低动能来流下背负式进气道非定常流动特性分析

为了改善飞翼布局背负式S弯进气道低动能来流状态下的流动性能，采用改进的延迟分离涡模拟（IDDES）方法对原型及改进型背负式进气道流场进行了数值模拟研究，对比分析了进气道流量特性及内部脉动压力特性。结果表明:低动能来流时背负式进气道上部唇口附近存在很大的气流转折角，导致唇口产生分离涡；原型进气道唇口分离涡强度高，高能量分离涡在进气道顶部破裂产生了大范围旋涡结构，进一步加剧了流动分离，从而引发进气道内产生强烈的压力脉动，声压级最大幅值高达145 dB；改进型进气道唇口分离涡得到了有效控制，强度大幅下降，进气道内部压力脉动幅值也显著降低，声压级降幅达8 dB；改进型进气道分离的抑制使进气道有效流通截面积增大，质量流量增加。同时，流场出口品质提升，进气道出口综合畸变指数降低了9.5%。 

Unsteady flow characteristics of dorsal inlet under low-energy inflow

To improve the dorsal S-shaped inlet flow performance of low-energy inflow.The flow fields of both original and improved dorsal inlet were studied by using improved delayed detached-eddy simulation (IDDES) method,and the mass flow and pressure fluctuation characteristics of the two inlets were compared. The results show that, influenced by the fuselage, airflow turning angle near the inlet lip is very large and this will cause the formation of separation bubbles. The intensity of the separation vortex at the lip of the original inlet is very high. When the separation bubbles with high energy break down at the top of the inlet, massive high-strength vortices are created. These high-strength vortices aggravate the separation near the inlet top and cause fierce pressure fluctuations inside the S-shaped inlet. The amplitude of the sound pressure level can reach 145 dB. The strength of separation bubbles inside the improved inlet issuccessfully decreased, which enlarges the effective flow area of the inlet and increases mass flux. The pressure fluctuations inside the S-shaped inlet decrease and the reduction of sound pressure level is up to 8 dB. Meanwhile, the comprehensive distortion coefficient decreased by 9.5% which improves the characteristic of outlet flow field.