本文關鍵詞： 湍流強度 預混燃燒 當量比 大渦模擬　出處：《上海應用技術學院》2015年碩士論文　論文類型：學位論文

【摘要】：湍流是經(jīng)典物理中尚未解決的問題之一,普遍存在于自然界和應用于實際工程當中,而研究湍流燃燒更是在湍流的基礎上增加了難度,因為燃燒的出現(xiàn)使得湍流場更加復雜。湍流燃燒過程的研究是近年來研究的熱點和前沿之一,隨著社會的進步和科學技術的發(fā)展,人們對于環(huán)境保護的意識也越來越高,因此對于低排放高效率的燃燒室的研發(fā)受到眾多研究人員的重視,許多新思路新方法也都應用在燃燒室。本文以某燃氣輪機的火焰筒為參數(shù)建立三維模型,致力于研究提高燃氣渦輪發(fā)動機燃燒室的燃燒效率和減少污染物的排放問題,建立了非穩(wěn)態(tài)三維湍流化學反應模型。文中數(shù)值模擬的湍流模型為大渦模擬方法(LES),燃燒模型采用有限速率／渦耗散模型(Finite Rate/Eddy Dissipation)。首先計算了燃燒室燃氣不同湍流強度條件下燃燒狀況,得到燃燒室內的速度場、溫度場、各組分濃度場和渦量場的分布情況,研究湍流強度對預混燃燒效率以及一氧化碳(C0)排放量的影響。然后計算了不同當量比的預混燃氣對預混燃燒效果的影響,研究了燃燒室的溫度場,一氧化碳濃度場,渦量場和壓力場的分布,分析預混燃氣當量比對預混燃燒效率和一氧化碳生成量的影響。最后使用EMD方法對數(shù)值模擬的數(shù)據(jù)進行了分析,主要對火焰界面、火焰內部或火焰外部三個區(qū)域的U、V、T間歇性進行了比較。計算得到的主要結論如下：(1)在預混燃氣當量比和入口速度不變的條件下,隨著預混燃氣入口湍流強度的增大,燃燒室內低溫區(qū)域逐漸減小,火焰的相對長度隨著湍流強度的增大而縮短,燃料更多的在燃燒室內充分的燃燒,提高了能源利用率,節(jié)約了能源。湍流強度的增大使得火焰表面的CO的分布區(qū)域越來越薄,在燃燒室內的總體分布區(qū)域變小,而且高濃度區(qū)域也隨著湍流強度的增大而減小,為減少C0的生成,可以適當提高預混燃料的湍流強度,減小對環(huán)境的污染。(2)預混燃氣中的甲烷的含量對燃燒產(chǎn)物溫度影響很大,在預混燃料入口速度和湍流強度不變的情況下,燃燒室的最高溫度隨當量比的增大而明顯升高,而且燃燒室的最高溫度隨當量比的變化呈現(xiàn)出一定的規(guī)律性。通過分析在預混燃料不同當量比條件下的燃燒,發(fā)現(xiàn)隨著當量比的提高,燃燒產(chǎn)生的CO濃度和分布區(qū)域增大因此,為減少C0的生成,可以適當減小預混燃料的當量比。(3)發(fā)現(xiàn)在火焰界面和火焰內部,當T的局部間歇性振幅較大時,U的局部間歇性頻率較高,這說明T波動的活躍程度受到U頻率的影響。當U周期越短,T的指數(shù)就越不穩(wěn)定,波動越劇烈,可以理解為當湍流脈動越劇烈時,燃燒反應也會加劇,溫度的變化也越大,表現(xiàn)為燃燒效率也會更高。
[Abstract]:Turbulence is one of the unsolved problems in classical physics. It is widely used in nature and applied in practical engineering, and the study of turbulent combustion is more difficult on the basis of turbulence. Turbulent combustion process is one of the hotspots and frontiers in recent years, with the progress of society and the development of science and technology. People are more and more aware of environmental protection, so the research and development of low emission and high efficiency combustor has been paid attention by many researchers. Many new ideas and new methods are also applied to the combustion chamber. In this paper, a three-dimensional model is built based on the flame tube of a gas turbine. To study the problem of improving combustion efficiency and reducing pollutant emission of gas turbine engine combustor. The unsteady three-dimensional turbulent chemical reaction model is established. The turbulent model in this paper is the large eddy simulation method (Les). The combustion model uses finite rate / vortex dissipation model (Finite Rate/Eddy dissipation). Firstly, the combustion conditions of combustor gas with different turbulent intensity are calculated. The distribution of velocity field, temperature field, concentration field and vorticity field in the combustor are obtained. The effect of turbulence intensity on premixed combustion efficiency and carbon monoxide (CO) C0 emission is studied. Then the effect of premixed gas with different equivalent ratio on premixed combustion efficiency is calculated and the temperature field of combustion chamber is studied. The distribution of carbon monoxide concentration field, vorticity field and pressure field, and the effect of premixed gas equivalent ratio on combustion efficiency and carbon monoxide production are analyzed. Finally, the numerical simulation data are analyzed by EMD method. Mainly for the flame interface, the flame inside or outside of the three regions of the UGV. T intermittency is compared. The main conclusions are as follows: 1) under the condition of constant equivalent ratio and inlet velocity of premixed gas, the turbulence intensity increases with the inlet of premixed gas. The low temperature region of the combustion chamber decreases gradually, the relative length of flame decreases with the increase of turbulence intensity, and the fuel is more fully burned in the combustion chamber, which improves the energy efficiency. The increase of turbulence intensity makes the distribution region of CO on the flame surface thinner and smaller in the combustion chamber, and the high concentration region also decreases with the increase of turbulence intensity. In order to reduce the formation of C _ 0, the turbulence intensity of the premixed fuel can be increased appropriately, and the pollution to the environment can be reduced. (2) the content of methane in the premixed gas has a great influence on the combustion product temperature. Under the condition of constant inlet velocity and turbulent intensity of premixed fuel, the maximum temperature of combustion chamber increases obviously with the increase of equivalent ratio. And the maximum temperature of combustion chamber shows certain regularity with the change of equivalent ratio. By analyzing the combustion under different equivalent ratio of premixed fuel, it is found that with the increase of equivalent ratio. Therefore, in order to reduce the formation of C0, the equivalent ratio of premixed fuel can be reduced appropriately. When the local intermittent amplitude of T is larger, the local intermittent frequency of U is higher, which indicates that the active degree of T fluctuation is affected by U frequency. When the U cycle is shorter, the exponent of T is more unstable and the fluctuation is more intense. It can be understood that when the turbulence pulsation is more intense, the combustion reaction will be intensified, and the change of temperature will be greater, and the combustion efficiency will be higher.
【學位授予單位】：上海應用技術學院
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TK16

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