In order to discover the effect of head cavity on resonance damping characteristics in solid rocket motors,large-eddy simulations with wall-adapting-local-eddy-viscosity subgrid scale turbulent model are implemented to study the oscillation flow field induced by vortex shedding based on the VKI(von Kármán Institute)experimental motor.Firstly,mesh sensitivity analysis and grid-independent analysis are carried out for the computer code validation.Then,the numerical method is further validated by comparing the calculated results and experimental data.Thirdly,the effects of head-end cavity on the pressure oscillation am-plitudes are studied in this paper.The results indicate that cavity volume,location and configuration have a cooperative effect on the oscillation amplitude.It is proved that Rayleigh criterion can be used as a guiding principle for the design of resonance damping cavity.The change of the head-end cavity breaks the balance between the mass flux and acoustic energy.Therefore,the pressure oscillation characteristics change accordingly.It is concluded that a large mass flux added at the pressure antinode could attribute to significant amplitude.Meanwhile,the damping effect of the cavity is stronger when the distance between cavity and pressure antinode becomes shorter.Finally,this method is applied to the modification of an engineering solid rocket motor.The static test of solid rocket motor reflects that the oscillations can be effectively suppressed by a head-end cavity.
ZHANG QiaoWANG NingFeiLI JunWeiSU WanXingZHANG Yan
Vortex-acoustic coupling is one of the most important potential sources of combustion instability in solid rocket motors (SRMs). Based on the Von Karman Institute for Fluid Dynamics (VKI) experimental motor, the influence of the thermal inhibitor position and temperature on vortex-shedding-driven pressure oscillations is numerically studied via the large eddy simulation (LES) method. The simulation results demonstrate that vortex shedding is a periodic process and its accurate frequency can be numerically obtained. Acoustic modes could be easily excited by vortex shedding. The vortex shedding frequency and second acoustic frequency dominate the pressure oscillation characteristics in the chamber. Thermal inhibitor position and gas temperature have little effect on vortex shedding frequency, but have great impact on pressure oscillation amplitude. Pressure amplitude is much higher when the thermal inhibitor locates at the acoustic velocity anti-nodes. The farther the thermal inhibitor is to the nozzle head, the more vortex energy would be dissipated by the turbulence. Therefore, the vortex shedding amplitude at the second acoustic velocity antinode near 3/4L (L is chamber length) is larger than those of others. Besides, the natural acoustic frequencies increase with the gas temperature. As the vortex shedding frequency departs from the natural acoustic frequency, the vortex-acoustic feedback loop is decoupled. Consequently, both the vortex shedding and acoustic amplitudes decrease rapidly.
Su WanxingLi ShipengZhang QiaoLi JunweiYe QingqingWang Ningfei
为探索涡-声效应对固体火箭发动机中压力振荡特性的影响,基于VKI(Von KarmanInstitute for Fluid Dynamics)发动机,通过改变挡板位置与燃气温度,对旋涡脱落引起的压力振荡进行了大涡模拟数值研究。耦合分析表明:挡板位于速度波腹附近,压力振荡最为严重;旋涡能量在输运过程中易于被湍流耗散,靠近喷管的二阶速度波腹处旋涡脱落压力振幅明显高于其它位置。解耦分析表明:温度对旋涡脱落频率影响不大,当旋涡脱落频率与声振频率分离后,压力振幅显著下降。
