Numerical Simulation Of Turbulent Premixed Combustion In A Sudden Expansion Combustion Chamber

Turbulence is one of the unresolved issues of the classical physics and is commonly found in nature and used in practical engineering, while difficulty of research of turbulent combustion is increased on the basis of turbulence, because burning makes the turbulent flow field more complex. Research of the turbulent combustion process is one of the hot spots and frontiers in recent years, with the development of social progress and scientific and technological development, people’s awareness of environmental protection has become higher, so that many researchers attach importance to research of a low-emission and high-efficiency combustion chamber, and many new ideas and new methods are also used in the combustion chamber.In this paper, a flame tube of a gas turbine is used as a parameter to establish a three-dimensional model to improve the combustion efficiency of the gas turbine engine combustor and reduce emission of pollutants, and a three-dimensional unsteady turbulence chemical reaction model is established. Large eddy simulation (LES) is applied to numerical simulation of the turbulence model, and the combustion model is a finite-rate/eddy dissipation model. Firstly, the combustion conditions of chamber gas under different turbulence intensities are calculated, so that the distribution conditions of velocity fields, temperature fields, component concentration fields and vorticity fields are obtained, and the influence of turbulence intensities on premixed combustion efficiency and emission load of CO is researched. Then, the influence of premixed gas of different equivalence ratios on the premixed combustion effect is calculated, distribution of the temperature field, the CO concentration field, the vorticity field and the pressure field of the combustion chamber are researched, and the influence of the equivalence ratios of premixed gas on premixed combustion efficiency and CO generation amount is analyzed. Finally, the EMD method is applied to analysis of numerical simulation data, the U, V, T intermittent of three areas, namely a flame interface, the inside of flame and the outside of flame is mainly compared. The main conclusions obtained through calculation are as follows:(1) Under the condition that the equivalence ratio of premixed gas and inlet speed are not changed, with the increase of inlet turbulence of premixed gas, the low-temperature region in the combustion chamber decreases gradually, the relative length of flame is shortened along with increasing of turbulence intensity, more fuel combusts fully in the combustion chamber, the energy utilization rate is improved, and energy is saved. Increasing of the turbulence intensity enables the distribution area of CO on the surface of flame to be thinner and thinner, the overall distribution area of CO in the combustion chamber is reduced, high-concentration areas are reduced along with increasing of the turbulence intensity, and to reduce generation of CO, the turbulence intensity of premixed fuel can be improved appropriately, and environment pollution is reduced.(2) The content of methane in the premixed gas has great influence on combustion product temperature, under the condition that the inlet speed of premixed fuel and turbulence intensity are not changed, the highest temperature of the combustion chamber is obviously increased along with increasing of the equivalence ratio, and the highest temperature of the combustion chamber has a certain regularity along with changing of the equivalence ratio. Through analysis of combustion of the premixed fuel under different equivalence ratios, the concentration and distribution area of CO generated by combustion are increased along with improving of the equivalence ratio, and therefore to reduce generation of CO, the equivalence ratio of the premixed fuel can be reduced appropriately.(3) At the flame interface and the inside of flame, when the local intermittent amplitude of T is large, the local intermittent frequency of U is high, it proves that the activeness degree of fluctuation of T is affected by the frequency of U. The shorter the cycle of U is, the more unstable is the index of T, and fluctuation is more acute, and it can be interpreted that when turbulent fluctuation is acute, combustion reaction is aggravated, temperature changing is larger, and combustion efficiency is higher.