单边膨胀喷管内流动分离非定常特性

Flow separation unsteadiness in single expansion ramp nozzle

结合聚焦纹影和动态压力测量技术,对基于特征线法设计的单边膨胀喷管(SERN)不同落压比(NPR)条件下喷管内流场结构和壁面压力进行了试验测量,通过壁面压力时域和频域综合分析获得了喷管内流动分离非定常特性。结果表明:过膨胀状态下单边膨胀喷管内流场结构具有明显的非对称特征,喷管上壁面流动分离模态为受限激波分离(RSS),而下壁面流动分离模态为自由激波分离(FSS);相比于FSS模态,RSS模态下出口附近壁面压力振荡更剧烈。喷管上、下壁面压力标准差峰值均在分离点附近,且概率密度函数分布向一侧偏斜或出现双峰现象。RSS模态下,激波运动呈明显低频特性;FSS模态下,激波非定常特性不仅受回旋区压力扰动的影响,且受分离剪切层的影响。

In combination with the focus schlieren and dynamic pressure measurement technology,the flow field and nozzle wall pressure were experimentally measured,under the different nozzle pressure ratios(NPR)of the single expansion ramp nozzle(SERN).Time and frequency domain analysis exhibited unsteady flow characteristics within the nozzle.Results showed that the flow field structure inside SERN was obvious asymmetrical.The flow separation mode on the upper wall of the nozzle was at restricted shock separation(RSS),and that on the lower wall at free shock separation(FSS);in RSS mode,the pressure on the wall near the outlet was sharply oscillated in relation to FSS mode.The pressure standard deviation of the upper and lower walls of the nozzle was peaked near the separation point,and the probability density function distribution was skewed to one side or showed double peaks.In RSS mode,the shock motion exhibited obvious low-frequency characteristics.In FSS mode,the unsteady characteristics of the shock wave were not only affected by the pressure disturbance of the recirculation region,but also affected by the separated shear layer.