钝头体激波诱导振荡燃烧现象的数值模拟

NUMERICAL RESEARCH ON BLUNT BODY SHOCK-INDUCED OSCILLATING COMBUSTION PHENOMENA

采用一种改进的化学非平衡流解耦方法对轴对称Euler反应流方程解耦处理,对流项采用五阶WENO格式离散,化学反应源项的刚性采用简化的隐式方法处理,时间步进采用二阶精度的Runge-Kutta方法,对H_2/Air预混气在来流Ma=4.48和Ma=4.79时的激波诱导振荡燃烧现象进行了数值研究.对比分析了网格尺度的影响,发现计算结果对法向网格尺度比较敏感,流向网格密度的变化对结果影响不大;Ma=4.48时,采用敏感性分析方法对各反应模型进行了对比分析,J和B-W模型在实验所处的温度和压力范围内能够比较准确的预测诱导时间,所得的振荡频率与实验结果相符,所揭示的振荡机理与McVey和Toong振荡机理吻合,而JM模型预测的诱导时间偏长,其振荡频率低于实验观测值;Ma=4.79时,J模型所得的振荡频率与实验值吻合,而B-W模型释热时间短,且对流场波动比较敏感,流场扰动引起了瞬时局部爆震现象,破坏了振荡的规律性;五阶WENO空间离散格式的应用使计算结果精度较好.

An improved uncoupled solver of non-equilibrium flow was used to split the axisymmetric Euler equations for a reacting flow.Inviscid flux was calculated with fifth-order WENO scheme.Simplified implicit formulation was adopted to deal with the stiffness generated by the chemical reacting source term of species equations.Time integration was performed with two-order TVD Runge-Kutta scheme.At the flow Mach number M of 4.48 and 4.79,shock-induced oscillating combustion phenomena around blunt body in H_2/Air mixture were calculated.It shows that the numerical results are more sensitive to the grid refinement on normal direction than on flow direction.To get accurate solution,there must be enough grid nodes in the heat release zone.At the flow Mach number of 4.48,sensitive analysis of different reaction mechanisms were studied.At the given experimental conditions,the values of induction time calculated from J and B-W mechanisms are close to each other and their calculated frequencies nearly equal to the experimental results.Density-time distribution along the stagnation streamline from J and B-W mechanisms agree well with McVey-Toong theory. Induction time calculated from JM mechanism is longer than others,and the calculated oscillating frequency is lower than experimental results.At flow Mach number of 4.79,calculated frequency of J mechanism agrees with experimental result.B-W mechanism is sensitive to fluctuations of flowfield,and its release time is short. Fiercely oscillating combustion front would easily lead to local detonations,which made the pressure history of stagnation point disordered.Due to using the fifth-order WENO scheme,relatively high-resolution of present calculation can be obtained.