced, and the practicability of the temperature field numerical simulation system is verified. By adopting the directional solidification temperature field numerical simulation system, the HRS and the LMC process simulation are respectively carried out on the crown turbine blades, and the multi-scheme analysis is carried out by setting different drawing speeds, and the simulation results are consistent with the actual process, The reliability of the numerical simulation system of the finite element directional solidification temperature field is proved, and the scientific guidance can be provided for the actual directional solidification production.
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：V261.31
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