Investigation On Distributon Pattern Of Counter Gradient Transport And Flame Instability Mechanism Of Turbulent Flame

The counter gradient transport phenomenon is a widespread phenomenon in turbulent combustion.The emergence of this phenomenon has a huge impact on the turbulence and combustion models established by using the traditional gradient transportation assumption.In addition,the key elements of counter gradient transport are thermal diffusion and turbulence,and its physical process mainly occurs at the microscopic scale.These factors are highly consistent with current research on flame instability.This article will mainly use theoretical analysis and numerical simulation methods to discuss the distribution of counter gradient transport in turbulent combustion,the influencing factors and its relationship with the flame instability.Theoretical derivation is carried out to establish the distribution pattern of counter gradient transport based on TFC model.At present,the well established models that incorporate counter gradient transport into the research category can’t achieve the unity of high accuracy and high efficiency.The theoretical method developed in this paper can be used for counter gradient transport on the basis of obtaining the premixed flame inlet conditions.Forecast of the occurrence area.The validity of this theory has been tested in the numerical simulation and statistical analysis of the Moreau combustion chamber case established in this paper.Based on standard calculation examples,a multi-mode analysis was conducted to verify the applicability of the counter gradient transport distribution theory,and the influence of multiple factors such as thermal diffusion,macro convection,and micro turbulence on counter gradient transport are analyzed.The results show that temperature plays the most important role in the distribution and intensity of inverse gradient transport.The mechanism of convection and turbulence factors is more complicated.Both of them have less influence on the intensity of inverse gradient transport,but they can affect the spatial distribution of inverse gradient transport by altering the mode of the flow field.A large eddy simulation is established based on the Flame-D experimental model,and the counter gradient transport distribution theory and Hilbert-Huang transform method are used to analyze the flow field transport characteristics and pressure spectrum,respectively.The results show that in most parts of the flame,the pressure frequency is basically unchanged,but in the fuel inlet area,the pressure frequency fluctuates in the radial direction.The trend is similar to the local counter gradient transport,which means counter gradient transport can reflect instability due to thermal diffusion and turbulence,but due to the existence of acoustic instability,it cannot reflect all the characteristics of instability.