Axisymmetric simulations of a liquid rocket engine are performed using a delayed detached-eddy-simulation (DDES) turbulence model with the Compressible Flamelet Progress Variable (CFPV) combustion model. Three different pressure instability domains are simulated: completely unstable, semi-stable, and fully stable. The different instability domains are found by varying the combustion chamber and oxidizer post length. Laminar flamelet solutions with a detailed chemical mechanism are examined. The β probability density function (PDF) for the mixture fraction and Dirac δ PDF for both the pressure and the progress variable are used. A coupling mechanism between the volumetric Heat Release Rate (HRR) and the pressure in an unstable cycle is demonstrated. Local extinction and reignition are investigated for all the instability domains using the full S-curve approach. A monotonic decrease in the amount of local extinctions and reignitions occurs when pressure oscillation amplitude becomes smaller. The flame index is used to distinguish between the premixed and non-premixed burning mode in different stability domains. An additional simulation of the unstable pressure oscillation case using only the stable flamelet burning branch of the S-curve is performed. Better agreement with experiments in terms of pressure oscillation amplitude is found when the full S-curve is used.

液体火箭发动机的轴对称模拟是使用带有可压缩小火焰进度变量（CFPV）燃烧模型的延迟分离涡模拟（DDES）湍流模型进行的。模拟了三个不同的压力不稳定性域：完全不稳定，半稳定和完全稳定。通过改变燃烧室和氧化剂柱的长度可以发现不同的不稳定性域。研究了具有详细化学机理的层流小火焰溶液。混合分数和狄拉克δ的β概率密度函数（PDF）使用压力和进度变量的PDF。证明了在不稳定循环中，体积放热率（HRR）与压力之间的耦合机制。使用完整的S曲线方法研究了所有不稳定区域的局部灭绝和重燃。当压力振荡幅度变小时，局部消光和复燃的数量单调减少。火焰指数用于区分不同稳定性域中的预混和非预混燃烧模式。对仅使用S曲线的稳定小火焰燃烧分支的不稳定压力振荡情况进行了附加仿真。当使用完整的S曲线时，发现在压力振荡幅度方面与实验更好地吻合。