单喷嘴火箭发动机高频燃烧不稳定的RANS和SBES数值模拟

Numerical simulation of RANS and SBES for high-frequency combustion instability of a single-element rocket engine

为了研究不同湍流模型对高频燃烧不稳定的捕捉能力,采用非稳态雷诺时均(Unsteady Reynolds averaged Navier-Stockes,URANS)和应力混合涡模拟(Stress-blended eddy simulation,SBES),开展了单喷嘴模型火箭发动机数值仿真。化学反应与湍流的相互作用采用基于详细化学反应机理(GRI Mech 3.0)的小火焰生成流模型(Flamelet-generated manifolds,FGM)。对比试验数据,验证了模型的准确性;全面对比了URANS和SBES仿真结果;分析了燃烧室的压力波模态特性和流场动态特性。发现两者都能捕捉到高频燃烧不稳定,但URANS对动态特性的捕捉明显不足,压力振荡峰峰值与试验值相比误差高达57.6%。而SBES对包含涡脱落、湍流混合、压力波的传播等动态特性能够实现较好的捕捉,压力振荡峰峰值与试验值误差仅为7.6%。URANS结果表现出高度的对称性,而SBES结果则更加合理。燃烧室和氧管的压力振荡相互耦合,引起推进剂质量流量脉动和燃烧室突扩面周期性涡脱落。涡脱落及其与燃烧室壁面的相互作用增强了脉动释热,是维持燃烧不稳定的关键。

To estimate the ability of various turbulence models in capturing the high-frequency combustion instability,the numerical simulations of a single element model rocket engine are performed by using unsteady Reynolds averaged Navier-Stockes(URANS)and stress-blended eddy simulation(SBES)methods.The turbu-lence and chemical reaction interactions are treated by flamelet-generated manifolds(FGM)based on a detailed chemical mechanism(GRI Mech 3.0).The accuracy of the numerical model is validated by comparing the pres-ent numerical results with the experimental data.A comprehensive comparison of URANS and SBES simulation results is made.The modal characteristics of the pressure wave and evolutions of the dynamic flow fields of the combustor are analyzed.Results suggested that the high-frequency combustion instability is captured by both tur-bulence models,but the URANS model shows powerless in identifying the dynamic characteristics of the combus-tor,and compared to the experimental results,the amplitude of pressure oscillations error is 57.6%.However,the dynamic characteristics including eddy shedding,turbulent mixing,and the propagating of the pressure waves are all captured by SBES model,and the amplitude of pressure oscillations error is only 7.6%compared to experimental data.The results of the URANS simulation show a high degree of symmetry,while the SBES results are more reasonable.Pressure oscillations in the combustion chamber are found to be coupled with that in oxidizer post,causing propellant mass flow pulsations and periodic eddy shedding at the combustion chamber step.The pulsated heat release is enhanced because of the eddy shedding and its interaction with the chamber wall,which plays a key role in sustaining the combustion instability.