用简化PDF方法分析温度脉动在超声速湍流燃烧中的作用

Examine the Effect of Temperature Fluctuation on Supersonic Combustion by Assumed PDF Approach

考虑湍流场中温度脉动,采用简化PDF方法(假设温度脉动服从截尾高斯分布),研究了湍流对化学反应速率常数的影响,分析了Reynold平均方法不能准确计算时均化学反应速率常数的原因,得到考虑温度脉动的超声速点火实验计算结果,优于不考虑温度脉动的计算结果.进一步应用数值算例说明时均的速率常数与温度脉动的关系,计算方法显著影响点火延迟时间的计算准确性,对超声速流场点火位置的计算比较重要.

An assumed probability density fuction （PDF） approach, developed by Girimaji and Baurle, was adopted tor modeling supersonic combustion. A clipped Gauss function was used to account for turbulence-reacting interaction, which demonstrated that reaction rate con,,tant was amplified or decreased variously by turbulence. Temperature variance was modeled h＇om entropy variance transport equation conjugated with Wilcoxg κ-ω turbulent model. The approach was applied to a supersonic, co-axial H2/air burner experiment conducted by Cheng et al. The result of the model using simplified kineties showed improvement in predicting of turbulence effects on the initiating step which was of first-order importance because of small residence time in supersonic fluid field. Comparison was made indicating a serious problem in estimation of average rate constant using a Reynold decomposition method. A set of numerical tests showed average reaction rate constant was greatly modified by temperature fluctuation and changed the time delay of ignition sufficiently.