过膨胀状态下轴对称收-扩喷管内外流场计算及分析

轴对称收-扩喷管在过膨胀状态下工作时, 喷管内部将产生强烈的激波以及附面层分离, 流态非常复杂.计算实践表明, 应用广泛采用的重整化群(RNG)k-ε湍流模型, 并结合标准壁面函数对其进行数值模拟时, 误差较大.针对标准壁面函数的不足, 采用增强型壁面函数处理固体壁面附近的流动, 对轴对称收-扩喷管的内外流场进行了数值模拟, 并与试验数据进行了分析比较.结果表明:增强型壁面函数更加适合处理此类存在强逆压梯度导致附面层分离的问题. 

Numerical investigation on internal and external flows for axisymmetric convergent-divergent nozzles on over-expansion state

When a axisymmetric convergent-divergent nozzle work at an over-expansion state,the strong shock wave and layer separation appear in the interior of the nozzle and the flow characteristic is very complex.The computed results were compared unfavorably with experimental data when adopting RNG k-ε turbulent model with standard wall functions.A wall treatment that combines a two-layer model with enhanced wall functions was employed in the numerical simulation and it was in good agreement with the experimental data.It is suggested that this enhanced wall treatment is more effective to deal with the problem of severe pressure gradients leading to boundary layer separations.